Accelerating consolidation of soft ground by aerosol injection technique: a field study

We present an aerosol injection technique (AIT) to accelerate the consolidation of soft soils for ground improvement. We employ high-pressure aerosol injections at different depths to enhance the drainage in soft soils for faster consolidation. The technique is briefly described. A well-instrumented field test is carried out to demonstrate its performance. Compared to the traditional methods, our approach gives rise to faster dissipation of excess pore pressure and larger ground settlement. This method is particularly attractive for the improvement in soft ground in medium depths.

     

The analysis of finite elasto-plastic consolidation

A theoretical formulation and a numerical solution method are proposed for the problem of the time dependent consolidation of an elasto-plastic soil subject to finite deformations. The soil is assumed to be a two-phase material with a skeleton which may yield according to a general yield criterion with plastic flow governed by a general flow law, and whose pore fluid flows according to Darcy's Law. Governing equations are cast in a rate form and constitutive laws are expressed in a frame indifferent manner. The method of analysis is illustrated by several examples of practical interest for both a soil with an elastic skeleton and a soil with an elasto-plastic skeleton which obeys a Morh–Coulomb yield criterion and a non-associated flow law.     

Probabilistic analysis of a one-dimensional soil consolidation problem

In this paper, a probabilistic study of a one-dimensional soil consolidation problem has been carried out. The Collocation-based Stochastic Response Surface Method (CSRSM) was employed for the probabilistic analysis. The Young modulus E, the Poisson ratio ν, the hydraulic conductivity k _h and the uniform surcharge loading q applied at the ground surface were considered as random variables. The probabilistic system responses considered in the analysis were the surface settlement and the consolidation time. Numerical simulations that make use of Biot theory were used for the computation of these system responses. A global sensitivity analysis based on Sobol indices was performed to identify the random variables that have the most contribution in the variability of the system responses. Also, a parametric study was undertaken to investigate the effect of the input geotechnical parameters and the statistical parameters of the random variables on the probability distribution functions of the system responses.     

Coupled consolidation and heat flow analysis of layered soils surrounding cylindrical heat sources using a precise integration technique

The engineering applications of energy piles, geological radioactive waste disposals, and mining wells of geothermal and petroleum are usually associated with strong coupled behaviour of consolidation and heat flow. This paper aims to present an efficient precise integration technique (PIT) for the analysis of such behaviour within layered saturated soils surrounding cylindrical heat sources (ie, with a cross section as a point, ring, or disc). Each soil layer, together with its embedded part of heat source, is divided into 2^N layer elements with equal thickness. Then any pair of adjacent two layer elements are merged into a heat source on the interface. With the aid of Taylor series expansion and recurrence formula for adjacent layer elements combination, such problems can be solved by means of an improved PIT. Typical examples are performed to examine the effects of heat source type and soils layered properties on the coupled consolidation and heat flow responses. The elevation of the clay surface increases with time because of thermal expansion and reaches a peak value before showing a tendency of getting stabilised because of the dissipation of pore pressure becoming dominant. Such a peak cannot be achieved in sand case because of no accumulation of pore pressure. The influencing area of the heat source was found to be limited to near the source. These quantitative results serve as good verification of the presented technique, which proves to be remarkably efficient and several orders more accurate than traditional numerical techniques in that it ideally reaches the accuracy limit of the hardware of the computers used.     

地基固结沉降随机有限元计算和可靠度分析

基于比奥（Biot）固结理论，采用邓肯-张本构模型，考虑随机场的影响，首次给出了地基固结沉降随机有限元分析方法，并基于随机有限元对点固结沉降和差异固结沉降的可靠度进行了分析。     

动力固结流—固耦合模型的求解方法

以三维多孔介质中基本方程为基础，提出了动力固结问题的力学模型，给出了相应的变分原理及其有限元格式，用轴对称问题的有限单元法模拟了单点单次夯击过程，给出了详细的求解方法及算例，并将计算结果与现场实测资料作了比较。     

碎石桩加固双层地基固结简化分析

碎石桩复合地基在工程上的应用非常广泛,其应力应变性状的研究已很深入,固结问题也得到了不同程度的研究,但已有的解析式大多较复杂,工程中难以应用。将桩间土径向整体作为一个研究对象,从而避开单独考虑因施工造成的涂抹作用的影响,根据排水量与体变等效原理,用平均超孔隙水压力的概念推导出碎石桩加固双层地基简化的固结计算式。由该方法可直接得到碎石桩和桩间土不同深度的平均超孔隙水压力和平均固结度,也可计算复合地基整体固结度。所推得的解析式简洁,且实用性强。     

Finite element consolidation analysis of embankments

The construction of earth embankments may lead to the development of excess pore pressures in foundation and embankment soils. The ability to predict the development and dissipation of these pore pressures is important in assessing the performance of such structures. This paper describes a finite element analysis method that allows the prediction of the behaviour of embankments including stress-deformation and consolidation behaviour. The application of the method is demonstrated through application to a reinforced embankment on peat and clay and to a high rockfill dam.     

考虑温度耦合效应的竖井地基固结有限元分析

针对塑料排水板(PVD)安装热源能提升PVD性能、加速竖井地基固结这一工程现象,基于热-水-应力 (T-H-M) 三场全耦合的有限元方法来模拟利用热源进行地基处理新技术(PVTD)。首先,以微分形式与等效弱形式分别给出T-H-M耦合控制方程,并推导出其有限元方程组。然后在多场耦合有限元软件中建立饱和土的T-H-M全耦合模型,并通过与已有解析解比较,验证了模型正确性。最后,对一个经典有涂抹区的竖井地基算例,分不耦合温度(UT)、耦合温度但不考虑其对饱和土物性影响(CT)、耦合温度考虑温度对饱和土渗透性影响(CTP) 3种情况进行固结计算分析。研究结果表明,相对于无热源竖井地基,CT情况下由于热源产生的附加孔隙水压力,固结速度略有下降;CTP情况下,由于热源有效改善涂抹区的渗透性能,竖井地基固结速率明显加快。上述研究结论从理论上较好地阐明了PVTD的作用机制。     

Finite layer analysis of consolidation. II

The theory developed in Part I of this paper is extended to apply to the consolidation of horizontally layered soils under both axially symmetric and general surface loading. The method again leads to a considerable reduction in the amount of core storage necessary for computer solution and can be implimented on a mini-computer.     

Finite layer analysis of consolidation. I

A method for the analysis of the consolidation of a horizontally layered soil under plane conditions is developed. The method depends upon the transformation of the governing equations by a Fourier trasform. This transformation has the effect of reducing the partial differential equations of consolidation to ordinary differential equations. The ordinary differential equations are then solved using a finite layer or finite difference approach. Once the solution in the transformed plane has been found, the actual solution is synthesized by Fourier inversion. The method leads to a considerable reduction in the amount of core storage necessary for solution and enables the solution of quite significant problems to be obtained on a mini-computer.     

An investigation of numerical errors in the analysis of consolidation by finite elements

A smoothing technique is developed to remove the oscillatory errors in initial nodal pore pressures, associated with the use of quadratic isoparametric elements to model soil consolidation. Numerical results using this technique are compared with the performance of other types of element in problems of one-and two-dimensional consolidation.     

Application of an optimum design technique for determining the coefficient of consolidation by using piezocone test data

For normally consolidated clay, several researchers have developed a number of theoretical time factors to determine the coefficient of consolidation from piezocone test results. However, depending on assumptions and analytical techniques, it could vary considerably, even for a specific degree of consolidation. In this paper a method is proposed to determine a consistent coefficient of consolidation by applying the concept of an optimum design technique over all ranges of the degree of consolidation. Initial excess pore pressure distribution is assumed to be capable of being obtained by the successive spherical cavity expansion theory. The dissipation of pore pressure is simulated by means of a two-dimensional linear-uncoupled axi-symmetric consolidation analysis. The minimization of differences between measured and predicted excess pore pressure was carried out by the BFGS unconstrained optimum design algorithm with a one-dimensional golden section search technique. By analyzing numerical examples and in-situ test results, it was found that the adopted optimum design technique gives consistent and convergent results.     

透水桩与不透水桩组合型复合地基固结解析分析

在深厚软土地基处理中,联合使用透水与不透水桩,既可以加速地基固结,又能较大地提高地基的承载力,具有广泛的应用价值。基于轴对称固结模型,并考虑透水桩的体积压缩,建立了透水与不透水桩组合型复合地基的固结微分方程,利用边界条件和初始条件,得到了外部荷载瞬时施加情况下的地基固结解析解,并将该解与现有解析解进行对比分析,验证其合理性;同时,对桩的扰动效应、井阻效应、压缩模量等影响因素进行了分析,探讨了该复合地基的固结特性。结果表明:不考虑透水桩体积变化将高估组合型复合地基的固结速率;减小透水桩的井阻效应和施工扰动效应,增大置换率及桩体模量,将加快组合型复合地基的固结速率,实际工程中可以从这些方面减少地基的工后沉降。     

地基固结变形反分析研究

某水库库底地基变形较大,蓄水初期曾引起库底沥青混凝土防渗护面开裂。为研究进一步蓄水后可能产生的更大沉降及对沥青混凝土防渗护面的影响,对库底地基土层进行了反分析,研究地基土层的有关参数,利用反分析得到的参数进行了有限元正分析,研究地基的固结特性,为预测进一步蓄水后地基的沉降提供了重要依据。     

Special finite elements for analysis of soil consolidation

Use of “singularity” elements to model pore pressures in the vicinity of free-draining loaded surfaces, immediately after application of loads at these surfaces is discussed. One-dimensional consolidation is considered. Comparison of numerical results with the exact solution shows that use of specially designed elements approaching “singularity” may succeed in reducing the error in pore pressures.     

高速公路砂井地基固结度时空变化规律探讨

软基固结度时空变化规律的研究对解决高速公路软基沉降预测问题具有十分重要的意义。本文在讨论固结度时空变化的实质与计算方法的基础上，结合京珠高速公路广珠段某软基试验资料，初步探讨了高速公路砂井地基固结度的时空变化规律，特别提出固结的滞后效应及其对固结沉降曲线形态的影响，并简要讨论了砂井直径和间距对固结度的影响，认为软基沉降中地下水微观动力学过程的研究将有助于揭示固结度时空变化规律。     

条形埋置基础固结分析计算图表

基于比奥固结理论,用有限元方法研究了有限饱和土层中条形埋置基础的固结沉降特性。仔细分析了影响固结度的3个参数：基础埋深与土层厚度的比值;土层厚度与基础宽度的比值;土骨架的泊松比。根据分析结果,提出了归一化无量纲时间,并给出了计算条形埋置基础固结度的计算图表。这些图表为基础设计提供了便捷准确的计算方法。运用文中图表计算固结度的最大误差不超过3 %。