Geotechnical assessment of Hilla City–Iraq

Abstract EN

Establishing a realistic working profile of soil properties has been, and is still, one of the most challenging problems facing geotechnical engineers.

Geotechnical assessment are important and plays a critical role in all construction works particularly in projects involved substantial amount of ground improvement, so, it was helped in suggesting design for appropriate control measures.

This study can provide and use as a reference and guidance to estimate site characterization of Hilla city that can be used as potential inputs for designing structures by the city planner, civil and geotechnical engineers.

In order to make a geotechnical evaluation and make a general description to determine types of the subsoil of the study area, Five boreholes was drilled to a depth of (15m) from existing ground surface at several sites and laboratory tests were carried out in each area of Hilla city, in addition to large existing data as a results of in-site and laboratory tests from previous geotechnical studies taken from 110 boreholes distributed over different area in Hilla city.

Chemical Analysis for soil and ground water were conducted and the results shows that ground water is small alkalinity, medium to high in salts and it has contain harmful amount of sulfates.

Result of chemical tests of soil shows that the sulphat contact of soil between (0.2-1.9) %, Percentage of Organic Matter Content (ORG) is between (0.03-0.06) %, Total soluble salts (T.S.S.) between (0.9-2.7) %, Gypsum content between (0.25-0.67) % and chloride content between (0.034-0.08) %.

The results shows that number of vales (N) of standard penetration test (SPT) is between (4-48) blow and elevation of water table is between (0.3-1.3) m below natural ground surface (N.G.S).

The moisture content (M.C) is between (19 %-34 %) of samples weight.

Specific gravity is between (2.67-2.76).

Results of analysis of grain size distribution indicate that the majority contents of soil profile consist of silt, sand and clay and this ratios are fluctuating with depth , also results indicates that the percentages of gravel content is between (0-7) %, clay content is between (10 %-66 %), silt content is between (14 %-70 %), and sand content is between (4 %-74 %).

Liquid limit (L.L) of soil is between (28 %-6١ %), Plastic limit (PL) is between (20-39) % and the plasticity index (P.I) is (4 %-26 %).

The average value of soil activity was between (0.56-0.7) and the soil is classified to non active soil.

Results from engineering properties of soil indicates the soil have permeability ranging between (6.1 x 10‾4 to 3.3 x 10‾3) cm / sec, compression index (Cc) between (0.06-0.3) for shallow depths, unconfined compression test (qu) between (47-155) Kn / m and the value of (cu) is between (2.6-4.4) ton / m2, and (u) is between (7-11) degree.

The dynamic and static methods was used to evaluate bearing capacity of soil and the results indicate that the allowable bearing capacity of soil are ranging between (4.3-7) Ton / m2 in different location in Hilla city.

The geotechnical assessment of Hilla city showed that the soil profile consist of clay-silt to silt-clay with small amount of sand below natural ground surface for shallow depths, therefore soil classified to clay with high and low plasticity limits, and silt with high and low plasticity limits fluctuating with depth and soil needs engineering treatments which depends on project type in some places in Hilla.