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The Experimental Study on Engineering Characteristics of the Soil with High Saturated Degree after Dynamic Consolidation and the Soil’s Constitutive Model

Author: YangWeiMin
Tutor: LiZhiYi
School: Chinese Geology University (Beijing)
Course: Geological Engineering
Keywords: Dynamic compaction method Unsaturated soil Microstructure Fractal Strength Deform Yield Elastoplastic constitutive model Engineering applications Century Garden
CLC: TU411
Type: PhD thesis
Year: 2003
Downloads: 771
Quote: 7
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Abstract


High saturation of foundation soil by dynamic compaction treatment of tamping the soil behind the deformation in the load of the building most of the elimination of the strength of the soil is the foundation stability control. But many projects due to the tight schedule, rammed often detected immediately foundation soil, resulting in a low index value of the field measured. Currently, most of the quality testing of the ram after high saturation of foundation soil with field technicians experience and the specification needs improvement. In fact, the ram after high saturation of foundation soil is compacted unsaturated soil, unsaturated soil mechanics theory can not meet the requirements of soil strength and deformation characteristics of the study after ramming unsaturated soil mechanics theory for the study of high saturation ram after the engineering properties of the foundation soil provides a theoretical basis. Rammed after high saturation of foundation soil engineering properties and constitutive model, is the key to solve the evaluation and prediction rammed foundation soil bearing capacity of foundation stability problems. Unsaturated soil mechanics theory modern soil science, soil micro-structural properties of macroscopic mechanical behavior combine research the high saturation after dynamic compaction foundation soil strength and deformation characteristics, a high saturation of foundation soil in this the constitutive model at home and abroad has not been reported in the literature, this this thesis innovative. The paper the century of Shijiazhuang City Garden II phase of the project, for example, through a large number of informative laboratory test data analysis, the following main results. (1) Century Garden foundation soil is alluvial-diluvial deposits formed in weakly alkaline media environment. From its mineral composition, teeth sub-test and the physical and mechanical indexes of view, it should be attributed to the silt, but due to the high clay content in the soil and intergranular filling aggregates, soil ion exchange capacity, exchangeable cations expensive calcium-based, it is still showing the engineering properties of silty clay. (2) indoor micro-structure and teeth test, for the first time found the foundation soil dynamic compaction refinement phenomenon. Scanning electron microscopy soil the larger particles of debris feldspar grain boundaries after the dynamic compaction disintegration; comparing the same layer before and after the dynamic compaction, soil samples of the same position, tamping the soil behind the particle size refinement phenomenon. This may be mainly related to particle contact Century Garden foundation soil. (3) for the first time from the micro-structural point of view to explain the mechanism of deformation and failure of the foundation soil dynamic compaction. Century Garden saturation of the foundation soil due to the presence of the cosmid and aggregates, dynamic compaction soil permeability variation, the excess pore pressure is difficult to dissipate rapidly, resulting in soil deformation and failure occurs. But due to the combination of soil particle surface water film thickness after ram intergranular repulsion small, the strength of a quick recovery, which showed good thixotropy. (4) particle size distribution, and pore distribution century garden foundation soil has the characteristics of fractal distribution. Tamping soil before the bimodal particle size distribution, fractal dimension value is larger, an average of 2.51; while the rammer Houtu particle size distribution performance single peak value of the fractal dimension becomes smaller, the average was 2.39. Different aperture range, the pore surface fractal dimension variation. Macropores area pores smaller fractal dimension values; small pore porous fractal value is larger. The fractal dimension of the size of the engineering properties of the soil is good or bad. Therefore, the fractal theory is an effective means to study unsaturated soil characteristics. (5) by a linear regression analysis of the physical and mechanical indicators before and after the dynamic compaction of foundation soil Century Garden, indicating a good correlation between the ram foundation soil physical and mechanical indexes. This is due to the dynamic compaction uniformity foundation soil changed for the better, and thus various indicators discrete smaller. A poor correlation between the ram before the soil physical and mechanical indexes, indexes between discrete large foundation soil depositional environment of alluvial-pluvial environment, resulting in the peaceful surface of the soil in the vertical not uniformity. (6) The to control suction conditions under unsaturated compacted silt triaxial shear test results show that the matric suction of unsaturated soil strength characteristics, with the the suction increase in soil shear strength increase. Different under ambient pressure increases with suction, effective cohesion C 'linear increase, effective internal friction angle towel' linearly decrease. Experimental suction within the effective cohesion C 'by the suction of' more obvious than the effective internal friction angle, and unsaturated soil testing failure envelope is not a plane, with a net average stress and increased suction was convergence like. Test high saturation of compacted silt, when high confining pressure, suction strength is no longer obvious, the confining pressure will play a leading role. In 'shaped variation decreases with suction and the strength envelope was convergence, this paper obtained one of the new understanding. (6) The triaxial shear test and to control suction pressure consolidation test results show that the volumetric changes of the performance characteristics for the consolidation process, the body becomes more shear body becomes large. Changes in the water content of the sample and the initial saturation of the soil, the higher initial saturation, the specimens are in the process of unity and shear drainage, lower initial saturation, sample pressure possible drainage, also possible water absorption. Each to pressure consolidation test and triaxial shear test data projections V ~ lgp curve bilinear, accordingly to determine the yield stress of the sample, in order to determine the yield of the sample surface. Confining pressure is relatively low, the yield stress and the size of the initial stiffness associated with soil initial saturation lower initial saturation, the greater the yield stress and initial stiffness. When high confining pressure, initial saturation smaller impact on the yield stress and initial stiffness. (8) using two independent stress variables - net stress exceeds the pore air pressure and suction, text to establish a high saturation of compacted soil yield surface elastoplastic constitutive model. The model can explain the change in stiffness caused by the soil suction, stress-strain relations reproduction stress and suction conversion, irreversible, soil stiffness change caused by suction changes linked to the plastic deformation. Stress strain test soil and volumetric changes of numerical simulations show that, the predicted constitutive relations overall trend is still satisfactory, the model is valid. The model is characterized by 12 parameters, it is more than the critical state model parameters seven additional seven parameters to explain the phenomenon of unsaturated soil characteristics. LC, SI, SS yield surface model by plastomers strain hardening parameters, P. (S) and the plastic shear strain control. Simple to use, the model does not consider the impact of the initial saturation of unsaturated compacted soil characteristics, and is still using the associated flow rule. However, due to the effect of dilatancy, the direction of the plastic strain increment is difficult to maintain, forecast shear volume change during certain error. Thus?

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