Large Strain Consolidation Research Articles

A FDM Solving Method of Large-Strain Consolidation of Multi-Layers Super Soft-Soil

The aim is to present a numerical method to solve the large-strain consolidation of super soft-soil. The theory of large-strain consolidation (LSC) is acted as the better method for analysis on the consolidation problem of super soft-soil foundation. The focal points are, based on practical engineering, the one-dimensional LSC equations being derived, the consolidation coefficients being inquired and so on. Based on these, one-dimensional nonlinear LSC equation is solved by the FDM, the e~p and e~k function that are according with the practical engineering is introduced into the solving progress, and the multi-layers super soft-soil is also considered in the progress successfully etc. Finally, a case showed the satisfied analysis result by LSCFDM. And some realizations about LSC analysis on super soft-soil are concluded.

압밀이 오염물질 이동에 미치는 장기적 영향

하저 또는 해저 퇴적오염물질 처리 및 제거는 준설과 매립에 의해 활발히 진행되었다. 그러나 준설과 매립은 준설과정에서 발생하는 퇴적오염물질의 교란, 매립지 선정문제, 고비용 공사비 등으로 인한 많은 제약이 따르고 있다. 이러한 문제로 인해 협소한 지역의 퇴적오염물질에 대해서는 오염물질의 용출 저감을 위한 현장 캡핑이 근래 들어 많이 사용되고 있다. 현장 캡핑에 따른 오염물질 이동에 관해서는 분자확산에 의한 영향이 지배적으로 해석되어 왔으나, 근래 들어 보다 정확한 모사를 하기 위하여 이류-확산을 복합적으로 해석할 필요성이 제기되었다. 퇴적물은 초기 함수율이 높은 슬러지(sludge)상태로 비교적 적은 상재하중과 자중에 의한 압밀이 발생하고, 압밀 과정에서 발생한 간극수 흐름의 변화는 오염물질의 이류에 의한 이동에도 영향이 미친다. 본 연구에서는 기존의 연구에서 수행된 압밀 과정에서 오염물질의 이동뿐만 아니라 압밀 후 간극비의 감소에 따른 오염물질 이동의 변화에 대하여 분석하고자 한다. Dredging and disposal is a conventional method to remove contaminated sediments. However, there are some problems in dredging and disposal, such as disturbance of contaminated sediments, disposal site determination, and high construction cost. Recently, in-situ capping which overcomes the problems of dredging and disposal is widely applied to isolate local contaminated sites. Numerical studies, which have been conducted to simulate contaminant transport during in-situ capping, have been concerned mainly with diffusive transport. However, contaminated sediments experience large strain consolidation induced by self-weight because of initially high moisture content of sediments, and contaminant transport results from advection and diffusion. Previous studies focus on contaminant transport during consolidation, but have neglected consolidation effect on long-term contaminant transport in sediments. This study presents numerical simulation results of consolidation effect on long-term contaminant transport in sediments.

Freeze–thaw and consolidation tests on Suncor mature fine tailings (MFT)

This paper presents the findings of a laboratory investigation of the effects of freeze–thaw, and sulfuric acid and quicklime amendment on Suncor mature fine tailings (MFT) post-thaw geotechnical behaviour and soil micro and macro-fabric. This paper gives the results of a consolidation test program on Suncor MFT using a large strain consolidation apparatus along with constant head flow tests to evaluate the void ratio versus effective stress and void ratio versus hydraulic conductivity data for three types of MFT specimens. The large scale and small scale fabric (macro-fabric and micro-fabric) of these specimens were also examined. The results indicated that freeze–thaw can effectively reduce the initial void ratio and the compressibility of untreated and amended MFT. Freeze–thaw can also significantly increase the hydraulic conductivity of MFT, which in combination with reduced compressibility enhances the MFT consolidation. These results were supported by changes observed in the macro and micro-fabric of the tested MFT specimens.

A New Alternative for Estimation of Geotechnical Engineering Parameters in Reclaimed Clays by Using Shear Wave Velocity

Abstract The consolidation behavior of reclaimed clay can be categorized as large strain deformation. Findings from previous studies indicate that the effective stress and the void ratio are important geotechnical engineering parameters for the characterization of large strain consolidation behavior. However, existing in situ consolidation characterization methods of reclaimed clay cannot adequately estimate changes of the effective stress and void ratio during a consolidation process. This paper suggests an alternative method for estimating the geotechnical engineering parameters of reclaimed clays using a shear wave. An in situ self-weight consolidation process of reclaimed clay is simulated in laboratory while shear wave velocity is continuously measured. Experimental results show that there are single trends in relationships among the shear wave velocity, effective stress, void ratio, and geotechnical engineering parameters for a normally consolidated clay (e.g., reclaimed clay). As a practical application, the in situ parameters and the expected settlement are predicted by incorporating the obtained relationships with the in situ shear wave velocity. The predicted values are in good accordance with the values measured in field. Therefore, the proposed method can be used effectively for geotechnical engineering parameter estimations of reclaimed clay during/after self-weight consolidation with the aid of in situ seismic exploration techniques.

Investigation of Consolidation-Induced Solute Transport. II: Experimental and Numerical Results

This paper presents an experimental and numerical investigation of consolidation-induced solute transport. Diffusion and large strain consolidation tests were performed on composite specimens of kaolinite clay consisting of an upper uncontaminated layer and a lower layer contaminated with potassium bromide. Experimental measurements of effluent concentration, solute mass outflow, and final concentration profiles were obtained for a variety of initial, boundary, and loading conditions, including unload/reload. Numerical simulations were conducted using a computational model in which solute transport occurs by advection, dispersion, and sorption and is consistent with temporal and spatial variations of porosity and seepage velocity in the consolidating layer. Large strains were taken into account as well as variation of effective diffusion coefficient with porosity and nonlinear nonequilibrium sorption effects. The numerical simulations are in good to excellent agreement with the experimental measurements. Results indicate that, depending on conditions, diffusion and consolidation-induced advection can make important contributions to solute transport and mass outflow. Thus, both mechanisms should be considered for transport analyses involving soft contaminated clays undergoing large volume change. Results also indicate that nonequilibrium sorption effects were not significant for the materials and test conditions used in this study.

Model for Consolidation-Induced Solute Transport with Nonlinear and Nonequilibrium Sorption

A numerical model, called CST2, is presented for coupled large strain consolidation and solute transport in saturated porous media. The consolidation and solute transport algorithms include the capabilities of a previous model, CST1, with the addition of a variable effective diffusion coefficient during consolidation and nonlinear nonequilibrium sorption. The model is based on a dual-Lagrangian framework that tracks separately the motions of fluid and solid phases. Verification checks of CST2 show excellent agreement with analytical and numerical solutions for solute transport in rigid porous media. A parametric study illustrates that, for the test cases considered, variation of effective diffusion coefficient during consolidation has an important effect on solute transport, whereas nonlinearity of the sorption isotherm has a less important effect. Additional simulations show that nonequilibrium sorption can have a strong effect on consolidation-induced solute transport and that this effect becomes more important as the rate of consolidation increases. The simulations also corroborate previous findings that consolidation can have a lasting effect on solute migration because transient advective flows change the distribution of solute mass which then becomes the initial condition for subsequent transport processes.

Geotechnical Hybrid Simulation System for One-Dimensional Consolidation Analysis

A system for a hybrid consolidation simulation was developed to predict more realistically the nonlinear behavior of the consolidation settlement of soft clay, including a large strain consolidation problem. The hybrid simulation method can introduce the mechanical behavior of the soils directly by combining numerical analysis and the soil element test in an online state. In this paper, a fundamental study to apply the hybrid simulation method to the consolidation settlement problem, a basic concept, and the corresponding algorithm and components are presented. Furthermore, using preconsolidated Kaolinite clays, verification studies were also conducted in the laboratory to verify the operational performance and data reliability of the system. On the basis of the test results, we concluded that the new consolidation analysis system using the hybrid simulation concept provided an adequate performance in the reproduction of the consolidation behavior of preconsolidated Kaolinite clays in the aspect of the dissipation of excess pore water pressure and corresponding consolidation settlement.

Coupled Large Strain Consolidation and Solute Transport. II: Model Verification and Simulation Results

The results of numerical simulations for coupled large strain consolidation and solute transport, obtained using the CST1 model, are presented. CST1 accounts for advection, longitudinal and transverse dispersion, first-order decay reactions, and linear equilibrium sorption. Verification checks of CST1 show excellent agreement with analytical solutions for one-dimensional (1D) transport in rigid porous media, including various Peclet numbers and concentration boundary conditions. Similarly excellent agreement is observed for two-dimensional advection-dispersion transport in rigid media and 1D advection-dispersion transport in compressible media undergoing large strain consolidation. CST1 is then used to investigate consolidation-induced solute transport for a single composite liner system and a confined disposal facility for dredged contaminated sediments. In both cases, solute transport was found to be strongly affected by consolidation-induced advection both during and after the consolidation period. Consolidation has a lasting effect on solute migration because transient advective flows change the distribution of solute mass, which then becomes the initial condition for subsequent transport processes.

Coupled Large Strain Consolidation and Solute Transport. I: Model Development

The development of a numerical model, CST1, for coupled large strain consolidation and solute transport in saturated porous media is presented. The consolidation algorithm is one-dimensional and includes the capabilities of a previous code, CS2, with the addition of time-dependent loading, unload/reload effects, and an externally-applied hydraulic gradient. The solute transport algorithm is two-dimensional and accounts for advection, longitudinal and transverse dispersion, first-order decay reactions, and linear equilibrium sorption. Solute transport is consistent with temporal and spatial variations of porosity and seepage velocity in the consolidating layer. The key to the transport model is the definition of two Lagrangian fields of elements that follow the motions of fluid and solid phases separately. This reduces numerical dispersion and simplifies transport calculations to that of dispersion mass flow between contiguous fluid elements. The effect of relative numerical resolution of fluid and solid elements on the accuracy of sorption/desorption is also discussed. This paper presents the theoretical and numerical development of the CST1 model. A companion paper presents verification checks of CST1 and the results of simulations that illustrate the significance of consolidation-induced solute transport for some interesting numeric examples.

Model for Large Strain Consolidation by Centrifuge

A numerical model, called CC1, is presented for one-dimensional large strain consolidation in a geotechnical centrifuge. The model includes all the capabilities of a previous large strain consolidation code, CS2, written for surcharge loading under normal gravity conditions. In addition, CC1 accounts for variation of acceleration factor N over the depth of a centrifuge test specimen. The development of CC1 is first presented, followed by a comparison of simulated time–settlement curves with experimental measurements for Singapore marine clay and a parametric study illustrating the effects of nonuniform N distribution on centrifuge consolidation behavior. Simulations indicate that the effect of spatially varying N is most strongly controlled by the ratio of specimen height to centrifuge arm length and that the error associated with the assumption of constant N is relatively small if this ratio is 0.2 or less. Finally, CC1 is used to calculate the optimal location within a centrifuge specimen of Singapore m...

Determination of consolidation behaviour of Haliç dredged material by using a seepage‐induced consolidation test

PurposeTo establish relationships between effective vertical stress‐void ratio and hydraulic conductivity‐void ratio on high water content dredged clays, which are then used to predict the field consolidation behavior.Design/methodology/approachThe large strain consolidation model is used for numerical modeling of large‐strain self‐weight consolidation. Material parameters determined from seepage‐induced consolidation tests provided satisfactory predictions of field compression behavior.FindingsIt is shown that realistic estimates of self‐weight consolidation behavior of dredged sea bottom sediments stored on land can be made by using a seepage‐induced consolidation test system and an appropriate consolidation model such as CS2, which is very important in storage capacity design and reclamation planning of such storage areas.Originality/valueIn this paper, the findings are presented of an experimental investigation of the consolidation behavior of Golden Horn dredge material using a seepage‐induced testing system. The experimentally determined consolidation properties have yielded useful relationships for the variation of void ratio with effective stress and coefficient of permeability with void ratio, and use of these has enabled a realistic prediction of the observed behavior.

Efficiency of Seepage Consolidation for Preparation of Clay Substrate for Centrifuge Testing

Abstract Seepage consolidation under normal gravity conditions can be used to prepare clay soil substrates for subsequent testing in a geotechnical centrifuge. Currently available information provides no information regarding the general efficiency of this method, which would be expected to vary widely depending on centrifuge, test specimen, and operating conditions. A numerical investigation is presented of the efficiency of the two-stage seepage/centrifuge consolidation method for the preparation of normally consolidated clay substrates. Large strain consolidation simulations and experimental data for centrifuge and seepage/centrifuge consolidation tests conducted on reconstituted Singapore marine clay are in excellent agreement. A parametric study illustrates the effects of initial specimen void ratio, initial specimen height, surcharge stress, swelling time, and acceleration factor on the efficiency of the two-stage substrate preparation method. Efficiency of the method for Singapore marine clay ranged from 55 to essentially 100% for the simulations conducted.

Similarity solution of self-weight consolidation problem for saturated soil

A more general assumption than that in the classical one-dimensional large strain consolidation theory is adopted and the exact analytical solution of nonlinear finite strain self-weight consolidation based on this assumption is obtained. By applying the same experimental data, the comparison of the solutions of linear and nonlinear finite strain theory, as well as the numerical calculating results based on finite element method is presented. The results of the comparison show that the analytical solution obtained here takes on better agreement with practical cases than that of linear one, and they also show that, compared with the solutions based on nonlinear theory, the settlement and the consolidation degree based on linear theory are smaller.

Modeling of compaction and overpressuring in sedimentary basins

This paper deals with the modeling of compaction and overpressure development in sedimentary basins during sedimentation. The modeling is based on an extension of a formulation for one-dimensional sedimentation and large-strain consolidation of sedimentary layers increasing in thickness with time. A modified formulation is presented using constitutive models for sediment compaction and permeability changes, which are based on experimental results for different clays compacted to effective stresses of up to 100 MPa. The main aim of the modeling is to improve the knowledge of overpressuring generated by mechanical compaction in sedimentary basins. Parametric studies were carried out to determine the effects of deposition rate and sediment properties on predicted overpressures, effective stress, porosity and permeability in sedimentary basins. Finally, a simplified North Sea sedimentary basin is analyzed in order to illustrate the use of the model, and to gain further understanding of how pore pressures have developed in some areas in the North Sea.

Model for large strain consolidation with compressible pore fluid

AbstractA numerical model, called CCPF1 (Consolidation with Compressible Pore Fluid 1), is presented for one‐dimensional large strain consolidation of a saturated porous medium with compressible pore fluid. The algorithm includes all the capabilities of a previous large strain consolidation code, CS2, written for incompressible pore fluid. In addition, fluid density and fluid viscosity are functions of fluid pressure in CCPF1. Generalization of the numerical approach to accommodate these functions requires several modifications to the CS2 method, including phase relationships, intrinsic permeability, pore pressure, fluid potential, and mass flux. Inertial forces are neglected and isothermal conditions are assumed. The development of CCPF1 is first presented, followed by an example that illustrates the effects of pore fluid compressibility on the mechanics of consolidation of saturated porous media. Copyright © 2004 John Wiley & Sons, Ltd.

Analytical solutions of one-dimensional large strain consolidation of saturated and homogeneous clays

Fully explicit analytical solutions are developed for one-dimensional large strain consolidation in both thick and thin soil layers. Numerical examples are given and comparisons are made with the classical small strain theory. It is shown that, unlike the results in classical small strain theory, the average degree of consolidation defined by stress (i.e. U p) and that defined by strain (i.e. U s) in large strain theory are different. The magnitude of settlement predicted by large strain theory is found to be smaller while both the development of settlement and the dissipation of excess pore water pressure (as shown by U s and U p) are found to be faster than in small strain consolidation in the cases studied. Another interesting observation is that the discrepancy between large and small strain theories diminishes with reducing compressibility (i.e. increasing stiffness) of soil and decreasing magnitude of applied load.

Compression Tests of Ultra-Soft Soil Using an Hydraulic Consolidation Cell

Abstract Compression behavior and compression parameters in the ultra-soft soil stage are still not well understood. In ultra-soft soil stage, the process of compression does not follow Terzaghi's unique relationship of deformation and effective stress gain principle, and the large deformation with little or no effective stress gain occurred in this stage. One-step loading compression tests were conducted, using a large diameter hydraulic consolidation cell (Rowe Cell). Vertical displacement and pore pressure behavior were measured during the deformation process. The transition point between slurry and soil stage determined from various methods are discussed. Approximate determination of compression indices in slurry stage from one-step high pressure loading was described in the paper. Step loading compression tests were also carried out with hydraulic consolidation cells on an ultra-soft soil with radial drainage conditions. Based on these test results, new compression parameters C*c1, C*c2, and C*c3 are introduced in this paper. The correlation between e*10 and void ratio at liquid limit eL is proposed. With this information, the total settlement at various loadings can be determined using the proposed equations. The prediction of time-rate of settlement could even be made using the coefficient of large strain consolidation CF estimated from the void ratio-permeability relationship. The computed magnitude and time rate of settlement agreed well with measured data. The dimensionless time factor curves for various radial drainage conditions are also proposed.

Sidere: numerical prediction of large-strain consolidation

Large-strain consolidation theory is widely used for the management of dredged disposal sites. The theory is universally accepted to deal with this problem, though the determination of the material properties is not yet standardised. Decisions made on this level can lead to the prediction of a totally different consolidation history. This paper describes the results of a prediction exercise, performed using a batch of sediment from the river Schelde (Antwerpen, Belgium). Numerical modellers were given the data of four calibration experiments and were then asked to predict another experiment. Settling column experiments (0·2–0·6 m in height) with density and pore pressure measurements provided the basis for the calibration data. The prediction demonstrated the significance of the soil compressibility at low effective stresses, when time-dependent behaviour is observed.

Sidere: numerical prediction of large-strain consolidation

Large-strain consolidation theory is widely used for the management of dredged disposal sites. The theory is universally accepted to deal with this problem, though the determination of the material properties is not yet standardised. Decisions made on this level can lead to the prediction of a totally different consolidation history. This paper describes the results of a prediction exercise, performed using a batch of sediment from the river Schelde (Antwerpen, Belgium). Numerical modellers were given the data of four calibration experiments and were then asked to predict another experiment. Settling column experiments (0·2–0·6 m in height) with density and pore pressure measurements provided the basis for the calibration data. The prediction demonstrated the significance of the soil compressibility at low effective stresses, when time-dependent behaviour is observed.

Laboratory properties of mine tailings

A vast amount and variety of mine tailings are produced around the world each day. These mining wastes must be properly managed. To evaluate mine tailings disposal technology, the appropriate engineering properties of the tailings must be ascertained. The results of a laboratory investigation on the engineering properties of four different tailings are presented. First, some of the basic properties of the tailings are described. Large-strain consolidation tests and hydraulic conductivity tests are then described. The techniques for saturating and placing the tailings sample prior to carrying out the consolidation tests are given. Column drying and shrinkage tests for investigating the desiccation behavior of mine tailings are outlined. Furthermore, water retention characteristic tests using both the pressure-plate extractor and the saturated salt solution desiccator are outlined. Finally, shear strength parameter tests are described. The engineering properties derived from these tests are then presented and compared with the published results on similar types of tailings.Key words: mine tailings, engineering properties, consolidation, hydraulic conductivity, water retention curve, evaporation rate.