Consolidation Behavior Of Soft Clay Research Articles

One-Dimensional Consolidation Properties of Soft Clay under Multi-Stage Loading

The consolidation characteristics of soft clay under multi-stage loading and single-stage loading exhibit significant differences. In order to investigate the consolidation behavior of soft clay under multi-stage loading, one-dimensional oedometer tests were conducted on marine sedimentary soft clay from northern China. The results indicate that the overall time-deformation pattern of multi-stage loading is a cyclic nonlinear extension of that of single-stage loading. The final deformation between multi-stage loading and single-stage loading is approximately equal; however, the consolidation rate of single-stage loading is four times that of multi-stage loading. Furthermore, the coefficient of consolidation (Cv) decreases with increasing stress. Subsequently, the traditional Terzaghi one-dimensional consolidation equation was modified and a consolidation equation suitable for multi-stage loading is proposed in this study. The analysis of engineering applications demonstrates that the traditional theory provides more accurate predictions of consolidation rate and settlement when the load is small. However, when the load is large, the settlement predicted using the Terzaghi one-dimensional consolidation equation may have an error of 0–25% compared to that using the modified equation. The modified Terzaghi one-dimensional consolidation equation provides a more accurate representation of the actual consolidation of soft soil.

One-Dimensional Nonlinear Consolidation for Soft Clays with Continuous Drainage Boundary Considering Non-Darcy Flow

Adopting the non-Darcy flow presented by Hansbo and considering the nonlinear compression and permeability characteristics of soils, the one-dimensional nonlinear consolidation problem of soft clays is investigated by means of a continuous drainage boundary. The numerical solutions of average consolidation degrees defined by settlement and excess pore water pressure are derived by using the finite difference method, and the correctness of these solutions is verified by comparing them with existing analytical and numerical solutions. Based on the proposed solutions, a parametric study is conducted to study the influence of interface parameter, non-Darcy flow parameter and soil nonlinearity on the consolidation behavior of soft clays. The results show that the solutions based on the continuous drainage boundary can be degenerated into the solutions based on the Terzaghi drainage boundary if the interface parameter is taken as a reasonable value. The soil consolidation behavior considering both non-Darcy seepage and nonlinear characteristics of soil is very complex.

Effect of Heat Injection through a Vertical Drain on Clay Consolidation

Temperature change affects the consolidation behavior of soft clay. An increase in temperature in soft clay leads to the dissipation of excess pore water pressure and the decrease of volume. This temperature-induced consolidation can be utilized as a novel approach to improve soft ground. In this study, in order to investigate the effect of heat injection through a vertical drain on soft ground consolidation, a test device was designed to install different-sized sand drains that enabled heat injection and temperature control of a vertical drain. Using the device, a series of consolidation tests was performed with varying heat injection and varying diameter of the vertical drain. During consolidation, vertical settlement and temperature at various locations in the ground were measured. After each consolidation test, the spatial distribution of void ratio in the ground was estimated. Test results showed that heat injection increased the radial temperature of the ground, and the increasing diameter of sand drain with an internal heat source also expanded the heating area in the ground. Furthermore, the larger diameter sand drain led to greater final settlement and lower void ratio.

A review of isotache modeling and secondary consolidation behavior of soft clays

Secondary consolidation of soils has gained much importance as a major contributor in the long term settlements of soft clays. In the scenario where constructions on such problematic soils are increasing, accurate prediction of long term settlements is very challenging. This paper reviews the evolution of the secondary compression characteristics from the concept of Cα to the creep isotaches. The generation of the 3 D elastic viscoplastic model from the equivalent time (isotache) approach is also discussed in this paper. This model is an extension of Maxwell’s rheological model. With relevance to Indian soils, the secondary compression characteristics of Kuttanad and Cochin marine clay are also reported in this paper.

Numerical Modelling of Prefabricated Vertical Drain for Soft Clay Using ABAQUS

Construction, buildings and infrastructure founded on soft clays are often affected by settlement problem. Therefore, Prefabricated Vertical Drain (PVD) is one of the best solutions to accelerate soil consolidation by shortening the drainage path. In this study, numerical investigation was carried out to pursue a better understanding of the consolidation behavior of soft clay improved with PVD. The consolidation process accelerated by PVD with surcharge of 50 kPa was analysed using the ABAQUS software by adopting an elastic model. The aim of this study is to compare the settlement and the required time to fully consolidate the soft soil at different drain spacings (1.0 m, 1.5 m and 2.0 m) for two different thickness of the clay layer. The results shows that the time required to completely consolidate the soft soil for 12 m and 20 m thickness of clay layer with different spacings are in the range of 3 months to 66 months. The settlement rate and excess pore water pressure dissipation are increased when the spacing of the drain closer.

Stress history effects on 1‐D consolidation of soft soils: a rheological model

SUMMARYStress history plays an important role in controlling the consolidation behavior of soft clays, but few models exist that can provide quantitative estimate of its influence. In this paper, the Gibson–Lo rheological model is used to simulate the coupled processes of drainage and creep of soft soils that takes stress history into account. A hybrid combination of analytical and numerical methods is adopted to solve the governing equations of consolidation with the nonlinear rheological model. The methodology is applied to a saturated soft soil subjected to surface loading. The soil profile is separated into normally consolidated and overconsolidated layers by a boundary that is allowed to move. Comparisons of the model predictions and its simulations are used to evaluate the effects of stress history, model parameters, and loading pattern on consolidation behavior. It is shown that stress history influences the location of the moving boundary, variations of the profiles of excess pore water pressure dissipation, stress and deformation‐based average degrees of consolidation. Parametric studies conducted show that when soil is stiffer, the excess pore water pressure dissipates much more quickly, and thus the soil consolidates much faster especially at the early stages. The results also show that soil viscosity influences the deformation‐based average degree of consolidation at the latter stages. The consolidation process of soil layer under linear loading is shown to lag behind those under instantaneous loading: the longer the loading period is, the smaller the average degrees of consolidation are no matter how they are defined. Copyright © 2012 John Wiley & Sons, Ltd.

피에조 콘 시험과 실내시험을 이용한 점토지반의 투수특성 연구

점성토의 압밀거동은 투수성과 변형성에 영향을 받으며 그 중 투수성은 흙의 종류 및 상태, 특히, 이방성에 영향을 받는다. 연약지반의 투수계수는 피에조 콘 소산시험 및 실내압밀시험 (Oedometer test)에 의해 구할 수 있으며, 피에조 콘 시험으로 과잉간극수압 소산측정이 가능하여 수평압밀계수와 수평투수계수 평가에 유용하게 사용된다. 본 연구에서는 국내 서해안 및 남해안 지역의 해성 점성토층을 대상으로 피에조 콘 소산시험을 실시하였으며, 불교란 시료에 대한 실내시험(Oedometer, Rowe cell)을 실시하고 각 이론해 별로 비교 분석을 실시하였다. 연구결과 Jamiolkowski(M적용) 등(1985)의 해로 추정한 kh/kv가 이 연구 대상지반의 투수특성과 가장 유사하게 나타나 국내의 연약지반에서 피에조 콘 소산시험 및 실내시험 (Oedometer test)에 의하여 투수특성(kh/kv, kh)을 평가하는 방법으로서 이들 이론해의 적용을 추천한다. The consolidation behavior of soft clay is controlled mainly by its compressibility and deformation characteristics. Soil permeability depends on various soil characteristics, including the soil type and anisotropy. The coefficient of permeability of soft clay is determined by using a laboratory test (the Oedometer test) or a piezocone test. The latter test is useful for estimating the permeability characteristics from <TEX>$c_h$</TEX> and <TEX>$k_h$</TEX> by performing an excess pore-pressure dissipation test. This study seeks to validate an existing theoretical formula in applying it to marine clay, and to assess the relation between <TEX>$k_h/k_c$</TEX> and the mechanical properties of soft clay. Piezocone tests and laboratory tests were performed using sediment from the Yellow Sea and from the South Sea near Korea. We compared <TEX>$k_h/k_v$</TEX> values obtained using the piezocone test and using laboratory consolidation tests. The obtained values are similar to the values obtained by Jamiolkowski et al. (M application); therefore, the latter values are recommended to be used as <TEX>$k_h/k_v$</TEX>.