Dissipation Of Water Pressure Research Articles

Influences of freezing\u2013thawing actions on mechanical properties of soils and stress and deformation of soil slope in cold regions

Freezing–thawing actions can affect the mechanical features of soil greatly, which is vital for the stability of soil slope in cold regions. Firstly, triaxial compression tests on sand samples under undrained conditions were performed to investigate the influences of freezing–thawing cycles, which shows that the freezing–thawing actions can weaken their strength and stiffness, and with the increasing freezing–thawing cycles, both the deviatoric stress and pore water pressure decrease gradually. Then, the double hardening constitutive model was revised to model the influences of freezing–thawing cycles in consideration of the influences of freezing–thawing actions, and the model was also validated by the test results. Finally, the proposed constitutive model was incorporated into a finite element code to numerically simulate the distribution of displacement and pore water pressure of sand slope subjected to freezing–thawing cycles, which shows that the freezing–thawing actions accelerate the dissipation of the pore water pressure and enlarge the displacement of the slope. The study here can provide a help in designing and construction of civil engineering in cold regions.

Vacuum Preconsolidation Settlement Characteristics and Microstructural Evolution of Marine Dredger-Filled Silt

The method of vacuum preloading for foundation treatments is used in the construction of the Fangchenggang coastal area in Guangxi province, China. The thick marine dredger-filled silt has a considerable impact on the treatment effort. In this study, the mineral composition and grain size distribution of these silts were analyzed to investigate their consolidation settlement property and microstructures. The scanning electron microscope and finite element method were adopted. The results reveal that the dredger-filled silt in this area is composed mainly of sand with particle size mostly smaller than 0.075 mm. To replicate the construction process, the process of drainage by the vacuum preloading method was simulated by setting different water levels in the finite element analysis. The displacement and the dissipation of the pore water pressure obtained by simulations were reasonably consistent with the field monitoring data. In addition, the results obtained using the scanning electron microscope indicate that the equivalent diameter of the structural unit and that of the pore unit decrease with the silt depth. However, the value of the structural abundance approaches one, whereas the pore abundance is significantly different from one.

Case study: footing load test using stone columns in Port Fouad-Egypt

Installation of stone columns is an efficient technique to improve very soft to soft clay deposits that exist at shallow depths in many coastal areas in Egypt. The stone columns provide vertical stiff permeable members in the deposit to be improved. Upon loading, the presence of stiff columns reduces settlement, and increases the overall shear strength of the deposit, thus bearing capacity. Further, the high permeability of the columns provides drainage boundary that accelerates the dissipation of excess water pressure and thus increases the consolidation time rate of the soft soil. This paper presents analysis of a case history of footing load test founded on soft clay improved by stone columns for a project in Port Fouad, Egypt. The stone columns are of end-bearing type. The footing is analyzed using 3D finite element method. The analysis aims to; (1) show the importance of increased post-column installation coefficient of lateral earth pressure in light of the pre-shearing effect (Mesri and Hayat in Can Geotech J 30:647–666, 1993), (2) show the importance of considering the time-dependent settlement in evaluation either of the improvement technique and/or the design method, and (3) use the field measurements to evaluate and compare between the FEA method and the other published methods of estimating the settlement improvement ratio.

Controlling the Permeability of Sandy Soil Using Different Local Waste Materials

Advanced developed technologies associated with people demands have caused production and expansion of different local wastes where the process of managing such waste becomes a real need for controlling the pollution risk. One of the procedures for recycling can be made through using local wastes in permeability control for sandy soil since the soil permeability plays a crucial function on the water drainage, pore water pressure buildup and dissipation, and ground movement for saturated sand during and after earthquake occurrences. In addition, any economical mixture should maintain hydraulic constraints for practice use. In this study, a laboratory experiment was prepared to perform tests for estimating the water movements and permeability in a pure sand column and treated sandy soil with different locally waste materials including plastic, glass, rubber, and aluminum. In addition, a numerical investigation including finite element method has been adopted to verify the experimental procedure. It was shown that the permeability could be controlled to different rates using these local wastes.

TIME TO THE END OF PRIMARY CONSOLIDATION (EOP) OF SOFT CLAYEY SOILS: CONCERNING THE EFFECT OF ATTERBERG’S LIMIT AND CYCLIC LOADING HISTORY

In order to observe the end of primary consolidation (EOP) of cohesive soils with and without subjecting to cyclic loading, reconstituted specimens of clayey soils at various Atterberg’s limits were used for oedometer test at different loading increments and undrained cyclic shear test followed by drainage with various cyclic shear directions and a wide range of shear strain amplitudes. The pore water pressure and settlement of the soils were measured with time and the time to EOP was then determined by different methods. It is shown from observed results that the time to EOP determined by 3-t method agrees well with the time required for full dissipation of the pore water pressure and being considerably larger than those determined by Log Time method. These observations were then further evaluated in connection with effects of the Atterberg’s limit and the cyclic loading history.

Numerical Analysis for Liquefaction Deformation of Low Embankment on Soft Foundation Based on Water Level Changes in Coastal Highway

Zhang, X.-G.; Zhu, J.-X.; Zeng, Y.; Jiang, P.; Yi, N.-P.; Yan, L.-E., and Li, Y.-J., 2019. Numerical analysis for liquefaction deformation of low embankment on soft foundation based on water level changes in coastal highway. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 321–326. Coconut Creek (Florida), ISSN 0749-0208.This paper mainly studies the water level change of coastal soft foundation by taking the soft foundation in the liquefaction zone of the Xiniujiao-Dafengjiang section of the coastal first-class highway in Guangxi, China as the research object. To this end, by arranging the saturated silt soft foundation of 6 1.5m inverted trapezoidal gravel wall low embankment structure in the vertical direction, the numerical simulation method was adopted to simulate its liquefaction deformation of the soft foundation problem under the traffic load in the working condition I (constant annual water level) and working condition II (temporary water level rise), and also judge its liquefaction potential, the development and dissipation of the pore water pressure, and the excess pore pressure ratio. Finally, the results show that under different water levels, the gravel-paving on embankment can effectively improve the liquefaction-resistant ability of the soft foundation and improve the uneven settlement of the original compacted fill embankment.

Deep Compaction Control of Sandy Soils

Abstract Vibroflotation, vibratory compaction, micro-blasting or heavy tamping are typical improvement methods for the cohesionless deposits of high thickness. The complex mechanism of deep soil compaction is related to void ratio decrease with grain rearrangements, lateral stress increase, prestressing effect of certain number of load cycles, water pressure dissipation, aging and other effects. Calibration chamber based interpretation of CPTU/DMT can be used to take into account vertical and horizontal stress and void ratio effects. Some examples of interpretation of soundings in pre-treated and compacted sands are given. Some acceptance criteria for compaction control are discussed. The improvement factors are analysed including the normalised approach based on the soil behaviour type index.

Study on Vehicle Speed in Pore Water Pressure of Rigid Pavement Base Using Poro-Elasticity

Water in pavement is a major contributor to pavement failure. Fine aggregates are pumped out near the joint of rigid pavement and cause the erosion of the base layer. In order to analyze the phenomenon, a two dimensional model using Finite Element Method (FEM) and Porous elasticity theory is developed to calculate the pore water pressure development in the base layer underneath joints. The model contains three parts, two cement concrete surface plates separated by a joint gap and a base layer with relatively small stiffness and large permeability. The constitutive behavior of porous medium material used in the model is introduced. Nodes along the depth direction of the base layer underneath the joint are analyzed to investigate the erosion of the base. Distributed loading is applied at the part area near the joint to simulate vehicle passing through the rigid pavement surface. Excess pore water pressure along the depth caused by external loading are calculated. The influence of vehicle speed on the base material is analyzed by adding a tire contacting with surface of the cement concrete. The results of the study show that vehicle speed does not only influence the magnitude but also the dissipation of the pore water pressure.

Two Dimensional Parametric Analysis of Time Variation Characteristics of Raft Foundation on Saturated Subsoil

For further discussing time variation characteristics of raft foundation on saturated subsoil due to consolidation, parameterized numerical analyses are completed based on Biot consolidation equations by developing elasto-plastic coupled FE model in plane strain state, together with adopting Mohr-Coulomb yield criterion. Computational results show that internal force and deformation of raft foundation display obvious non-monotonic features, which is associated with dissipation of excess pore water pressure. The disequilibrium of dissipation of excess pore water pressure displays more intensive between subsoil areas near raft center and the border due to less Poission’s ratio of subsoil, which leads to more dissipation time and regulation magnitude of distribution of stress and deformation in subsoil. When subsoil is of low permeability coefficients and Poission’s ratios, the non-monotonic features become more clearly and sustain with longer term variation characteristics.

STOCHASTIC CONSOLIDATION OF MULTILAYERED SOIL WITH RANDOM HEIGHT

In this paper, stochastic 1D primary consolidation of a multilayered soil is investigated. Monte Carlo simulations are combined with the thin layer method to evaluate the effect of the soil height profile randomness property on the final settlement and the consolidation time duration. Soil height is modeled herein as a uniform and lognormal random variable, and the statistics regarding output parameters are investigated by performing a parametric study that integrates the influence of the soil height profile coefficient of variation. Obtained results indicate that heterogeneity significantly influences the primary consolidation of the soil profile, i.e., increases the final settlement and induces a quite different way of soil grain rearrangement and water pressure dissipation in comparison to the homogeneous case, which results in a significant increase of the final settlement and an important delay of the consolidation process.

Consolidation Statistics Investigation via Thin Layer Method Analysis

In this paper, the Thin Layer Method (TLM) is adapted for solving one-dimensional primary consolidation problems. It is also combined with a stochastic formulation integrating Monte Carlo simulations to investigate primary consolidation of a random heterogeneous soil profile. This latter is modeled as a set of superposed layers extending horizontally to infinity, and having random properties. Spatial variability of soil properties is considered in the vertical direction only. Soil properties of interest are elastic modulus and soil permeability, modeled herein as spatially random fields. Lognormal distribution is chosen because it is suitable for strictly non-negative random variables, and enables analyzing the large variability of such properties. The statistics regarding final settlement and its corresponding time are investigated by performing a parametric study, which integrates the influence of variation coefficient of both elastic modulus and soil permeability, and vertical correlation length. Obtained results indicate that heterogeneity significantly influences primary consolidation of the soil profile, generating a quite different way of soil grain rearrangement and water pressure dissipation in comparison to the homogeneous case, and causing a delay in the consolidation process.