Consolidation Theory Research Articles

Advances in modelling of hydro-mechanical processes in gas migration within saturated bentonite: A state-of-art review

Bentonite is a key material for the construction of Engineered Barrier Systems (EBSs) in deep geological repositories (DGRs) for radioactive waste. Modelling of gas migration in saturated bentonite, as well as the accompanied hydromechanical (HM) processes is crucial for conducting a performance assessment for the safety of a deep geological repository (DGR). The objective of this paper is to review the state-of-the-art of coupled HM models for simulating the gas migration behaviors in saturated bentonite. To this end, the paper has reviewed and discussed the coupled HM models from several aspects, including governing equations, HM constitutive models, fracture theories and related numerical approaches. Moreover, these models are discussed in terms of their merits and limitations to simulate the observed experimental behaviors. It is found that the previous HM models were generally established in the framework of Biot's consolidation theory or mixture theory. The adopted mechanical models include linear/nonlinear elastic models, elastoplastic models, damage models and swelling models. The incorporation of plastic and damage models into the coupled HM framework has enabled to account for the effect of the development of preferential pathways. However, these mechanical models don't enable to explicitly simulate the preferential pathways. The gas flow in saturated bentonite has been generally modelled by the generalized Darcy's law. Visco-capillary two-phase flow model with enriched intrinsic permeability (gas-pressure-based model, porosity-based model, strain-based model, damage-based model, Embedded Fracture Model, EFM) is the most used hydraulic model to simulate the gas flow. The EFM and its variations are the most widely used permeability models to simulate the gas migration process in saturated bentonite. The development of preferential pathways has been commonly considered in an implicit way by using the embedded fracture model as intrinsic permeability model or by adopting plastic or damage models to describe the mechanical behaviors. Current numerical models that can explicitly simulate the gas-driven fracturing process in saturated bentonite were not frequently reported. The existing ones are not complete enough to simulate all the key experimental behaviors associated with the preferential pathways. Advanced numerical approaches, such as XFEM or DEM based approaches, and proper fracture theories, such as the cohesive zone model, need to be employed to explicitly describe the development of preferential pathways. At the end of this paper, conclusions and recommendations for future modelling studies on gas migration in bentonite barrier are given. • Review and discussion of existing coupled HM models for simulating gas migration in saturated bentonite • The merits and limitations of previous coupled HM models are provided • Explicitly simulating the development of preferential pathways is critical to evaluate the sealing ability of bentonite • Cohesive zone model is a promising fracture theory to simulate the gas-driven fracturing process in bentonite

Numerical analysis for the vertical bearing capacity of composite pile foundation system in liquefiable soil under sine wave vibration

Composite pile foundation has been widely used in ground engineering. This composite pile foundation system has complex pile-soil interactions under seismic loading. The calculation of vertical bearing capacity of composite pile foundation is still an unsolved problem if the soil around piles is partially or completely liquefied under seismic loading. We have completed indoor shaking table model tests to measure the vertical bearing capacity in a liquefiable soil foundation under seismic loading. This paper will use a numerical approach to analyze the change of this vertical bearing capacity under seismic loading. Firstly, the Goodman contact element is improved to include the Rayleigh damping. Such an improvement can well describe the reflection and absorption of seismic waves at the interface of soil and piles. Secondly, the Biot’s dynamic consolidation theory incorporated an elastoplastic model is applied to simulate the soil deformation and the generation and accumulation of pore water pressure under seismic loading. Thirdly, after verification with our indoor shaking table test data, this approach is used to investigate the effects of pile spacing on liquefaction resistance of the composite pile foundation in liquefiable soil. The time histories of pore water pressure ratio (PPR′) are calculated for the liquefiable soil and the vertical bearing capacity in partially liquefied soil is calculated and compared with our indoor shaking table test data at the 3D, 3.5D, 4D, 5D and 6D cases (D is the pile diameter). It is found that the pile spacing has some influence on the extent of soil liquefaction between piles. The vertical bearing capacity varies with liquefaction extent of inter-pile soil. The optimization of pile spacing varies with liquefaction extent. These results may provide some reference for the design of composite pile foundation under seismic loading.

Analytical solutions and simplified design method for large-strain radial consolidation

Vertical drains combined with vacuum pressure is widely used to accelerate soil consolidation in land reclamation, where the effective prediction of the consolidation behaviour is needed to decide the improvement plan. In this paper, analytical solutions are presented for the large-strain radial consolidation theory using three equivalent coefficients that reduce the order of the high nonlinear governing equation. The effectiveness of solutions is verified by comparing the predictions of them with finite element method (FEM) simulations in common ranges of all parameters. By simplifying the proposed solution, a practical design method is further presented to be utilized by practical engineers. The practical method's efficiency and accuracy are proved by comparing the calculated results based on two case histories with numerical simulations and the field measurements.

Sleep Facilitates Problem Solving With No Additional Gain Through Targeted Memory Reactivation.

According to the active systems consolidation theory, memories undergo reactivation during sleep that can give rise to qualitative changes of the representations. These changes may generate new knowledge such as gaining insight into solutions for problem solving. targeted memory reactivation (TMR) uses learning-associated cues, such as sounds or odors, which have been shown to improve memory consolidation when re-applied during sleep. Here we tested whether TMR during slow wave sleep (SWS) and/or rapid eye movement (REM) sleep increases problem solving. Young healthy volunteers participated in one of two experiments. Experiment 1 tested the effect of natural sleep on problem solving. Subjects were trained in a video game-based problem solving task until being presented with a non-solved challenge. Followed by a ~10-h incubation interval filled with nocturnal sleep or daytime wakefulness, subjects were tested on the problem solving challenge again. Experiment 2 tested the effect of TMR on problem solving, with subjects receiving auditory TMR either during SWS (SWSstim), REM sleep (REMstim), or wakefulness (Wakestim). In Experiment 1, sleep improved problem solving, with 62% of subjects from the Sleep group solving the problem compared to 24% of the Wake group. Subjects with higher amounts of SWS in the Sleep group had a higher chance to solve the problem. In Experiment 2, TMR did not change the sleep effect on problem solving: 56 and 58% of subjects from the SWSstim and REMstim groups solved the problem compared to 57% from the Wakestim group. These findings indicate that sleep, and particularly SWS, facilitates problem solving, whereas this effect is not further increased by TMR.

An analytical solution for self-weight consolidation based on one-dimensional small-strain consolidation wave theory

Terzaghi's consolidation theory neglects inertial effects on the consolidation of saturated soils. To quantify the inertial effects, in this paper an original one-dimensional small-strain consolidation wave (C-wave) theory is developed, based upon a proposed modified Darcy's law with relaxation time and the equation of motion for soil ensemble. The one-dimensional governing equations were first formulated for self-weight consolidation, followed by a closed-form solution employing the method of separation of variables. The proposed model was then validated against wave velocity measurements and verified against finite-difference analysis. The half-closed self-weight consolidation behaviour was subsequently investigated, compared with Terzaghi's theory, Fillunger–Heinrich's dynamic theory and the u–p form of Biot's wave theory. This research indicates that: (a) superior to conventional models under comparison, the C-wave model enhances the predictability of the C-wave velocity; (b) the dimensionless C-wave coefficient (Cw) dominates the fundamental consolidation behaviour; (c) a wave-diffusion duality underlying the consolidation mechanism contributes qualitatively to the spatial bottom-up pattern and temporal response delay in consolidation observations; and (d) Terzaghi's theory can afford a practically accurate solution provided the Cwand time factor are below and above approximately 0·01, respectively. The C-wave theory may enrich the understanding of consolidation-related phenomena involving an appreciable Cw.

Simulation Analysis on Drainage Consolidation Characteristics of Hydraulic Fill Soft Soil

Based on the treatment of dredger fill soft soil foundation in Eastern Shantou, Guangdong Province, consolidation theory and numerical simulation based on composite consolidation coefficient are used to study the consolidation characteristics of dredger fill soft soil, and the results are compared with the field monitoring results. The calculation results show that the theoretical consolidation degree of the site is 93.4%, which is basically consistent with the final consolidation degree of field monitoring. In the first two stages of surcharge loading, field monitoring is faster than theoretical calculation. The field monitoring value of the final settlement is 1342 mm, which is about 10% less than the theoretical value. The final average consolidation degree of the two models is 97.9%, which is 4.7% more than the field monitoring value. The results show that the pore water pressure law is obvious, the dissipation rate is about 16% higher than the field monitoring value, and the consolidation effect is more obvious. The numerical simulation of the composite coefficient model has certain applicability and can be used to guide the design and construction of similar projects.

Estimating Hydraulic Conductivity of Overconsolidated Soils Based on Piezocone Penetration Test (PCPT)

Overconsolidated (OC) soils may develop a low or negative pore pressure during PCPT. Thus, it is challenging to develop an “on-the-fly” estimation of hydraulic conductivity from PCPT results. This study presents a method to estimate the hydraulic conductivity of OC soils from PCPT results based on a previously developed method for normally consolidated (NC) soils. To apply the existing method, PCPT pore pressure in OC soils is adjusted by using a correction factor. An equation for the correction factor is derived based on the concepts of critical state soil mechanics, cavity expansion, and consolidation theories. Then, it was reformulated so that traditional cone indices could be used as input parameters. It is shown that the correction factor is mainly influenced by the cone tip resistance, pore pressure, and the rigidity index. The comparison of predicted, which is based on corrected pore pressure and measured hydraulic conductivity showed a good match for four well documented data sets. With the findings of the study, it is expected that an “on-the-fly” estimation of hydraulic conductivity of overconsolidated soils is possible.

PERBANDINGAN METODE PRELOADING DENGAN VAKUM KONSOLIDASI TANAH PADA PEMODELAN DI LABORATORIUM

ABSTRACT This study aims to determine the parameter comparison of the magnitude of the primary reduction and consolidation time in the preloading method using PVD and vacuum method using PVD with modeling in the laboratory. The benefit of this research is that it can provide a comparison of the preloading method and the vacuum method in terms of accelerating the consolidation time as well as contributing to science in the field of soil improvement. Primary consolidation theory is used in this research. Quantitative descriptive research method with testing data collection techniques by means of modeling in the laboratory. The modeling of the vacuum method used a test tub measuring (1.2 × 0.6 × 0.9) m, the vacuum pump suction capacity of 5 Pa, the air hose as PHD and geomembrane cloth as PVD material. The preloading method with PVD uses a test tub measuring (0.8 × 0.6 × 0.9) m, preloading load in the form of bangka sand (ɣ = 1.532 t / m³) with a thickness of 10 cm and a geomembrane cloth as PVD material. In each test basin filled with soil and water with a soil volume weight of 1.3 t / m³, a ground surface height of 0.5 m and a groundwater level of 0.42 m. The results showed that with the same amount of reduction, namely 7.26 mm preloading method using PVD took 81 hours while in the vacuum method the time needed was 41 hours. Thus it can be concluded that the reduction in the vacuum method is faster than the preloading method with PVD. Keywords: Primer settelment, PVD, Vacum, consolidation time

Design charts for consolidation settlement of marine clays using finite strain consolidation theory

In this study, design charts for estimating consolidation settlement are proposed according to finite strain consolidation theory using a nonlinear constitutive relationship equation. Results of parametric sensitivity analysis shows that the final settlement, initial height, and initial void ratio exerted the greatest effect, and the coefficients of the void ratio–effective-stress. Proposed design charts were analyzed for three regions using a representative constitutive relationship equation that enables major dredged-reclaimed construction sites in Korea. The regional design charts can be calculated accurately for the final settlement because it is applied directly to the numerical analysis results, except for reading errors. A general design chart applicable to all marine clays is proposed through correlation analysis of the main parameters. A final self-weight consolidation settlement with various initial void ratios and initial height conditions should be estimated easily using the general design chart and constitutive relationship. The estimated final settlement using the general design chart is similar to the results of numerical analysis obtained using finite strain consolidation theory. Under an overburden pressure condition, design charts for estimating consolidation settlement are proposed for three regions in Korea.

Remembering more than you can say: Re-examining “amnesia” of attended attributes

Attribute amnesia (AA) describes a phenomenon whereby observers fail a surprise memory test which asks them to report an attribute they had just attended and used to fulfil a task goal. This finding has cast doubt on the prominent theory that attention results in encoding into working memory (WM), to which two competing explanations have been proposed: (1) task demands dictate whether attended information is encoded into WM, and (2) attended information is encoded in a weak state that does not survive the demands of the surprise memory test. To address this debate our study circumvented the limitations of a surprise memory test by embedding a second search task within a typical color-based AA search task. The search task was modified so that the attended attribute would reappear in the second search as either the target, a distractor, or not at all. Critically, our results support encoding of the attended attribute in WM though to a weaker extent than the attribute that is required for report. A second experiment confirmed that WM encoding only occurs for the attended attribute, though distractor attributes produce a bias consistent with negative priming. Our data provide novel support for a theory of memory consolidation that links the strength of a memory's representation with expectations for how it will be used in a task. Implications for the utility of this procedure in future investigations previously limited by single trial data (i.e., surprise question methodology) are discussed.

Influence of Foundation Pit Excavation and Precipitation on Settlement of Surrounding Buildings

With the large-scale development of urban underground space, foundation pit engineering has become one of the important geotechnical engineering topics in urban construction. In this paper, the effects of foundation pit excavation and precipitation on adjacent buildings are studied in detail. The main research work includes the following aspects: summarizing and analyzing the soil consolidation theory, foundation pit excavation, and precipitation process; the influencing factors of the adjacent soil layer displacement; the influence mechanism and influence types of foundation pit excavation and precipitation on adjacent buildings. The finite element model considering the whole process of foundation pit excavation is established, and the variation law of the upper layer displacement around the foundation pit is analyzed. The deformation law of the retaining structure, the calculation results of precipitation and nonprecipitation, and different excavation methods will be analyzed and compared. The calculation results show that the displacement of the soil layer around the foundation pit is also different between different excavation methods. As the distance between the foundation pits increases, the lateral displacement of the underground continuous wall near the frame structure gradually decreases. The distance from the foundation pit wall is 30 m. The maximum value of the lateral shift is reduced by 4.7% compared with 5 m. The foundation pit is studied, as well as the law of internal force variation of adjacent buildings caused by digging and precipitation, and checking the safety and adaptability of structural members. The calculation results show that a large additional internal force will be generated on the bottom floor of the adjacent building, and some structural members will be damaged by the bearing capacity.

Party System Fragmentation and Institutionalization: Japan’s Party System in the 2010s

The paper analyzes the party system change at the level ofJapan’s national politics. The party system after the 1990s can be classified into three periods according to some indicators to measure party system change. The present party system in the 2010s is characterized by the LDP dominance and fragmentation and fluidity of opposition parties. It is called ikkyō politics (安倍一強政治)” which means the LDP dominance under Abe administration. At the final section of the paper the problem of party system fragmentation and ruling party dominance is argued referring to the theory of party system institutionalization and democratic consolidation.

Semi‐analytical analysis of fractional derivative rheological consolidation considering the effect of self‐weight stress

AbstractStudies have revealed that rheological characteristics and self‐weight stress are nonnegligible during a consolidation process, especially for land reclamation projects or dredged soils. However, they are rarely considered simultaneously in traditional consolidation theories. This paper presents a general solution to the consolidation system of rheological soils that incorporates a fractional derivative model and self‐weight stress. First, the theory of the fractional derivative is introduced to the Merchant model to describe the consolidation behaviours of rheological soils, and the self‐weight stress of soils is simultaneously considered. Based on this model, the governing equation of a rheological consolidation system that considers self‐weight stress is obtained. Second, the analytical solutions of the effective stress and settlement in the Laplace domain are obtained by applying the Laplace transform to the consolidation governing equation. Further, the actual solutions in the real domain are obtained by a numerical Laplace transform inversion method (Abate's fixed Talbot method). Finally, the reliability and correctness of the consolidation theories and the proposed solutions are verified by comparing the calculated results with the degenerate solutions and experimental results in the existing literature. Furthermore, parametric studies are conducted to investigate the influence of rheological parameters and self‐weight parameters on the consolidation settlement and consolidation rate.

Deformation behaviour and influence mechanism of thaw consolidation of embankments on the Qinghai-Tibet Railway in permafrost regions

With the thermal disturbance caused by engineering construction and global warming, thaw consolidation has become a primary source of subgrade deformation in permafrost regions. Based on the large-strain consolidation theory described by the updated Lagrangian, we study the thermal stability and the thaw consolidation in an ordinary subgrade at the warm and ice-rich permafrost (WIRP) site of the Beiluhe Qinghai-Tibet Railway (QTR) by establishing a thermo-mechanical coupled model. The research results are as follows: The initial mean annual ground temperature (MAGT) of the site influences the permafrost degradation on the Qinghai-Tibet Plateau due to construction and climate warming, exacerbating the thaw consolidation and creep of the ice-rich permafrost. The settlement rate and subgrade settlement increase with increasing embankment height, ice-rich permafrost layer thickness, and initial MAGT. Railway maintenance methods, such as ballast filling and track lifting, increase the subgrade weight, thus increasing the WIRP subgrade settlement. Furthermore, we predict the thaw consolidation of the DK1136 section of the QTR for the next 50 years. The prediction formulas of the cumulative settlements of the subgrade top and permafrost are established, and various suggestions for maintaining the railway subgrade of the WIRP site are proposed.

Mechanism of pore water seepage in soil reinforced by step vacuum preloading

A laboratory model experiment of step vacuum preloading (SVP) for dredger fills was performed. The soil moisture content and water discharge rate were measured. The seepage mechanism of pore water was analyzed based on the theory of drainage consolidation. The results indicated that the seepage fluid mostly consisted of free water during self-weight sedimentation and under 10 kPa vacuum pressure in the SVP test. The stage corresponding to the application of 20 kPa vacuum pressure was the transitional stage in which both the free water and the loosely bound water participated in the seepage. When higher vacuum pressure was applied, the loosely bound water mostly participated in the seepage. In the SVP test, the complete potential difference channels were established in the test bucket during self-weight sedimentation. The vacuum channels at the center began to form when 10 kPa vacuum pressure was applied, and the free water near the sidewall was discharged through the potential difference channel. With 20 kPa vacuum pressure, the vacuum channel developed continuously from the drainage board to the sidewall of the test bucket, completing the process and ultimately stabilizing as the vacuum pressure increasing. The study of the seepage mechanism of pore water during SVP test is significant for the analysis of pore water seepage under vacuum pressure during the consolidation of soft soil foundation. This study contributes to the existing theory related to vacuum preloading consolidation methods, providing theoretical guidance for the analysis of soil consolidation under drainage conditions.

Consolidation of Unsaturated Drainage Well Foundation with Smear Effect under Time-Dependent Loading

In real practice, the construction of drainage wells is always accompanied by smear effect, whereas it is scarcely discussed in the field of unsaturated soils. In this case, on the basis of the widely-accepted consolidation theory for unsaturated stratum by Fredlund, this paper studies the equal strain consolidation characteristics of unsaturated foundation with drain wells affected by smear effect under time-varying loading (exponential loading as a case). Firstly, with the consideration of corresponding boundary conditions, the governing equations under the equal strain hypothesis are obtained. Afterwards, decoupling process, constant variation method and Fourier series expansion theory are utilized to get the analytical solutions, which are then verified to be credible by means of the finite difference method. Finally, the consolidation patterns of the drainage well foundation modeling in unsaturated soils are studied against hydraulic coefficients, modeling sizes and loading parameter. It reveals that the smear effect can significantly restrain the consolidation process of the foundation by drain wells, while different parameters will lead to various results.

Deformation prediction and anti floating analysis of a raft foundation

This paper mainly studies the deformation and stress of the concrete plat under the uniform load considering the thickness of the compression layer of layered ground. Firstly, the load characteristics and the ground strategy are discussed in detail to clarify the boundary condition. Then the deformation of the ground in each layer is calculated by GEO-Cal program and the final settlement and uneven deformation is also predicted using consolidation theory. Ground stress and settlement is also calculated by FEM to verify the previous calculation.

Wave-induced residual pore pressure around a buried pipeline

Seabed instability caused by cyclic wave loading is one of the main factors affecting the foundation instability of marine structures, and it is a key problem that needs to be paid attention in the design of marine structures. Based on Biot’s consolidation theory and a semi-empirical formula for calculating residual pore water pressure, the wave-induced residual seabed response around a buried pipeline was investigated by numerical simulation. The correctness of the numerical results is verified by comparing with experimental results. Effect of the self-weight of the buried pipeline on residual pore pressure development and the characteristics of residual pore pressure near the pipeline are discussed.

CALCULATION OF STRESSES IN THE BUILDING STRUCTURES, TAKING INTO ACCOUNT GROUND BASE DEFORMATIONS

The paper reflects the assessment of the effect the heterogeneity of the ground base has on the stress-strain state of the reinforced concrete slab foundation and the structure of the building. It takes into account the development of deformations of ground base in time. Different filtration properties of subfoundation show the heterogeneity of the slab foundations. There is a lens of loam soil in series of saturated sands under the foot portion of the base slab. The paper shows the comparison of calculation results for the building structure and the base slab within the discrete time with the results obtained by the calculation of the steady-state deformations. The calculations contain the conditional soil deformation modulus. It is assumed that, at the initial time of application of the load, the conditional deformation modulus of the ground base Et tends to infinity, but at the final moment of deformation stabilization, it tends to the actual size E instead. The conditional deformation module is calculated using the approximate dependence obtained from the basic equation of the theory of soil filtration consolidation. SCAD software package serves for building modeling and numerical calculation

Nonlinear consolidation theory for prefabricated vertical drains with elliptic cylindrical assumption

Based on the influence of the non-linear change in the consolidation process of permeability coefficient and compressibility of soft soils and the theory of elliptic cylinders, derived the control equation of the nonlinear consolidation of the vertical foundation of the strip plastic drainage board. Further, according to the complete orthogonal space theory, the equivalent polynomial analytical expression of the nonlinear term is given. Then, the analytic solutions of the nonlinear consolidation are given, and through numerical calculation and verification analysis, it is considered that the Indrarantna (2005) approximation has a relatively small error at Cc/Ck (close to 1) and Nu (<4), but when Cc/Ck (difference from 1) and Nu are large (>4), the error is large.