饱和软粘土的不排水循环累积变形特性

在上海地区典型饱和软粘土不排水循环三轴试验的基础上,分析了影响软粘土塑性累积变形的主要因素:循环荷载的作用次数,初始静偏应力和循环加载动偏应力。基于临界状态土力学理论,引入了相对偏应力水平参数,考虑初始静应力、循环动应力和不排水极限强度的相互影响,研究了不同静、循环动应力组合应力历史影响下饱和软粘土的不排水循环累积变形特性。     

Influence of sand incorporation on unconfined compression strength of cement-based stabilized soft clay

Cement-based stabilization by deep mixing or grouting is a popular method used to enhance soft clay ground because clay gradation has a significant effect on its unconfined compression strength. However, the functional relationship between the gradation and the strength is currently unclear, which limits the assessment and cognition for the strength formation of cement-based stabilized soft clay. Strength experiments controlling the sand ratio were conducted, in addition to the literature review, to clarify the sand incorporation effect on the strength. An effective cement ratio (the mass ratio of cement to involved clay) was proposed to evaluate the strength of stabilized clay with sand incorporation. In order to combat data dispersion and the labour-intensive nature of these experiments, meso-mechanical numerical simulations were carried out by the finite element method. This served to enrich the data and clarify the mesoscopic mechanism. The numerical result indicates that the strength of stabilized clay at low sand incorporation ratio is mainly controlled by the strength of the cement-clay-water matrix, thus verifying the rationality of studying the effective cement ratio. Subsequently, the threshold sand ratio in the cement-clay-water matrix was discussed to optimize the stabilization of soft clay.     

一维压缩蠕变前后软土的微观结构变化

软土在蠕变前后微观结构的演变,对了解软土的蠕变机理,探讨软土变形与时间关系以及建于软土地基上建筑物的稳定性有重要意义。对黄石地区软土进行一维压缩蠕变试验,提取原状样与蠕变破坏后土样的结构参数,对比分析这些结构参数在蠕变前后的变化规律。建议用丰度与圆形度辅助分析以更真实反映微观结构实际情况,将复杂度作为一个衡量软土在蠕变过程中孔隙或颗粒形状规则程度的重要参数。采用雷达图反映定向频率分布,可以同时对比多组数据,便于观察分布强度。研究结果表明:软土蠕变过程是结构逐渐破损,结构趋向稳定的过程;在蠕变条件下,竖直与水平方向微观异性变得不明显,孔隙变化遵循孔隙均匀化原理,小孔隙数量大量增多,孔隙与颗粒总体形状趋向扁圆形,外形更趋于"圆滑",颗粒定向性变得更有序了,而孔隙定向性变化不明显。     

Radial deformation and failure of stabilised soft clay under uniaxial compression

This study examined the performances of four newly developed binders in stabilising soft Finnish clay by considering both the mechanical behaviour and environmental effect (i.e., carbon footprint). Thirty-six compacted clay-binder mixtures were investigated via uniaxial compression tests, during which photogrammetric scans were performed at axial strains of 0, 1, 3, and 7.5%. The testing protocol enabled the characterisation of full-field radial deformations and fracture developments. Experimental results demonstrated that varying the amounts and types of industrial by-products used in the production of binders has substantial potential to reduce carbon footprints. In terms of radial deformations, their distributions were highly non-uniform at different heights and loading stages. Radial displacements increased continuously at axial strains smaller than 3% (corresponding to peak strength point), whereas such a continuity disappeared afterwards, and global failures appeared. Based on three-dimensional (3D) reconstructions, the observed failures were categorised into three modes: inclined shearing (IS), axial splitting (AS) and hybrid shearing-splitting (HSS). For the studied specimens, shearing was the most common mechanism leading to failure.     

Using fiber and liquid polymer to improve the behaviour of cement-stabilized soft clay

This work studies the effect of using two types of polymer (fibers and liquid) to enhance the strength of cemented soft clay. Four polymer contents were used (0, 0.1, 0.2, 0.5 and 1% by dry weight of the soil) to investigate the unconfined compressive strength, q_un of soft clay mixed with three cement contents (5, 10 and 15%). For wide understanding to the polymer/cemented soil behaviour several factors were considered in this study such as curing time, dry unit weight, the mixture workability and the behaviour after disturbance. This investigation revealed that both fibers and liquid polymers can improve the cemented soft clay strength, however the fiber mechanism in improving the mixture is totally different than the liquid. Increasing the fiber content shall increase q_un till a peak point at fiber content of 0.5%, where the strength started to reduce after. The mixture workability has been improved with increasing the liquid polymer content, and reduced with increasing the fiber content. Fibers can be used to raise up the strength of disturbed cemented soft clay up to 240% by using fiber content of 0.5%. Both fibers and liquid polymers showed a remarkable mechanically, economically and environmentally dominance to be used as additive to cement in improving the soft clay.     

超载卸荷后再压缩软土的次压缩特征及变形计算

采用软土重塑试样进行了超载卸荷后再压缩过程的一维压缩试验。试验表明:超载卸荷后软土的再压缩过程较原压缩过程的主固结时间大大缩短,次固结系数在较长的时间内和时间无关,随再加荷压力的增大而增大,随着预固结压力的增大而减小,次固结系数和超载比之间具有规则的对应关系,可以用双曲线简化模型模拟;根据次固结系数双曲线模型建立的次压缩变形计算公式,既反应了软土本身性质的影响,也反应了预固结压力和再加荷压力的影响。工程算例数据和工程实测的工后沉降数据表明,使用改进的次压缩变形计算公式得到的结果,较之采用传统次压缩变形计算方法具有更高的可靠性,采用传统的次压缩变形公式计算再压缩软土的次压缩变形会产生较大的正偏差。     

Long-term desalination leaching effect on compression/swelling behaviour of Lianyungang marine soft clays

Bulletin of Engineering Geology and the Environment - In this study, Lianyungang (LYG) soft marine clays were long-term leached by the distilled water and synthetic NaCl solutions, respectively,...     

微波技术在黏土烧结制品干燥中的应用

介绍了微波技术在黏土烧结制品干燥中的应用.通过给微波干燥室送入和排出空气,使空气流动的干燥室对黏土制品进行微波干燥,在确保坯体干燥质量的前提下大幅缩短干燥时间.     

软土地基路堤施工监控

软土地基上高速公路路堤施工中的监测是保证工程质量和安全的重要手段。文中结合具体工程监测数据,讨论了软土地基路堤施工监测方法、控制标准和注意事项等问题,可以为同类工程提供借鉴。     

关于“超载卸载后再压缩软土的次压缩特征及变形计算”的讨论

近年来,李国维先生在《岩土工程学报》上发表了一系列有关软土次固结论文[1-4],最新的一篇发表在2009年第一期[1]。这些论文主要采用试验手段对软土次固结特性进行了系统分析,取得了一些有益的试验成果。笔者把土体看作是软体材料,从非平衡态热力学超黏弹性理论出发,对软土次固结的特性也进行了一些研究,其中有些观点与李国维先生有所差别。为了能使岩土力学的研究园地百花齐放,进一步深入认识软土次固结变形特性,现与李国维先生就软土次固结的某些观点进行讨论,如有不当之处,敬请谅解。     

对“超载卸载后再压缩软土的次压缩特征及变形计算”讨论的答复

笔者收到《岩土工程学报》编辑部转来的讨论文章后,认真学习并思考胡亚元副教授(以下简称讨论文)提出的问题。首先,为有同行如此关注笔者研究的问题而倍感荣幸,其次对讨论文提出的问题颇感为难。讨论文涉及5篇论文和1部专著,其中有2篇论文笔者为第一作者,1篇为第二作者,1篇为第四作者,还有1篇和专著未参与。因此,对文章或专著主旨的理解,除为第一作者的文章外,笔者不敢说是准确地或是真正体现第一作者原意的。笔者本着互相学习、互相促进的态度在此商榷,不当之处请指正。     

矿物成分相关的黏土一维压缩特性分析

为了探索不同黏土矿物成分对黏土一维压缩特性的影响,采用高岭土、伊利土、蒙脱石及绿泥石,按不同质量比例混合来制备重塑土样,进行室内标准一维压缩试验。大量试验结果对比表明：①高岭土与伊利土混合土样的压缩指数（C_c）和回弹指数（C_s）都随伊利土含量的增加而增加;②高岭土、伊利土与蒙脱石混合土样的C_c和C_s随蒙脱石含量的增加而增大,且蒙脱石的作用占主导地位;③高岭土、伊利土、蒙脱石及绿泥石混合土样的C_c和C_s随蒙脱石与绿泥石二者含量之和的增加而增大,且蒙脱石的作用占主导地位。基于试验结果,总结出各黏土矿物成分影响的压缩指数与回弹指数的非线性表达式。此外,试验表明所有混合土样的压缩指数与回弹指数的比值（C_c/C_s）介于6.1和9.1之间变化。     

Vertical compression of soft clay within PVD-improved zone under vacuum loading: Theoretical and practical study

Reliably estimating soil vertical compression under vacuum loading is still challenging for geotechnical engineers. In this paper, the soil vertical compression within the prefabricated vertical drain (PVD)-improved zone under vacuum pressure was investigated based on the theoretical analysis, reported laboratory tests and the case histories. A theoretical equation was developed to evaluate the effect of lateral displacement on the soil vertical compression. The observed small overall lateral-to-vertical strain ratio at the perimeter of the PVD-improved zone soil showed that the vertical compression of PVD-improved zone was close to one-dimensional (1-D) state, but 1-D compression method yielded smaller predictions than the measurements from the case histories. The back-analyzed soil modulus of the natural soft clay in Shanghai Disneyland Resort project showed considerable degradation as compared to the corresponding constrained modulus from the laboratory test. Such degradation could be due to the soil disturbance caused by PVD installation. The 1-D compression method was modified by introducing two factors to consider the effect of soil lateral displacement and to correct the constrained modulus due to the soil disturbance caused by PVD installation, respectively. The recommendations were provided after applying the proposed method to a case history.     

深厚软基超长桩工程性状试验研究

通过温州软土地基中超长钻孔灌注桩静载荷试验和桩身轴力的测试 ,探讨了软土地基中超长钻孔灌注桩的承载力性状和荷载传递机理。超长桩桩身轴力的传递规律和侧摩阻力的发挥性状对软土地基中超长桩的理论研究和工程应用具有重要的参考价值。     

结构性软土力学特性的试验研究

对扰动程度不同的原状样和重塑样分别进行单向固结试验和固结排水及不排水三轴剪切试验,研究结构性对上海软土的变形、强度特性的影响。压缩试验结果表明:结构性强的原状样具有明显的结构屈服应力,结构性一般的原状样,结构屈服应力不明显;原状样比重塑样具有更大的压缩指数Cc和膨胀指数Cs。剪切试验结果表明:相同固结压力下,结构性强的土样强度不仅低于结构性弱的土样强度,而且低于重塑样的强度。这是由剪切时土样的孔隙比差异造成的。若消除孔隙比的影响,则结构性将使原状样具有更高的强度,且结构性越强,土体强度越高。     

Reliability-based analysis of embankment on soft Bangkok clay

Six slope failures occurred at random locations along a 10 km embankment adjacent to an irrigation canal. The slope failures occurred when the embankment was raised to 2.05 m above MSL from an average elevation of 1.7 m above MSL coinciding with the lowering of the canal water level at the end of the dry season. Slope stability analysis was carried out using both conventional and reliability-based procedures. The spatial variability of undrained strength, the actual variation in embankment geometry, and the varying water level in the canal were considered in the analysis. Both idealized and empirical autocorrelation functions (ACF) of the undrained shear strengths were used in the analyses. An analysis using a factor of safety based on the deterministic soil profile defined by the mean undrained strength resulted in a prediction favoring a reverse failure pattern along the embankment. Using the probability of failure which incorporates spatial variation of undrained strength and uncertainties associated with stability prediction yielded a result conforming to the actual failure pattern along the embankment. The use of empirical autocorrelation function (ACF) seems to confirm and explain better the occurrence of the failure zones than utilizing the idealized ACF.     

饱和软粘土的再固结性状研究

围绕“动静结合排水固结法”课题,通过室内试验研究饱和软粘土在冲击荷载作用下的再固结性状,重点分析排水条件对土体固结和再固结的影响,指出孔隙压力升高与再固结体应变之间的唯一性关系。提出再固结体积压缩系数和再固结压缩指数的概念并给出其确定方法。对冲击荷载作用后软土地基沉降计算方法进行讨论,包括多遍冲击和部分排水条件的情形,并给出试验验证。     

Generalized stability analysis of reinforced embankments on soft clay

By modifying Janbu's generalized procedure of slices (GPS), the stability of a reinforced embankment constructed on a non-homogeneous clay deposit of finite depth is analysed to compute the factor of safety. The non-circular critical surface corresponding to the minimum factor of safety is obtained by a sequential unconstrained minimization technique in conjunction with a conjugate direction method for a multidimensional search and a quadratic interpolation technique for a unidimensional search. The effect of the thickness of the desiccated zone and the variation of undrained shear strength of clay with depth on the factor of safety is considered in the analysis. The influence of the tensile reinforcement force on the location of the critical surface is presented. The effects of the tensile reinforcement force and its orientation as well as the number of reinforcing layers on the stability of embankment have also been studied. The results obtained from the present analysis are compared with solutions reported in the literature.     

A microstructural investigation on hydraulic conductivity of soft clay

Bulletin of Engineering Geology and the Environment - The hydraulic conductivity is a key parameter in geotechnical engineering. It is closely associated to soil microstructure. In practice,...