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1.
Soil liquefaction can cause disastrous consequences to buildings and human lives. Regular countermeasures against soil liquefaction are often overly expensive for normal buildings and structures. This could be the major reason that liquefaction induced damage is still widely encountered in large- and mid-size earthquakes in recent years. In this paper, a new method for the mitigation of soil liquefaction using the microbially induced soil desaturation is proposed and tested. The desaturation effect in soil is achieved by the generation of nitrogen gas produced from the microbial denitrification process. Some major issues related to this method are experimentally investigated. These include soil desaturation procedures, shapes and distribution of gas bubbles in soil, mechanical responses and liquefaction resistance of desaturated soils, and stability of gas in soils. The desaturation treatment of soils is made simply by introducing denitrifying bacteria and a desaturation solution into soil pores by mixing, flushing, or injection. The degree of saturation can be reduced as the microbial reaction proceeds. Experimental results show that the final degree of saturation is related to the initial nitrate concentration added to the soil: the higher the concentration of nitrate in the desaturation solution, the lower the degree of saturation that can be achieved. The existence of gas bubbles in soil is evidenced by computer tomography (CT) technology. The CT images reveal that gas is in the form of small pockets which has a size a little larger than the mean size of sand grains. It is shown in the shaking table tests that microbially induced desaturation can effectively improve the liquefaction resistance of soil by showing a much lower pore pressure generation, much smaller volumetric strain, and much smaller settlement of the structure in desaturated soil, as compared with those in saturated soil. Triaxial consolidated undrained tests reveal that the desaturation treatment of soil can improve the undrained shear strength of loose sand. The stability of gas is tested under hydrostatic and water flow conditions. The gas phase is stable under the hydrostatic condition, but unstable under water flow conditions. So measures ought to be taken to prevent steady flow in practice. 相似文献
2.
Failure criterion of saturated soft clay is studied under cyclic loads through different experiments. A large number of cyclic torsional shear and cyclic triaxial tests on saturated soft clay under unconsolidated undrained condition are conducted. From the test result analysis, it is seen that the failure of saturated soft clay under static and cyclic loads satisfies Mises criterion. The result from different test stress states is not related to the test stress states or confining pressures. It can be applied in general stress states. Then according to the Mises criterion, the equivalent relationship on failure moment between the test stress state and the general stress state can be established. So the cyclic mechanics characteristics of saturated soft clay at failure moment are clarified in this paper. Furthermore, a theory basis is provided for using pseudo-static elasto-plastic cyclic strength model to evaluate cyclic bearing capacity. 相似文献
3.
Correlation of liquefaction resistance with shear wave velocity based on laboratory study using bender element 总被引：1，自引：0，他引：1
INTRODUCTION Evaluation of soil liquefaction resistance is an important aspect of geotechnical engineering practice, and several types of evaluating procedures have evolved over the last three decades. The well known “simplified procedure” originated by Seed and Idriss (1971) can be used to evaluate liquefaction resistance based on standard penetration test (SPT) blow counts. Over the years, the simplified procedure has been modified and updated with additional data, and has become th… 相似文献
4.
Undrained anisotropy and non-coaxial behavior of clayey soil under principal stress rotation 总被引：2，自引：0，他引：2
In this study, a series of undrained tests were conducted on both intact and reconstituted clay using an automatic hollow cylinder apparatus. Monotonic shearing tests with fixed principal stress directions were carried out, pure and cyclic prin- cipal stress rotation tests were also performed. The non-coaxiality, defined as the non-coincidence of the principal plastic strain increment direction and the corresponding principal stress direction, of clayey soil was studied experimentally. The effects of the intermediate principal stress, shear stress level, and inherent anisotropy were highlighted. Clear non-coaxiality was observed during pure principal stress rotation, in both intact and reconstituted clay. The influence of the intermediate principal stress pa- rameter, shear stress level, and inherent anisotropy on the non-coaxial behavior of the clayey soil was found to be insignificant when compared with the sand. The non-coaxial behavior of the clayey soil depended more on the stress paths. Under undrained conditions, the contribution of elastic strain to the direction of the total principal strain increment cannot be ignored. 相似文献
5.
In this paper, the steady-state response of a saturated half-space with an overlying dry layer subjected to a moving rectangular
load is investigated. The governing partial differential equations are solved using the Fourier transform. The solutions in
time-space domain are expressed in terms of infinite Fourier type integrals, which can be evaluated only by numerical quadrature.
Numerical results show that the influence of a drained or undrained interface on the response is related to the permeability
of the underlying saturated soil. Moreover, the effect due to the upper dry layer is associated with the thickness of the
layer. 相似文献
6.
研究了采用离心模型试验来研究波浪与土相互作用的方法,并针对渤海某油田的波浪及土质条件进行了试验研究.结果表明,在最大波高作用下,软粘土层的上部发生了软化,但这种影响随着深度的增加而逐渐减小;在波浪荷载的作用下,软粘土层下的粉砂层没有液化迹象. 相似文献
7.
There exists a critical cyclic stress ratio when sand or clay is subjected to cyclic loading. It is an index distinguishing stable state or failure state. The soil static and dynamic universal triaxial and torsional shear apparatus developed by Dalian University of Technology in China was employed to perform different types of tests on saturated soft marine clay in the Yangtze estuary. Undisturbed samples were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consolidation parameters. The effects of initial orientation angle of major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and stress mode of cyclic shear on the critical cyclic stress ratio were investigated. It is found that the critical cyclic stress ratio decreases significantly with increasing initial orientation angle of major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientation angle of major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident. Under the same consolidation condition, the critical cyclic stress ratio from the cyclic coupling shear test is lower than that from the cyclic torsional shear test, indicating that the stress mode of cyclic shear has an obvious effect on the critical cyclic stress ratio. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of soil more than the cyclic torsional shear does. 相似文献
8.
The mechanical behavior of sand is very complex, and depends on factors including confining pressure, density, and drainage condition. A soil mass can be contractive or dilative when subjected to shear loading, and eventually reaches an ultimate state, referred to as the critical state in soil mechanics. Conventional approach to explore the mechanical behavior of sand mainly relies on the experimental tests in laboratory. This paper gives an alternative view to this subject using discrete element method （DEM）, which has attracted much attention in recent years. The implementation of the DEM is carried out by a series of numerical tests on granular assemblies with varying initial densities and confining pressures, under different test configurations. The results demonstrate that such numerical simulations can produce correct responses of the sand behavior in general, including the critical state response, as compared to experimental observations. In addition, the DEM can further provide details of the microstructure evolutions during shearing processes, and the resulting induced anisotropy can be fully captured and quantified in the particle scale. 相似文献
9.
In this paper we propose a degradation model to describe the damage-dependent behavior of saturated soft clay under cyclic loading, which is then applied to the analysis of a caisson breakwater. The degree of damage and remolding of soft clay is quantified by a damage parameter related to the accumulated plastic deviatoric strain. Through the correlation between the maximum pore pressure and the undrained strength of soft clay, we obtain a damage-dependent degradation model that employs the post-cyclic undrained strength degradation coefficient in terms of the cyclic stress ratio and the number of cycles. Based on the Tresca yield criterion, the degradation model of undrained strength of soft clay is numerically implemented in the user interface USDFLD of ABAQUS. The performance of this model is verified by a comparison between numerical results (finite element method) and experimental data (cyclic triaxial test). The model is applied to the numerical simulation of a caisson breakwater resting on a partially sand-filled soft clay seabed under cyclic wave loading. The cyclic stress distribution, pore pressure development, and strength degradation of the seabed soil are presented to illustrate the applicability and efficiency of the model in the analysis of the interaction between offshore structures and soft ground. 相似文献
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11.
盘锦市体育中心地质情况表现为在地下14m范围内存在粉砂夹粉质粘土土层,在地震荷载作用下,将会产生砂土液化现象。针对这一情况,采用了碎石桩复合地基进行处理,处理后地基液化现象基本消除,地基承载力也满足要求。工程完工后,运行情况良好。 相似文献
12.
1 Ｉｎｔｒｏｄｕｃｔｉｏｎ Ｍｏｄｅｌｉｎｇｏｆｓｏｉｌｂｅｈａｖｉｏｕｒｐｌａｙｓａｎｉｍｐｏｒｔａｎｔｒｏｌｅｉｎｄｅａｌｉｎｇｗｉｔｈｐｒｏｂｌｅｍｓｒｅｌａｔｅｄｔｏｓｏｉｌｍｅｃｈａｎｉｃｓａｎｄｆｏｕｎｄａｔｉｏｎｅｎｇｉｎｅｅｒｉｎｇ .Ｏｖｅｒｔｈｅｐａｓｔｆｏｕｒｄｅｃａｄｅｓ ,ｍａｎｙｒｅｓｅａｒｃｈｅｒｓｈａｖｅｄｅｖｏｔｅｄｅｎｏｒｍｏｕｓｅｆｆｏｒｔｓｔｏｆｏｒｅｃａｓｔｉｎｇｔｈｅｌｉｑｕｅｆａｃｔｉｏｎｏｆｓａｔｕｒａｔｅｄｓｏｉｌｕｎｄｅｒｖａｒｉｏｕｓａｓｓｕｍ… 相似文献
13.
Constitutive model of saturated soft clay with cyclic loads under unconsolidated undrained condition
An equivalent visco-elastic model of saturated soft clay was studied under unconsolidated undrained (UU) condition, which can be used to evaluate the stability of ocean foundation. Cyclic triaxial compression and extension tests were conducted to study the parameters of the model. Results showed that the relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain were nearly unique, when the initial octahedral shear stress ratios of specimens were equal to 0.3, 0.5 and 0.7. The relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain determined from the cyclic triaxial compression tests were basically the same as those determined from the cyclic triaxial extension tests. Furthermore, the relationships were not related to the initial stress condition, the test stress state and the octahedral cyclic shear stress ratio. The relationships determined from the cyclic triaxial tests under no deviatoric stress were basically the same as those determined from the cyclic triaxial tests under deviatoric stress. The change of the octahedral cyclic accumulative strain with the number of cycles was unique under different tests stress states. An equivalent visco-elastic constitutive model of saturated soft clay under UU condition was initially established. 相似文献
14.
刘子剑 《常熟理工学院学报》2009,23(10):74-79
研究时滞系统的鲁棒方差约束控制问题．针对带有不确定参数和白噪声干扰的离散时滞系统,设计一类反馈控制器,使通过反馈控制所得到的闭环系统不仅一致渐进稳定,而且系统各状态分量的稳态方差在给定约束范围之内．利用线性矩阵不等式的方法,得出了满足这一反馈控制器的充分条件．给出了一个数值算例,验证了所提出算法的有效性． 相似文献
15.
INTRODUCTION Adequate information on dynamic soil proper-ties, especially dynamic shear modulus and dampingratio, is essential for accurate computations of groundresponse and soil-structure interaction problems.Many experimental investigations carried out onsandy soils through resonant column test or improvedcyclic triaxial test in early studies (Hardin and Richart1963; Hardin and Black, 1968; Drnevich and Richart,1970; Seed and Idriss, 1971; Kokusho, 1980) showedthat the small … 相似文献
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By means of the improved split Hopkionson pressure bar(SHPB) with axial pre-pressure and confined pressure,two series of experiments on sandstone are earned out to research the failure mode of rock during the course of exploitation of resources in deep.One is under the conditions that the confining pressure is fixed and the axial pressure is changeable.The other is under the conditions that the confining pressure becomes and the axial pressure is fixed.It is found that samples break up evenly after impacting when axial static pressures are low,there is great disparity in size of fragments when axial static pressures are high,and the main bodies of samples after the tests under the combination of dynamic and static loads frequently show the type of V or X.The samples are more close-grained at the elastic stage and impacts make many cracks be generated and developed,as makes samples more crackable.At the initial phase of damage stage,the static pressures make some cracks in the samples which are undeveloped and the impacts' role is similar to that at the elastic stage.At the metaphase or anaphase of damage stage,these cracks in the samples develop adequately and the impacts mainly accelerate samples' failure.The main bodies of samples show the type of V or X after impacting due to the confining pressures' restraining samples' lateral formation at the elastic stage or the initial phase of damage stage,the main bodies of samples have almost formed at the stage loading static pressures and the results after impacting usually are similar to those under the axial pressures tests. 相似文献
18.
Numerical Analysis of Soil Plug Inside Suction Foundations During Suction Penetration by Discrete Element Method 总被引：2，自引：1，他引：2
The phenomenon of the soil plug usually rising inside the suction foundations during suction penetration was quantitatively described and predicted. The formation process of the soil plug was simulated and calculated by DEM （discrete element method） model. The seepage flow, the self-weight of soil, the friction on the chamber wall as well as the suction inside the chamber are considered as the main external forces in the process. The results are compared with a set of laboratory model tests performed by using three soil types （sand, silty clay and clay） in the Bohai Sea area. The heights of soil plug from numerical estimations are lower than those from model test results, mainly because the suction pressure and friction resistance are applied in an ideal way under the numerical simulation. 相似文献
19.
Using the self-developed visualization test apparatus, centrifuge model tests at 20g were carried out to research the macro and microscopic formation mechanism of coarse sand debris flows. The formation mode and soil-water interaction mechanism of the debris flows were analyzed from both macroscopic and microscopic points of view respectively using high digital imaging equipment and micro-structure analysis software Geodip. The test results indicate that the forming process of debris flow mainly consists of three stages, namely the infiltration and softening stage, the overall slide stage, and debris flow stage. The essence of simulated coarse sand slope forming debris flow is that local fluidization cause slope to wholly slide. The movement of small particles forms a transient stagnant layer with increasing saturation, causing soil shear strength lost and local fluidization. When the driving force of the saturated soil exceeds the resisting force, debris flow happens on the coarse sand slope immediately. 相似文献
20.
Wind-induced internal pressure response for structure with single windward opening and background leakage 总被引：3，自引：0，他引：3
Shi-ce YU Wen-juan LOU Bing-nan SUN 《浙江大学学报(A卷英文版)》2008,9(3):313-321
Theoretical analysis and wind tunnel tests were carried out to study wind-induced intemal pressure response for the structure with single windward opening and background leakage. Its goveming differential equation was derived by the Bemoulli equation in an unsteady-isentropic form. Numerical examples were provided to study the additive damping caused by background leakage in laminar and turbulent flow, and the influence of background leakage on fluctuating internal pressure response was quantized. A series of models for low-rise building with various opening ratios and background leakage were designed and wind tunnel tests were conducted. It is shown that the fluctuating intemal pressure reduces when the background leakage are considered and that the effect of background leakage can be predicted accurately by the governing differential equation deduced in this paper. 相似文献