Research On The Geological Properties Of Key Geological Layer Group In Suzhou

With the rapid development of urban economy, the rapid growth of population and the expasion of urban scale, urban engineering construction, especially underground engineering, occupied a pivotal position in the urban development. But urban engineering construction is restricted to geological environment. Many fragile and sensitive factors of urban geological environment became the key constraints of urban engineering construction, especially the distribution, geological characteristics and properties of weak and sensitive strata.The main work of this paper focused on studying the geological properties of key engineering geological formations in Suzhou region, and undertaking the regional evaluation of shallow foundation bearing stratum and pile load bearing stratum. By this way basic information and reference can be provided for urban engineering construction in Suzhou city.First of all, the sedimentary evolution characteristics of formations since the Quaternary in Suzhou region was summarized. And the engineering geological formations were generalized and divided into10formations according to a large amount of borehole data in Suzhou region.Secondly, the engineering geological formations were diagnosed. Then the weak sensitive layers and advantage bearing layer which influence the underground engineering construction were chosen, and their distribution was also got. We undertook reliability test on drilling test results and supplementary12boreholes data provided by Institute of Geological Survey of Jiangsu Province during the geological survey in Suzhou region, to reduce the measurement error, exclude the abnormal data and select the independent samples while ensuring that the sample size of statistical demand was achieved.Thirdly, we statistically analyzed the above data and got representative indicators of key soil layer in Suzhou region, and compared the mean value of the same soil layer properties under different sedimentary environments. It was concluded that the difference between the mean values of marine soil layer was bigger than that between the mean values of terrestrial soil layer, and that paleogeographic environment had certain effects on the physical and mechanical properties of the sediment layers. Then we undertook linear regression on the above data and got many empirical relationships of each key layer group, such as the relationship between void ratio, compressibility, compression modulus and water content, plasticity index and liquid limit, internal friction angle and water content. Creep test was done on the samples taken from the third layer and the seventh layer soil, and the test result was compared with soft soil from other area, then the empirical relationship between creep coefficient and the plasticity index was fitted.Fourth, the geological properties of the seventh layer soil in Suzhou region were systematically studied. The seventh layer soil in Suzhou region was Coastal facies and mainly composed of Silty clay clip powder soil and silty sand, and was soft plastic-plastic flow state with a layered structure. The undisturbed soil was in plastic-soft plastic state. The micro structural of clay soil layer was not very strong, and silt and sand interlayer could play a reinforced role in undisturbed soil, so the undisturbed soil was in a good condition. While during the liquid-plastic limits test, the structure of undisturbed soil (mainly layered structure) was completely destroyed, meanwhile the join of silt and silty sand reduced the liquid limit of remolded soil largely, but the whole water content changed little, thus the state indicators of remolding soil became softened.Finally, according to the above research results, regional division was undertaken on the basis of advantage bearing stratum in Suzhou region. By this way a reference was provided for the investigation, evaluation and basic design of foundation in this region since now on.