The collapse behavior of a compacted soil during inundation

1991 ◽  
Vol 28 (4) ◽  
pp. 477-488 ◽  
Author(s):  
Rambabu Tadepalli ◽  
D. G. Fredlund
Keyword(s):  
Experimental Data ◽  
Pore Water ◽  
Unsaturated Soil ◽  
Transient Flow ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Coefficient Of Consolidation ◽  
Compacted Soil ◽  
Collapse Behavior

The collapse behavior of a compacted, uncemented soil is studied within a theoretical context consistent with the concepts of unsaturated soil mechanics. Experimental data are presented relating the initial matric suction of a compacted soil to its volume decrease during inundation. The laboratory results indicate a unique relationship between the changes in matric suction (i.e., Δ(ua − uw), where ua is the pore-air pressure and uw is the pore-water pressure) of the compacted soil and the resulting volume reduction during inundation. Changes in the matric suction and total volume with respect to time were modelled using the theory of transient flow through an unsaturated soil. The predicted results show reasonable agreement with the experimental observations. The comparisons between the simulated results and the experimental data indicate that the coefficient of consolidation of the soil varies linearly with matric suction during the inundation process. Key words: unsaturated soil, matric suction, collapsible soils, negative pore-water pressures.

scholarly journals Experimental insights into consolidation rates during one-dimensional loading with special reference to excess pore water pressure

2020 ◽  
Vol 15 (12) ◽  
pp. 3571-3591
Author(s):  
Bartłomiej Szczepan Olek
Keyword(s):  
Pore Water ◽  
Large Scale ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Small Scale ◽  
Coefficient Of Consolidation ◽  
Consolidation Process ◽  
Factors Affecting ◽  
Fine Grained ◽  
Fine Grained Soil

AbstractConsolidation rate has significant influence on the settlement of structures founded on soft fine-grained soil. This paper presents the results of a series of small-scale and large-scale Rowe cell consolidation tests with pore water pressure measurements to investigate the factors affecting the consolidation process. Permeability and creep/resistance structure factors were considered as the governing factors. Intact and reconstituted marine clay from the Polish Carpathian Foredeep basin as well as clay–sand mixtures was examined in the present study. The fundamental relationship correlating consolidation degrees based on compression and pore water pressure was assessed to indicate the nonlinear soil behaviour. It was observed that the instantaneous consolidation parameters vary as the process progresses. The instantaneous coefficient of consolidation first drastically increases or decreases with increase in the degree of consolidation and stabilises in the middle stage of the consolidation; it then decreases significantly due to viscoplastic effects occurring in the soil structure. Based on the characteristics of the relationship between coefficient of consolidation and degree of dissipation at the base, the consolidation range that complies with theoretical assumptions was established. Furthermore, the influence of coarser fraction in clay–sand mixtures in controlling the consolidation rates is discussed.

Mini suction probe for matric suction measurements

2002 ◽  
Vol 39 (6) ◽  
pp. 1427-1432 ◽  
Author(s):  
Inge Meilani ◽  
Harianto Rahardjo ◽  
Eng-Choon Leong ◽  
Delwyn G Fredlund
Keyword(s):  
Pore Water ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Lateral Direction ◽  
Triaxial Apparatus ◽  
Specimen Height ◽  
Pressure Changes ◽  
Accurate Reading

A modified triaxial apparatus with mini suction probes was fabricated to study the matric suction along the specimen height during unsaturated triaxial testing. Three mini suction probes were placed at 3/4, 1/2, and 1/4 height of the specimen, each at 120° apart in the lateral direction. This paper presents the development of the mini probe for matric suction measurements. Evaluation of the performance shows that the fabricated mini probe provides a rapid response and accurate reading under negative and positive pore-water pressure changes. Matric suctions as high as 400 kPa were successfully measured on soil specimens over a time span of 15 h. On the other hand, the mini suction probes were also found to be able to measure a matric suction of 200 kPa for a longer period of 155 h.Key words: matric suction, mini suction probe, triaxial, unsaturated soils, mid-height pore-water pressure measurement.

Experimental verification of the theory of consolidation for unsaturated soils

1995 ◽  
Vol 32 (5) ◽  
pp. 749-766 ◽  
Author(s):  
Harianto Rahardjo ◽  
Delwyn G. Fredlund
Keyword(s):  
Water Content ◽  
Pore Pressure ◽  
Pore Water ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Water Volume ◽  
Loading Tests ◽  
Undrained Loading

An experimental program was designed to study the behavior of unsaturated soils during undrained loading and consolidation. A Ko cylinder was designed and built for the testing program. Simultaneous measurements of pore-air and pore-water pressures could be made throughout a soil specimen using this Ko cylinder. Four types of tests were performed on a silty sand. These are (1) undrained loading tests where both the air and water are not allowed to drain, (2) constant water content tests where only the water phase is not allowed to drain, (3) consolidation tests where both the air and water phases are allowed to drain, and (4) increasing matric suction tests. Undrained loading tests or constant water content loading tests were conducted for measuring the pore pressure parameters for the unsaturated soil. Drained tests consisting of either consolidation tests or increasing matric suction tests were conducted to study the pore pressure distribution and volume change behavior throughout an unsaturated soil during a transient process. The experimental pore pressure parameters obtained from the undrained loadings and constant water content leadings agreed reasonably well with theory. The pore-air pressure was found to dissipate instantaneously when the air phase is continuous. The pore-water pressure dissipation during the consolidation test was found to be faster than the pore-water pressure decrease during the increasing matric suction test. The differing rates of dissipation were attributed to the different coefficients of water volume change for each of the tests. The water volume changes during the consolidation test were considerably smaller than the water volume changes during the increasing matric suction tests for the same increment of pressure change. Key words : consolidation, Ko loading, matric suction, pore-air pressures, pore-water pressures, unsaturated soils

scholarly journals Numerical Simulation Of The Treatment Of Soil Swelling Using Grid Geocell Columns

2015 ◽  
Vol 23 (2) ◽  
pp. 9-18 ◽  
Author(s):  
Mohammed Y. Fattah ◽  
Raid R. Al-Omari ◽  
Haifaa A. Ali
Keyword(s):  
Finite Element ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Expansive Soil ◽  
Matric Suction ◽  
Degree Of Saturation ◽  
Axial Forces ◽  
Column Material ◽  
Cap Model

Abstract In this paper, a method for the treatment of the swelling of expansive soil is numerically simulated. The method is simply based on the embedment of a geogrid (or a geomesh) in the soil. The geogrid is extended continuously inside the volume of the soil where the swell is needed to be controlled and orientated towards the direction of the swell. Soils with different swelling potentials are employed: bentonite base-Na and bentonite base-Ca samples in addition to kaolinite mixed with bentonite. A numerical analysis was carried out by the finite element method to study the swelling soil's behavior and investigate the distribution of the stresses and pore water pressures around the geocells beneath the shallow footings. The ABAQUS computer program was used as a finite element tool, and the soil is represented by the modified Drucker-Prager/cap model. The geogrid surrounding the geocell is assumed to be a linear elastic material throughout the analysis. The soil properties used in the modeling were experimentally obtained. It is concluded that the degree of saturation and the matric suction (the negative pore water pressure) decrease as the angle of friction of the geocell column material increases due to the activity of the sand fill in the dissipation of the pore water pressure and the acceleration of the drainage through its function as a drain. When the plasticity index and the active depth (the active zone is considered to be equal to the overall depth of the clay model) increase, the axial movement (swelling movement) and matric suction, as a result of the increase in the axial forces, vary between this maximum value at the top of the layer and the minimum value in the last third of the active depth and then return to a consolidation at the end of the depth layer.

Calculation of Consolidation Coefficient and Percent Consolidation from Measured Pore Water Pressure of Soft Clay

2011 ◽  
Vol 250-253 ◽  
pp. 1889-1892
Author(s):  
Yong Mou Zhang ◽  
Jian Chang Zhao
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Soft Clay ◽  
Coefficient Of Consolidation ◽  
Consolidation Process ◽  
Consolidation Coefficient

Consolidation coefficient and percent consolidation of soft clay were calculated according to the measured pore water pressure of a project in Pudong Shanghai. Calculated coefficient of consolidation was one magnitude larger than the experimental one. This was in conformity with the actual consolidation process of dynamically-consolidated soft soil.

scholarly journals Numerical Analysis of the Effects of Crack Characteristics on the Stress and Deformation of Unsaturated Soil Slopes

Water ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 194 ◽  
Author(s):  
Liuxin Yang ◽  
Enlong Liu
Keyword(s):  
Pore Water ◽  
Unsaturated Soil ◽  
Crack Width ◽  
Evaporation Rate ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Infiltration Rate ◽  
Soil Slope ◽  
Soil Slopes ◽  
Stress And Deformation

Cracks induced by evaporation or rainfall have a great influence on the stability of unsaturated soil slopes, which can lead to landslides during the rainfall process. In order to study the effect of crack characteristics on the evolution of stress and deformation of unsaturated soil slopes, a series of numerical analyses under different conditions were performed using a coupled elastoplastic finite element program that we developed for unsaturated soil. When carrying out the numerical analyses, the effective stress for unsaturated soil proposed by Bishop and an elastoplastic double-hardening constitutive model for the soil skeleton were employed. The varying parameters, including the crack location, the discharge speed, evaporation rate, infiltration rate, and tensile strength, were investigated to study the coupling process of pore water pressure and deformation in the process of evaporation and rainfall infiltration. The numerical results showed that the minimum pore water pressure of the soil slope at the end of evaporation/rainfall decreased gradually and the crack width increased gradually as the crack set closer to the slope; the larger the discharge speed of pore air, the greater the crack width. With the increase in the evaporation rate, the pore water pressure of the soil slope reduced and the crack initiated earlier and became wider. As the infiltration rate increased, the pore water pressure of the soil slope and the crack width increased, but the decreasing duration became shorter. The change of tensile strength had little effect on the pore water pressure, but the development of the crack width changed with evaporation and rainfall infiltration.

Study on Pore Water Pressure Model of Soft Clay

2012 ◽  
Vol 446-449 ◽  
pp. 1510-1513
Author(s):  
Yong Zhang ◽  
Li Wan ◽  
Yang Huang ◽  
Jia Fu
Keyword(s):  
Experimental Data ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Clay ◽  
State Theory ◽  
Volume Strain ◽  
Nonlinear Stress ◽  
Strain Relationship ◽  
New Formula

Based on the consolidated undrained triaxial test of soft clay, a formula for computing pore water pressure is developed, by using of the critical state theory of volume strain and the characteristic normalization of soft clay. It is shown that the new proposed formula is reasonable to reveal the nonlinear stress-strain relationship and the dilatancy characteristics of soft clay. With the comparison between the pore water pressure simulation results by the new formula and the experimental data, it is shown that the simulation values agree well with the experimental data. Meanwhile, based on the failure criterion, a formula for the critical pore water pressure is proposed. It is shown that the new formula is reasonable to simulate the critical pore water pressure. It is very useful to predict the foundation stability.

scholarly journals Behavior analysis by model slope experiment of artificial rainfall

2015 ◽  
Vol 3 (6) ◽  
pp. 4159-4187
Author(s):  
M. C. Park
Keyword(s):  
Stability Analysis ◽  
Slope Stability ◽  
Pore Water ◽  
Slope Failure ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Slope Stability Analysis ◽  
Model Slope ◽  
Rainfall Seepage

Abstract. In this study, we performed a model slope experiment with rainfall seepage, and the results were compared and verified with the unsaturated slope stability analysis method. In the model slope experiment, we measured the changes in water content and matric suction due to rainfall seepage, and determined the time at which the slope failure occurred and the shape of the failure. In addition, we compared and verified the changes in the factor of safety and the shape of the failure surface, which was calculated from the unsaturated slope stability analysis with the model experiment. From the results of experiment and analysis, it is concluded that the unsaturated slope stability analysis can be used to accurately analyze and predict rainfall-induced slope failure. It is also concluded that in seepage analysis, setting the initial conditions and boundary conditions is very important. If engineers will use the measured pore water pressure or matric suction, the accuracy of analysis can be enhanced. The real-time monitoring system of pore water pressure or matric suction can be used as a warning of rainfall-induced slope failure.

Effectiveness of Capillary Barrier and Vegetative Slope Covers in Maintaining Soil Suction

2016 ◽  
pp. 51-69
Author(s):  
Harianto Rahardjo ◽  
S. Krisnanto ◽  
E.C. Leong
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Numerical Analyses ◽  
Soil Suction ◽  
Vetiver Grass ◽  
Capillary Barrier ◽  
Maximum Rainfall

Capillary barrier and vegetative slope covers can be used to improve slope stability during rainfall by maintaining matric suction in the slope. A study was performed to investigate the effectiveness of capillary barrier system (CBS) and vegetative slope covers (Orange Jasmine and Vetiver grass) in maintaining soil suction. Performance of slopes with and without slope covers was investigated using field instrumentations and numerical analyses. Laboratory tests were performed to measure hydraulic and shear strength properties of the soil, the soils with Orange Jasmine and Vetiver grass root, and CBS materials. Numerical analyses were performed to investigate the variation of pore-water pressure profiles at a selected location and factor of safety during low, high, and maximum rainfall intensities. Pore-water pressures measured in the field were used to calibrate the numerical models. Laboratory test results showed that the presence of root increased the shear strength of soil. Numerical analyses and field monitoring results showed that the slope with covers can maintain negative pore-water pressure better than the original slope. Performance of Orange Jasmine, Vetiver grass, and CBS in maintaining matric suction in the slope is essentially similar during low, high, and maximum rainfall intensities.

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