Detailed Study On Structure Of Quaternary Stratum In Land Subsidence Area In Suzhou

In this paper, soil layer in which serious subsidence has happened in Shengze, Wuzhong, Suzhou was studied to conduct detailed study on structure of Quaternary stratum in land subsidence area in Suzhou. Specifically, structure of Quaternary soil layer in the observation hole in Shengze Middle School, Suzhou was particularly analysed through surface drilling sample, and laboratory test on liquid and plastic limits, shearing strength, consolidation, particle size analysis and qualitative and quantitative analysis of soil structure base on scanning electron microscope (SEM) image. The results can be illustrated below:(1) The stratum age and detailed stratifying were confirmed on the basis of field catalog of observation hole and existed stratum and water level data, besides the main compression layer as well as its aquifuge and aquifer were divided according to soil layer properties.(2) It was found from SEM analysis on soil layer microstructure that: with the increase of depth, soil microstructure changes from honeycomb to matrix, then to turbulent flow and last to laminar flow, while structure becomes compact and particle directionality improves, resulting in a smaller potential on compression deformation of soil layer.(3) According to particle size analysis, particle size of stratum of upper Pleistocene decreases with depth, while particle gradation improves and sorting worsens, hence this stratum was seafront phase sedimentary; Particle size of stratum of middle Pleistocene varies similar with upper Pleistocene with less clay content and this stratum was lakefront phase sedimentary; Late Pleistocene has multi-source sediments which is similar with upper and middle Pleistocene and soil particle experiences several upper to down and coarse to fine circles, hence this stratum was fluvial facies sedimentary. To the whole stratum, particle gradation worsens and sorting improves with depth and the potential of compaction deformation diminishes.(4) With the increase of depth, soil moisture declines and liquid index changes from plastic-flow-plastic to hard-plastic-hard, while cohesion grows and compressibility decreases. This finding meets the conclusion of detailed study on soil layer structure.(5) According to the results of consolidation test, most soil layers in Suzhou are medium compression soil. Hence, there is still a big compression potential in this area and land subsidence in Suzhou will be a long continuous process.(6) Taking test results of stratum structure, particle size analysis, Hydro-mechanical property into account, currently the primary potential of land subsidence is confined aquifer. However II confined aquifer is the main production layer of underground water, therefore, compression deformation in II confined aquifer will keep on developing if lacking a suitable control of underground water production; On the other hand, the potential of compression deformation in III confined aquifer is tiny considered its compact structure.