Construction of Foundation -

Procedure for construction of foundation starts with decision on its depth, width and marking layout for excavation and centerline of foundation. Foundation is the part of structure below plinth level in direct contact of soil and transmits load of super structure to soil. Generally it is below the ground level. If some part of foundation is above ground level, it is also covered with earth filling. This portion of structure is not in contact of air, light etc., or to say that it is the hidden part of the structure.

Footing is a structure constructed in brickwork, masonry or concrete under the base of a wall or column for distributing the load over a large area.

Depth of Foundation

Depth of foundation depends on following factors:

1. Availability of adequate bearing capacity

2. Depth of shrinkage and swelling in case of clayey soils, due to seasonal changes which may cause appreciable movements.

3. Depth of frost penetration in case of fine sand and silt.

4. Possibility of excavation nearby

5. Depth of ground water table

6. Practical minimum depth of foundation should not be less than 50 cm. to allow removal of top soil and variations in ground level.

Hence the best recommended depth of foundation is from 1.00 meter to 1.5 meter from original ground level.

Width of Foundation / Footings

The width of footings should be laid according to structural design. For light loaded buildings such as houses, flats, school buildings etc. having not more than two stores, the width of foundation is given below:

1. The width of footing should not be less than 75 cm for one brick thick wall.

2. The width of footing should not be less than 1 meter for one and half brick wall.

Processes involved in Construction of Foundation

The processes executed in the foundation works are given below:

1. Excavation of earth work in trenches for foundation.

2. Laying out cement concrete.

3. Laying the footing in case of raft or column construction.

4. Laying Anti termite treatment.

5. Laying Brick work up to plinth level.

Laying Damp proof course on the walls.

1. Refilling of earth around the walls

2. Refilling of earth in the building portion up to the required height according to plinth level.

Precautions while designing a Foundation

1. A foundation should be designed to transmit combined dead load, imposed load and wind load to the ground.

2. Net loading intensity of pressure coming on the soil should not exceed the safe bearing capacity.

3. Foundation should be designed in such a way that settlement to the ground is limited and uniform under whole of the building to avoid damage to the structure.

4. Whole design of the foundation, super structure and characteristics of the ground should be studied to obtain economy in construction work.

Ratio of Cement Concrete and Mortar for Foundation

1. The cement concrete 1:8:16 is generally used in the foundation of walls in construction work.

2. In case of column raft cement concrete 1:4:8 is the best recommended ratio for it in the foundation. For brick masonry cement mortar 1:4 to 1:6 is used as loading condition.

In case of column and raft footings up to plinth level cement concrete 1:2:4 or 1:1.5:3 are used.

Soil having Safe Bearing Capacity

Dry coarse and well graded dense sand have maximum shear resistance and maximum bearing capacity. In general submerged soil and clay have less bearing capacity.

Precautions during Excavation for Foundation

The depth and width of foundation should be according to structural design.

1. The depth of the foundation should not be less than 1 meter in case the design is not available.

2. The length, width and depth of excavation should be checked with the help of center line and level marked on the marking pillars.

3. The excavated material/ earth should be dumped at a distance of 1 meter from the edges.

1. Work should be done on dry soil.

2. Arrangement of water pump should be made for pumping out rain water.

3. The bottom layer of the foundation should be compacted.

4. There should be no soft places in foundation due to roots etc.

5. Any soft/ defective spots should be dug out and be filled with concrete/ hard material .

Demarcation / layout Procedure for foundation

The following procedure is recommended for demarcation of a building.

1. For layout of a building baseline is marked on the ground either from center line of the road or from any permanent building nearby. This line helps to mark out the front of a building. Side baseline is also marked with the help of side structure or road or it can be marked with the help of first baseline or boundary of the plot.

2. Fix temporary pegs at the center line of walls/columns on both sides of walls and columns in front and back side.

3. Fix peg at the center line of walls/columns on both sides of wall and columns in left and right side of front of building.

4. Check diagonals of the square or rectangle formed after fixing pegs.

5. Construct marking pillars with pegs at a distance of 1.5 meter to 2 meters and their top surface should be plastered.

6. Mark center line on the top of marking pillars with the help of thread (Soot) or with the Theodolite in big projects and the diagonal and other dimension should be checked.

7. Level marking pillars on all corners of building and the top level is fixed at a proposed plinth level.

8. Mark the foundation of walls/columns according to drawing on the ground with the help of center line marked on the marking pillars .

9. Mark foundation trenches on the ground with chalk powder.

1. Excavate the foundation of the walls /columns up to required level and the excavation must be checked with the help of center line and level marking pillars to avoid any complication later on.

Advantages of Layout with the help of marking pillars -

o It saves time for measuring and setting of point again and again at the time of construction.

o It increases the efficiency of mason and foreman for doing their jobs.

o Accuracy can be checked at any time at any step.

o If any mistake is found, it can be easily be rectified at early stage. It is very difficult to rectify the mistake in later.

o Cross check can be done by senior engineer in minimum time.

o A qualitative work is maintained.

Disadvantages for doing the work without layout -

At some sites of work the contractor brings steel pieces, erects the same on the ground and start the work of excavation. In due course these steel pieces are just discarded. Thus no proper reference point is available while doing further jobs.

o It involves extra time for measuring the offset again and again.

o Accuracy can not be checked at early stage and it will be very difficult to rectify the same in later stage.

o It involves wastage of time and money while doing rectification. This also leads to bad quality of work.

Materials used during Setting up of Layout -

1. Leveling Instrument

2. Long Nails

3. Hammer

4. Right Angle

5. Steel Tape

6. Thin Cotton Thread

7. Bricks

8. Cement

9. Screen Sand

10. Lime Powder

11. Theodolite

WORK PROCEDURE OF EXCAVATION AT CONSTRUCTION SITE -

Work procedure for excavation at construction site involves understanding of centre line and excavation drawings, setting out of plan on ground, excavation of soil and removal of excess soil. Quality checks such as recording ground level and marking of reference points should be done.

Excavation is the process of moving earth, rock or other materials with tools, equipment or explosives. It also includes trenching, wall shafts, tunnelling and underground. It is the preliminary activity of the construction project.

Drawings Required for Excavation -

1. Centerline Drawing or Gridline Drawing

Gridline drawings represents the grids marked in numbers and alphabets whose measurements are shown for site marking out reference. These grid lines are so aligned that the line falls on the excavation and footing.

Excavation Drawing

Excavation drawing represents the length, width and depth of the excavation. Excavation line is marked in dotted line.

Scope of the work for Excavation -

The major works done before, while and after excavation are as follows,

1. Setting out of corner benchmarks.

2. Survey for ground levels.

3. Survey for top levels

4. Excavation to approved depth.

5. Dressing of loose soil.

6. Making up to cut off level

7. Constructing dewatering wells and interconnecting trenches.

8. Marking boundaries of the building.

9. Constructing protection bunds and drains.

Working Procedure of Excavation -

1. The first and primary step involved in the excavation is to find out the extent of soil and Clearing of construction site is of unwanted bushes, weeds and plants.

2. Setting out or ground tracing is the process of laying down the excavation lines and centre lines etc. on the ground before the excavation is started.

3. Maximum of 4 and minimum of 2 benchmarks are marked in the corner for the measurement of level. These benchmarks are marked on permanent structures like, plinth, road or tree.

4. The tracing is marked by lime powder.

1. With the reference of drawing and benchmarks the depth of the excavation is fixed.

2. Excavation is done by manual or machine means depending on the availability.

3. The excavated soil is to either removed out the site or stocked around the excavation pit. Minimum of 1m distance must be maintained between the stocking of excess soil and pit, so that due to rain or other forces the soil should not sweep into the pits.

4. Dressing of excavated pits is to be done as specified in the drawings.

5. If the site is located in loose soil area, proper shoring must be done to hold the loose soil.

6. Construction of dewatering wells and interconnecting trenches are to provided if needed.

7. All the sides of the building must be sealed for the safety propose.

Removal of Excess Soil

Estimate the excavated stuff to be re-utilized in filling, gardening, preparing roads, etc.As far as possible try to carry excavation and filling simultaneously to avoid double handling. Select and stack the required material in such a place that it should not obstruct other construction activities. The excess or unwanted material should immediately be carried away and disposed off.

Quality Checks for Excavation

1. Recording initial ground level and check size of bottom.

2. Disposal of unsuitable material for filling.

3. Stacking suitable material for backfilling to avoid double handling.

4. Strata classification approval by competent authority.

5. Dressing bottom and sides of pits as per drawing with respect to centerline.

6. Necessary safety measures observed.

uality Checks for Filling

1. Recording initial ground level

2. Sample is approved for back filling.

3. Necessary marking/ reference points are established for final level of backfilling.

4. Back filling is being carried out in layers (15cm to 20cm).

5. Required watering, compaction is done.

6. Required density is achieved.

Earthwork and excavation -

Earthwork & Excavation Estimation and Costing Earthwork & Excavation1Earthwork & Excavation Earthwork & Excavation2 } Generally all the Civil Engineering projects like roads, railways, earth dams, canal bunds, buildings etc. involves the earth work. } This earth work may be either earth excavation or earth filling or Some times both will get according to the desired shape and level. } Basically the volume of earthwork is computed from length, breadth, and depth of excavation or filling.

Excavation Classification The materials to be excavated shall be classified as follows unless otherwise specified. Earthwork & Excavation3Earthwork & Excavation4 a) Soft / Loose Soil b) Hard/Dense Soil c) Mud d) Soft/Disintegrated Rock ( Not Requiring Blasting ) e) Hard Rock( Requiring Blasting ) f) Hard Rock( Blasting Prohibited)

Earthwork & Excavation5 } Soft / Loose Soil - Generally any soil which yields to the ordinary application of pick and shovel, or to PHA WRA. rake or other ordinary digging implement; such as vegetable or organic soil, turf, gravel, sand, silt, loam, clay peat, etc.

Earthwork & Excavation6 } Hard/Dense Soil - Generally any soil which requires the close application of picks, or jumpers or scarifiers to loosen; such as stiff clay, gravel, cobblestone, water bound macadem and soling of roads. Earthwork & Excavation7 } Mud - A mixture of soil and water in fluid or weak solid state.

Earthwork & Excavation8 } Soft/Disintegrated Rock ( Not Requiring Blasting ) - Rock or boulders which may be quarried or split with crowbars. This will also include laterite and hard conglomerate.

Earthwork & Excavation9 } Hard Rock( Requiring Blasting ) – Any rock or boulder for the excavation of which blasting is required.

Earthwork & Excavation10 } Hard Rock( Blasting Prohibited) – Hard rock requiring blasting but where blasting is prohibited for any reason and excavation has to be carried out by chiselling, wedging or any other agreed method.

METHOD OF CALCULATING THE EARTH WORK QUANTITIES Lead and Lift Earthwork & Excavation11

Lead and Lift Lead: Lift : Earthwork & Excavation12 } It is the average horizontal distance between the centre of excavation to the centre of deposition. The unit of lead is 50m. } It is the average height through which the earth has to be lifted from source to the place of spreading or heaping. The unit of lift is 2.00m for first lift and one extra lift for every 1.0m.

DETAILED SPECIFICATIONS Earthwork in excavation in foundation - Earthwork & Excavation

Excavation Earthwork & Excavation14 } Foundation trenches shall be dug out to the exact width of foundation concrete and the side shall be vertical. If the soil is not good and does not permit vertical side ,the sides should be back or protected with timber shoring. Excavated earth shall not be placed with in 1m (3’) of the edge of the trench.

Finish of trench Earthwork & Excavation15 } The bottom of foundation trenches shall be perfectly levelled both longitudinally and transversely and the side of the trench shall be dressed perfectly vertical from bottom up to the lest thickness of loose concrete so that concrete may be laid to the exact width as per design. The bed of the trench shall be lightly watered and well rammed. Excess digging if done through mistake shall be filled with concrete at the expense of the contractor. Soft or defective spots shall be dug out and remove filled with concrete shall not be laid before the inspection and approval of the trench by the engineer-in- charge.

Finds Earthwork & Excavation16 } Any treasure and valuables or materials found during the excavation, shall be property of the government. Water in foundation-water, if any accumulates in the trench, should be bailed or pumped out without any extra payment and necessary precautions shall be taken to prevent surface water to enter into the trench

Water in Foundations Earthwork & Excavation17 } Trench fillings- After the concrete has been laid masonry has been constructed the remaining portion of the trenches shall be filled up with earth in layers of 15cm(6”) and watered and well remmed . The earth filling shall be free from rubbish and refuse matters and all clods shall be broken before filling. Surplus earth not required , shall be removed and disposed , and site shall be levelled and dressed.

Trench fillings Earthwork & Excavation18 } After the concrete has been laid masonry has been constructed the remaining portion of the trenches shall be filled up with earth in layers of 15cm(6”) and watered and well remmed . The earth filling shall be free from rubbish and refuse matters and all clods shall be broken before filling. Surplus earth not required , shall be removed and disposed , and site shall be levelled and dressed.

Earthwork & Excavation19 Measurement } The measurement of the excavation shall be taken in cu m (cu ft) as for rectangular trench bottom width of concrete multiplied by the length of trenches even though the contractor might have excavated with sloping side for his convenience. Rate shall be for the completion of work for 30m(100ft) lead and 1.50m(5’) lift, including all tools and plants required for the completion of work. For every extra lead of 30m and every extra life of 1.5 separate extra rate is provided.

Earthwork & Excavation20 Excavation in saturated soil } Excavation in saturated soil or below sub-soil water level shall be taken under a separate item and shall be carried out in the same manner as above. Pumping or bailing out of water and remove of slush shall be included in the item. Timbering of the sides of trenches if required shall be taken under a separate item and pair separately. } Note – excavation on different kinds of soil mixed with mooram or karnkar or shingle, soft rock or decompose rock or shale hard rock , etc, shall be taken under separate items. The excavation shall be done on the same principle .

EARTH FILLING Earthwork Earth used for filling shall be free from saltpeter and white ants and only foamy and clayey soil free from clods shall be used.

It shall be laid in 15 cm layers and each layer shall be well watered and rammed with iron rammers. In case of high embankments, the layers shall not exceed 30 cm depth and the settlement allowances shall be made @ 10% of the height of uncomapacted fills.

Cross-section of earthwork of road in banking or in cutting is usually in the form of trapezium , and the quantity of earthwork may be calculated by the following methods: } Quantity or Volume = Sectional area x Length } Sectional area = Area of central rectangular portion + Area of two side triangular portions = Bd+2(1/2 sdxd) = Bd+sd2 } S:1 is the ratio of side slopes as horizontal : vertical. } Quantity = (Bd+sd2) x L } When the ground is in a longitudinal slope, the height of the bank or depth of cutting will be different at the two ends of the section, and mean height or depth may be taken for ‘d’ and sectional area at mid-section is taken out for mean height. Mean height = d1+d2 2 ROAD ESTIMATING 22 Earthwork & Excavation

ROAD ESTIMATING } Alternatively, sectional area of the two ends may be calculated and the mean of two sectional area is taken out. } Different kinds of soil as sandy, rocky, clayey etc., estimated separately as the rates vary. 23 Earthwork & Excavation.

ROAD ESTIMATING } METHOD 1. MID-SECTIONALAREA METHOD } Quantity = Area of mid-section x Length } Let d1 and d2 be the height of bank at two ends portion of embankment, L the length of the section, B the formation width and S:1 the side slope then, Area of mid-section = Area of rectangular portion + Area of two triangular portion = Bdm+2(1/2 sdm 2 )=Bdm+sdm 2 Quantity of earthwork = (Bdm+sdm 2)x L } The quantities of earthwork may be calculated in a tabular form as below : 24 Earthwork & Excavation.

ROAD ESTIMATING } AREA OF SIDE SLOPING SURFACE } The area of sides which may require turfing or pitching, may be found by multiplying the mean sloping breadth by the length. } The mean sloping breadth = √(sd2 +d2) } Area of both side slopes = 2L x d√s2 +1 } This may also be calculated in a tabular form 25 Earthwork & Excavation

ROAD ESTIMATING - MEAN SECTIONALAREA METHOD } Quantity = Mean sectional area x Length } Sectional area at one end A1=Bd1+sd1 2 } Sectional area at other end A2=Bd2+sd2 2 } d1 and d2 are heights or depth at the two ends Mean sectional area A= A1+A2 2 Quantity Q=A1+A2 x Length 2 } The quantities of earthwork may be calculated in a tabular form as below : 26 Earthwork & Excavation.

ROAD ESTIMATING } METHOD 3.PRISMOIDAL FORMULA METHOD } Quantity or Volume = L/6 (A1+A2+4Am) } Where A1 and A2 are the cross-sectional areas at the two ends of a portion of embankment of a road of length L, and Am is the mid-sectional area } Let d1 and d2 be the heights of bank at two ends, and dm be the mean height at the mid-section, B be the formation width and S:1 be the side slope. } Cross-sectional area at one end A1=Bd1+sd1 2 } Cross-sectional area at other end A2=Bd2+sd2 2 } Cross-section at middle dm= d1+d2 2 Am=Bdm+sdm 2 =B(d1+d2)+s(d1+d2)2 2 2 } Quantity = L/6 (A1+A2+4Am) = {B(d1+d2)+s(d1 2+d2 2+2d1d2)}x L 2 3 } The same is also applicable for cutting. 27 Earthwork & Excavation

1)Before the earthwork is started,the whole area where the work is to be done should be cleared of grass,roots of trees and unwanted debris.

2)Excavation should be carried out exactly in accordance with the dimensions shown on the drawings or any other dimension,as decided by the Site-in-Charge.

3)Sides of the trenches shall be vertical and it's bottom shall be perfectly levelled,both longitudinally and transversely.Where the soil is soft,loose or slushy,the trench shall be widened for allowing steps on either side or the sides sloped or shored up.

4)During excavation if rocks or rocky soils are found,they shall be levelled as far as possible and the small spaces which are difficult to level shall be filled in with concrete.

5)If the excavation is in earth,the bottom of the trenches shall be sprinkled with a little water and rammed.

6)No material excavated from the foundation trenches shall be placed nearer than one metre to the outer edges of the excavation.

7)Water in trenches must be bailed or pumped out and where it is apprehended that the sides may fall down or cave in,arrangement shall be made for adequate timber shoring.

8)When it is specified that the work is to be carried out without removing cables,pipes,sewers etc. all of them shall be temporarily shored and saved from any damage.

9)The cost of all materials and labour required for fencing/barricading in and protection against risk of accidents due to open excavation should be provided.

Types of excavation - excavation is the process of removing earth to form a cavity in the ground.

On small sites or in confined spaces, excavation may be carried out by manual means using tools such as picks, shovels and wheelbarrows. Larger scale excavation works will require heavy plant such as bulldozers and backactors. For more information, see Excavating plant.

Material types -

A common method of classification is by the material being excavated:

Topsoil excavation -

This involves the removal of the exposed layer of the earth’s surface, including any vegetation or decaying matter which could make the soil compressible and therefore unsuitable for bearing structural loads. The depth will vary from site to site, but is usually in a range of 150-300 mm.

Earth excavation

This involves the removal of the layer of soil directly beneath the topsoil. The removed material(referred to as 'spoil') is often stockpiled and used to construct embankments and foundations.

Rock excavation -

This is the removal of material that cannot be excavated without using special excavation methods such as drilling (by hand or with heavy machinery) or blasting with explosives.

Muck excavation

This is the removal of excessively wet material and soil that is unsuitable for stockpiling.

Unclassified excavation

This is the removal of a combination of the above materials, such as where it is difficult to distinguish between the materials encountered.

Excavation purpose -

Excavation can also be classified according to the purpose of the work:

Cut and fill excavation

This is the process of excavation whereby the material that is cut or stripped. The removed topsoil and earth can be used as fill for embankments, elevated sections, and so on. It can also be used to form a level surface on which to build, as elevated sections of the site are ‘cut’ and moved to ‘fill’ lower sections of the site.

Trench excavation

A trench is an excavation in which the length greatly exceeds the depth. Shallow trenches are usually considered to be less than 6 m deep, and deep trenches greater than 6 m.

Trench, or footing, excavation is typically used to form strip foundations, buried services, and so on. The choice of technique and plant for excavating, supporting and backfilling the trench depends on factors such as; the purpose of the trench, the ground conditions, the trench location, the number of obstructions, and so on.

The common techniques that are used include:

§ Full depth, full length: Suitable for long narrow trenches of shallow depth, such as pipelinesand sewers.

§ Full depth, successive stages: Suitable for deep trenches where works can progress in sequence, reducing the risk of collapse.

§ Stage depth, successive stages: Suitable for very deep trenches in confined areas, deep foundations and underpinning.

Basement excavation

A basement is part of a building that is either partially or completely below ground level. For more information, see Basement excavation.

Road excavation

This typically involves stripping topsoil and cut-and-fill. For more information, see Road construction.

Bridge excavation

This typically involves the removal of material for the footing and abutments of bridges. The work may be subdivided into wet, dry and rock excavation. Underwater excavations may require special methods of drill and blast. For more information, see Bridge construction.

Dredging

Dredging is the process of excavating and removing sediments and debris from below waterlevel, typically from the bottom of lakes, rivers, harbours, and so on. For more information, see Dredging.

Over excavation

Excavation that goes beyond the depth which is required for the formation of a below groundstructure due to the presence of unsuitable material that must be removed.

Materials have different stability characteristics during excavation works. The ‘angle of repose’ of the material describes the steepest angle at which it will remain stable without support. The exact angle of repose will depend on the presence of groundwater, but some typical angles are:

§ Drained clay: 45-degrees.

§ Wet clay: 16-degrees.

§ Gravel and dry sand: 40-degrees.

§ Wet sand: 22-degrees.

The type and extent of temporary support that is required will depend on the following factors:

§ The stability and angle of repose of the subsoil.

§ The proximity of the excavation to vehicles, services and buildings.

§ The level of the water table.

§ The type/s of subsoil.

§ The depth of the excavation.

§ The length of time the excavation will be left open.

§ The time of year and weather conditions.

The types of support that can be used include:

§ Timber supports: Commonly used for low risk, narrow trenches, shafts or headings.

§ Trench boxes: Can be placed in pre-excavated trenches in low-risk situations.

§ Trench sheets: Can be overlapping or interlocking, and are used to provide continuous support for deeper trenches.

§ Ground anchors and rock bolting.

§ Caissons.

§ Cofferdams.

Detail specification of earthwork in excavation in foundation are as below:-

Excavation- Foundation trenches shall be dug out to the exact width of foundation concrete and the side shall be vertical. If the soil is not good and does not permit vertical sides, the sides should be sloped back or protected with timber shoring. Excavated earth shall not be placed within 1m (3’) of the edge of the trench.

Finish of trench- The bottom of foundation trench shall be perfectly levelled both longitudinally and transversely and the sides of the trench shall be dressed perfectly vertical from bottom up to the least thickness of loose concrete may be laid to the exact width as per design. The bed of the trench shall be lightly watered and well rammed. Excess digging if done through mistake shall be filled with concrete at the expense of the contractor. Soft or defective spot shall be drug out and removed filled with concrete or with stabilized soil. If rock or boulder are found during excavation, these should be removed and the bed of the trenches shall be levelled and made hard by consolidating the earth. Foundation concrete shall not be laid before the inspection and approval of the trench by the engineer-in-charge.

Finds- Any treasure and valuables or materials found during the excavation, shall be property of the Government.

Water in foundation- Water, if any accumulates in the trench should bailed or pumped out without any extra payment and necessary precaution shall be taken to prevent surface water to enter into the trench.

Trench filling- After the concrete has been laid masonry shall be constructed the remaining portion of the trench shall be filled up with earth in layer of 15cm (6”) and watered and well rammed. The earth filling shall be free from rubbish and refuse matters and all clods shall be broken before filling. Surplus earth not required, shall be removed and disposed and site shall be levelled and dressed.
Measurement- the measurement of the excavation shall be taken in cu m (cu ft) as for rectangular trench bottom width of concrete multiplied by the vertical depth of foundation from general level and multiplied by the length of trenches even through the contractor might have excavated with sloping side for his convenience. Rate shall be for complete work for 30m (100 ft) lead and 1.50m (5’) lift, including all tools and plants required for the completion of the works. For extra lead of 30m and extra lift of 1.5m separate extra rate is provided.

Excavation in saturated soil- excavation in saturated soil or below sub-soil water level shall be taken a separate item and shall be carried out in the same manner as above. Pumping and bailing out of water and removal of slush shall be included in the item. Timbering of the sides of the trench if required shall be taken under a separate item and paid separately.

· Earthwork shall be taken in cu.m. and the length, breadth and height or depth shall be measured to get the cubic content.

· Earthwork of different nature as in excavation in foundation, in trenches, etc., and in filling in plinth, in banking, etc., shall be measured under separate items.

· Earthwork in different kinds of soil as ordinary soil, hard soil, ordinary rock, hard rock, etc., shall be classified separately and measured under separate item.

· Excavation shall include throwing of the excavated earth at least one meter clear of the edge of excavation.

· Dressing or trimming and leveling or grading, ramming and consolidation thickness of each layer, etc., shall be described and included in the item of earthwork.

· Measurement of excavation or trenches or borrow pits shall be taken for average dimensions.

· When the ground is fairly uniform ‘Deadman” or “Tell-Tales” which shall be left at suitable intervals to determine the average depth of excavation.

· For uneven or sloping ground, diagonal ‘Tell-Tales’ shall be left.

· No deduction shall be made for Deadman, Tell-Tales which shall be removed after the measurements have been taken and checking has been completed.

· When the ground is very uneven, levels shall be taken before the start and after the completion of the earthwork by leveling instrument and the average depth of excavation or filling shall be determined from these levels.

· Whenever it is not possible or convenient to make measurements from cutting, the filling or banking shall be measured and deduction for shrinkage or voids (settlement allowances) shall be made from actual measured cubic contents depending on the nature of the soil and methods of consolidation.

· Generally, 10% deduction shall be made in caser of ordinary consolidated fills and in case of consolidation done by heavy machinery, a deduction of 5% shall be made.

· Lead and lift:

a) The measurement shall be taken separately for every 30 m lead or distance and every 1.5 m lift or height or depth.

(b) The lead shall be measured from the centre of the area of excavation to the centre of the area of spoil heap.

(d) The normal rate is for each unit of 30 m lead and 1.5 m lift. For grater lead or lift, the rate shall be different for every unit of 30 m lead, and for every unit of 1.5 m lift.

· Foundation trench:

a) Unless otherwise specified, the foundation trench shall be measured in cu.m. for rectangular section, bottom width being width of concrete and the depth shall be measured as vertical depth even though the contractor might have excavated with sloping sides for convenience.

· Return, fill and ram:

(a) Returning, filling and ramming excavated earth shall be taken in cu.m. under a separate item and shall include spreading in layers of 20 cm in depth, watering, ramming and leveling.

· Puddling:

(a) Clay puddle work shall be taken in cu.m. and shall be described including supply of clay, its preparation, placing in layer of 15 cm, ramming, etc.

· Surface dressing:

(a) Trimming and dressing of natural ground to remove vegetation and small irregularities not exceeding 15 cm deep shall be taken in sq.m. under a separate item ‘Surface Dressing’.

(b) Cutting down of trees exceeding 30 cm girth shall be accounted separately and enumerated i.e., taken in numbers, stating the girth at 1 m above ground and paid separately.

· Surface excavation:

(a) Excavation exceeding 1.5 m in width as well as 10 sq.m. in plan but not exceeding 30 cm in depth shall be described as Surface excavation and measured in sq.m.

· Pumping:

(a) When spring water requires pumping, the work of pumping and dewatering shall be taken under separate item.

· Timbering:

(a) Timbering or ‘Planking and Strutting’ for protecting the sides of trench or loose earth, shall be measured in sq.m. of face supported, and shall be classified under separate items as: –

(b) Depth not exceeding 1.5 m,

(d) Depth exceeding 5 m.

(e) Timbering shall include all necessary timber work including walls, struts, poling boards, etc.

(f) Both sides of trench shall be taken as one side area and shall be equal to length x depth of timbering.

As per I.S. 1200 of 1974, the measurement of the item of earth work shall be carried out as follows:

· Earth work in excavation and earthwork in filling or embankment are to be considered separately under different items and shall be measured in cubic metres by multiplying the length of excavation (or filling) by its width (or breadth) and the depth (or height). i.e., Quantity of earth work = L x B x D (or H) cubic metres subject to the dimensions of L,B and D (or H) as shown on the drawings.

· It is necessary to record the measurement of excavation item separately for every additional 1.5 m lift and also for additional different leads (i.e., disposing off the excavated material beyond the boundary of the proposed work) as the rates of excavation will vary according to different lifts and leads.

· As the same excavated material is usually used for ‘back filling’ (i.e., return fill and ramming the portion of the gap between the original portion of the excavated ground and the completed masonry in foundations) no separate provision is necessary for this work.

· In case of sand filling in plinth, this item is to be taken separately and measured in cubic metres.

· The Excavation in different soil strata is usually classified as follows:

1. Ordinary loose soft soil

2. Hard soil

3. Soft murum

4. Hard murum

5. Soft rock

6. Hard rock requiring blasting

7. Hard rock requiring chiseling

· Usually shoring, strutting, preparing the foundation bed and dewatering, if necessary, is also included under this item.

Rate analysis of excavation in earthwork is the measure of quantity of excavation to be carried out, the cost of equipment, machineries and labors required for the same.

The cost of excavation depends on the depth of excavation, type of soil, method of excavation to be carried out and the distance where the excavated soil has to be disposed. The cost of all these are added for unit volume of excavation to get the rate of excavation.

The cost of excavation based on depth is generally divided into categories as:

o For depth upto 1.5m

o For depth between 1.5m to 3m.

o For depth between 3.m to 4.5m.

o For depth more than 4.5m

The depth of excavation required varies from project to project and from place to place. Many factors influence the depth of excavation. We will not go into the details about the same.

Summarizing above points, it can be seen that the rate analysis for excavation work can be divided by following ways:

The first method is the selection of type of soil to be excavated and lead distance where the soil has to be disposed off. Then the other variable that is considered is the depth of excavation and is presented in the rate analysis description as follows:

1. Excavation in earthwork for soft soil for a lead distance of 1km for following depths:

a) Up to 1.5m

b) 1.5m to 3m

c) 3m to 4.5m

Excavation in earthwork for hard soil/ hard rock for a lead distance of 1km for following depths:

a) Up to 1.5m

b) 1.5m to 3m

c) 3m to 4.5m

In the above examples of excavation, more number of descriptions are possible with different lead distance and type of soil. During tendering of civil engineering works, all the possible combinations are presented for quotations depending on the project requirements and site conditions.

Rate Analysis of Excavation:

Following points to be noted before starting rate analysis of soil:

o Type of soil

o Lead distance and transport for carrying excavated soil

o Depth of excavation

o Method of excavation – manual excavation or mechanical excavation

o Capacity of labor for manual excavation

o Capacity of equipment for mechanical excavation and their cost per unit quantity.

o Water charges if used

o Profit of contractor

We will see an example of excavation of soft soil for a depth up to 1.5m and lead distance of 50m per 10m³ of concrete.

Items	Units	Qty.	Rate	Amount
Hydraulic Excavator	Day	0.04125	5000	206.25
Tractor/Dumper	Day	0.04125	1500	61.88
Unskilled Labor	Day	1.20	311.2	373.44
Total				641.57
Water charges @1% total				6.42
Contactor Profit @15%				96.23
			SUM	744.22
Gross Amt./CUM up to 1.5m depth		COST	74.42

In the above example, the coefficient of quantity of hydraulic excavator, tractor / dumper and unskilled labors are based on their capacity per day (8 hours of work).

Lets say for 10m3, the hydraulic excavator is taking 0.04125 day. Then its capacity considered is ((1×10)/0.04125) = 242.4242 m³ / day.

That means, a hydraulic excavator can excavate 242.4242 m³ of soil in one day. Its cost per day including driver and fuel is Rs. 5000. Then the cost of 10m³ of excavation can be calculated as:

No. of days required for 10m³ excavation = 10/242.4242 = 0.04125 days.

The cost of hydraulic excavator for 10m³ excavation = 0.04125×5000 = Rs.206.25

Likewise, based on the capacity of other equipment, labors etc., their cost is calculated. Contractors profit is also added to the total cost of labors and machineries. Then grand total gives the rate of excavation per 10m³ of soil excavation.

Different mechanical equipment have different capacity per day for excavation work. Their coefficient per m³ or per 10m³ should be considered for calculation.

1. EARTHWORK: EXCAVATION AND PREPARATION FOR FOUNDATIONS

EXCAVATION.

GENERAL. In general, excavation for subsurface structures will consist of open excavation as well as shaft and tunnel excavation. Where excavation to great depths is required, a variety of soils and rock may be encountered at a single site. Soils may range through a wide spectrum of textures and water contents. Rock encountered may vary from soft rock, very similar to a firm soil in its excavation requirements, to extremely hard rock requiring extensive blasting operations for removal. Groundwater may or may not be present. The groundwater conditions and the adequacy of groundwater control measures are important factors in excavation, in maintaining a stable foundation and in backfilling operations. The extent to which groundwater can be controlled also influences the slopes to which the open excavation can be cut, the bracing required to support shaft and tunnel excavation, and the handling of the excavated material.

GOOD CONSTRUCTION PRACTICES, AND PROBLEMS. A majority of the problems encountered during excavation are related to groundwater conditions, slope stability, and adverse weather conditions. Many of the problems can be anticipated and avoided by preconstruction planning and by following sound construction practices.

GROUNDWATER. Probably the greatest source of problems in excavation operations is groundwater. If the seepage of groundwater into an excavation is adequately controlled, other problems will generally be minor and can be easily handled. Several points should be recognized that, if kept in mind, will help to reduce problems attributable to groundwater. In some instances, groundwater conditions can be more severe than indicated by the original field exploration investigation since field explorations provide information only for selected locations and may not provide a true picture of the overall conditions.

IF GROUNDWATER SEEPAGE BEGINS to exceed the capacity of the dewatering system, conditions should not be expected to improve unless the increased flow is known to be caused by a short-term condition such as heavy rain in the area. If seepage into the excavation becomes excessive, excavation operations should be halted until the necessary corrective measures are determined and affected. The design and evaluation of dewatering systems require considerable experience that the contractor or the owner often does not possess, and therefore the assistance of specialists in this field should be obtained.

GROUNDWATER WITHOUT SIGNIFICANT SEEPAGE flow can also be a problem since excess hydrostatic pressures can develop below relatively impervious strata and cause uplift and subsequent foundation or slope instability. Excess hydrostatic pressures can also occur behind sheet pile retaining walls as well as shoring and bracing in shaft and tunnel excavations. Visual observations should be made for indications of trouble, such as uncontrolled seepage flow, piping of material from the foundation or slope, development of soft wet areas, uplift of ground surface, or lateral movements.

ACCURATE DAILY RECORDS should be kept of the quantity of water removed by the dewatering system and of the piezometric levels in the foundation and beneath excavation slopes. Separate records should be kept of the flow pumped by any sump-pump system required to augment the regular dewatering system to note any increase of flow into the excavation. Flowmeters or other measuring devices should be installed on the discharge of these systems for measurement purposes. These records can be invaluable in evaluating “Changed Condition” claims submitted by the contractor.

The contractor should be required to have “standby” equipment in case the original equipment breaks down.

1.1.2.2 SURFACE WATER. Sources of water problems other than groundwater are surface runoff into the excavation and snow drifting into the excavation. A peripheral, surface-drainage system, such as a ditch or berm, should be required to collect surface water and divert it from the excavation. In good weather there is a tendency for the contractor to become lax in maintaining this system and for the inspection personnel to become lax in enforcing maintenance. The result can be a sudden filling of the excavation with water during a heavy rain and consequent delay in construction. The surface drainage system must be constantly maintained until the backfill is complete. Drifting snow is a seasonal and regional problem, which can best be controlled by snow fences placed at strategic locations around the excavation.

1.1.2.3 SLOPE INTEGRITY. Another area of concern during excavation is the integrity of the excavation slopes. The slopes may be either unsupported or supported by shoring and bracing. The lines and grades indicated in the plans should be strictly adhered to. The contractor may attempt to gain additional working room in the bottom of the excavation by steepening the slopes; this change in the plans must not be allowed.

1.1.2.3.1 WHERE SHORING AND BRACING ARE NECESSARY to provide a stable excavation, and the plans and specifications do not provide details of these requirements, the contractor should be required to submit the plans in sufficient detail so that they can be easily followed and their adequacy checked. The first principle of excavation stabilization, using shoring and bracing, is that the placing of supports should proceed with excavation. The excavation cut should not be allowed to yield prior to placing of shoring and bracing since the lateral pressures to be supported would generally be considerably greater after yield of the unshored cut face than if no

movement had occurred prior to placement of the shoring. All safety requirements for shoring and bracing should be strictly enforced.

1.1.2.3.2 THE INSPECTOR must be familiar with stockpiling requirements regarding the distance from the crest of the excavation at which stockpiles can be established and heavy equipment operated without endangering the stability of the excavation slopes. He must also know the maximum height of stockpile or weight of equipment that can be allowed at this distance.

1.1.2.3.3 EXCESSIVE EROSION of the excavation slopes must not be permitted. In areas subject to heavy rainfall, it may be necessary to protect excavation slopes with polyethylene sheeting, straw, silt fences, or by other means to prevent erosion. Excavation slopes for large projects that will be exposed for several seasons should be vegetated and maintained to prevent erosion.

1.1.2.4 STOCKPILING EXCAVATED MATERIAL. Generally, procedures for stockpiling are left to the discretion of the contractor. Prior to construction, the contractor must submit his plans for stockpiling to the contracting officer for approval. In certain cases, such as where there are different contractors for the excavation and the backfill phases, it may be necessary to include the details for stockpiling operations in the specifications. In either case, it is important that the stockpiling procedures be conducive to the most advantageous use of the excavated materials.

1.1.2.4.1 AS THE MATERIALS ARE EXCAVATED, they should be separated into classes of backfill and stockpiled accordingly. Thus the inspection personnel controlling the excavation should be qualified to classify the material and should be thoroughly familiar with backfill requirements. Also, as the materials are placed in stockpiles, water should be added or the materials should be aerated as required to approximate optimum water content for compaction. Field laboratory personnel can assist in

determining the extent to which this is necessary. The requirements of shaping the stockpile to drain and sealing it against the entrance of undesirable water by rolling with spreading equipment or covering with polyethylene sheeting should be enforced. This step is particularly important for cohesive soils that exhibit poor draining characteristics and tend to remain wet once saturated by rain. Stockpiles must be located over an area that is large enough to permit processing where they will neither interfere with peripheral drainage around the excavation nor overload the slopes of the excavation.

IN CASES where significant energy and cost saving can be realized, special stockpiling requirements should be implemented. An example would be a large project consisting of a number of excavation and backfilling operations. The excavation material from the first excavation could be stockpiled for use as backfill in the last excavation. The material from the intermediate excavations could in turn be immediately used as backfill for the subsequent phases of the project and thereby eliminate double handing of excavated backfill for all but the first-phase excavation.

PROTECTION OF EXPOSED MATERIAL. If materials that are exposed in areas, such as walls of a silo shaft, foundation support, or any other area against which concrete will be placed, are susceptible to deterioration or swell when exposed to the weather, they should be properly protected as soon after exposure as possible. Depending on the material and protection requirements, this protection may be pneumatic concrete, asphalt spray, or plastic membrane. In the case of a foundation area, the contractor is required to underexcavate leaving a cover for protection, as required, until immediately prior to placement of the structure foundation. Any frost- susceptible materials encountered during excavation should be protected if the excavation is to be left open during an extended period of freezing weather.

EXCAVATION RECORD. As the excavation progresses, the project engineer should keep a daily record of the type of material excavated and the progress made.

This record would be of value if subsequent claims of “Changed Conditions” are made by the contractor.

FOUNDATION PREPARATION.

1- GENERAL

In this discussion, preparation applies to foundations for backfill as well as those for structures to be placed in the excavation. Generally, if proper excavation procedures have been followed, very little additional preparation will be required prior to backfill placement GOOD CONSTRUCTION PRACTICES, AND PROBLEMS. As mentioned previously, the problems associated with foundation preparation are greatly reduced by following such proper excavation procedures as maintaining a dry excavation and planning ahead. The principles of good foundation preparation are simple, but enforcing the provisions of the specifications concerning the work is more difficult. Inspection personnel must recognize the importance of this phase of the work since, if not properly controlled, problems can result.

IT IS MOST IMPORTANT that a stable foundation be provided. Thus it may be necessary, particularly in the case of sensitive fine grained materials, to require that the final excavation for footings be carefully done with hand tools and that no equipment be allowed to operate on the final cut surface. To provide a working platform on which to begin backfill placement on these sensitive materials, it may be necessary to place an initial layer of granular material.

IF THE FOUNDATION IS TO BE SUPPORTED ON ROCK, the soundness of the exposed rock should be checked by a slaking test (soaking a piece of the rock in water to determine the resulting degree of deterioration) and visual observation to determine if the rock is in a solid and unshattered condition. If removal of the rock below.

the foundation level is required, the space should be filled with concrete. A qualified geological or soils engineer should inspect the area if it is suspected that the material will deteriorate or swell when exposed to the weather. If necessary, the materials must be protected from exposure.

BEFORE PLACEMENT OF ANY STRUCTURE FOUNDATION is begun, the plans should be rechecked to ensure that all required utilities and conduits under or adjacent to the foundation have been placed, so that excavating under or undermining the foundation to place utilities and conduits will not become necessary later.

OCCASIONALLY, it may be found upon completion of the excavation that if a structure was placed as shown on the plans, it would be supported on two materials with drastically different consolidation characteristics, such as rock and soil, rock and backfill, or undisturbed soil and backfill. This situation could occur because the predesign subsurface information was inadequate, because the structure was relocated or reoriented by a subsequent change in the plans, because of an oversight of the design engineer, or because of the excavation procedures followed by the contractor. Regardless of the reason, measures such as overexcavation and placement of subsequent backfill should be taken, where possible, and in coordination with the design office to provide a foundation of uniform material. Otherwise, the design office should evaluate the differences in foundation conditions for possible changes to the structural foundation elements.

PREPARING THE AREA TO RECEIVE THE BACKFILL consists of cleaning, leveling, and compacting the bottom of the excavation if the foundation is in soil. All debris and foreign material, such as trash, broken concrete and rock, boulders, and forming lumber, should be removed from the excavation. All holes, depressions, and trenches should be filled with the same material as that specified to be placed immediately above such a depression, unless otherwise designated, and compacted .

the density specified for the particular material used. If the depression is large enough to accommodate heavy compacting equipment, the sides of the depression should have a positive slope and be flat enough for proper operation of compaction equipment. After the area is brought to a generally level condition by compacting in lifts in accordance with specifications, the entire area to receive backfill should be sacrificed to the depth specified, the water content adjusted if necessary, and the area compacted as specified. If the foundation is in rock, the area should be leveled as much as possible and all loose material removed.

ALL WORK IN THE EXCAVATION - should be accomplished in the dry; therefore, the dewatering system should be operated for the duration of this work. Under no circumstances should the contractor be allowed to dry an area by dumping a thick layer of dry material over it to blot the excess water. If soil exists at the foundation level and becomes saturated, it cannot be compacted. The saturated soil will have to be removed and replaced or drained sufficiently so that it can be compacted. Any frozen material in the foundation should be removed before placement of concrete footings or compacted backfill.

BACKFILL OPERATIONS

2.1 PLACEMENT OF BACK FILL.

GENERAL. Backfill construction is the refilling of previously excavated space with properly compacted material. The areas may be quite large, in which case the backfilling operation will be similar to embankment construction. On the other hand, the areas may be quite limited, such as confined areas around or between and beneath concrete or steel structures and areas in trenches excavated for utility lines. Prior to construction of the backfill, the inspection personnel should become thoroughly familiar with the various classes of backfill to be used. They should be able to readily identify the materials on sight, know where the various types of material should be placed, and be familiar with the compaction characteristics of the soil types.

GOOD CONSTRUCTION PRACTICES, AND PROBLEMS. Problems with placement of backfill will vary from one construction project to another. The magnitude of the problems will depend on the type of materials available such as backfill, density requirements, and the configuration of the areas in which compaction is to be accomplished. Problems should be expected during the initial stages of backfill compaction unless the contractor is familiar with compaction characteristics of backfill materials. The inspector can be of great assistance to the contractor during this period by performing frequent water content and density checks. The information from these checks will show the contractor the effects of the compaction procedures being used and point out any changes that should be made.

BACKFILLING PROCEDURES - Problems associated with the compaction of backfill can be minimized by following good backfilling procedures. Good backfilling procedures include: processing the material before it is placed in the excavation; placing the material in a uniformly spread loose lift of the proper thickness suited to the compaction equipment and the type of material to be used; applying the necessary compaction effort to obtain the required densities; and ensuring that these operations are not performed during adverse weather. Proper bond should be provided between each lift and also between the backfill and the sides of the excavation.

COMPACTION EQUIPMENT, BACKFILL MATERIAL - and zones. The type of compaction equipment used to achieve the required densities will usually depend upon the type of backfill material being compacted and the type of zone in which the material is placed.

IN OPEN ZONES, coarse-grained soils that exhibit slight plasticity (clayey sands, silty sands, clayey gravels, and silty gravels) should be compacted with either sheepsfoot or rubber-tired rollers; close control of water content is required where silt is present in substantial amounts. For sands and gravelly sands with little or no fines, good compaction results are obtained with tractor compaction. Good compaction can also be achieved in gravels and gravel-sand mixtures with either a crawler tractor or rubber-tired and steel-wheeled rollers. The addition of vibration to any of the means of compaction mentioned above will usually improve the compaction of soils in this category. In confined zones, adequate compaction of cohesionless soils in either the air-dried or saturated condition can be achieved by vibratory-plate compactors with a static weight of at least 100 pounds. If the material is compacted in the saturated condition, good compaction can be achieved by internal vibration (for example, by using concrete vibrators). Downward drainage is required to maintain seepage forces in a downward direction if the placed material is saturated to aid in compaction.

INORGANIC CLAYS- inorganic silts, and very fine sands of low to medium plasticity are fairly easily compacted in open zones with sheepsfoot or rubber-tired rollers in the 15,000-pound and above wheel-load class. Some inorganic clays can be adequately compacted in confined zones using rammer or impact compactors with astatic weight of at least 100 pounds provided close control of lift thickness and water content is maintained.

FINE-GRAINED, HIGHLY PLASTIC MATERIALS - though not good backfill materials, can best be compacted in open zones with sheepsfoot rollers. Sheepsfoot rollers leave the surface of the backfill in a rough condition, which provides an excellent bond between lifts. In confined areas the best results, which are not considered good, are obtained with rammer or impact compactors.

LIFT THICKNESS - The loose-lift thickness will depend on the type of backfill material and the compaction equipment to be used.

AS A GENERAL RULE -, a loose-lift thickness that will result in a 6-inch lift when compacted can be allowed for most sheepsfoot and pneumatic-tired rollers. Cohesive soils placed in approximately l0-inch loose lifts will compact to approximately 6 inches, and cohesionless soils placed in approximately 8-inch base lifts will compact to 6 inches. Adequate compaction can be achieved in cohesionless materials of about 12- to 15-inch loose-lift thickness if heavy vibratory equipment is used. The addition of vibration to rolling equipment used for compacting cohesive soils generally has little effect on the lift thickness that can be compacted, although compaction to the desired density can sometimes be obtained by fewer coverages of the equipment.

IN CONFINED ZONES- where clean cohesionless backfill material is used, a loose-lift thickness of 4 to 6 inches and a vibratory plate or walk-behind, dual-drum vibratory roller for compaction is recommended. Where cohesive soils are used as backfill in confined zones, use of rammer compactors and a loose-lift thickness of not more than 4 inches should be specified. Experience has shown that “two-by-four” wood rammers, or single air tampers (commonly referred to as “powder puffs” or “pogo sticks”) do not produce sufficient compaction.

DENSITY REQUIREMENTS- In open areas of backfill where structures will not be constructed, compaction can be less than that required in more critical zones. Compaction to 90 percent of CE 55 maximum dry density as obtained by MIL-STD-621 should be adequate in these areas. If structures are to be constructed on or within the backfill, compaction of cohesionless soils to within 95 to 100 percent of CE 55 maximum dry density and of cohesive soils to at least 95 percent of CE 55 should be required for the full depth of backfill beneath these structures. The specified degree of compaction should be commensurate with the tolerable amount of settlement, and the compaction equipment used should be commensurate with the allowable lateral pressure on the structure. Drainage blankets and filters having special gradation requirements should be compacted to within 95 to 100 percent of CE 55 maximum dry density. Table 5-1 gives a summary of the type of compaction equipment, number of coverages, and lift thickness for the specified degree of compaction of various soil types

COLD WEATHER- In areas where freezing temperatures either hamper or halt construction during the winter, certain precautions can and should be taken to prevent damage from frost penetration and subsequent thaw. Some of these precautions are presented below.

PLACEMENT OF PERMANENT BACKFILL - should be deferred until favorable weather conditions prevail. However, if placement is an absolute necessity during freezing temperatures, either dry, cohesionless, non-frost-susceptible materials or material containing additives, such as calcium chloride, to lower the freezing temperature of the soil water, should be used. Each lift should be checked for frozen material after compaction and before construction of the next lift is begun. If frozen material is found, it should be removed; it should not be disked in place. Additives should not be used indiscriminately since they will ordinarily change compaction and water content requirements. Prior laboratory investigation should be conducted to determine additive requirements and the effect on the compaction characteristics of the backfill material.

UNDER NO CIRCUMSTANCES - should frozen material, from stockpile or borrow pit, be placed in backfill that is to be compacted to a specified density.

PRIOR TO HALTING CONSTRUCTION- during the winter, the peripheral surface drainage system should be checked and reworked where necessary to provide positive drainage of surface water away from the excavation.

FOUNDATIONS BENEATH STRUCTURES- and backfill around structures should not be allowed to freeze, because structural damage will invariably develop. Structures should be enclosed as much as possible and heated if necessary. Construction should be scheduled so as to minimize the amount of reinforcing steel protruding from a partially completed structure since steel will conduct freezing temperatures into the foundation.

PERMANENT BACKFILL - should be protected from freezing. Records should be made of all temporary coverings that must be removed before backfilling operations are resumed. A checklist should be maintained to ensure that all temporary coverings are removed at the beginning of the next construction season.

DURING FREEZING WEATHER, records should be kept of the elevation of all critical structures to which there is the remotest possibility of damage or movement due to frost heave and subsequent thaw. It is important that frost-free bench marks be established to which movement of any structure can be referenced. Bench marks also should be established on the structures at strategic locations prior to freezing weather.

AT THE BEGINNING OF THE FOLLOWING- construction season and after the temporary insulating coverings are removed, the backfill should be checked for frozen material and ice lenses, and the density of the compacted material should be checked carefully before backfilling operations are resumed. If any backfill has lost its specified density because of freezing, it should be removed.

ZONES HAVING PARTICULAR GRADATION REQUIREMENTS- Zones that have particular gradation requirements include those needed to conduct and control seepage, such as drainage blankets, filters, and zones susceptible to frost penetration. Drainage zones are often extremely important to the satisfactory construction and subsequent performance of the structure. To maintain the proper functioning of these zones, care must be taken to ensure that the material placed has the correct gradation and is compacted according to specifications.

SPECIAL PROBLEMS- In open zones, compaction of backfill will not generally present any particular problems if proper compaction procedures normally associated with the compaction of soils are exercised and the materials available for use, such as backfill, are not unusually difficult to compact. The majority of the problems associated with backfill will occur in confined zones where only small compaction equipment producing a low compaction effort can be used or where because of the confined nature of the backfill zone even small compaction equipment cannot be operated effectively.

CONSIDERABLE LATITUDE- exists in the various types of small compaction equipment available. Unfortunately, very little reliable information is available on the capabilities of the various pieces of equipment. Depending upon the soil type and working room, it may be necessary to establish lift thickness and compaction effort based essentially on trial and error in the field. For this reason, close control must be maintained particularly during the initial stages of the backfill until adequate compaction procedures are established.

CIRCULAR, ELLIPTICAL AND ARCHED WALLED STRUCTURES - are particularly difficult to adequately compact backfill beneath the underside of haunches because of limited working space. Generally, the smaller the structure, the more difficult it is to achieve required densities. Rock, where encountered, must be removed to a depth of at least 6 inches below the bottom of the structure and the overdepth backfilled with suitable material before foundation bedding for the structure is placed. Some alternate bedding and backfill placement methods are discussed below.

ONE METHOD is to bring the backfill to the planned elevation of the spring line using conventional heavy compaction equipment and methods. A template in the shape of the structure to be bedded is then used to reexcavate to conform to the bottom contours of the structure. If the structure is made of corrugated metal, allowance should be made in the grade for penetration of the corrugation crests into the backfill upon application of load. Success of this method of bedding is highly dependent on rigid control of grade during reexcavation using the template. This procedure is probably the most applicable where it is necessary to use a cohesive backfill.

ANOTHER METHOD of bedding placement is to sluice a clean granular backfill material into the bed after the structure is in place. This method is particularly adapted to areas containing a maze of pipes or conduits. Adequate downward drainage, generally essential to the success of this method, can be provided by sump pumps or, if necessary, by pumping from well points. Sluicing should be accompanied by vibrating to ensure adequate soil density. Concrete vibrators have been used successfully for this purpose. This method should be restricted to areas where conduits or pipes have been placed by trenching, or in an excavation that provides confining sides. Also, this method should not be used below the groundwater table in seismic zones, since achieving densities high enough to assure stability in a seismic zone is difficult.

ANOTHER METHOD is to place clean, granular bedding material with pneumatic concrete equipment under the haunches of pipes, tunnels, and tanks. The material is placed wet and should have an in-place water content of approximately 15 to 18 percent. A nozzle pressure of 40 pounds per square inch is required to obtain proper density. Considerable rebound of material (as much as 25 percent by volume when placed with the hose nozzle pointed vertically downward and 50 percent with the nozzle pointed horizontally) occurs at this pressure. Rebound is the material that bounces off the surface and falls back in a loose state. However, the method is very satisfactory if all rebound material is removed. The material can be effectively removed from the backfill by dragging the surface in the area where material is being placed with a flat-end shovel. Two or three men will be needed for each hose operated.

FOR STRUCTURES AND PIPES that can tolerate little or no settlement, lean grouts containing granular material and various cementing agents, such as portland cement or fly ash, can be used. This grout may be placed by either method discussed above. However, grouts may develop hard spots (particularly where the sluice method is used that could cause segregation of the granular material and the cementing agent),

which could generate stress concentrations in rigid structures such as concrete pipes. Stress concentrations may be severe enough to cause structural distress. If lean grouts are used as backfill around a rigid structure, the structure must be designed to withstand any additional stress generated by possible hard spots.

INSTALLATION OF INSTRUMENTS. Installation of instrumentation devices should be supervised, if not actually done, by experienced personnel that specialize in instrumentation installation. The Owner must be familiar with the planned locations of all instruments and necessary apparatus or structures (such as trenches and terminal houses) so that necessary arrangements and a schedule for installation can be made. Records must be made of the exact locations and procedures used for installation and initial observations. Inspectors should ensure that necessary extensions are added for the apparatus (such as lead lines and piezometer tubes) installed within the backfill as the backfill is constructed to higher elevations. Care must be used in placing and compacting backfill around instruments that are installed within or throughthe backfill. Where necessary to prevent damage to instruments, backfill must be placed manually and compacted with small compaction equipment such as rammers or vibratory plates

POSTCONSTRUCTION DISTRESS. Good backfill construction practices and control will minimize the potential for post-construction distress. Nevertheless, the possibility of distress occurring is real, and measures must be taken to correct any problems before they become so critical as to cause functional problems with the facility. Therefore, early detection of distress is essential. Some early signs of possible distress include settlement or swelling of the backfill around the structure; sudden or gradual change of instrumentation data; development of cracks in structural walls; and adverse seepage problems. Detailed construction records are important for defining potential distress areas and assessing the mechanisms causing the distress.

THE PLANS AND SPECIFICATIONS define the project in detail and show how it is to be constructed. They are the basis of the contractor’s estimate and of the construction contract itself. The drawings show the physical characteristics of the structure, and the specifications cover the quality of materials, workmanship, and technical requirements. Together they form the guide and standard of performance that will be required in the construction of the project. Once the contract is let, the plans and specifications are binding on both the owner and the contractor and are changed only by written agreement. For this reason, it is essential that the contractor and the owner’s representative anticipate and resolve differences that may arise in interpreting the intent and requirements of the specifications. The ease with which this can be accomplished will depend on the clarity of the specifications and the training and experience of the individuals concerned. Understanding of requirements and working coordination can be improved if unusual requirements are brought to the attention of prospective bidders and meetings for discussion are held prior to construction. Situations will undoubtedly arise that are not covered by the specifications, or conditions may occur that are different from those anticipated. Close cooperation is required between the contractor and the inspection personnel in resolving situations of this nature; if necessary, to be fair to both parties a change order should be issued.

PREPARATION OF CONTRACT SPECIFICATIONS is easier if an outline of general requirements is available to the specification writer. However, it would be virtually impossible to prepare a guide specification that anticipates all problems that may occur on all projects. Therefore, contract specifications must be written to satisfy the specific requirement of each project. Some alternate specification requirements that might be considered for some projects are discussed below.

EXCAVATION. The section of the specifications dealing with excavation contains information on drainage, shoring and bracing, removal and stockpiling, and other items, and refers to the plans for grade requirements and slope lines to be followed in excavating overburden soils and rock.

DRAINAGE. For some projects the specifications will require the contractor to submit a plan of his excavation operations to the owner for review. The plans and specifications will require that the excavation and subsequent construction and backfill be carried out in the dry. To meet this requirement, a dewatering system based on the results of groundwater studies may be included in the plans. Also, for some projects the specifications may require the contractor to submit his plan for controlling groundwater conditions. The specifications should likewise indicate the possibility of groundwater conditions being different from those shown in the subsurface investigation report due to seasonal or unusual variations or insufficient information, since the contractor will be held responsible for controlling the groundwater flow into the excavation regardless of the amount. To this end, the specifications should provide for requiring the contractor to submit a revised dewatering plan for review where the original dewatering plan is found to be inadequate.

SHORING AND BRACING. The specifications either will require the contractor to submit for review his plans for the shoring and bracing required for excavation or will specify shoring and bracing required by subsurface and groundwater conditions and details of the lines and grades of the excavation. In the latter case, the contractor may be given the option to submit alternate plans for shoring and bracing for review by the owner. The plans will present the necessary information for the design of such a system if the contractor is allowed this option.

STOCKPILING. Provisions for stockpiling materials from the required excavation according to the type of backfill may or may not be included in the specifications. Generally, procedures for stockpiling are left to the discretion of the contractor, and a thorough study should be made to substantiate the need for stockpiling before such procedures are specified. There are several conditions under which inclusion of stockpiling procedures in the specifications would be desirable and justified. Two such conditions are discussed in the following paragraphs.

UNDER CERTAIN CONDITIONS, such as those that existed in the early stages of missile base construction where time was an important factor, it may be necessary or desirable to award contracts for the work in phases. As a result, one contractor may do the excavating and another place the backfill. It is probable that the excavation contractor will have little or no interest in stockpiling the excavated materials in a manner conducive to good backfilling procedures. When such a situation can be foreseen, the specifications should set forth stockpiling procedures. The justification for such requirements would be economy and optimum use of materials available from required excavation as backfill.

THE SPECIFICATIONS will contain provisions for removing, segregating, and stockpiling or disposing of material from the excavation and will refer to the plans for locations of the stockpiles. The subsoil conditions and engineering characteristics requirements may state that the specifications must be quite definite concerning segregation and stockpiling procedures so that the excavated materials can be used most advantageously in the backfill. The specification may require that water be added to the material or the material be aerated as it is stockpiled to the approximate optimum water content, that the stockpile be shaped to drain and be sealed from accumulation of excess water, and that the end dumping of material on the stockpile be prohibited to prevent segregation of material size or type along the length of the stockpile.

AN ALTERNATIVE to this latter action would be to specify the various classes of backfill required and leave the procedure for stockpiling the materials by type to the discretion of the contractor. In this case, the contractor should be required to submit a detailed plan for excavating and stockpiling the material. The plan should indicate the location of stockpiles for various classes of backfill so that the material can be tested for compliance with the specifications. The contractor may elect to obtain backfill material from borrow or commercial sources rather than to separate and process excavated materials. Then the specifications should require that stockpiles of the various classes of needed backfill be established at the construction site in sufficient quantity and far enough in advance of their use to allow for the necessary testing for approval, unless conditions are such that approval of the supplier’s stockpile or borrow source can be given.

FOUNDATION PREPARATION. The provisions for preparation for structures will generally not be grouped together in the specifications but will appear throughout the earthwork section of the specifications under paragraphs on excavation, protection of foundation materials, backfill construction, and concrete placement. When a structure is to be founded on rock, the specifications will require that the rock be firm, unshattered by blasting operations, and not deteriorated from exposure to the weather. The contractor will be required to remove shattered or weathered rock and to fill the space with concrete.

SPECIFICATIONS FOR STRUCTURES FOUNDED ON SOIL require the removal of all loose material and all unsuitable material, such as organic clay or silt, below the foundation grade. When doubt exists as to the suitability of the foundation materials, a soils engineer should inspect the area and his recommendations should be followed. When removal of rock material below the planned foundation level is required, the overexcavation will usually require filling with concrete. The specifications also

require dewatering to the extent that no backfill or structural foundation is placed in the wet.

SPECIFICATIONS FOR PREPARATION OF THE SOIL FOUNDATION - to receive backfill require removing all debris and foreign matter, making the area generally level, and scarifying, moistening, and compacting the foundation to a specified depth, generally 12 inches. Specific provisions may or may not be given with respect to leveling procedures.

BACKFILL OPERATIONS - The specifications define the type or types of material to be used for backfill construction and provide specific instructions as to where these materials will be used in the backfill, The percentage of CE 55 maximum dry density to be obtained, determined by a designated standard laboratory compaction procedure, will be specified for the various zones of backfill. The maximum loose-lift thickness for placement will also be specified. Because of the shape of the compaction curve, the degree of compaction specified can be achieved only within a certain range of water content for a particular compaction effort. Though not generally specified, the range of water contents is an important factor affecting compaction.

THE SPECIFICATIONS SOMETIMES STIPULATE- the characteristics and general type of compaction equipment to be used for each of the various types of backfill. Sheepsfoot or rubber-tired rollers, rammer or impact compactors, or other suitable equipment are specified for fine-grained, plastic materials. Noncohesive, freedraining materials are specified to be compacted by saturating the material and operating crawler-type tractor, surface or internal vibrators, vibratory compactors, or other similar suitable equipment. The specifications generally will prohibit the use of rock or rock-soil mixtures as backfill in this type of construction. However, when the use of backfill containing rock is permitted, the maximum size of the rock is given in the specifications along with maximum lift thickness, loading, hauling, dumping, and

spreading procedures, type of compaction equipment, and method of equipment operation. The specifications should protect areas where heavy equipment cannot operate. Rock-soil mixtures having greater than 8 to 10 percent binder should be prohibited in all areas.

Earth Work

EARTH WORK /EXCAVATION WORK