Nonlinear Finite Strain Consolidation Research Articles

Consideration of radial flow in nonlinear finite-strain self-weight consolidation of dredged soil

The application of vertical drains along with preloading to accelerate the consolidation rate of dredged soil has been widely used. However, the conventional analytical or numerical models cannot predict the nonlinear finite-strain consolidation behavior of dredge-soil deposits accurately because the vertical drains are installed in the middle of a self-weight-consolidation process. This paper establishes a mathematical and numerical model for a 2-D axisymmetric nonlinear finite-strain consolidation, for which the self-weight consolidation and the radial drainage through vertical drains are considered. Besides, a series of lab-scale self-weight-consolidation tests were conducted, which can simulate the vertical-drain installation. Experimental results along with those of the simplified method (Lee et al., 2016) were then utilized to verify performance of the proposed model. The results demonstrate that the proposed model appropriately predicts the nonlinear finite-strain self-weight consolidation behavior of dredged soils, and its application with vertical drains is suitable for designing dredged-soil improvement. Moreover, the most important advantage of the proposed model is to optimize the schedule of dredging/landfilling construction.

Nonlinear Finite-Strain Self-Weight Consolidation of Dredged Material with Radial Drainage Using Carrillo’s Formula

AbstractEstimation of the time-rate consolidation of dredged deposits is considerably complicated when vertical drains are installed to enhance the consolidation process of the soft-soil stratum, because the vertical drains are commonly installed before self-weight consolidation is complete. In this paper, two new methods are proposed to take into account both vertical and radial drainage conditions during the nonlinear finite-strain self-weight consolidation of dredged soil deposits (i.e., precise prediction of the self-weight consolidation behavior considering radial flow to the vertical drain). For one-dimensional nonlinear finite-strain consolidation in the vertical direction, the simplified Morris’s analytical solution and the primary consolidation, secondary compression, and desiccation of dredged fill (PSDDF) analysis are adopted. In addition, to consider the radial drainage, Barron’s vertical drain theory is used. The overall average degree of self-weight consolidation of the dredged soil is estim...

인천 송도지역 준설토의 침강 및 압밀특성에 대한 실험 및 해석적 연구

연약지반의 특성에 부합하는 이론을 이용하여 침하량을 합리적으로 예측하는 것은 건설방재적 관점에서도 대단히 중요하다. 특히, 준설매립지반과 같은 초연약지반의 압밀거동 모사를 위해서는 비선형 유한변형 압밀이론을 적용할 필요성이 있다. 본 연구에서는 인천 송도지역 준설토의 침강 및 압밀특성을 파악하기 위하여 침강압밀시험, 자중압밀시험 및 CRS 압밀시험을 수행하였으며, 그 결과를 PSDDF를 이용한 수치해석의 입력치로 사용하여 준설매립지반의 거동을 해석하였다. 본 지역의 준설토는 통일 분류법에 의해 저압축성 실트(ML)로 분류되었으며, Yano법 및 수치해석을 통하여 얻어진 최종 체적변화비는 각각 1.56, 1.17로 나타났다. 이러한 결과의 차이는 계면고가 상대적으로 높고 투수성이 큰 해당 구간 준설매립토의 토질 특성에 기인한 것으로 사료된다. Accurate settlement estimation of dredged soft soil deposits is significantly important to prevent potential disasters during land reclamation. An application of the non-linear finite strain consolidation theory is inevitable in dealing with a very soft ground formation such as dredged fill. In this paper, a series of the sedimentation-consolidation test, self-weight consolidation test and CRS test were conducted to clarify sedimentation and consolidation characteristics of dredged fill in the Songdo area, Incheon. In addition, the settlement of dredged fill was numerically simulated using the PSDDF program. The dredged soil obtained from the Songdo area was classified as low-compressible silt (ML) based on USCS (Unified Soil Classification System), and the final bulking factors were estimated to be 1.56 and 1.17 by Yano's method and the numerical simulation, respectively. This difference is attributable to relatively high reclaimed height and large permeability of dredged soil in this region.

Variation of hydraulic gradient in nonlinear finite strain consolidation

In the research field of ground water, hydraulic gradient is studied for decades. In the consolidation field, hydraulic gradient is yet to be investigated as an important hydraulic variable. So, the variation of hydraulic gradient in nonlinear finite strain consolidation was focused on in this work. Based on lab tests, the nonlinear compressibility and nonlinear permeability of Ningbo soft clay were obtained. Then, a strongly nonlinear governing equation was derived and it was solved with the finite element method. Afterwards, the numerical analysis was performed and it was verified with the existing experiment for Hong Kong marine clay. It can be found that the variation of hydraulic gradient is closely related to the magnitude of external load and the depth in soils. It is interesting that the absolute value of hydraulic gradient (AVHG) increases rapidly first and then decreases gradually after reaching the maximum at different depths of soils. Furthermore, the changing curves of AVHG can be roughly divided into five phases. This five-phase model can be employed to study the migration of pore water during consolidation.

Nonlinear Finite Strain Consolidation Analysis with Secondary Consolidation Behavior

This paper aims to analyze nonlinear finite strain consolidation with secondary consolidation behavior. On the basis of some assumptions about the secondary consolidation behavior, the continuity equation of pore water in Gibson’s consolidation theory is modified. Taking the nonlinear compressibility and nonlinear permeability of soils into consideration, the governing equation for finite strain consolidation analysis is derived. Based on the experimental data of Hangzhou soft clay samples, the new governing equation is solved with the finite element method. Afterwards, the calculation results of this new method and other two methods are compared. It can be found that Gibson’s method may underestimate the excess pore water pressure during primary consolidation. The new method which takes the secondary consolidation behavior, the nonlinear compressibility, and nonlinear permeability of soils into consideration can precisely estimate the settlement rate and the final settlement of Hangzhou soft clay sample.

Case Studies of PSDDF for Phased Placement of Dredged Soils

Use of Terzaghi's one-dimensional consolidation theory is not suitable for consolidation of highly deformable soft clays such as dredged soils. To model this condition, it is necessary to consider non-linear finite strain consolidation behavior, i.e., changes in compressibility and permeability with increasing stress. A one-dimensional non-linear finite strain numerical model, Primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill (PSDDF), has been used to predict the stress-dependent settlement of fine-grained dredged materials. In this paper, two case studies of using PSDDF are discussed to illustrate the applicability and accuracy of PSDDF. The first case study involves PSDDF simulations of laboratory-phased placement of a marine clay dredged from Busan, Korea. PSDDF results are in good agreement with the corresponding results of the laboratory large strain consolidation tests. The other involves estimating the service life of the Craney Island Dredged Material Management Area near Norfolk, Virginia, in the United States. The excellent agreement between measured and calculated values shows that PSDDF is a reliable tool for predicting settlement of dredged material.

준설매립지반의 자중압밀을 고려한 2차원 축대칭 비선형 유한변형 압밀 모델

준설매립지반 설계시 압밀 소요시간 단축을 위해 연직배수공법와 선행재하공법등의 연약지반 개량공법을 주로 적용한다. 준설매립지반의 자중에 의한 압밀이 완료되기까지는 많은 시간이 소요되므로 공사비 절감, 공기단축의 이유로 연약지반 개량공법은 일반적으로 자중압밀 도중 적용된다. 본 논문에서는 준설매립지반에서 연직방향으로 자중압밀이 진행되는 도중 연직배수재 타설에 의해 방사방향의 흐름이 추가로 발생하는 경우의 압밀거동 예측을 위하여 자중압밀을 고려한 2차원 축대칭 비선형 유한변형 압밀 지배방정식과 이를 적용하기 위한 수치모델(Axi-Selcon)을 개발하였다. Axi-Selcon의 검증과 자중압밀 도중 연직배수재가 타설된 준설매립지반을 모사하기 위해 일련의 실내시험을 수행하였다. 이를 위해 연직배수재가 타설된 준설매립지반을 모사하는 대형자중압밀 시험기를 고안하였다. 모델의 추가적인 검증을 위하여 기존에 제안된 간편 해석법을 적용한 결과와 Axi-Selcon의 해석결과와 비교하였다. 마지막으로, Axi-Selcon을 적용하여 가상의 대심도 준설매립지반의 거동을 예측하였다. 이와 같은 일련의 모델 검증과정을 통해 본 논문에서 개발된 Axi-Selcon은 자중압밀 도중 연직배수재 타설과 선행재하공법이 적용될 경우에 대한 초연약 준설매립지반의 압밀 거동을 적절히 예측할 수 있음을 보였다. Vertical drains along with the preloading technique have been commonly used to enhance the consolidation rate of dredged placement formation. In practice, vertical drains are usually installed in the process of self-weight consolidation of a dredged soil deposit because this process takes considerable time to be completed, which makes conventional analytical or numerical models difficult to quantify the consolidation behavior. In this paper, we propose a governing partial differential equation and develop a numerical model for 2-D axisymmetric non-linear finite strain consolidation considering self-weight consolidation to predict the behavior of a vertical drain in the dredged placement foundation which is installed during the self-weight consolidation. In order to verify the developed model in this paper, results of the numerical analysis are compared with that of the lab-scaled self-weight consolidation test. In addition, the model verification has been carried out by comparing with the simplified method. The comparisons show that the developed model can properly simulate the consolidation of the dredged placement formation with the vertical drains installed during the self-weight consolidation. Finally, the effect of construction schedule of vertical drains and of pre-loading during the self-weight consolidation is examined by simulating an imaginary dredged material placement site with a thickness of 10 m and 20 m, respectively. This simulation infers the applicability of the proposed method in this research for designing a soil improvement in a soft dredged deposit when vertical drains and pre-loading are implemented before the self-weight consolidation ceases.

초연약 준설 매립지반의 비선형 유한변형 압밀해석기법 - Part II: 해석기법과 Craney Island 사례분석

This paper presents two analysis methods for characterizing the non-linear finite strain consolidation behavior of highly deformable dredged soil deposits along with the fundamental parameters obtained in the companion paper; that is, the zero effective stress void ratio, the non-linear relationships of void ratio-effective stress and void ratio-hydraulic conductivity. The simplified Morris`s analytical solution (2002) and the widely recognized numerical program, PSDDF (primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill) for both single and double drainage conditions are adopted in this paper to verify a series of laboratory experiments for self-weight consolidation of the Incheon clay and Kaolinite. The comparisons show that the analysis methods proposed herein can properly simulate the long-term non-linear finite strain consolidation behavior for dredged soils in the field. In addition, a case study for the artificial Craney Island has been conducted to illustrate the importance of obtaining appropriate non-linear finite strain consolidation parameters and the applicability of PSDDF in promoting dredged soil disposal.

초연약 준설 매립지반의 비선형 유한변형 압밀해석기법 -Part I: 해석 물성치 평가

The renowned Terzaghi`s one-dimensional consolidation theory is not applicable to quantification of time-rate settlement for highly deformable soft clays such as dredged soil deposits. To deal with this special condition, a non-linear finite strain consolidation theory should be adopted to predict the settlement of dredged soil deposits including self-weight and surcharge-induced consolidation. It is of importance to determine the zero effective stress void ratio (), which is the void ratio at effective stress equal to zero, and the relationships of void ratio-effective stress and of void ratio-hydraulic conductivity for characterizing non-linear finite strain consolidation behavior for deformable dredged soil deposits. The zero effective stress void ratio means a transitional status from sedimentation to self-weight consolidation of dredged soils. In this paper, laboratory procedures and equipments are introduced to measure such key parameters in the non-linear finite strain consolidation analysis. In addition, the non-linear finite strain consolidation parameters of the Incheon clay and kaolinite are evaluated with the aid of the proposed methods in this paper, which will be used as input parameters for the non-linear finite strain consolidation analyses being performed in the companion paper.

Numerical Modeling of Tailings Thickening for Improved Mine Waste Management

The environmental footprint of mining can be minimized by developing and improving the waste management technologies. Thickening involves the conversion of dilute tailings to paste-like materials with superior engineering and environmental properties. The process of tailings thickening is not well-understood in geotechnical engineering. The primary objective of this paper was to model the dewatering behavior of slurries during thickening. Two separate numerical models were developed using constitutive relationships based on the nonlinear finite strain consolidation theory and on the inclusion of a hindered sedimentation regime in the consolidation theory. In the coupled sedimentation-consolidation model, the transition zone was numerically modeled between a maximum suspension void ratio corresponding to the initial development of a distinct slurry microstructure and a structural void ratio referring to the development of a soil skeleton transferring effective stresses. For the investigated tailings material, sedimentation was found to be complete at em = 8.0 and consolidation was observed to start at es = 6.5. Both of the models closely matched at e  6.5 confirming the validity of the coupled sedimentation-consolidation model.

Negative skin friction on piles based on finite strain consolidation theory and the nonlinear load transfer method

The development of dragload and downdrag on single piles in consolidating ground is investigated in this study with a simplified one-dimensional soil-pile model that combines the nonlinear load transfer method and finite strain consolidation theory to analyze soil-pile interaction under the effects of negative skin friction. In order to directly relate the soil settlements and effective stresses through the strain as a function of time and depth during the consolidation process, the prediction of the soil settlements imposing downdrag are based on Mikasa’s generalized one-dimensional consolidation theory that are formulated in terms of finite strain. An illustrative example and a case study of test pile were analyzed and predicted results of dragload and pile shortening by the presented model were shown to be in fair agreement with measured reference data. The model presented in this study offers a simple and flexible method for the analysis of a variety of soil-pile interaction problems under negative skin-friction that can account for nonlinearity of the soil and pile, a rigid and deformable bearing stratum, and can be applicable for the analysis of floating and end-bearing piles as well as for shafts socketed in rocks.

Settlement of Dredged and Contaminated Material Placement Areas. I: Theory and Use of Primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill

A 1D nonlinear numerical model, Primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill (PSDDF), is presented to predict the settlement of fine-grained dredged material and/or underlying compressible foundation materials that may be over-, under-, or normally consolidated. The three most important natural processes affecting the long-term settlement and thus service life of dredged material placement areas are primary consolidation, secondary compression, and desiccation. Nonlinear finite-strain consolidation theory is used to predict the settlement due to self-weight and surcharge-induced consolidation. The Cα ∕ Cc concept is used to predict the settlement from secondary compression, and an empirical desiccation model is used to describe the settlement from removal of water from confined dredged material by surface drying. This paper describes the modifications and improvements of PSDDF that present new functions and enhanced numerical efficiency. A companion paper describes the inp...

Analytical solutions of linear finite- and small-strain one-dimensional consolidation

Analytical solutions are presented for linear finite-strain one-dimensional consolidation of initially unconsolidated soil layers with surcharge loading for both one- and two-way drainage. These solutions complement earlier solutions for initially unconsolidated soil layers without surcharge and initially normally consolidated soil layers with surcharge. Small-strain solutions for the consolidation of initially unconsolidated soil layers with surcharge loading are also presented, and the relationship between the earlier solutions for initially unconsolidated soil without surcharge and the corresponding small-strain solutions, which was not addressed in the earlier work, is clarified. The new solutions for initially unconsolidated soil with surcharge loading can be applied to the analysis of low stress consolidation tests and to the partial validation of numerical solutions of non-linear finite-strain consolidation. They also clarify a formerly perplexing aspect of finite-strain solution charts first noted in numerical solutions. Copyright (C) 2004 John Wiley Sons, Ltd.

Analytical Solutions of Linear Finite-Strain One-Dimensional Consolidation

Numerical solutions of linear finite-strain one-dimensional consolidation of both initially unconsolidated and initially fully consolidated soil layers with both one-way and two-way drainage have been available for some time. However, no solutions of the limiting cases for initially unconsolidated soil have been available. Nor, except for the limiting cases corresponding to small-strain consolidation of initially fully consolidated layers, has the accuracy of these solutions and the solution charts based on them been evaluated. Analytical counterparts of the earlier numerical solutions and solution charts, analytical solutions of the limiting cases for initially unconsolidated soil, and analytical solutions of the small-strain Terzaghi equation expressed in material coordinates are presented in this paper. The analytical solutions clarify aspects of the numerical solutions, improve marginally the accuracy of the solution charts, and enable the latter to be easily replicated and extended. They may also be applied to the validation of numerical solutions of nonlinear finite-strain consolidation.

Approach to Thickening and Dewatering Using a One-Dimensional Finite Strain Consolidation Model

Gravity thickening and pressure filtration are described with a one-dimensional nonlinear finite strain consolidation model. Basic assumptions of a consolidation model are discussed. The consolidation coefficient κ for different types of sludges was found to vary less with solids concentration than the permeability and the compressibility. This leads to a simplified model. A comparison of model to experimental results reveals the basic validity of the outlined approach and serves to discuss the model limits. For pressure filtration a method to determine the κ-value of a given sludge from filter experiments is verified.

The consolidation of soft marine sediments

This paper outlines the governing relationships of nonlinear finite strain consolidation. A short review of current literature is presented. Nonlinear finite strain consolidation theory is applied to the analysis of the slow deposition of Gulf of Mexico Holocene sediments. It is shown that the conventional means of calculating rates of sediment accumulation are highly inaccurate. It is further shown that the state of effective stress and excess pore-water pressure, as calculated by nonlinear finite strain theory, is substantially different than when calculated by conventional Terzaghi-Frohlich theory.