earthwork and excavation

Earthwork & Excavation1

Earthwork & Excavation

Estimation and Costing


Earthwork & Excavation

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.


a) Soft / Loose Soilb) Hard/Dense Soilc) Mudd) Soft/Disintegrated Rock ( Not Requiring Blasting )e) Hard Rock( Requiring Blasting )f) Hard Rock( Blasting Prohibited)


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.


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.


Mud - A mixture of soil and water in fluid or weak solid state.


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.


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


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


Lead and Lift

Lead: Lift :

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 -


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 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 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 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


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 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.


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.


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 as above item 1.


EARTH FILLING 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


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.


ROAD ESTIMATING METHOD 1. MID-SECTIONAL AREA 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+sdm2

Quantity of earthwork = (Bdm+sdm2)x L

The quantities of earthwork may be calculated in a tabular form as below :


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


ROAD ESTIMATING

METHOD 2. MEAN SECTIONAL AREA METHOD Quantity = Mean sectional area x Length Sectional area at one end A1=Bd1+sd1

2

Sectional area at other end A2=Bd2+sd22

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 :


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(d12+d2

2+2d1d2)}x L

2 3 The same is also applicable for cutting.