等效变形模量的非线性特性分析

在瞬时沉降或最终沉降计算中，都要用到土的变形模量Ｅ０，由于室内试验和原位测试方面存在的困难，过去对变形模量研究的报导有限。本文用载荷试验结果证明了变形模量具有非线性特征。在此基础上，通过北京地区三类土的原位平板载荷试验的压力－变形曲线的数学表达式及其特征值分析了等效变形模量Ｅ０，ｅｑ随压力的变化特征，并推导出相应的表达式。     

黄土湿陷弦线模量计算例证

古典土力学的变形模量是根据载荷试验沉降曲线中直线段的斜率(压力和沉降量之比),用半无限均值弹性体公式计算的线性模量。这只能用于变形的线性阶段。弦线模量是根据载荷试验全过程沉降曲线上任意点压力Р所在线段的弦线斜率(压力增量和沉降增量之比)取代变形模量的直线段斜率计算的相应于压力Р的非线性模量。弦线模量可以计算土的非线性变形,变形模量是弦线模量的特解,弦线模量是通解。黄土湿陷变形是非线性变形,因而可以用弦线模量进行计算。     

基于载荷试验计算土体变形模量的新方法

目前地基沉降计算选取的参数大都依据室内试验确定的压缩模量,并采用经验系数对计算结果进行修正。该方法简单,但计算结果与实际沉降大小相差甚远。究其原因主要是由于压缩模量是在侧向无变形的假定下而得,且室内试验取土无法避免土体的扰动。模量的选取是影响沉降计算准确性的一个重要因素,欲改进计算沉降的传统方法,量化土体的实际变形,优化土体的模量则变得十分必要。土的原位试验中,载荷试验既能克服土体的扰动,又无侧限变形的假定,可测得不同含水量、孔隙比、密度及应力状态下土体的变形特性,故依据载荷试验寻求新的方法确定土体的变形模量。     

地基非线性沉降计算的原状土切线模量法

根据原状地基的载荷试验曲线,建立原状土的切线模量与应力水平关系的切线模量方程,对地基不同点根据其应力水平由切线模量方程确定计算点原状土的切线模量,用该切线模量对地基沉降进行分层总和法计算,其特点是切线模量是由原位试验得到的,能反映原状地基土的特点,同时考虑应力水平的影响,反映了土的非线性特点。     

深层平板静力载荷试验测定土的变形模量

本文介绍了通过原位深层平板载荷试验测求深层土的变形模量的方法。并根据荷载作用在地基内部的 Mindlin解 ,验证了文中提出的土的变形模量计算公式。同时还介绍了该试验的装置和试验步骤。     

探讨复合地基工作性状研究的新方法

通过在某施工现场的单桩静载荷试验中的载荷板下埋设土压力盒的方法,测试出试验加载过程中的桩土应力比,并结合静载荷试验中记录的沉降数据推断桩土应力比与搅拌桩复合地基的承载力以及变形之间的关系,阐述搅拌桩复合地基的工作性状。     

超固结土静止侧压力系数的确定

本文讨论了在侧向变形ε２＝ε３＝０的条件下，超团结土的加载、卸载的应力路径。提出了根据室内试验成果确定原位静止倒压力系数的方法。     

地基沉降计算的新方法

根据原位土压板试验的P-S曲线来建立沉降计算的新方法.在假设压板试验P-S曲线为双曲线方程时,建立双曲线模型方法,同时通过双曲线求得土体的切线和割线模量,把所求得的模量用于分层总和法进行基础的沉降计算,建立原位土的双曲线切线和割线模量法.在假设压板试验P-S曲线为双曲线方程时,所需要参数只是土体的初始切线模量Es0、土体内摩擦角(及黏聚力c.对压板试验P-S曲线为其他任意曲线时,建立土体切线模量与荷载水平的关系,用于分层总和法进行基础的沉降计算,建立一般曲线的切线模量法.由于切线或割线模量是随着荷载水平的不同而呈现非线性特点的,新的计算方法可以计算接近地基极限承载力时的沉降,由此形成以原位土切线和割线模量法的地基非线性沉降全过程计算新方法.由于这样确定的土体变形参数能较好地考虑地基土的原状性和非线性性,因而可以较准确地计算基础的非线性沉降过程,同时该方法所需土体参数较少.将该方法分别应用于桩基、筏基以及复杂的路堤地基和复合地基的沉降计算,通过实际工程的检验,验证该方法的实用性和有效性,这可能是地基沉降计算的一个重大进展.     

武汉地区淤泥质软土、粘性土的压缩模量与变形模量的相关关系

根据武汉地区104组载荷试验与室内对比试验资料统计回归分析结果，得出该地区淤泥质软土、一般粘性土和老粘性土的变形模量E0与压缩模量Es之间的经验公式，该经验公式可供武汉地区岩土工程实践参考使用。     

关于“地基非线性沉降计算的原状土切线模量法”的讨论

<正>《岩土工程学报》2006年第11期发表了"地基非线性沉降计算的原状土切线模量法"一文(以下简称"原文")[1],该文提出了一种依据载荷试验成果确定原状土切线模量,然后按分层总和法计算地基沉降的新方法。原文指出,弦线模量法"直     

Procedure for Determination of the Long-Term Creep Rate and Creep Deformation of Semi-Hard and Hard Clayey Soils

A procedure is proposed for determination of the creep rate and creep deformation at any time from results of short-term tests of the single-plane shear or uniaxial crushing of semi-hard and hard clays. Calculations performed from proposed formulas indicated completely satisfactory convergence of creep parameters with parameters observed in long-term tests. This enables us to recommend these calculations for the design and construction of appropriate structures.__________Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 11–15, May–June, 2005.     

Analysis of Results of Consolidation Tests of Saturated Clayey Soils

It is shown that the dependence of soil deformation on the distance to the drainage boundary, which is noted by a number of experimenters for the stage of secondary consolidation, is explained by incorrect interpretation of test data. Laboratory results demonstrating an apparent lack of creep in the stage of primary consolidation are explained by characteristic features of the generalized consolidation equations and relationships between their parameters.__________Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 3, pp. 7–10, May–June, 2005.     

地下硐室岩爆的相似材料模拟试验研究

提出了模拟岩爆的新的相似系数Ｅ／λ。指出不同Ｅ／λ的材料，可模拟不同类型、不同震级的岩爆。研制出了模拟岩爆的系列脆性破坏材料，可应用于不同模拟比例、不同类型和不同震级的岩爆模拟试验。对圆形硐室的岩爆进行了模拟试验研究，证明所研制的相似材料可行，试验还证明存在岩爆发生的临界荷载，并验证了理论分析的结果     

An analytical solution of equivalent elastic modulus considering confining stress and its variables sensitivity analysis for fractured rock masses

The equivalent elastic modulus is a parameter for controlling the deformation behavior of fractured rock masses in the equivalent continuum approach. The confining stress, whose effect on the equivalent elastic modulus is of great importance, is the fundamental stress environment of natural rock masses. This paper employs an analytical approach to obtain the equivalent elastic modulus of fractured rock masses containing random discrete fractures (RDFs) or regular fracture sets (RFSs) while considering the confining stress. The proposed analytical solution considers not only the elastic properties of the intact rocks and fractures, but also the geometrical structure of the fractures and the confining stress. The performance of the analytical solution is verified by comparing it with the results of numerical tests obtained using the three-dimensional distinct element code (3DEC), leading to a reasonably good agreement. The analytical solution quantitatively demonstrates that the equivalent elastic modulus increases substantially with an increase in confining stress, i.e. it is characterized by stress-dependency. Further, a sensitivity analysis of the variables in the analytical solution is conducted using a global sensitivity analysis approach, i.e. the extended Fourier amplitude sensitivity test (EFAST). The variations in the sensitivity indices for different ranges and distribution types of the variables are investigated. The results provide an in-depth understanding of the influence of the variables on the equivalent elastic modulus from different perspectives.     

An investigation of the excavation damaged zone at the KAERI underground research tunnel

The disturbance of a rock due to a blasting impact or stress redistribution can significantly influence the overall performance of an underground excavation. In order to investigate the characteristics of the EDZ (Excavation Damaged Zone) developed during the construction of the KAERI underground research tunnel in Korea (KURT), which is an underground research tunnel for a Korean high-level radioactive waste disposal program, various in situ and laboratory tests were carried out. A Goodman jack test showed that the deformation modules were influenced by a blasting to a depth of 1.5–2 m. With empirical equations, the EDZ could be predicted as 0.3–2.3 m. The average RQD from the rock cores at 0–2 m, where the blasting impact was significant, was 17% lower than that from the deeper regions. From the laboratory tests, the EDZ size could be estimated to be around 0.9–1.5 m. The elastic modules in the EDZ were decreased by about 56%. From a borehole radar reflection survey and a subtracting technique, it was possible to detect the new reflectors generated by a tunnel blasting. By using the determined EDZ size and the properties from the laboratory and in situ tests, a sensitivity analysis was performed. From the sensitivity analysis with seven parameters, it was possible to determine that the in situ stress ratio, Young’s modules, and EDZ size were the three main parameters.     

Strength of Clayey Soils Subject to Large Shear Strains

Results are presented for determination of the peak _p, residual _r, and standard _f,st strengths of clayey soils containing up to 35% of particle inclusions ranging in size from 1 to 10 mm. It is established that on transition from _p to _r, the parameter C of Coulomb's law becomes essentially equal to zero, while the angle remains constant. A method is examined for repeated torsional testing of soil samples under conditions where shear strain s and torsional moments M _tor are controlled to establish their strength.     

利用Mogi模型预测盐岩储气库地表沉降

 盐岩储气库运营期间腔体体积的蠕变收缩是库区地表持续沉降的主要原因。假设盐腔体积收缩的等效弹性变形引发的地表沉降是实际蠕变沉降的一阶近似量,将盐腔转化为相同埋深、相同体积的球形腔体,并受到均匀向内收缩的弹性等效面力作用,将盐岩储气库地表沉降近似为弹性半无限空间内球型空洞受力收缩导致的边界位移问题。在上述弹性模型的基础上,引入火山地震学中用于预测火山喷发区地表变形的Mogi模型,得到库区地面垂直位移和水平位移的弹性解析解。Mogi模型的优势在于可以直接通过盐腔体积收缩量求得储气库地表位移,并与相同条件下的数值模拟沉降结果有着良好的近似效果,表明Mogi模型在储气库地表沉降预测研究中具有一定的可行性,并给出利用Mogi模型研究盐岩储气库地表沉降的研究方向及建议方法。     

On the Stress State of the Foundation Bed during Installation and Loading of a Pile Cast in a Hole Predrilled in Clayey Soils

Results are presented for field investigations of the stress state of the shaft of a cast-in-place pile and the surrounding soil mass in stages of the pile's installation, and its static loading in loess soils with the natural moisture content. Data indicating that the soil mass functions preferentially in an elastic state both during pile fabrication, and its vertical loading are obtained.     

Numerical evaluation of strength and deformability of fractured rocks

Knowledge of the strength and deformability of fractured rocks is important for design, construction and stability evaluation of slopes, foundations and underground excavations in civil and mining engineering. However, laboratory tests of intact rock samples cannot provide information about the strength and deformation behaviors of fractured rock masses that include many fractures of varying sizes, orientations and locations. On the other hand, large-scale in situ tests of fractured rock masses are economically costly and often not practical in reality at present. Therefore, numerical modeling becomes necessary. Numerical predicting using discrete element methods(DEM) is a suitable approach for such modeling because of their advantages of explicit representations of both fractures system geometry and their constitutive behaviors of fractures, besides that of intact rock matrix. In this study, to generically determine the compressive strength of fractured rock masses, a series of numerical experiments were performed on two-dimensional discrete fracture network models based on the realistic geometrical and mechanical data of fracture systems from feld mapping. We used the UDEC code and a numerical servo-controlled program for controlling the progressive compressive loading process to avoid sudden violent failure of the models. The two loading conditions applied are similar to the standard laboratory testing for intact rock samples in order to check possible differences caused by such loading conditions. Numerical results show that the strength of fractured rocks increases with the increasing confning pressure, and that deformation behavior of fractured rocks follows elasto-plastic model with a trend of strain hardening. The stresses and strains obtained from these numerical experiments were used to ft the well-known Mohr-Coulomb(MC) and Hoek-Brown(H-B) failure criteria, represented by equivalent material properties defning these two criteria. The results show that both criteria can provide fair estimates of the co     

K0固结软土的循环剪切特性及其流变模拟

对原状温州黏土进行了三轴不排水循环剪切试验,系统分析了黏土在循环剪切过程中应变和孔压的累积特性以及加载频率的影响。考虑到天然黏土不等向固结历史的影响,试验土样在循环剪切前均先K0固结至原位应力状态。研究表明,对于K0固结软黏土,以剪应变累积曲线出现拐点作为循环破坏标准较为合适,此拐点对应的单幅破坏峰值剪应变es,tp大小基本恒定为3%,与加载频率、循环偏应力幅值等因素无关;循环荷载幅值一定时,荷载持续时间t对黏土的循环剪切性状起控制作用,可综合反映加载频率和振次的影响。根据黏性不排水循环累积效应与静力蠕变过程的相似性,按静力蠕变等效的思路,采用建立的各向异性弹黏塑性本构模型对其进行模拟分析,并通过试验验证了此流变等效方法的有效性。