Seismic Refraction Survey for Subsurface Soil Layer Characterization at a Residential Complex Site in Hilla, Babylon Governorate, Iraq

The study's goal is to find the number of layers, their depths, velocities, elasticity coefficients, and geotechnical coefficients at the location. The geotechnical survey was calculated by using the refraction seismic survey method by calculating the velocity of compressional waves (P waves) and shear waves (S waves) by extending two perpendicular lines with forward, intermediate and reverse strokes for each line. The obtained data were processed by using the SeisImager program, where the velocity of waves for the first layer ranged from 263 to 306 m/s and VS range from 120 to 156 m/s, and the thickness of the first layer is 3 m. While the second layer VP range from 378 to 404 m/s and VS from 198 to 201 m/s, the thickness of the second layer is 6.5 m, the third layer VP range from 581to 783 m/s and VS from 316 to 411 m/s, the thickness of the third layer 11 m and the forth layer of VP range gtom 943 to 1106 and VS from 525 to 627 m/s. The dynamic elasticity coefficients were calculated, where Poisson's ratio ranged from 0.26 to 0.37, Young's modulus ranged from 65.14 to 1808.83 MPa, shear modulus ranged from 23.8 to 316.7 MPa, oedometric modulus ranged from 114.31 to 2309.92 MPa, and bulk modulus ranged from 82.58 to 681.32 MPa. The geotechnical coefficients were: concentration coefficient 3.71-4.80, material modulus -0.05--0.47, lateral earth pressure coefficient at rest (0.38-0.58), internal friction angle 10-41, and maximum bearing capacity 4.18-55.6 Tons/m2 in the site. The study showed no significant variation in wave velocity, and that the geotechnical coefficient values are low, indicating the absence of gaps or caverns at the depths reached.