Characteristics of Soils with Low Plasticity: Intermediate Soil from Ishinomaki,Japan and Lean Clay From Drammen,Norway

Two soils with low plasticity are investigated; intermediate soil from Ishinomaki, Japan and lean clay from Dram- men, Norway. Since both the soils were retrieved using the Japanese sampling method, the test results from these samples are comparable. Though they have the same order of plasticity index (I_p), there is a significant difference in the grain size distribution characteristics between these soils. Ishinomaki intermediate soil contains a lot of sand or silt sized particles, its I_p value being nearly proportional to its clay content. On the other hand, Drammen clay consists of a large proportion of rock flour, which contains little clay mineral. The study shows that the unconfined compression test significantly underestimates the undrained shear strength for both soils, and their residual effective stress (p'_r) is also very low. It has been found that to compensate for loss of p'_r, recompression tests are useful methods to evaluate the strength of such soils.     

簸箕山大型老滑坡滑动带的结构特征及形成机制试验研究

 上更新世红色黏土岩是黄土高原大型滑坡的易滑地层,对其滑动带的结构特征及形成机制研究较少。在对黏土岩滑动带的组构、构造特征进行解析的基础上,通过三轴应力–应变试验、残余强度试验及滑带土蠕变试验,分析大型滑坡黏土岩滑动带的形成机制。研究表明：(1) 簸箕山黏土岩滑动带发育密集的近水平剪切面,伴随滑带土结构改变的是塑性变形、剪切变形,运动方式上以块体滑动为主;(2) 黏土岩转变为滑带土后,裂隙增多,平均吸水速率达2.7 g/h,其标准岩样单位时间吸水速率是原岩的1.5倍,活性为0.83,比表面积、活性均高于原岩;(3) 与原岩结构改变相应的是强度的衰减,含水率为19.1%时,黏土岩原岩的峰值强度的黏聚力613 kPa,内摩擦角26.7°,簸箕山滑带土长期强度的黏聚力57.4 kPa,内摩擦角20.47°,残余强度的黏聚力8.79 kPa,内摩擦角为17.2°。     

含水率和干密度对残积土抗剪强度参数的影响

在分析闽东南地区花岗岩残积土物理力学特性的基础上,对3类非饱和残积土的含水率(ω)和干密度(ρ_d)与抗剪强度指标(c、φ)进行相关分析,建立了针对闽东南地区花岗岩残积土含水率和干密度与抗剪强度指标之间的经验公式。研究结果表明:粘聚力的对数与含水率呈负相关,随着含水率的增大,残积土黏聚力总体呈减小趋势;内摩擦角在含水率增大过程中具有非线性衰减的趋势,且集中在一个范围内变化;3类残积土在高密实度下的ω~φ具有峰值点,土体密实度对粘聚力的影响可用线性正相关来反应;一般情况下,干密度值越大,残积土粘聚力值和内摩擦角也越大。利用建立的经验公式,可为花岗岩残积土边坡的勘察、设计和施工过程中土性参数的合理选取及可靠性分析提供参考。     

青藏斜坡黏土冻融循环物理力学性质试验

 冻融过程使土体的结构、物理力学性质等发生变化,导致其工程性质恶化,影响线路稳定和列车的正常运行。为考察青藏铁路多年冻土区斜坡路基土体的长期稳定性,针对典型斜坡黏土在冻融循环条件下的主要物理力学性质,进行试验研究。试验结果表明：试样经历10次冻融后,其含水量、密度、黏聚力、内摩擦角等物理力学性质趋于稳定。土体冻融最终平衡状态与初始状态相关,其中初始干密度的影响尤为重要。随冻融循环过程增加,低密度土体的黏聚力有所提高,而高密度土体的黏聚力下降,内摩擦角变化较小。进行冻土斜坡路基稳定性分析时,建议取土体冻融平衡状态时的参数。     

Problem of assessing the design resistance of beds with a weak underlying stratum

A procedure for determination of the design resistance of a weak soil stratum is cited. The coefficients M_δ, M_q, and M_c to Eq. (7) of Construction Rule and Regulation 2.02.01-83, which depend not only on the angle of internal friction of the weak soil layer, but also on the depth of its embedment, have been obtained for the first time. The influence exerted by a weak underlying layer on the design resistance of the bearing soil layer is analyzed. The study was conducted with the participation of R. T. Gabdullinoi and A. M. Moshkin. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 7–9, November–December, 1997.     

Assessment of the strength characteristics of soils of the glacial system from results of their static-penetration testing

Results of investigations of correlation relations between the strength φ and c and static-penetration data on soils of the glacial system are cited. Equations for determination of φ and c with respect to the specific resistance of the soil to the cone of the probe and in the friction coupling are obtained on the basis of the processing of research data with allowance for type of soil. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov. No. 4, pp. 6–8, July–August, 1995.     

异常温度作用对粉质黏土抗剪性能的影响

异常气候对粉质黏土抗剪性能有重要影响,通过对重庆市典型粉质黏土进行异常温度下力学性能研究,分析了异常温度作用下土体抗剪性能的变化规律。结果表明,高温及其持续作用可增强土体的抗剪强度,黏聚力对抗剪性能的影响大于内摩擦角,当高温作用达到一定时间后,内摩擦角则呈现出弱化抗剪性能的作用;黏聚力在各温度作用下,随作用时间的增加而增大,当作用时间超过48 h后,在10～50 ℃温度范围内,温度的变化对土体黏聚力的影响不显著,超过50 ℃以后,黏聚力随温度的增加而增大,当作用时间超过7 d后黏聚力则增加明显;内摩擦角随温度作用时间的增加而增大,当作用时间超过12 h后,在10～40 ℃范围内,温度影响不显著,超过40 ℃后,内摩擦角随温度增加有小幅减小。     

黄土节理抗剪强度特性试验研究

试验得出表面形态、干密度和含水量对黄土节理的强度特性的影响,揭示出黄土节理表面形态对抗剪强度参数c、φ值的影响规律。在相同含水量和干密度的情况下,粗糙表面的节理粘聚力c值较平整表面节理的大,而节理的摩擦角φ值相差较小,说明黄土节理形态特征对节理粘聚力c值有较大影响,而对摩擦角φ值影响较小。干密度对黄土节理粘聚力c值的影响较大,而对内摩擦角φ值的影响较小。当试样含水量在一定范围之内,黄土节理的摩擦角随含水量的增加呈二次曲线变化。但当试样含水量较大时,测得试样抗剪强度稍有增大,是因为节理表面部分土体在法向压力作用下发生重塑,破坏面已不是原有节理面,重塑土体自身的抗剪强度发生作用,引起试验所测抗剪强度的增大。     

不同养护龄期下凹凸棒土改良黏性土三轴压缩试验研究

随着人们对环境保护的重视,凹凸棒土被越来越多的用于土体改良中。目前研究主要针对凹凸棒土对土壤污染修复、团粒结构和水力参数的影响,缺少对黏性土土体强度特性改善方面的研究。本文通过不固结不排水三轴压缩试验,探究凹凸棒土改良黏性土在不同养护龄期条件下的强度变化规律,结合扫描电镜图像(SEM)对凹凸棒土改良土体的作用机理进行讨论。研究发现,随着凹凸棒土置换量和养护时间的增加,试样的脆性增加,内摩擦角逐渐增大,黏聚力表现出先增加后减小的趋势。凹凸棒土吸附周围土颗粒和水形成的团聚体增加了改良试样内部的滑动摩擦力和咬合摩擦力,从而提升了改良试样的内摩擦角。在团聚体趋于稳定过程中形成的表观黏聚力变化是试样黏聚力先增后降的主要原因。研究结果为凹凸棒土在道路路基工程与边坡防护工程中的应用提供一定的参考依据。     

黏粒含量对固化淤泥力学性质的影响

采用人工配制不同黏粒含量的淤泥研究黏粒含量对固化淤泥力学性质的影响。研究发现,淤泥中黏粒含量对固化淤泥的力学性质存在显著影响,当水泥量为5.0%时,固化淤泥强度随黏粒含量的增加呈增加趋势;当水泥量高于7.5%时,对于不同水泥量都存在一个对应的适宜黏粒含量CCop,在该黏粒含量时固化淤泥的无侧限抗压强度最大,破坏应变最小。适宜黏粒含量CCop随着水泥量增加而有所增加,但龄期对其没有影响。三轴试验结果发现,当黏粒含量为CCop时固化淤泥黏聚力c达到最大,内摩擦角?则随黏粒含量的增加呈现减小趋势。对于不同黏粒含量下固化淤泥的应力–应变关系的研究发现,当水泥量不超过5.0%时,固化淤泥都表现出理想弹塑性的特性;当水泥量大于5.0%时固化淤泥都存在破坏峰值,表现出脆性破坏模式,而且随着黏粒含量的增加破坏应变先减小后增加;当黏粒含量为CCop时,固化淤泥对应的破坏应变接近最小。因此,当黏粒含量为CCop时,固化淤泥将出现最大强度和最小变形。该研究结果对淤泥固化实际应用中的材料配制具有重要意义。     

Influence of particle shape on the shear strength and dilation of sand-woven geotextile interfaces

The influence of particle shape on the mechanical behavior of sand-woven geotextile interfaces over a wide domain of soil density and normal stress is studied. A uniformly graded angular fine sand, and a blend of well rounded glass beads with identical particle size distributions, were selected as granular material. Experiments revealed the impact of particle shape on peak and residual friction angles as well as the maximum dilation angle of interfaces between both granular media and woven geotextile. It was observed that the residual friction angles of interfaces between angular sand/glass-beads and woven geotextile are very similar to the residual friction angles of angular sand and glass-beads in soil–soil direct shear test. It is understood that the peak friction angle and maximum dilation angle of angular sand-woven geotextile were slightly lower than corresponding values for angular sand in soil–soil direct shear test. While the peak friction angle and maximum dilation angle of angular sand-woven geotextile interface decrease with the increase in normal stress, experiments showed that these factors are insensitive to normal stress for glass beads-woven geotextile interfaces, at least for the range studied herein. All interfaces with woven geotextile as the contact surface exhibit an abrupt loss of shear strength in the post-peak regime of behavior. Finally, a unified stress-dilation law for the angular sand-woven geotextile, glass beads-woven geotextile, and angular sand-roughened steel interfaces is obtained.     

Fluage et glissement d’un terrain

Résumé On suit depuis 1964 le fluage d’un terrain en bordure de la retenue d’un barrage (fig. 1, 4). La résistance résiduelle de l’argile dans la zone de fluage (fig. 2, 3) n’est que légèrement supérieure à celle indipensable pour la stabilité (fig. 5). Un léger accroissement des pressions interstitielles peut compromettre la stabilité. En cas de glissement, le coefficient de frottement dynamique f (≡. 3) diminue à cause de l’accroissement de la pression intersititelle (fig. 6, 7) et de la diminution de l’angle effectif de frottement. Tandis que l’ approche du coefficient f vers zéro provoquerait un glissement dangereux pour la retenue (fig. 8), le glissement serait sans danger pour f=0,12 (6,5°). A l’heure acutelle, aucune étude expérimentale ou théorique ne peut confirmer si cette valeur, même faible, peut être assurée.

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Summary The creep of a reservoir bank has been followed since 1964 (fig. 1, 4). The residual strength of the clay in the creep zone is only slightly higher (fig. 2, 3) than that required for the stability (fig. 5). A slight increase in pore pressure can render the mass unstable. When a slide occurs, the coefficient of dynamic friction f (eq. 3) decreases with an increase of the pore pressure (fig. 6, 7) and decrease in the effective angle of friction. While the coefficient f approaching to zero would result in a dangerous slide in the reservoir (fig. 8), there would be no danger in the case of f=0,12 (6,5°). At the present time, theoretical or experimental studies cannot confirm whether this value, even if small, could be assured.

     

冻融作用对黏土力学性能影响的试验研究 TitleFilter('chTitle');

为揭示冻融作用对黏土力学性能的影响规律,对原状土及不同冻融条件下的融土进行了压缩试验和固结排水剪切试验。试验结果表明:黏土冻融后,压缩系数大于原状土的压缩系数;封闭型冻融时,冷端温度越低、含水率越大,则压缩性的变化越大;融化温度对融土压缩特性基本无影响;冻融对不同干密度的重塑黏性土具有双向作用,使松散的低密度土压缩性减小,密实的高密度土压缩性增大。黏土冻融后,黏聚力降低,内摩擦角增大;封闭型冻融时,冷端温度越低,内摩擦角变化越大;融化温度对融土的强度影响很小。更多还原 AbstractFilter('ChDivSummary','ChDivSummaryMore','ChDivSummaryReset');     

Effects of Sampling Tube Geometry on Soft Clayey Sample Quality Evaluated by Nondestructive Methods

Sample disturbance caused by difference in sampling tube geometry was evaluated by two nondestructive methods: the measurement of the residual effective stress (p_r') by ceramic disc; and the use of the bender element to ascertain the shear wave velocity (V_s), and thus the maximum shear modulus (G_BE). Samples were measured under atmosphere, i.e., not under confined stress conditions. The soil samples were obtained from two sources: reconstituted Kasaoka clay prepared in the laboratory, and at the test site at Takuhoku, Hokkaido, Japan. Samplers with different geometrical designs, referring to the Japanese standard stationary piston sampler, were used for the model ground and field sampling. The geometrical effects of the sampling tube, for example, the thickness of the tube wall, the edge angle, and the existence of a piston were carefully examined. The quality of the samples taken with different samplers was evaluated by p_r' and G_BE, values which were normalized by the in situ vertical effective stress (σ'_vo) and G_f measured by the seismic cone test in the field. It was found from these studies that p_r'/σ'_vo and G_BE/G_f vary considerably due to the geometry of the sampler, with the edge angle of sampling tubes being the most important feature in obtaining high quality samples. The wall thickness, and thus, the area ratio of the sampler is not critical to the sample quality if the edge angle is sharp enough. The existence of the piston does not significantly influence the sample quality in field samples. Furthermore, the correlation between G_BE and p_r' was also investigated, and it was found that the two parameters are strongly dependent.     

挡土墙土压力非线性分布的计算方法研究

基于数学方法对斜单元体进行力和力矩的平衡分析, 得到了墙背粗糙且填土坡面倾斜情况下的土压力解析解, 并进一步分析了填土坡面倾角对土压力的影响。对比分析表明: 经典朗肯土压力理论可看作是解析解在墙背光滑、填土坡面水平情况下的特例; 在填土内摩擦角一定时, 挡土墙墙后滑动楔体的极限破裂角随着填土坡面倾角或墙土之间摩擦角的增大而减小。基于解析解得到的土压力分布呈现明显的非线性特征, 且在填土面水平情况下挡土墙墙脚处的土压力为0, 这与实测数据取得了很好的一致。分析还表明, 随着填土坡面倾角的增大, 墙脚处的土压     

非饱和土抗剪强度与含水量关系研究

非饱和土的含水量对其的抗剪强度有一定的影响,所以研究非饱和土的含水量与抗剪强度之间的关系有实际的工程意义。以长春重塑粉质黏土为研究对象,通过固结排水试验和不固结不排水试验,研究含水量对非饱和土的抗剪强度指标的影响。结果表明:非饱和土的抗剪强度指标受到含水量的影响,黏聚力随着含水量的增加而升高,存在一个临界含水量,当超过这个含水量时,黏聚力反之降低;内摩擦角随着含水量增加而降低,存在一个临界含水量,超过这个含水量时,内摩擦角反之升高。     

Evaluation of shear strength of clayey soils by using their liquidity index

 It is well known that overconsolidated clays have higher shear strength than unconsolidated clays. The liquidity index makes possible an evaluation of the consolidation degree of clays. However, there is no empirical information about this relation. In this study, clayey soil samples have been collected from various locations and tested. The tests include the determination of liquidity index and shear strength. Obtained parameters were correlated and regression equations were established among liquidity index and undrained shear strength, presenting high coefficients of correlation (R=–0.93). So, an equation [c_u=e^{(0.026–1.21 IL)}] that makes possible a rough evaluation of the shear strength of clayey soils by using their liquidity index value is an improvement. Received: 10 December 1999 · Accepted: 4 April 2000     

Application of the ZEL method in the prediction of foundation bearing capacity considering the stress level effect

There are a number of factors affecting the bearing capacity of shallow foundations. Among them, the scale effect can be mentioned as one of the most important factors. Unlike the theoretical equations, experiments show that the bearing capacity of foundations does not increase without limit when the foundation size increases. The effect of stress level on soil shear strength parameters has been known as the main reason for this observation. The method of the zero extension lines (ZEL) for the solution of plasticity problems in soil mechanics has been utilized to take this effect into account by incorporating the stress level − dependent soil friction angle. The bearing capacity of shallow foundations is then computed with the aid of this method, showing a decreasing tendency in the third factor, N _γ, which is the main contributor in shallow foundations. Comparisons have been made with experimental data, showing good consistency between experiments and theoretical predictions with the ZEL method.     

Influence of drainage condition on Coulomb-type active earth pressure

The present paper focuses on the computing of Coulomb-type active earth pressure acting on a retaining wall provided with a drainage system or without and supporting a soil mass subject to steady water seepage. The influence of drainage conditions on the critical inclination of the failure surface and the coefficient of active earth pressure is investigated by discussing their variations with increasing effective internal friction angle of the soil mass. The results indicate that when the soil effective internal friction angle is increased, the critical inclination increases, but the coefficient of active earth pressure decreases. It is better to provide the drainage at the base of the backfill as well as at the bottom of the wall base rather than providing the drainage along the vertical face of the wall. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 5–8, September–October, 2008.     

Ring shear characteristics of discontinuous plane

Residual shear strength is an essential parameter in evaluating the long-term stability of reactivated landslides in geotechnical engineering. According to previous studies, earthquake-induced landslides may occur on discontinuous planes, such as bedding planes, between weathered and unweathered mudstones having different cementation properties resulting from diagenesis. However, the shear behaviour at the contact surfaces between the cemented and the non-cemented soil layers has not yet been sufficiently investigated. The objective of this study is to elucidate the residual strength characteristics of artificial bedding planes that model the actual behaviour of slip surfaces occurring between two layers with different degrees of cementation. The experimental tests were conducted with a ring shear test apparatus. Additionally, in order to simulate the realistic mechanical behaviour of naturally cemented clay, artificial cementation bonds were created by adding a cementing agent at different ratios to clay slurry. A series of ring shear tests was performed under various conditions on one-layer non-cemented and cemented kaolin samples, respectively, as well as on two-layer specimens composed of one layer each of cemented kaolin and non-cemented kaolin. The test results showed that the residual friction angle of the two-layer combinations of non-cemented and cemented kaolin was approximately 33.6% lower than that of pure kaolin. In contrast, the residual friction angle of cemented kaolin may be as much as 6.2° greater than that of non-cemented kaolin. At cement ratios of up to 2%, the stress ratio of cemented kaolin increased as the shear displacement rate increased. As the cement content was increased beyond 2%, the degree of increase was not significant. These results suggest that the residual strength of cemented kaolin at cement contents greater than 2% is independent of the shear rate.