Sample Disturbance in Soft and Sensitive Clays: Analysis and Assessment     

K. Nagendra Prasad  S. Triveni  T. Schanz  Late T. S. Nagaraj 《Marine Georesources & Geotechnology》2013,31(3-4):181-197

Despite the sophisticated methods employed to obtain high quality samples, they are prone to disturbance, due to stress release, let apart, due to sampling tools and techniques adopted. Critical reappraisal of different methods suggest that any method of sample quality assessment involving strength and deformation parameters would enable easier implementation and correct other engineering parameters for estimated sample disturbance. In this technical paper, sample disturbance index, using merely the slopes of compression paths, (representing mechanical response), in the pre- and post-yield stress regimes under odeometric loading conditions is proposed. This method is based on single oedometer test results on samples of unknown degrees of disturbance during sampling and handling. The unique feature of this approach is that the ideal rigid plastic material behavior is taken as reference. This eliminates the need for any additional experimental data or any calculations from the relationships formulated with any set of assumptions.  相似文献   

Consolidation Parameters Interpretation of CPTU Dissipation Data Based on Strain Path Theory for Soft Jiangsu Quaternary Clays     

Guojun Cai  Songyu Liu  Anand J. Puppala 《Marine Georesources & Geotechnology》2013,31(4):310-319

When a piezocone (CPTU) penetrates the ground, pore pressures are set up due to the stress changes. Pore pressure dissipation occurs in the subsequent consolidation process in a manner dependent on the initial stress distribution. The process of analysis can be used to interpret the consolidation parameters from CPTU data based on strain path approach. For the two approaches to the CPTU analysis, the Houlsby and Teh method used an elastic-plastic model, while the Levadoux and Baligh solution used parameters specifically appropriate for Boston Blue Clay. This article discusses a comparison between the two theoretical predictions and field CPTU measurements deployed in Jiangsu (China) Quaternary clays. The values of the coefficient of consolidation calculated from the two methods are then compared with high-quality laboratory tests. Both theoretical predictions provide good agreement for the shape of the dissipation curve, but the predicted c _h values are different and thought should indeed be given to the use of an appropriate value of G/s _u.  相似文献   

Modified approach to evaluation of undrained shear strength from piezocone tests in soft clays     

Yaguo Zhang  Fayun Liang  Rui Fang  He Li 《Marine Georesources & Geotechnology》2017,35(1):80-88

This paper proposes a modified-theoretical approach to interpreting the undrained shear strength from piezocone tests in clays. Assuming the shear and normal stresses on the cone face to be the friction at the cone–soil interface and the ultimate expansion pressure, respectively, an expression of the tip resistance is first derived at force equilibrium. The undrained shear strength is then determined by combining the derived expression of tip resistance with the formulation for pore pressure at the cone shoulder position. Many factors, such as the penetration rate and the cone roughness, are considered in this model. Different shaped model penetrometers, including cone- and ball-shaped ones, are adopted in centrifuge tests to investigate the validity of the proposed method. The undrained shear strength estimated from the piezocone test is found to agree well with that from ball penetrometer test. Case studies are also presented to show the application of the proposed method. Comparisons between the predicted and measured values of undrained shear strength indicate that the proposed approach is generally applicable for nonfissured clays, especially intact clays.  相似文献   

Bounding surface model for overconsolidated clays with new state parameter formulation of hardening rule     

《Computers and Geotechnics》2017

  相似文献   

频率对K_0固结饱和粘土动力特性影响的试验分析     

王建华  赵致艺  赵晨玲 《世界地震工程》2010,(Z1)

通过循环三轴试验,研究了k0固结饱和粘土在0.5 Hz、0.1 Hz与0.01 Hz循环应力作用下,循环强度与土样破坏时最终累积孔压的变化。结果表明,当循环频率从0.1 Hz减少至0.01 Hz时,若循环应力作用下三轴土样发生应力反向,k0固结饱和粘土循环强度大约降低3%左右;若没有应力反向,且当循环破坏次数从10变化至1 000时,循环强度的降低不超过1%,若循环破坏次数大于1 000时,循环频率的改变对循环强度基本没有影响。对于有应力反向情况,循环频率减小将导致最终累积孔压比增加;对于无应力反向情况,循环频率改变对最终累积孔压比的影响并不显著。循环频率对最终累积孔压比的影响与其对循环强度的影响一致。  相似文献   

疏浚淤泥流动固化处理与流动性试验研究   总被引：1，自引：0，他引：1  

丁建文  洪振舜  刘松玉 《岩土力学》2011,32(Z1):280-284

疏浚淤泥由于含水率高、强度低、渗透性低等特性,在工程上难以直接利用而往往作废弃处理,造成了资源的浪费和土地的占用。针对我国疏浚施工的特点,基于传统固化方法,提出了将高含水率疏浚淤泥进行流动固化处理,并进行了流动性试验研究。结果表明,固化淤泥拌合物的流动值与初始含水率及固化材料掺量之间均具有良好的线性关系,初始含水率2.5wL是能否进行流动固化处理的临界值。基于影响流动性的两个重要因素,即初始含水率和固化材料掺量,提出了广义水灰比的概念,建立了流动值的预测方法,并对预测公式进行了验证  相似文献   

天然沉积结构性土的次固结变形预测方法   总被引：1，自引：0，他引：1  

曾玲玲  洪振舜  刘松玉  章定文  杜延军 《岩土力学》2011,32(10):3136-3142

结构性土存在着其特有的变形和强度特性,次固结特性也表现出明显区别于与重塑土。通过对连云港天然沉积原状土和重塑土进行一维压缩次固结试验,研究了典型结构性土的次固结特性。试验结果表明,土体由于受结构性影响,结构破坏前后其次固结特性发生明显变化;结构屈服前（固结压力小于固结屈服压力）不发生次固结变形或次固结变形甚微;当土体处于屈服状态时,土体次固结变形突然增大,次固结系数Cα出现峰值;结构屈服后（固结压力大于固结屈服压力）,Cα随固结压力的增大而减小,表现为与当前的应力水平和时间密切相关的特性,应力水平对Cα的影响会随着次固结时间的增长而削弱。基于以上机制,建立了考虑结构性影响的次固结变形计算模型,该模型中Cα不仅与压缩指数Cc有关,且也与时间有关,基于该模型计算得到的Cα值和次固结变形均与试验值吻合较好。  相似文献   

A three-scale model for ionic solute transport in swelling clays incorporating ion–ion correlation effects     

《Advances in water resources》2015

A new three-scale model is proposed to describe the movement of ionic species of different valences in swelling clays characterized by three separate length scales (nano, micro, and macro) and two levels of porosity (nano- and micropores). At the finest (nano) scale the medium is treated as charged clay particles saturated by aqueous electrolyte solution containing monovalent and divalent ions forming the electrical double layer. A new constitutive law is constructed for the disjoining pressure based on the numerical resolution of non-local problem at the nanoscale which, in contrast to the Poisson–Boltzmann theory for point charge ions, is capable of capturing the short-range interactions between the ions due to their finite size. At the intermediate scale (microscale), the two-phase homogenized particle/electrolyte solution system is represented by swollen clay clusters (or aggregates) with the nanoscale disjoining pressure incorporated in a modified form of Terzaghi’s effective principle. At the macroscale, the electro-chemical–mechanical couplings within clay clusters is homogenized with the ion transport in the bulk fluid lying in the micro pores. The resultant macroscopic picture is governed by a three-scale model wherein ion transport takes place in the bulk solution strongly coupled with the mechanics of the clay clusters which play the role of sources/sinks of mass to the bulk fluid associated with ion adsorption/desorption in the electrical double layer at the nanoscale. Within the context of the quasi-steady version of the multiscale model, wherein the electrolyte solution in the nanopores is assumed at instantaneous thermodynamic equilibrium with the bulk fluid in the micropores, we build-up numerically the ion-adsorption isotherms along with the constitutive law of the retardation coefficients of monovalent and divalent ions. In addition, the constitutive law for the macroscopic swelling pressure is reconstructed numerically showing patterns of attractive forces between particles for bivalent ions for particular ranges of bulk concentrations. The three-scale model is applied to numerically simulate ion diffusion in a compacted clay liner underneath a sanitary landfill. Owing to the distinct constitutive behavior of the swelling pressure and partition coefficient for each ionic species, different compaction regimes and diffusion/adsorption patterns, with totally different characteristic time scales, are observed for sodium and calcium migration in the clay liner.  相似文献   

Dynamic properties and liquefaction resistance of two soil materials in an earthfill dam—Laboratory test results     

V.C. Xenaki  G.A. Athanasopoulos 《Soil Dynamics and Earthquake Engineering》2008,28(8):605-620

Results are presented of laboratory resonant column and cyclic triaxial tests on specimens of two compacted soils (a sandy–silty clay and a sand–gravel mixture), planned to be used in the core and the shells, respectively, of a proposed earthfill dam. The values of low-amplitude shear modulus of the clayey material were found to increase with increasing confining pressure and decreasing water content, with deviations of ±20% from the predictions of the “Hardin equation”. On the other hand, the low-amplitude damping ratio was found to be at least four times higher than the values corresponding to natural undisturbed cohesive soils. The proposed G/G₀−γ_c curve for the compacted cohesive soil was found to be independent of confining pressure and small variations of the water content on either side of the optimum value and showed a remarkable agreement with recently published similar curves for natural cohesive soils. For the case of the sand–gravel mixture, normalized G/G₀–γ_c and D–γ_c curves are proposed, based on recently published results for gravelly soils and the limited data of the present study. The liquefaction resistance of the saturated sand–gravel mixture was found to be strongly dependent on its relative density, especially for high values of cyclic stress ratio. A relative density of at least 55% was found to be necessary to assure safety against earthquake-induced liquefaction of the material. The results presented herein may be used (directly or as guide) in the seismic analysis of (new or existing) earth dams constructed from similar soil materials and in addition they provide insight into the dynamic behavior of compacted soils.  相似文献   

Hydraulic conductivity of remolded fine-grained soils versus index properties   总被引：1，自引：0，他引：1  

A.?SridharanEmail author  H.?B.?Nagaraj 《Geotechnical and Geological Engineering》2005,23(1):43-60

Hydraulic conductivity is a dominant parameter in the design of engineered waste disposal facilities such as landfill liners and covers, lagoon liners and slurry walls. It is of interest to a geotechnical or geo-environmental engineer to develop a predictive method of determining the hydraulic conductivity of fine-grained soils, in order to assess its suitability as a liner material. To predict the hydraulic conductivity of soils, researchers and geotechnical engineers have attempted to correlate it with index properties of the soils, such as the liquid limit, void ratio and specific surface. Based on the present study a predictive method has been developed in this paper to predict the hydraulic conductivity in terms of void ratio and shrinkage index (Liquid limit – shrinkage limit) for remoulded fine-grained soils. Though the initial conditions for the soil will affect the hydraulic conductivity behaviour to some extent, both the void ratio and soil characteristics are primary factors in affecting the hydraulic conductivity. Therefore for predictive purpose, the study of hydraulic conductivity behaviour of remoulded fine-grained soils as presented in this paper can be found to be useful for compacted soils also.  相似文献