Engineering Characteristics And Utilization Study Of Crust Layer Of Highway Subgrade

Based on a case study of crust and underlying soft soil abtained form a highway subgrade in Hunan lakes region, mechanical properties of the crust and underlying soft soil were studied systematically by means of laboratory test, field test and numerical analysis.First, the causes and basic engineering characteristics of crust layer were analyzed. Physical and mechanical properties of the crust and underlying soft soil were compared through consolidation, permeability, triaxial shear test, the internal relation between two layers were also illustrated clearly.Second, through plate loading test, dynamic penetration test of unsame thinkness of crust layer and underlying soft soil carrying out in the field, planting earth pressure cell and pore water pressure sensors in different depth of subgrade to observe earth pressure and pore water pressure with the upper load variation, analyse of crust layer effect(diffusion), closure effect, lagged effect of settlement, surporting effect and back beam effect was presented. Then, a quick method of determining crust layer and its thickness was produced by proposed use of CPT.Third, influence of various Physical and mechanical parameters of crust layer on stress distribution was analyzed by means of numerical analysis.Results showed the major effect factors for the proliferation of crust layer including thickness, compression modulus and Poisson's ratio.Factors affecting proliferation of vertical stress were in order:thickness>compression modulus, Posson's ratio affected the vertical stress proliferation subtlely; level stress in order:Posson's ratio>thickness>compression modulus; with comprehensive consideration, factors affecting proliferation of stress in order:thickness> compression modulus>Posson's ratio.Finally, the engineering utilization conditions and technology of crust utilization were given based on the existing examples of projects, then, construction measures of excessive sedimentation, key points during construction and so on were disscussed, man-made hard shell layer were also analyzed and summarized.