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Experimental Study on the Consolidation Bahavior of Soft Clay under Vacuum Preloading

Author: TongJun
Tutor: ZhanLiangTong;ChenYunMin
School: Zhejiang University
Course: Geotechnical Engineering
Keywords: soft clay vacuum preloading vacuum combined surcharge preloading Rowe cell yield stress stress path compressibility coefficient of consolidation
CLC: TU411
Type: Master's thesis
Year: 2007
Downloads: 184
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The vacuum preloading method is utilized extensively in ground improvement engineering featuring with the advantage of exempting the hazard of instability of the foundation. Much of the former laboratory research production on vacuum preloading is obtained from the remolded soil sample experiment, so it is hard to reflect the\ influence of anisotropy of the natural clay and stress path imposed by the loading on the consolidation and compressible behavior of the soil.So the elemental experimental study simulating vacuum preloading consolidation for the undisturbed soil sample is carried out using the adapted Rowe cell consolidation system. It includes consolidation tests of 3 groups of soil sample with different initial stress level under vacuum and surcharge loading, respectively; the vacuum consolidation test with 3 different drainage boundaries and consolidation tests of 3 groups of soil sample with different initial stress level under vacuum combined surcharge loading, respectively. On the basis of the experimental results, the thesis analyzes and discusses the influence of initial stress, stress path and drainage boundary on the compressible and consolidation behavior of soft clay, and the consolidation and compressible behavior of soft clay under vacuum combined surcharge loading. Based on the experimental results and former research production, the methods to determine field compressible curves and the corresponding methods for calculating the settlement are proposed, the analytical solution to one dimensional consolidation of finite thickness homogeneous structural soft clay ground is employed to calculate the settlement and degree of consolidation of a given soil stratum, then the comparisons and analysis for the calculated results are made.The experimental results show that because of the anisotropy of the natural soil, the yield stress of undisturbed sample under vacuum loading(isotropic loading) is significantly less than that under surcharge loading(k0 loading). The ratio between the decrement under vacuum and surcharge loading is relevant with the initial stress state and the amount of the applied loading. The decrement of the soil sample under vacuum combined surcharge loading(80kPa surcharge+80kPa vacuum) is approximately 1.1~1.2 time to the summation of the decrement under surcharge and vacuum loading. The value of coefficient of consolidation under vacuum combined surcharge loading is greater than that under surcharge or vacuum loading. The computing results of the settlement and degree of consolidation on the field stratum demonstrate that the shallow stratum (such as less than 4m) induced by the vacuum loading yields less decrement than that induced by the corresponding surcharge loading, the deep stratum induced by both two types of loading basically yields equivalent decrement. Since the soil structure is destroyed earlier under vacuum loading than under surcharge loading, the consolidation velocity under vacuum loading is slower than that under surcharge loading.

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CLC: > Industrial Technology > Building Science > Soil mechanics,foundation engineering > Soil Test > Laboratory tests (indoor soil test )
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