IDAX Consulting and Research Pvt. Ltd.has bagged a contract from RITES Ltd. for the work “Geotechnical Investigation for Six Railway Tunnels between Km.138.475 to Km.147.625 in connection with doubling between Sikarpai and Randikena (IBS) section on Koraput – Singapur Road Doubling Project, East Coast Railway”
- Tender Reference Number: RITES/IS/GT/ECOR/SR/GT INVESTIGATION/2021
- Name of work: Geotechnical Investigation for Six Railway Tunnels between Km.138.475 to Km.147.625 in connection with doubling between Sikarpai-Randikena (IBS) section on Koraput-Singapur Road Doubling Project, East Coast Railway.
- Awarded Value: INR 24.44 lakhs
In February this year, the RITES had invited e-tenders for the Tender: RITES/IS/GT/ECOR/SR/GT INVESTIGATION/2021.
Brief Scope of Work:
According to the tender document, the brief scope of work includes:
- Exploratory drilling of vertical Boreholes of depths 30 to 80m in general (depth may slightly vary as per actual site condition). These bore holes shall be drilled at tunnel portals / along the alignment of tunnel.
- Conducting in-situ permeability test in bedrock at depth specified by Engineer Collection & preservation of core samples properly in core boxes as per IS 4078 (1980) and handing over of core boxes after completion of field work.
- Proper packing, handling and transportation of selected rock core samples from site to RITES GT Laboratory, RITES Bhawan, Plot No.1, Sector 29, Gurugram.
- Preparation of field and computer generated Geological bore logs of drilled boreholes and calculations of lugeon value from field permeability tests.
Field Investigation-soil/Overburden Drilling:
Boreholes:
- Boreholes shall be taken at specified locations to obtain information about the subsurface profile, its nature and strength. The diameter of the bore shall be 150 mm and boring shall be carried out in accordance with the provisions of IS: 1892 as per this specification.
- Casing pipe shall be used in the borehole to support its sides when a side fall is suspected to occur inside the borehole. When casing pipe is used, it shall be ensured that its bottom end is at all times less than 15 cm above the bottom of the borehole and not below the level at which the test has to be conducted or sampling has to be done. In case of cohesion less soils the advancement of the casing pipe shall be such that it does not disturb the soil to be tested or sampled. The casing shall be advanced by slowly turning the casing pipe and not by driving.
- The bore hole shall be cleaned using suitable tools up to the depth of testing or sampling, ensuring that there is minimum disturbance of the soil at the bottom of the bore hole. The process of jetting through an open tube sampler shall not be permitted. In cohesive soils, the bore hole may be cleaned using a bailer with a flap valve. Gentle circulation of drilling fluid shall be done when rotary mud circulation boring is adopted.
- On completion of the bore hole, the same shall be backfilled as directed by the Engineer In charge.
- It has to be ensured that casing does not advance ahead of the borehole under any circumstances.
Ground Water:
Ground water shall be recorded in all boreholes as per IS: 6935.
Field Investigation- Rock Drilling:
Drilling:
Hydraulic Rotary core drilling rigs shall be adopted by open holing through soft materials, or by drilling ahead in soft ground boring which has already been made. The substrata to be cored, may be soft, or may contain mixture of hard rock and soft weathered rocks. The drilling equipment used shall have an adequate capacity so as to ensure that required depths are reached and good quality rock core is recovered. The drilling equipment shall be hydraulically operated. The equipment, method and the procedure for drilling shall conform to IS: 1892.
- Drilling shall be carried out using NX / EX size diamond tipped drill bits, a double core barrel with core catchers shall be used to ensure continuous and good core recovery. Core barrels and core catchers shall be used for breaking off the core and retaining it when the rods are withdrawn, double tube core barrels shall only be permitted.
- Water shall be circulated continuously down the hollow rods and the washings at the surface shall be collected.
- A very high recovery ratio shall be aimed at in order to get a satisfactory undisturbed sample. Core of 1.5m length shall be aimed at. If the Engineer determines that poor core recovery is due to the inability of the drilling crew a new borehole will be drilled at no cost to the client.
- No drilling run shall exceed 1.5 m in length. If the core recovery is less than 80 % in any run, the Engineer shall be informed and the length of the subsequent run shall be reduced to 0.75 m.
- Prior to commencement of the drilling operations, the rig shall be properly weighted down, or anchored, so as to minimize vibrations and ensure maximum core recovery.
- Full observations in respect of the colours and nature of the return drill water, water loss and permeability, speed of drilling, core loss and other relevant details, shall be described as per relevant IS codes:
- The colour of return water at regular intervals, the depth at which any change of colour of return water is observed, the depth of occurrence and amount of flow of hot water, if encountered, shall be recorded.
- The depth through which a uniform rate of penetration was maintained, the depth at which marked change in rate of penetration of sudden fall of drill rod occurs, the depth at which any blockage of drill bit causing core loss, if any, shall be recorded.
- Any heavy vibration or torque noticed during drilling should be recorded together with the depth of occurrence.
- Special conditions, like the depth at which grouting was done during drilling, presence of artesian conditions, loss of drilling fluid, observations of gas discharge with return water etc., shall also be observed and reported.
Source: RITES-Tender update | Image Credit (representational): MoR
