02-SITE CLEARANCE& E.W
Before the earthwork is started, the area coming under cutting and filling shall be cleared of shrubs, vegetation, grass, brushwood, trees and saplings of girth up to 30 cm measured at a height of one metre above ground level and rubbish removed up to a distance of 50 metres outside the periphery of the area under clearance. The roots of trees and saplings shall be removed to a depth of 60 cm below ground level. The holes or hollows due to removal of old foundation shall be filled up with the earth, well consolidated to the required compaction and levelled.
The trees of girth above 30 cm measured at a height of one metre above ground shall be cut only after obtaining written permission of the Engineer. The roots of trees shall also be removed. Existing structures and services such as old buildings, culverts, fencing, water supply pipe lines, sewers, power cables, communication cables, drainage pipes etc. within or adjacent to the area if required to be diverted/removed, shall be diverted/dismantled as per directions of the Engineer.
If the site of a structure is such that surface water shall drain towards it, land may be dressed or drains laid out to divert the water away from the site.
Excavation in Soil
- During the excavation, the natural drainage of the area shall be maintained. Excavation shall be done from top to bottom. Undermining or undercutting shall not be done.
- In firm soils, the sides of the trenches shall be kept vertical up to a depth of 2.0 m from the bottom. For greater depths, the excavation profiles shall be widened by allowing steps of 50 cm width on either side after every 2.0 m from the bottom. Alternatively, the excavation can be done so as to give slope of 1:4 (1horizontal to 4 vertical).
- Where the soil is soft, loose or slushy, the width of steps shall be suitably increased or sides sloped or the soil shored up as directed by the Engineer.
- The excavation shall be done true to levels, slope, shape and pattern indicated by the Engineer.
- In case of excavation for foundation in trenches or over areas, the bed of excavation shall be to the correct level or slope and consolidated by watering and ramming. If the excavation for foundation is done to a depth greater than that shown in the Drawings or as required by the Engineer, the excess depth shall be made good with the concrete of the mix used for levelling/bed concrete for foundations.
- Soft/defective spots at the bed of the foundations shall be dug out and filled with concrete as directed by the Engineer.
- While carrying out the excavation for drain work care shall be taken to cut the side and bottom to the required shape, slope and gradient. The surface shall then be properly dressed. If the excavation is done to a depth greater than that shown on the Drawing or as required by the Engineer, the excess depth shall be made good with ordinary earth, properly watered and rammed.
Excavation in Ordinary/ Hard rock
- In ordinary rock, excavation shall be carried out by crowbars, pick axes or pneumatic drills and blasting operation shall not be generally adopted. Where blasting operations are not prohibited and it is practicable to resort to blasting for excavation in ordinary rock.
- Where hard rock is met with and blasting operations are considered necessary, shall obtain the approval of the Engineer in writing for resorting to the blasting operations. Blasting operations shall be done as specified and chiselling shall be done to obtain correct levels, slopes, shape and pattern of excavation as per the Drawings or as required by the Engineer.
- Rock excavation consists of the excavation and satisfactory disposal of all unaltered and un-weathered firm and rigid igneous, metamorphic and sedimentary solid rock that in the opinion of the Engineer can only be excavated by the use of pneumatic hammers or other such similar apparatus.
- Where blasting operations are prohibited or are not feasible, excavation in hard rock shall be done by chiselling.
- Blasting will not be permitted without prior approval from concerned authorities.
- Blasting work shall be done under careful supervision and trained personnel shall be employed.
- Blasting operations shall be carried out under the supervision of a responsible authorized agent, during specified hours as approved in writing by the Engineer.
- All procedures and safety precautions for the use of explosives, drilling and loading of explosives before and after shot firing and disposal of explosives shall be taken care as detailed in IS: 4081.
- The maximum of eight boreholes shall be loaded and fired at one occasion. The charges shall be fired successively and not simultaneously. Immediately before firing, warning shall be given and the agent shall see that all persons have retired to a place of safety. The safety fuses of the charged holes shall be ignited in the presence of the agent, who shall see that all the fuses are properly ignited.
- Careful count shall be kept by the agent and others of each blast as it explodes. In case all the charged boreholes have exploded, the agent shall inspect the site soon after the blast but in case of misfire the agent shall inspect the site after half an hour and mark red crosses (X) over the holes which have not exploded.
- The Engineer shall be informed of all cases of misfires, their causes and steps taken in that connection.
- The excavation shall be done manually or by mechanical means as directed by the Engineer after considering the feasibility, urgency of work, availability of labour/mechanical equipments and other factors involved.
- Earthwork by mechanical means involves careful planning keeping in view site conditions i.e. type of soil, nature of excavation, distances through which excavated soil is to be transported and working space available for employing these machines. The earthmoving equipment shall be selected accordingly.
- The earthmoving equipment consists of equipment for excavating and transporting materials. Excavating equipments may be further classified as excavators and tractor based equipment.
Excavation in under Water
- At locations where the excavation extends below the groundwater table, a dewatering system is to be provided which will lower ambient groundwater levels. The resulting groundwater level shall be at a depth which is sufficiently below the excavation level so as to allow the safe and proper execution of the work. The resulting foundation level shall be stable, which is suitable for the execution of subsequent operations.
- The Contractor is to design the dewatering methods and settling basins so that no critical amounts of soil, sand or silt are removed during dewatering operations.
- Complete working drawings showing the type of dewatering and groundwater control system proposed shall be submitted to the Engineer for his review and approval. The proposed location(s) should be indicated for the discharge of extracted groundwater. Guidelines to be followed shall be as per IS: 9758.
- The dewatering system design shall also include the details of measures required to prevent damage due to settlement of roads, pavements, utilities, sewers, buildings and other structures outside the excavation but within the area affected by the dewatering.
- All water that may accumulate in excavations during the progress of the work from springs, tidal or river seepage, broken water mains or drains and seepage from subsoil aquifer shall be bailed, pumped out or otherwise removed.
- Adequate measures for bailing and/or pumping out water from excavations and construct diversion channels, bunds, sumps, cofferdams etc.
- Pumping shall be done directly from the foundation trenches or from a sump outside the excavation in such a manner as to preclude the possibility of movement of water through any fresh concrete or masonry and washing away parts of concrete or mortar.
- During laying of concrete or masonry and for a period of at least 24hours thereafter, pumping shall be done from a suitable sump separated from concrete or masonry by effective means.
- Capacity and number of pumps, location at which the pumps are to be installed, pumping hours etc. shall be decided from time to time in consultation with the Engineer.
- Pumping shall be done in such a way as not to cause damage to the work or adjoining property by subsidence etc. Disposal of water shall not cause inconvenience or nuisance in the area or cause damage to the property and structure nearby.
- To prevent slipping of sides, planking and strutting may also be done with the approval of the Engineer.
Planking and Strutting
- When the depth of trench in soft/loose soil exceeds 2 m, stepping, sloping and/or planking and strutting of sides shall be done. In case of loose and slushy soils, the depths at which these precautions are to be taken shall be determined by the Engineer according to the nature of soil.
- Planking and strutting shall be ‘close’ or ‘open’ depending on the nature of soil and the depth of trench. The types of planking and strutting shall be determined by the Engineer.
- Guidance shall be taken from IS: 3764 for designing the shoring and strutting arrangements and specifying the profile of excavation. Works Department - Quality Control Manual
1. Fill Materials
- Suitable material for fill shall be approved soil with a liquid limit not exceeding 35% and a plasticity index not exceeding 10%. The material passing the 0.075 mm sieve shall not exceed 20% and the organic matter content shall not exceed 2% (As determined by relevant BIS).
- Where excavated rock is to be used as fill material elsewhere on the site, the excavated rock shall meet the requirement of the specification for fill material.
- The Contractor is responsible for mixing the excavated rock with suitable fill material imported and/or excavated from within the site should it be necessary in order to produce a suitable fill material that complies with the requirementsof the Specification.
- Unsuitable materials include the following:
- Organic material containing greater than 2% stumps and other perishable material.
- Material susceptible to spontaneous combustion.
- Soils of liquid limit exceeding 35% and/or plasticity index exceeding 10%.
- Material containing more than 5% of water soluble salts by weight of dry soil (Individually, water soluble chloride exceeding 1% or water soluble sulphate exceeding 1.5%) or more than 10% of acid soluble salts (Individually, acid soluble chloride exceeding 2% or acid soluble sulphate exceeding 3.0%) as determined by relevant BIS.
- Any other material which the Engineer may deem to be unsuitable for earthworks.
- All excavated material determined as suitable by the Engineer, is to be utilized as backfill.
2 Fill/ Backfill
- Back filling of the trench shall be carried out only after the permanent works therein have been approved and after the removal of any building debris or deleterious material from the trench.
- Selected excavated material will normally be used for backfilling in the manner described in the specifications or as directed by the Engineer. Where the excavated material is not considered suitable, selected material from an approved source is to be used.
- The backfill will be brought to a suitable level above ground to provide for anticipated settlement and unless indicated otherwise, is to be sloped away from the structure.
- The bottom of all excavations is to be probed and any poor bearing area shall be reported to the Engineer who will direct remedial work. Soft spots and other unsound materials are to be dealt with suitable measures as instructed by the Engineer.
- Fill shall be compacted by a suitable plate type vibrator, pedestrian operated vibrator roller, small tandem roller or other approved compaction plant.
- The material shall be placed in layers within the effective range of compaction of the plant provided that the maximum loose thickness of each layer does not exceed 200 mm.
- The material is to be watered and mixed as necessary to ensure that prior to compaction the moisture content of the whole layer is ±3% of the optimum moisture content. Compaction of each layer is to continue till 95% of the maximum dry density (MDD) has been achieved.
- All fill material used in earthwork shall be compacted as stipulated in the specification using equipment approved by the Engineer for that purpose.
- Potable water shall be preferred for compaction of all fill material within the area of excavation.
- All adjustment of moisture content shall be carried out in such a way that the specified moisture content remains uniform throughout compaction.
- No completed fill layer shall be covered by the next layer until it has been inspected and approved by the Engineer.
- Where fill material is to be deposited in areas where the existing ground is sloping, shall excavate benches so that fill material is deposited onto a horizontal surface. The levels of the benching terraces shall match the layers of the fill material that are deposited in the adjacent areas.
- Termites form nests or colonies underground in the soil near ground level in a stump or other suitable piece of timber in a conical or dome shaped mound. The termites find access to the superstructure of the building either through the timber buried in the ground or by means of mud shelter tubes constructed over unprotected foundations.
- Termite control in existing as well as new building structures is very important as the damage likely to be caused by the termites to wooden members of building and other house hold article like furniture, clothing, stationery etc. is considerable.
- Anti-termite treatment can be done either during the time of construction i.e. pre-constructional chemical treatment or after the building has been constructed i.e. treatment for existing building
- Prevention of the termite, from reaching the super-structure of the building and its contents can be achieved by creating a chemical barrier between the ground, from where the termites come and other contents of the building which may form food for the termites. This is achieved by treating the soil beneath the building and around the foundation with a suitable insecticide.
- Chemical treatment for the eradication and control of termites in existing building shall be done as per IS: 6313 (Part-3).
- Treatment shall be got done only from the approved specialized agencies using the chemical procured directly from reputed and authorized dealers.
QUALITY CONTROL ASPECTS
- The dry density/moisture content relationship will be determined by the heavy compaction test as per IS: 2720 (Part-8) for ensuring compaction of fill material at optimum moisture content.
- The test shall carry out moisture content determinations at frequent intervals or when there is a change in the material on the soils undergoing compaction so as to ensure that the moisture content of the soil is within the optimum range for the field compaction determined from compaction trials.
- Density of the compacted layers shall be determined regularly or as and when required by the Engineer in accordance with IS: 2720 (Part-28) or by any appropriate method.
- The control tests shall be carried out if the quantity of filling to be done is more than 50 m3.
1. IS:1904-Design and construction of foundations in soils: General requirements.
2. IS:3764-Code of safety for excavation work.
3. IS:9758-Guidelines for dewatering during construction.
4. IS:4081-Safety code for blasting and related drilling operation.
5. IS:4988-Glossary of terms and classification of earth-moving machinery:
6. IS: 12138-Earthmoving equipments.
7. IS: 6313-Code of practice for anti-termite measures in buildings:
(Part-2)-Pre-constructional chemical treatment measures.
(Part-3)-Treatment for existing buildings.
8. IS: 6940-Methods of test for pesticides and their formulations.
9. IS: 632-Gamma–BHC (Lindane) emulsifiable concentrates.
10. IS: 8944-Chlorpyrifos emulsifiable concentrates.
11. IS: 8963-Chlorpyrifos –Technical specifications.
12. IS: 2720-Methods of test for soils. (Parts 7 & 8)