The seismic loading on saturated soil deposits induces a decrease in effective stress and a rearrangement of the soil-particle structure, which may both lead to a degradation in undrained stiffness and strength of soi...The seismic loading on saturated soil deposits induces a decrease in effective stress and a rearrangement of the soil-particle structure, which may both lead to a degradation in undrained stiffness and strength of soils. Only the effective stress influence on small strain shear modulus Gmax is considered in seismic response analysis nowadays, and the cyclic shearing induced fabric changes of the soil-particle structure are neglected. In this paper, undrained cyclic triaxial tests were conducted on saturated sands with the shear wave velocity measured by bender element, to study the influences of seismic loading on Gmax. And Gmax of samples without cyclic loading effects was also investigated for comparison. The test results indicated that Gmax under cyclic loading effects is lower than that without such effects at the same effective stress, and also well correlated with the effective stress variation. Hence it is necessary to reinvestigate the determination of Gmax in seismic response analysis carefully to predict the ground responses during earthquake more reasonably.展开更多
Based on Taylor series expansion and strain components expressions of elastic mechanics, we derive formulae of strain and rotation tensor for small arrays in spherical coordinates system. By linearization process of t...Based on Taylor series expansion and strain components expressions of elastic mechanics, we derive formulae of strain and rotation tensor for small arrays in spherical coordinates system. By linearization process of the formulae, we also derive expressions of strain components and Euler vector uncertainties respectively for subnets using the law of error propagation. Taking GPS velocity field in Sichuan-Yunnan area as an example, we compute dilation rate and maximum shear strain rate field using the above procedure, and their characteristics are preliminarily car- ried on. Limits of the strain model for small array are also discussed. We make detailed explanations on small array method and the choice of small arrays. How to set weights of GPS observations are further discussed. Moreover relationship between strain and radius of GPS subnets is also analyzed.展开更多
Discrete element modeling was used to investigate the effect of particle size distribution on the small strain shear stiffness of granular soils and explore the fundamental mechanism controlling this small strain shea...Discrete element modeling was used to investigate the effect of particle size distribution on the small strain shear stiffness of granular soils and explore the fundamental mechanism controlling this small strain shear stiffness at the particle level. The results indicate that the mean particle size has a negligible effect on the small strain shear modulus. The observed increase of the shear modulus with increasing particle size is caused by a scale effect. It is suggested that the ratio of sample size to the mean particle size should be larger than 11.5 to avoid this possible scale effect. At the same confining pressure and void ratio, the small strain shear modulus decreases as the coefficient of uniformity of the soil increases. The Poisson's ratio decreases with decreasing void ratio and increasing confining pressure instead of being constant as is commonly assumed. Microscopic analyses indicate that the small strain shear stiffness and Poisson's ratio depend uniquely on the soil's coordination number.展开更多
Accurate prediction of displacements associated with deep excavations is essential to ensure safety and stability of the excavation and to prevent any damage and distress to the adjoining infrastructures.This paper pr...Accurate prediction of displacements associated with deep excavations is essential to ensure safety and stability of the excavation and to prevent any damage and distress to the adjoining infrastructures.This paper presents a numerical approach for prediction of ground displacements related to a zone-divided deep excavation construction executed in Shanghai soft clays based on a new elasto–plastic con-stitutive model(small-strain Shanghai model)that incorporates small strain stiffness.This model can describe the mechanical properties and structural and over-consolidated characteristics of natural clays.The model is implemented into a finite element analysis software.Numerical analysis on the deep excavation in Shanghai using zone-divided method is conducted.A comparison between monitored and simulated results of horizontal displacements along the diaphragm wall,the settlements in the surroundings,and the effects on the adjoin-ing metro tunnel due to excavation construction is carried out.Special attention is paid to the stiffness degradation of representative elements in the ground.The simulated displacements show a good agreement with the monitored data.Overall,this study provides an integrated solution for predicting displacements related to deep excavation in soft clays.展开更多
This paper was focused on the elasticoluminescence(ELS)characteristics,especially a response to small strain(below 1000μst),of mechanoluminescence(ML)sensor using strontium aluminate doped with small amount of europi...This paper was focused on the elasticoluminescence(ELS)characteristics,especially a response to small strain(below 1000μst),of mechanoluminescence(ML)sensor using strontium aluminate doped with small amount of europium(SrAl_(2)O_(4):Eu)synthesized by different methods.By using nitrate decomposition method as a synthetic method of SrAl_(2)O_(4):Eu,the response to small strain of the ML sensor was enhanced in comparison with using a conventional solid-state reaction method.Based on SEM observation and thermoluminescence(ThL)measurement,we proposed a hypothesis that the sensing characteristic of small strain affect the platelike shape of SrAl_(2)O_(4):Eu grain and/or shallower carrier trap levels formed by nitrate decomposition method.展开更多
The importance of soil small strain effect on soil-structure behavior was investigated by researchers in last decades. The finite element method (FEM) is always used to predict the excavation behavior, whereas there a...The importance of soil small strain effect on soil-structure behavior was investigated by researchers in last decades. The finite element method (FEM) is always used to predict the excavation behavior, whereas there are not many soil models available to consider this effect in analysis. This paper introduces a simple small strain soil model—hardening small-strain (HSS) in PLAXIS 8.5 and exhibits its application in excavation problems via studying the history of two cases. The analyses also use two familiar soil models: hardening-soil (HS) model and Mohr-Coulomb (MC) model. Results show that the HSS predicts more reasonable magnitudes and profiles of wall deffections and surface settlements than other models. It also indicates that the small strain effect relies on the strain level which is induced by excavation.展开更多
In the general theory of relativity, the fundamental metric tensor plays a special role, which has its physical basis in the peculiar aspects of gravitation. The fundamental property of gravitational fields provides t...In the general theory of relativity, the fundamental metric tensor plays a special role, which has its physical basis in the peculiar aspects of gravitation. The fundamental property of gravitational fields provides the possibility of establishing an analogy between the motion in a gravitational field and the motion in any external field considered as a noninertial system of reference. Thus, the properties of the motion in a noninertial frame are the same as those in an inertial system in the presence of a gravitational field. In other words, a noninertial frame of reference is equivalent to a certain gravitational field. This is known as the principle of equivalence. From the mathematical viewpoint, the same special role can be played by the small deformation strain tensor, which describes the geometrical properties of any region deformed because of the effect of some external agent. It can be proved that, from that tensor, all the mathematical structures needed in the general theory of relativity can be constructed.展开更多
The traditional methods of surface movement and deformation prediction seldom take account of the effects of small structures. However, because of the effects of small structures, the buildings located at the bottom o...The traditional methods of surface movement and deformation prediction seldom take account of the effects of small structures. However, because of the effects of small structures, the buildings located at the bottom of subsidence trough for full-extraction can not be protected by the flat bottom, but destroyed severely by concentrated strains in the fault-half-trough. Under this coudition, if tbere is an important building at the bottom of subsidence trough, it is significant to accurately determinate the directions and values of concentrated strains and the location of concentrated strain zone. The mechanical method can calculate the maximum principal strain, including bi-directional horizontal deformation, shearing strain and their directions, which are necessary to reinforce the buildings. The mechanical method has more advantages than the method of scalar quantity horizontal deformation. This paper dwells on the effects of small structures on surface movement and deformation using the mechanical method in Pingdingshan mining area.展开更多
小应变硬化土(hardening soil with small strain stiffness,HSS)模型能反映土体在小应变范围内的非线性,广泛应用于土工变形分析。海上风电基础对变形控制要求高,需考虑土体的小应变特性。通过固结试验、三轴固结排水试验、三轴固结排...小应变硬化土(hardening soil with small strain stiffness,HSS)模型能反映土体在小应变范围内的非线性,广泛应用于土工变形分析。海上风电基础对变形控制要求高,需考虑土体的小应变特性。通过固结试验、三轴固结排水试验、三轴固结排水加卸载试验与共振柱试验,获得了江苏大丰海域海洋土HSS模型主要参数,并建立了HSS模型相关模量参数与土体物理参数之间的关系。试验成果可为海洋土HSS模型分析及参数取值提供重要参考,具有一定的工程价值。展开更多
小应变土体硬化(hardening soil model with small strain stiffness,HSS)模型能够反映土体小应变阶段的非线性特性和应力相关性,在深基坑工程领域已被广泛应用。但由于模型参数众多,目前对参数确定方法尚缺乏系统研究。分析了HSS模型...小应变土体硬化(hardening soil model with small strain stiffness,HSS)模型能够反映土体小应变阶段的非线性特性和应力相关性,在深基坑工程领域已被广泛应用。但由于模型参数众多,目前对参数确定方法尚缺乏系统研究。分析了HSS模型各参数的意义及常规确定方法,采用数值模拟方法开展了HSS模型参数的敏感性分析,基于统计的大量研究成果,建立了土体参数与孔隙比之间的非线性关系,进一步通过2处深基坑工程的变形分析进行验证。结果表明:在基坑数值分析中,参考动剪切模量G_(0)^(ref)的敏感性最高,参考切线模量E_(oed)^(ref)的敏感性最低,建立的非线性关系能够较好地反映土体模量与孔隙比的相关性,围护结构侧移的计算值及实测值较为吻合,验证了提出的参数确定方法的适用性,可为相关工程提供参考。展开更多
基金Project supported by the National Natural Science Foundation ofChina (No. 10372089) and Provincial Department of EducationZhejiang Province (No. 20010572) China
文摘The seismic loading on saturated soil deposits induces a decrease in effective stress and a rearrangement of the soil-particle structure, which may both lead to a degradation in undrained stiffness and strength of soils. Only the effective stress influence on small strain shear modulus Gmax is considered in seismic response analysis nowadays, and the cyclic shearing induced fabric changes of the soil-particle structure are neglected. In this paper, undrained cyclic triaxial tests were conducted on saturated sands with the shear wave velocity measured by bender element, to study the influences of seismic loading on Gmax. And Gmax of samples without cyclic loading effects was also investigated for comparison. The test results indicated that Gmax under cyclic loading effects is lower than that without such effects at the same effective stress, and also well correlated with the effective stress variation. Hence it is necessary to reinvestigate the determination of Gmax in seismic response analysis carefully to predict the ground responses during earthquake more reasonably.
基金State Key Basic Research Development and Programming Project of China (2004CB418403)Special Foundation of Seismological Science (200708030)Basic Scientific Research Program of Institute of Earthquake Science (2007-22)
文摘Based on Taylor series expansion and strain components expressions of elastic mechanics, we derive formulae of strain and rotation tensor for small arrays in spherical coordinates system. By linearization process of the formulae, we also derive expressions of strain components and Euler vector uncertainties respectively for subnets using the law of error propagation. Taking GPS velocity field in Sichuan-Yunnan area as an example, we compute dilation rate and maximum shear strain rate field using the above procedure, and their characteristics are preliminarily car- ried on. Limits of the strain model for small array are also discussed. We make detailed explanations on small array method and the choice of small arrays. How to set weights of GPS observations are further discussed. Moreover relationship between strain and radius of GPS subnets is also analyzed.
基金The work presented in this paper was supported by the National Natural Science Foundation of China (Grant Nos. 51308408, 41272291,51238009) and the Fundamental Research Funds for the Central Universities, and the Open Foundation of State Key Labo- ratory of Hydrology-Water Resources and Hydraulic Engineering (Grant No. 2014492311 ).
文摘Discrete element modeling was used to investigate the effect of particle size distribution on the small strain shear stiffness of granular soils and explore the fundamental mechanism controlling this small strain shear stiffness at the particle level. The results indicate that the mean particle size has a negligible effect on the small strain shear modulus. The observed increase of the shear modulus with increasing particle size is caused by a scale effect. It is suggested that the ratio of sample size to the mean particle size should be larger than 11.5 to avoid this possible scale effect. At the same confining pressure and void ratio, the small strain shear modulus decreases as the coefficient of uniformity of the soil increases. The Poisson's ratio decreases with decreasing void ratio and increasing confining pressure instead of being constant as is commonly assumed. Microscopic analyses indicate that the small strain shear stiffness and Poisson's ratio depend uniquely on the soil's coordination number.
基金support of the National Nature Science Foundation of China(Grant Nos.42072317,41727802)is gratefully acknowledged.
文摘Accurate prediction of displacements associated with deep excavations is essential to ensure safety and stability of the excavation and to prevent any damage and distress to the adjoining infrastructures.This paper presents a numerical approach for prediction of ground displacements related to a zone-divided deep excavation construction executed in Shanghai soft clays based on a new elasto–plastic con-stitutive model(small-strain Shanghai model)that incorporates small strain stiffness.This model can describe the mechanical properties and structural and over-consolidated characteristics of natural clays.The model is implemented into a finite element analysis software.Numerical analysis on the deep excavation in Shanghai using zone-divided method is conducted.A comparison between monitored and simulated results of horizontal displacements along the diaphragm wall,the settlements in the surroundings,and the effects on the adjoin-ing metro tunnel due to excavation construction is carried out.Special attention is paid to the stiffness degradation of representative elements in the ground.The simulated displacements show a good agreement with the monitored data.Overall,this study provides an integrated solution for predicting displacements related to deep excavation in soft clays.
基金supported by Adaptable and Seamless Technology Transfer Program through target-driven R&D(AS251Z02284M)Japan Science and Technology Agency as well as Grant-in-Aid for Scientific Research(A)(Grant Number:25249100)from Japan Society for the Promotion of Science.
文摘This paper was focused on the elasticoluminescence(ELS)characteristics,especially a response to small strain(below 1000μst),of mechanoluminescence(ML)sensor using strontium aluminate doped with small amount of europium(SrAl_(2)O_(4):Eu)synthesized by different methods.By using nitrate decomposition method as a synthetic method of SrAl_(2)O_(4):Eu,the response to small strain of the ML sensor was enhanced in comparison with using a conventional solid-state reaction method.Based on SEM observation and thermoluminescence(ThL)measurement,we proposed a hypothesis that the sensing characteristic of small strain affect the platelike shape of SrAl_(2)O_(4):Eu grain and/or shallower carrier trap levels formed by nitrate decomposition method.
基金the National Natural Science Foundation of China (No. 50679041)
文摘The importance of soil small strain effect on soil-structure behavior was investigated by researchers in last decades. The finite element method (FEM) is always used to predict the excavation behavior, whereas there are not many soil models available to consider this effect in analysis. This paper introduces a simple small strain soil model—hardening small-strain (HSS) in PLAXIS 8.5 and exhibits its application in excavation problems via studying the history of two cases. The analyses also use two familiar soil models: hardening-soil (HS) model and Mohr-Coulomb (MC) model. Results show that the HSS predicts more reasonable magnitudes and profiles of wall deffections and surface settlements than other models. It also indicates that the small strain effect relies on the strain level which is induced by excavation.
文摘In the general theory of relativity, the fundamental metric tensor plays a special role, which has its physical basis in the peculiar aspects of gravitation. The fundamental property of gravitational fields provides the possibility of establishing an analogy between the motion in a gravitational field and the motion in any external field considered as a noninertial system of reference. Thus, the properties of the motion in a noninertial frame are the same as those in an inertial system in the presence of a gravitational field. In other words, a noninertial frame of reference is equivalent to a certain gravitational field. This is known as the principle of equivalence. From the mathematical viewpoint, the same special role can be played by the small deformation strain tensor, which describes the geometrical properties of any region deformed because of the effect of some external agent. It can be proved that, from that tensor, all the mathematical structures needed in the general theory of relativity can be constructed.
文摘The traditional methods of surface movement and deformation prediction seldom take account of the effects of small structures. However, because of the effects of small structures, the buildings located at the bottom of subsidence trough for full-extraction can not be protected by the flat bottom, but destroyed severely by concentrated strains in the fault-half-trough. Under this coudition, if tbere is an important building at the bottom of subsidence trough, it is significant to accurately determinate the directions and values of concentrated strains and the location of concentrated strain zone. The mechanical method can calculate the maximum principal strain, including bi-directional horizontal deformation, shearing strain and their directions, which are necessary to reinforce the buildings. The mechanical method has more advantages than the method of scalar quantity horizontal deformation. This paper dwells on the effects of small structures on surface movement and deformation using the mechanical method in Pingdingshan mining area.
文摘小应变硬化土(hardening soil with small strain stiffness,HSS)模型能反映土体在小应变范围内的非线性,广泛应用于土工变形分析。海上风电基础对变形控制要求高,需考虑土体的小应变特性。通过固结试验、三轴固结排水试验、三轴固结排水加卸载试验与共振柱试验,获得了江苏大丰海域海洋土HSS模型主要参数,并建立了HSS模型相关模量参数与土体物理参数之间的关系。试验成果可为海洋土HSS模型分析及参数取值提供重要参考,具有一定的工程价值。
文摘小应变土体硬化(hardening soil model with small strain stiffness,HSS)模型能够反映土体小应变阶段的非线性特性和应力相关性,在深基坑工程领域已被广泛应用。但由于模型参数众多,目前对参数确定方法尚缺乏系统研究。分析了HSS模型各参数的意义及常规确定方法,采用数值模拟方法开展了HSS模型参数的敏感性分析,基于统计的大量研究成果,建立了土体参数与孔隙比之间的非线性关系,进一步通过2处深基坑工程的变形分析进行验证。结果表明:在基坑数值分析中,参考动剪切模量G_(0)^(ref)的敏感性最高,参考切线模量E_(oed)^(ref)的敏感性最低,建立的非线性关系能够较好地反映土体模量与孔隙比的相关性,围护结构侧移的计算值及实测值较为吻合,验证了提出的参数确定方法的适用性,可为相关工程提供参考。