Usually open excavation shall be done with braced cut. Excavated soil shall be directly loaded dump trucks/tractors and transported to separate yard approved by the Engineer. The excavated soil suitable for backfilling shall be stock piled in the site/separate locations as. Any unsuitable excavated shall be disposal yard.
Excavation for structures such as thrust blocks, valve chambers shall be allowed 800mm working spaces in minimum.
Excavation length shall depend on,
• duration of ground water lowering
• effect of settlements to adjoining properties
• width of the road and traffic density
• existing services.
PRIOR TO THE EXCAVATION
Before starting excavation in any road, the approval shall be obtained from the Engineer and the relevant authorities (RDA) shall be informed with the detailed
work program and the relevant details (chainage of the roads, date of commencement, completion date of backfilling, planned dates of completion of temporary reinstatement and the date of handing over).
Excavation work shall be started only after,
• Granting the approval for the program by Engineer/relevant authorities.
• Granting the approval for the pipe and fittings.
• All the required plants are available for speedy work.
The available details of underground services shall be obtained by the relevant authorities and respective residence. The Contractor shall protect the underground services and utilities as far as possible.
6.2 CONTROL OF WATER
The Contractor shall keep the excavation free from water during the time of the construction and pipe installation by installing and operating all necessary machinery, appliances and equipments. Disposal of water shall not damage any private property, or should not create any nuisance to the public.
A suitable dewatering system shall be used for the excavation depths passes the water table level and for the excavation in the rainy season. The dewatering system shall be supervised and monitored by appropriate qualified personnel. Dewatering system shall be inspected by the Engineer if he/she needs.
EXCAVATION IN NARROW ROADS
Police permission shall be obtained in a rerouting of traffic.
Special consideration shall be paid to reroute traffic and make provisions to access adjoining building. Before start of the excavation the existing situation shall be photographed with the consent of property owner.
Possible damages to the boundary walls and other properties, the possibilities of repairing such damages with the least inconvenience to the owners and cost effective manner shall be discussed with the owners. The vicinities shall be informed at least one week earlier about the excavation. Excavation length along such roads shall be limited to the minimum. Excavation shall be carried out with an optimum care. Parking spaces and security for the parking premises shall be provided for the residents in case if they cannot use their usual parking place due to construction.
EXCAVATION NEAR UTILITIES
Edges of the trench shall be marked on the ground, cut with asphalt cutter and removed by JCB/excavator. Details of house connections for shops, etc shall be inquired and marked on the ground prior to the excavation work.
All services lines crossing or along the trench shall be exposed. Such services shall be temporary rerouted/modified wherever possible, to perform trenching operation. Every precaution shall be taken to avoid any damage to the existing services. Under the worst scenario they will be left as they are by providing the supports without disturbing to such services.
In case of interrupting water supply due to Contractor’s work, such situation shall be coordinated with the NWS&DB to rectify the situation immediately.
Overhead electric wires shall be protected from the construction vehicle operations. Temporary disconnecting the electric services/temporary shifting of electrical wires shall be arranged by coordinating with the relevant authority.
EXCAVATION NEAR EXISTING STRUCTURES
Any existing structures that cannot be temporarily relocated shall be preserved prior to the excavation proceed in the opinion of the Engineer. Above mentioned structures shall be carefully protected from damages by the Contractor.
In order to protect existing structure, the Contractor shall do shoring where required. The shoring method shall be submitted for the approval of the Engineer. For deep excavation very near to the existing structure, sheet pile shoring shall be used to protect the structures.
The arrangement made shall be approved by the Contractor and work should be hold until the Engineer’s decisions are issued.
Weathered rocks shall be removed by mechanical means as far as possible. Hard rock shall be removed by other means as agreed with the Engineer/reroute the pipeline trace.
HANDLING OF EXCAVATED MATERIAL
Excavated materials shall be dumped only in locations approved by the Engineer and relevant local authorities.
Materials that can be reused for backfilling shall be approved by the Engineer. Such material shall be protected from weather as far as possible.
All the other material shall be dumped legally.