郑西客运专线黄土路基震陷研究

以郑（州）西（安）高速铁路为例,选择潼关段为研究区,采集大量原状黄土样品,将合成的人工地震动输入到动三轴,进行了固结不排水的动三轴实验,估算了黄土路基的震陷量。建立了高速铁路黄土路基动力学数值模型,研究了50年10%和2%的超越概率水平的地震作用下黄土路基的永久变形,以及地基处理后黄土地基的永久变形。结果显示, 沉降主要发生在Q3黄土中,强夯、DDC桩等地基处理措施可以有效的减少地基黄土的沉降变形,但是当处理深度不够时,在强地震作用下仍然可以产生较大沉降。研究成果为地基抗震处理提供了依据。     

延安Q3原状黄土渗透各向异性及微结构分析

为研究原状马兰黄土的渗透各向异性,以延安削山造地重大工程开挖所揭露的完整黄土剖面中的马兰黄土层为研究对象,采用室内变水头渗透试验获取不同埋深不同渗流时长原状黄土垂直向和水平向的渗透系数,并对试验前后黄土试样垂直向和水平向SEM（scanning electron microscope）电镜扫描结果进行分析,从微观结构上揭示原状马兰黄土结构各向异性的原因。结果表明：原状黄土垂直向和水平向饱和渗透系数具有显著各向异性,且垂直向和水平向渗透系数都随渗流时间的持续而减小,各向异性渗透性能在时间尺度上具有某种衰减关系;同时,原状黄土各向异渗透性能随埋深的增大而逐渐减弱;土颗粒结构的接触、排列方式是导致黄土原生各向异性的根本原因,也是导致渗流初始阶段渗透系数各向异性的原因,而渗流作用产生的次生结构各向异性则使渗透系数各向异性在时间尺度上表现得更为明显。     

冻融循环对黄土渗透系数各向异性影响的试验研究

为了反映冻融循环作用对原状黄土渗透各向异性及原状、 重塑黄土渗透差异的影响, 以西安Q₃黄土为研究对象, 通过三轴固结渗透试验对比分析了冻融前后水平、 竖直向原状黄土及重塑黄土的渗透系数随初始含水率、 围压、 冻融循环次数变化的规律。结果表明： 未冻融时各级围压下竖直向原状黄土的渗透系数为2×10^-6 ~ 18×10^-6 cm?s^-1, 水平向原状黄土和重塑黄土的渗透系数为0 ~ 4×10^-6 cm?s^-1; 经历冻融循环后, 水平、 竖直向原状黄土及重塑黄土的渗透系数与初始含水率的关系曲线分别呈现逐渐上升、 抛物线形式与变化平缓的不同特征, 而三者的渗透系数均随冻融循环次数的增加呈现数量级增大的趋势; 原状黄土的竖直 - 水平渗透系数比（k_v /k_h ）由冻融前的4.38逐渐减小到0.90, 可见冻融循环作用在显著提高黄土渗透性能的同时, 可以强烈弱化其各向异性特征。通过建立围压、 渗透系数与土体孔隙率的相关关系可知, 原状、 重塑黄土的孔隙率与围压存在极强的负线性相关性, 渗透系数随围压的增大呈典型指数衰减特征, 渗透系数与孔隙率具有相似的变化趋势, 因此冻融循环过程中土体孔隙率的改变是导致其渗透性质变化的主要原因。     

Some specific problems of wetted loessial soils in civil engineering

Bally, R.J., 1988. Some specific problems of wetted loessial soils in civil engineering. Eng. Geol., 25: 303–324.

Loessial soils, wetted above the limit of collapsibility, remain in the category of difficult foundation grounds. Some case histories are presented herein: surpassing soil bearing capacity and non-stabilized settlements of buildings after initially dry loess wetting; slow but nondamped settlements or damped but great and, eventually, non-uniform settlements of structures erected on wet loess; supplementary settlements by water level lowering in loessial ground; great settlements of deep foundations passing through the collapsible loess to the underlaying wet but noncollapsible loess. Research on wetted loess performed in the laboratory (oedometer, triaxial) or in situ (full-scale experiments or real constructions) have emphasized the dependence of the soil structural resistance, deformability (compressibility and deformation under constant volume) and final resistance on both the moisture content or stress-state and on their history; the depth propagation of the active zone of surface loadings on wetted loess is different from that of the linear elastic theory; some suggestions to estimate the depth of the active zone are presented. The usual foundation systems on wetted loessial grounds, or in their vicinity, adopted in Romania include: loessial or gravel cushions; surface compaction (very efficient results of intensive dynamic compaction); foundation “stamping” or loessial ground “reinforcing”. It is recommendable to take into consideration: surveyed wetting under construction until maximum moisture content of the loessial ground; in situ columns of stabilized loess; the efficiency of geotextiles for filter-drainage and antierosional functions in loessial soils.     

结构性软土力学特性试验研究

选取广州南沙典型软土为研究对象,进行了剪切、无侧限抗压、固结等室内试验.从强度和变形两方面对试样的结构性进行了研究,分析了原状土和重塑土的变形特性、强度特性和固结特性,揭示了所研究的区域性软土的结构性特征以及这一特征对软土工程性质的影响.试验结果表明:结构性软士经扰动后强度明显降低,压缩性增加;原状土的同结特性与结构屈服压力有关,压缩曲线呈现3阶段特征.在同一级荷载下扰动后的土体变形规律较原状土有更明显的主次固结划分界限.结构屈服压力是变形规律的控制因素之一,可以通过压缩系数-固结压力曲线近似确定.试验结果还表明,当崮结压力较大时,原状土的结构被完伞破坏,此时结构性对土体力学特性的影响可被削弱,甚至消失.     

马兰黄土孔隙结构参数与渗透性关系研究

利用改进的ZC-2015型渗气仪和TST-55型渗透仪进行马兰黄土渗气及饱和渗透试验,得到两个渗透性参数渗气率k_a和饱和渗透系数K_w,通过室内常规试验得到的孔隙比e,并利用图像处理软件（IPP）处理扫描电镜（SEM）照片得到的平面孔隙比e₀,结合试验结果并利用数学模型建立宏-微观孔隙参数与渗透参数之间的关系。结果表明:重塑土干密度增大,单位体积内颗粒数量增多,孔隙面积减少。原状风干土样埋深增大,大孔和中孔的孔隙面积、孔隙数量、孔隙平均直径明显减小;半对数线性模型可以消除K_w和k_a与孔隙结构参数在量级上的差异,拟合效果更好。lgK_w、lgk_a与e、e₀之间都呈现较好的线性关系;含水率变化时,渗气率拟合直线的斜率和截距的变化规律更明显。重塑土由于制样均匀,曲线的拟合度更高,而不同深度的原状黄土试样由于沉积过程造成的结构性的差异,致使其拟合度较重塑土偏低。     

原状黄土的压缩曲线特性

原状黄土是一种具有结构强度的欠压密土,其侧限压缩变形特性区别于一般土。为研究原状黄土侧限压缩变形的共性,对西安、兰州6个场地不同含水率的原状Q3、Q2黄土进行了侧限压缩试验,得到了相应场地不同含水率原状黄土的压缩曲线,分析了其压缩曲线的形态,通过曲线对应的压缩屈服应力及初始孔隙比,将各黄土不同含水率下的压缩曲线归一化为同一曲线,且形成时代相同的黄土归一化曲线位置相同,并利用复合幂?指数模式分别描述了Q3、Q2黄土归一化的曲线。将文献中试验黄土的初始孔隙比与压缩屈服应力代入归一化曲线的表达式,计算得其压缩曲线和压缩性指标。经对比,与文献实测压缩曲线及压缩性指标很接近,验证了黄土压缩曲线的归一化特性并对其进行了应用。结果表明：试验黄土压缩曲线具有可被其初始孔隙比和压缩屈服应力归一化的特性,此特性为黄土侧限变形性质的分析提供了一条便捷的途径。     

黄土的湿陷性与击实试验指标关系研究

进行了黄土的击实试验,提出了击实率的概念,拓展了CART(classification and regression trees)决策树算法的功能。将其用于相关性挖掘,进行了原状黄土湿陷性与击实率等指标的相关性挖掘,结果表明,击实率与湿陷系数具有相关性,击实率与最优含水率状态的击实率呈显著负相关性。根据试验及分析结果提出黄土在击实过程中的变形特性可反映黄土的湿陷性,黄土的击实效果同其湿陷性具相关性。这一研究为黄土湿陷性的评价提出了一条新的思路,同时成果具有实用性。     

兰州Q4黄土各向异性的初步研究

水敏感性和结构性是黄土区别于其他类型土的主要特点,得到了广泛的研究,但大多数试验研究都采用垂直方向制备的试样,仅考虑了黄土垂直方向的力学特性,这对于以承受上部垂直荷载为主的黄土地基基础等工程类型来说是合理和准确的,而对于受力状态较为复杂的边坡和隧道及地下结构等工程类型,黄土力学性质的各向异性可能更为重要。分别从垂直向和水平向制取兰州Q4黄土的原状土试样,通过三轴剪切试验研究了其抗剪强度和变形参数在不同围压下和不同方向上的差异性,并与直剪试验获得的强度参数进行对比。结果表明：兰州Q4黄土力学性质的各向异性是较为显著的,强度方面的差异主要体现在黏聚力,而内摩擦角的差异性较小;变形特征具有随围压增加而从脆性向塑性转化的特点,垂直方向的变形模量比水平方向的变形模量平均要大2倍左右。用黄土的结构性强度及其形成机制解释了试验结果,认为黄土力学性质的各向异性特点是其结构性的另一种表现方式,应重视黄土在不同方向上强度和变形特征的差异性,以获得更安全合理的参数。     

常州地区含水层系统土层压缩变形特征研究

根据近十几年来分层标和含水层水位观测资料分析了常州地区土层压缩变形特征,表明承压含水砂层中的压缩变形不容忽视,且含水砂层的压缩变形与弱透水层的粘土、粉质粘土相似,均表现出明显的变形滞后现象.为此从水位与时间关系、土层变形与时间关系和水位与变形关系出发,结合室内试验方法,通过选取常州地区含水层系统中第一、二、三承压含水层以及二、三承压含水层间弱透水层和第三承压含水层下覆弱透水层的原状土样,采用单轴侧限压缩试验,分析了常州地区砂土和粉质粘土的次固结（蠕变）特性.试验结果表明常州地区不论是粉质粘土还是砂土,均存在一定的次固结变形,从而启示我们该地区地面沉降模拟中应同时考虑含水砂层的蠕变特性.     

Deformation zones under square footings supported by clayey soils

Footing settlements depend not only on physical and mechanical properties of base soils, but also on applied load intensities and their distributions with depth, as well as on footing rigidity, shape and dimensions. An analytical expression relating rigid bearing plate and/or footing settlements to thicknesses of deformation (active) zones, which form below footing bottoms, has been previously offered by the author. The results of tests performed with 0.5, 1.0 and 4.0 m²-area square footings, constructed on undisturbed clayey soils and containing data describing active zone development, were collected from literature and analyzed. This paper presents graphical relationships between square footing settlements, active zone thicknesses and footing dimensions, which are verified by published test results performed with experimental square footings, having areas different than the ones selected for statistical analyses.     

原状与重塑黄土冻融过程渗透特性对比试验研究

通过冻融条件下西安Q₃原状和重塑黄土的电镜扫描观测和三轴固结渗透试验,对比分析了冻融作用对原状和重塑黄土渗透特性的影响规律。结果显示:冻融条件下原状与重塑黄土微观结构均发生明显变化,土体胶结连接强度变差且颗粒排列更加松散,孔隙比增加,渗透性增强。冻融作用对原状和重塑黄土表面结构破坏均较严重,但原状黄土表面结构破坏程度较重塑黄土更为强烈;冻融过程产生的裂缝使得土中水分渗流和迁移的通道形成,导致原状与重塑黄土体渗透性增强。冻融条件下原状与重塑黄土渗透系数随含水率增加均先增大后减小,表现出抛物线变化特征;渗透系数随冻融次数增加均先增大然后趋于稳定,表现出指数增大特征;渗透系数随围压增大均先减小然后趋于稳定,表现出指数下降特征;相同条件下原状黄土渗透系数高于重塑黄土;原状与重塑黄土渗透系数差异随围压增大逐渐减小。     

论湿陷起始压力

本文以实测数据为依据,以工程应用为主题,从七个方面对湿陷起始压力进行了广泛的讨论,为工程中多方面应用湿陷起始压力提供了系统允分的依据。     

Shear induced collapse settlement of arid soils

This paper presents the results of studies of deformation, strength and collapsibility of loess soils. Samples were taken from Al Dalam in central Saudi Arabia, which resembles an arid region. These samples were subjected to various laboratory tests to determine their physical and engineering properties. Sets of oedometer and direct shear tests were carried out in which the initial dry density and the normal pressure at wetting and shearing were each varied in turn. Oedometer results indicate that collapse potential decreases with density and increases logarithmically with normal pressure. Shear induces further collapse potential which increase with density due to further destruction of soil fabric. A unique shear stress–shear strain relationship was obtained for specimens prepared at different initial fabrics. Dry and soaked failure envelopes were both non-linear in the low-pressure range. Wetting induced a reduction in the shear strength parameters. The results of the tests are reported, and the significance of each variable is assessed.     

A comparison of direct shear box tests with triaxial compression tests for a residual soil

Summary Residual soils are known to be bonded. The mechanical behaviour of undisturbed residual soils depends, therefore, not just on initial porosity and stress history but mainly on these bonds. This paper compares the stress-strain behaviour obtained from sets of drained triaxial compression tests and direct shear tests, both from undisturbed samples of residual soil. It shows how the same undisturbed bonded structure behaves differently when tested using the two different procedures.     

Seismic piezocone interpretation for shear wave velocity (<Emphasis Type="Italic">V</Emphasis><Subscript>S</Subscript>) determination in the Persian Gulf

Shear wave velocity is one of the important factors representing the dynamic characteristics of soil layers. Hence, many researchers have focused their studies on determining shear wave velocity by direct field measurements or expressions developed by other soil parameters. The shear module and damping ratio of the soil layers also play a similar role in the majority of dynamic soil response analyses. Nevertheless, since they have to be measured in the laboratory by resonant column or cyclic triaxial tests on undisturbed samples, the possibility of preparing such samples and the reliability of the obtained results are of great concerns. In the present study, great effort has been made to determine the above dynamic factors by means of field data obtained from a versatile instrument, namely the seismic piezocone (SPCT_U), and to derive expressions correlating them with some parameters obtainable by much simpler instruments. The reliability of laboratory measurements on undisturbed samples is also evaluated. The seismic piezocone test apparatus has been employed to evaluate the soil properties at 1-m depth intervals by means of measuring tip resistance, sleeve resistance, pore pressure and shear wave velocity. The shear module and the damping ratio are calculated using field data. Meanwhile, in order to assess the laboratory measurements of these parameters, some resonant column tests and cyclic triaxial tests on undisturbed samples of the same soil layers have been carried out. In order to compare the field results of shear modulus and damping ratios with those obtained from laboratory tests, the influences of the soil nature and sample disturbance on the conventional laboratory methods are evaluated and discussed. The shear wave velocity is correlated to overburden pressure and the corrected tip resistance for two groups of fine soils, namely silty clays and carbonate clayey silts, which mainly cover the areas under study in this project, are located in southern parts of Iran near the Persian Gulf. According to the results of the present study, there are narrow limits of shear modulus regarding soils for which the laboratory tests and the field measurements yield approximately the same shear modulus. This limit of shear modulus is about 30–50(MPa) for clay deposits and 70–100 (MPa) for sandy deposits. Also the shear wave velocity can be calculated by a simple expression from total overburden pressure and the tip resistance of simple cone penetration test results conventionally available in many soil explorations prior to engineering practices. However, if the pore pressure inside the saturated soil deposits can be measured by a piezocone apparatus, the shear wave velocity may be calculated using another suggested equation in terms of effective overburden pressure in the present study. Regarding the shear module and the damping ratio, due to the disturbances of the stiff deposits in the sampling process and great deviations of laboratory results from field results, the laboratory measurements of these parameters out of the above limits are not recommended.     

陕西延安Q_2原状黄土抗拉强度试验研究

对陕西延安新宝塔山隧道Q2原状黄土进行了不同加载速率的无侧限抗压与贯入抗拉试验,研究了Q2原状黄土抗压与抗拉强度的影响因素。结果表明:加载速率对宝塔山Q2原状黄土抗压和抗拉强度影响较大,抗压强度与抗拉强度随加载速率增大而增大;高径比对抗拉强度也有较大影响,试验时当高径比控制在1.0左右时,高径比对宝塔山Q2原状黄土的抗拉强度影响相对较小,因此采用轴向压裂法测量黄土的抗拉强度时,高径比宜控制在1.0;在试验加载速率范围内,加载速率对宝塔山Q2原状黄土的压拉比影响不大,其压拉比在9.88~13.68范围内变化。     

预压作用下软土微观结构试验及弹黏塑性模型研究

为了揭示软土固结蠕变机制,计算软基“工后沉降”,开展了室内模拟真空、堆载以及真空-堆载联合预压加固软土的固结蠕变三轴试验及三轴试验前、后的微观结构试验。建立了能考虑微观结构改变的弹黏塑性(EVP)软土蠕变模型。研究结果表明：原状软土样在真空预压、堆载预压、联合预压3种预压荷载作用下,固结过程和蠕变过程具有耦合效应;土体微观结构参数的改变与宏观工程性质的改变具有相辅相成的关系;EVP模型弱化了具体应力路径的变化,其反映弹性的参数和反映黏塑性的参数可由微观结构参数确定;改进的EVP模型既能计算土体的弹黏塑性变形,也考虑了土体微观结构的变化,能更全面地反映土变形的实质。     

考虑含水率影响的结构性黄土临界状态模型

根据不同初始含水率原状黄土结构性演化规律,基于临界状态土力学理论,以应力、初始含水率和应变为基本变量,提出了一个可以反映原状黄土结构性演化规律及软化特性的临界状态本构模型。模型通过对比不同初始含水率下重塑与原状黄土等向压缩曲线,建立了不同含水率下原状黄土的结构性参数及其演化方程。此外,模型采用非相关联流动法则,以剪胀方程的形式来求解塑性偏应变。模型共计9个材料参数,均可由压缩试验和常规三轴剪切试验求得。通过与已有试验数据的对比发现,本模型不仅可以较好地体现初始含水率对原状黄土结构强度、变形特性以及结构破坏规律的影响,而且能较为合理地预测原状黄土的硬化及软化特性。所建立的结构性黄土临界状态模型为深化黄土力学特性研究提供了可能,同时为有效计算黄土地基湿陷变形提供了一定的理论依据。     

水泥固化铅污染土的基本应力-应变特性研究

采用水泥系固化剂,对铅污染土进行了固化处理,对固化后污染土的无侧限压缩变形特性进行了研究。试验所用的铅污染土通过人工制备而成,并考虑了不同的铅离子浓度和水泥掺量。研究结果表明,随着污染土中铅含量的变化,水泥固化铅污染土的应力-应变特性、破坏应变、变形模量值不同。铅浓度为0.01%、0.1%试样的破坏应变大于不含铅试样,且随着强度的增加、龄期的增长呈幂函数减小。韧性指数可用来定量描述铅离子浓度对固化土样韧性特征的影响程度。固化铅污染土的变形模量与其无侧限抗压强度呈线性关系,线性拟合参数与铅离子浓度和水泥掺量有关。