PROVN OF RETAINING WALL NEAR BLDG NO P-4 (OFFRS MD ACCN) AT KATAPAHAR UNDER AGE (I) DARJEELING

PHASE-I

SOIL / GEOTECHNICAL INVESTIGATION a) Mobilization of suitable tools & equipment, personnel and materials from laboratory to site for conducting geo-technical investigation work including all accessories, transportation, temporary setting etc and demobilization of the same complete as per the directions of Engineer- In - Charge. The soil investigation should aim to provide data for design of soil strengthening/ control measures, slope stabilization, retaining walls with appropriate foundation depth. Sub Surface Investigation Conduct of SPT by making 100 mm dia or prescribed size dia bore in any strata/rock up to minimum 12m depth at every 10m running length of the proposed area ( number of bore holes-12), collecting/conducting tests at the depths of 1m ,2m, 3m,4.5m, 6m, 9m, 10.5m,12 m as per IS-1892 : 2021 and related latest IS Codes for soil investigation to include as stipulated in IS 2131 and IS 2720 latest editions. Location of the bore holes will be as per the directions of Engineer-In - Charge. b) Soil Investigation of Proposed site comprises with following test:- (i) Direct/Triaxial Shear Test (ii) Grain Distribution curves & pattern in bore holes (iii) Type of soil,C-values (iv) Bulk Density (v) Natural moisture content (vi) Dry Density Item Continued as 1.02

(vii) water table (viii) specific Gravity (ix) Atterberg limit (x) Hydrometer analysis (xi) Liquid & plastic limit (xii) Swelling index. Completion of laboratory test, collection of data, calculation of gross and net safe bearing capacity and preparation of report. NOTE : In order to conduct slope stability analyses and to design appropriate control measures for landslides, physical properties such as strength of slide plane, location and depth of slide plane and stable ground areas shall be determined. The appropriate tests out of the ones listed below shall be generally performed:- (a) Liquefaction analysis (As per IS 1893 Part-l (2016) for Earthquake analysis). (b) Soil mechanic tests as stipulated and applicable for the proposed site as per IS 2720 Parts 1 to 41 to include unconfined compression, tri-axial compression box shear, ring shear, and in- situ shear (Also refer to IS:7746-1991 for in-situ data sheet of shear test of rocks; IS:13047- 1991; section 3.2 of chapter 12 of the TRB Special Report 247, Landslides; Investigation and mitigation).

CONTOUR & DIGITAL TOPOGRAPHICAL SURVEY CONTOUR SURVEY : The site reconnaissance of area 1000.00 sqm shall include both site inspection and local enquiries concerning existing and proposed features on and adjacent to the site. With an approximate understanding of the overall topographic feature and knowledge of the distinction(s) of movement and aerial extent of the slide, a detailed field investigation plan can be developed to delineate the aerial extent and a general direction of movement of the landslide zone/scouring due to rain water assess the geology and geologic structure, estimate the cause(s) of the sliding/scouring, and predict future movement. The survey should include both the existing stretch of retaining walls and the stretch without retaining walls in order to evolve viable and sustainable structural solutions to stabilize the proposed stretch. Detailed Field Investigations and Mapping : A detailed investigation plan shall be drafted to delineate the : (a) Type of landslide, its size and mechanism and future possibilities. (b) Aerial extent of the slide, identification of the direction of deformation. (c) Location and shape of slide plane(s). (d) Nature of landslide block(s). (e) Possibility of further or future movement on slopes above the existing slide. (f) Distribution of ground water and its seasonal variation. (g) Type of soil in the site area. Item Continued as 1.04

A detailed geomorphological map should be evolved which should assist in design of ground strengthening and slope stabilizing measures. DIGITAL TOPOGRAPHICAL SURVEY : The digital topographical survey of the area shall be carried out with DGPS/suitable levelling instruments/appropriate field survey methods, capturing all existing major topographical feature of the area like trees, nalias, water bodies, roads railway lines, structure etc. Spot level shall be provided in 5m center and contours at 0.30 m interval or as specified by Engineer-in-Charge. The contour map evolved should include the profile of the Vulnerable damaged retaining wall from the foundation level to existing infrastructures in proposed area which should assist in design of retaining walls.

GEOPHYSICAL INVESTIGATION (a) Laboratory testing for soils : The geotechnical engineer should conduct sufficient in situ and/or laboratory testing to characterize the physical geotechnical parameters of the earth materials affecting the proposed development as specified in IS 2720 from Part 1-41. (b) Laboratory testing for rocks : The following testing of rocks shall be carried out :- (i) Preparation of rock specimen for laboratory testing as per IS:9179:1979. (ii) Determination of slope mass rating as per IS 13365. (iii) Determination of point load strength index of rocks as per IS:8764: 1998. (iv) Determination of unconfined compressive strength of rock materials as per IS 9143. (v) Determination of modulus of elasticity and Poisson's ratio of rock materials in uniaxial compression as per IS 9221. (vi) Determination of slake durability index of rocks as per IS 10050. (vii) Determination of tensile strength by indirect tests on rock specimens as per IS 10082. (viii) Determination of dynamic modulus of rock core specimens as per IS 10782. (ix) Determination of strength of rock materials in triaxial compression as per IS 13047. (x) Seismic testing of rock mass as per IS 13372.

GROUND WATER INVESTIGATION & SLOPE STABILITY ANALYSIS Investigation of ground water, shall includes determining ground water level, pore water pressure, ground water logging, ground water tracing test, pumping test, water quality analysis, electricity survey, geothermal survey, and geophysical logging (electric logging and radioactive logging). The seasonal variations in ground water and influence of ground water due to flooding by nearby natural source of water should be mapped during the investigation. Based on the results of the above measurements and tests, ground water control works can be planned and designed if affecting the stability of the proposed area as marked on Site Plan.