scholarly journals Behaviour of Unsaturated Subgrade Soil Under Highway Load

2019 ◽  
Vol 12 (1) ◽  
pp. 23-33
Author(s):  
Ghassan Nasser Jaffer
Keyword(s):  
Water Table ◽  
Pore Water Pressure ◽  
Layer Structure ◽  
Water Pressure ◽  
Degree Of Saturation ◽  
Fe Model ◽  
Center Line ◽  
Water Table Level ◽  
Subgrade Soil ◽  
Dynamic Loadings

This paper studied the application of 2-D Plaxis (v8.6, 2011) software on a pavement layer structure set on unsaturated subgrade soil. An axisymmetric finite element (FE) model was used to analyze the behavior of pavement layers subjected to dynamic loadings. The model was loaded with an incremental contact pressure from 50 to 550 kPa with different variable such as water table level (1,2 and 3m), suction of soil and degree of saturation (100, 90, 80, 70 and 20%). The results indicated that during loading on pavement layer with increases water table level and different degree of saturation the vertical settlement was decreased by about (11, 15, and 18%) for water table level= 1m, (9, 13, 16%) for water table level= 2m and (28%) for water table level= 3m (dry soil) respectively. The effect of degree of saturation on the vertical settlement is apparent at the lower value for water table level (1 and 2m) and the vertical settlement is decreased with increasing soil suction. The results also show the negative pore water pressure decreased with decreased of degree of saturation and development increases with depth and beginning of dynamic load. The effect of unsaturation greater at the center line of pavement layer and limited far away the center line.

scholarly journals Impact of the moisture content in medium sands on CPTU test results

2016 ◽  
Vol 48 (3) ◽  
pp. 221-231 ◽  
Author(s):  
Łukasz Zawadzki ◽  
Marek Bajda
Keyword(s):  
Moisture Content ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Degree Of Saturation ◽  
Test Results ◽  
Time Dynamic ◽  
Tip Resistance ◽  
The Impact ◽  
Resistance Value

Abstract Soils occurring in the soil “active zone” are in contact with the surface and are directly influenced by external factors (mainly climatic changes) that cause variation in their parameters over time. Dynamic and uncontrolled changes of soil properties e.g. due to rainfall and evapotranspiration processes may affect field test results leading to the misinterpretation of the obtained data. This paper presents investigations on the influence of moisture content changes in sandy soils on CPTU results. For this purpose, a field ground model has been constructed and five CPTU tests with a different moisture content of soil were carried out. During the investigations, the tip resistance (qc), friction on sleeve (fs), and pore water pressure (u2) were measured. Moreover, a TDR probe was applied to determine the distribution of the moisture content in the studied soil columns. Differences between CPT results obtained in saturated and unsaturated soils have been shown. Furthermore, a simple equation to correct the tip resistance value due to the impact of the degree of saturation has been proposed.

Soil-water characteristics of compacted sandy and cemented soils with and without vegetation

2015 ◽  
Vol 52 (9) ◽  
pp. 1331-1344 ◽  
Author(s):  
W.M. Yan ◽  
Guanghui Zhang
Keyword(s):  
Soil Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Rapid Development ◽  
Characteristic Curve ◽  
Degree Of Saturation ◽  
Material Density ◽  
Water Characteristics ◽  
Field And Laboratory Conditions ◽  
Humidity Monitoring

Experiments were undertaken to study the soil-water characteristics of compacted sandy soil (SS) and cemented soil (CS) in field and laboratory conditions. The influence of vegetation and material density on the development of negative pore-water pressure (PWP) and degree of saturation (Sr) in the studied materials was investigated. The field planting experiments demonstrated a promising survival rate of Schefflera heptaphylla in both types of material, while the (SS) promoted better growth of the seedlings than the cemented one. In the field study, PWP and Sr of the compacted SS responded noticeably and promptly to natural drying–wetting cycles. However, the responses in the CS were relatively mild. When subjected to the same drying–wetting cycles, PWP responded more slowly and to a smaller magnitude compared with that of the uncemented counterpart. In addition, Sr changed little in CS. An increase in the density of the SS promoted rapid development of negative PWP, while an opposite trend was observed for CS. Attempts have been made to explain the observations from the perspectives of material permeability and change in water content during a drying period in both soil types. Furthermore, in SS, the development of PWP (with a measurement limit of −90 kPa) was minimally affected by the presence of vegetation, while vegetation noticeably helped the development of negative PWP in CS. Bounds of the soil-water characteristic curve (SWCCs) of the studied materials were presented based on estimates from the drying and wetting scanning curves derived from the field monitoring. A corresponding laboratory study was carried out in an environmental chamber with controllable temperature and humidity. Monitoring results from the laboratory agreed qualitatively with those obtained from the field.

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.

scholarly journals Stability and Consolidation of Sediment Tailings Incorporating Unsaturated Soil Mechanics

Fluids ◽  
2021 ◽  
Vol 6 (12) ◽  
pp. 423
Author(s):  
Alfrendo Satyanaga ◽  
Martin Wijaya ◽  
Qian Zhai ◽  
Sung-Woo Moon ◽  
Jaan Pu ◽  
...  
Keyword(s):  
Unsaturated Soil ◽  
Pore Water Pressure ◽  
Soil Mechanics ◽  
Water Pressure ◽  
High Water ◽  
Degree Of Saturation ◽  
High Water Content ◽  
Consolidation Process ◽  
Time Required ◽  
Unsaturated Zones

Tailing dams are commonly used to safely store tailings without damaging the environment. Sand tailings (also called Sediment tailings) usually have a high water content and hence undergo consolidation during their placement. As the sediment tailings are usually placed above the ground water level, the degree of saturation and permeability of the sediment tailing is associated with the unsaturated condition due to the presence of negative pore-water pressure or suction. Current practices normally focus on the analyses saturated conditions. However, this consolidation process requires the flow of water between saturated and unsaturated zones to be considered. The objective of this study is to investigate the stability and consolidation of sediment tailings for the construction of road pillars considering the water flow between saturated and unsaturated zones. The scope of this study includes the unsaturated laboratory testing of sediments and numerical analyses of the road pillar. The results show that the analyses based on saturated conditions overestimate the time required to achieve a 90% degree of consolidation. The incorporation of the unsaturated soil properties is able to optimize the design of slopes for road pillars into steeper slope angles.

Earth Pressures Due to Compaction: Comparison of Theory with Laboratory and Field Behavior

1996 ◽  
Vol 1526 (1) ◽  
pp. 28-37 ◽  
Author(s):  
George M. Filz ◽  
James M. Duncan
Keyword(s):  
New York ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Retaining Wall ◽  
New York State ◽  
Rehabilitation Program ◽  
Silty Sand ◽  
Degree Of Saturation ◽  
Earth Pressures ◽  
Pressure Development

Compaction of backfill adjacent to stiff and unyielding structures induces earth pressures in the compacted fill that exceed normal at-rest earth pressures. A numerical method that can be used to calculate compaction-induced lateral earth pressures has been proposed by Duncan and Seed. The purpose of the study described in this paper is to evaluate the theory by comparing calculated and measured compaction-induced lateral earth pressures. The data for the comparisons is from values measured in backfills behind three stiff, unyielding walls: the instrumented retaining wall in the Transport and Road Research Laboratory in Crawthorne, England; the instrumented retaining wall in the Virginia Tech Geotechnical Laboratory in Blacksburg, Virginia; and the lock walls at Eisenhower and Snell Locks in New York state. The lock walls were found to be cracked, apparently by high earth pressures induced by compaction, and an extensive rehabilitation program was required. The measurements from all three walls confirm the existence of compaction-induced lateral earth pressures. For clean sand backfill, pressures calculated using the theory of Duncan and Seed are shown to be in reasonable agreement with measured values. Laboratory test data indicate that for moisture-sensitive silty sand backfill the applicability of the Duncan and Seed theory, which does not include considerations of pore water pressure development during backfill placement and compaction, depends on the degree of saturation of the backfill.

The Denholm landslide, Saskatchewan. Part II: analysis

1983 ◽  
Vol 20 (2) ◽  
pp. 208-220 ◽  
Author(s):  
E. Karl Sauer
Keyword(s):  
Shear Zone ◽  
Water Table ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Back Analysis ◽  
Sensitivity Analyses ◽  
Horizontal Shear ◽  
Successive Block ◽  
Geological Evidence ◽  
Slide Mass

A procedure incorporating geological evidence with analytical methods was developed for the back analysis of a multiple retrogressive landslide in Cretaceous clay shale. The slide mass, apparently inactive, extends 2 km back from the toe at the river and is seated on a shear zone 100 m deep at the main scarp. Historical evidence of the slope movement was established from radiocarbon dating of the river alluvium over which the landslide moved. The geometry of the landslide when the factor of safety was near unity was determined from historic and stratigraphic evidence and sensitivity analyses.The stratigraphy of the slide mass showed that the beds are stretched with very little vertical displacement, indicating a mainly translational mechanism along a nearly horizontal shear zone. Apparently movement has taken place at a slow but steady rate over 11 000 years, resulting in a horizontal displacement of 390–430 m at the toe. The landslide, therefore, was analyzed as a series of sliding blocks with a common failure surface retrogressing from the toe up to the scarp. Each successive block was combined and considered to be moving as a single unit. Unknown factors, such as pore-water pressure at failure and the influence of cohesion, were evaluated by sensitivity analyses. The effective angle of shearing resistance required for limiting equilibrium was relatively constant, ranging from 7.6 to 8.7°, assuming the water table to be near the ground surface. For a lower water table, the values ranged from 6.5 to 8.0°. The equivalent values of cohesion required for equilibrium with [Formula: see text] ranged from 42 to 82 kPa depending on the size of the block, suggesting that c′ must be zero for the retrogressive mechanism analyzed by combining successive blocks. Keywords: slope stability, multiple-block, back analysis, residual strength, sensitivity analysis.

Centrifuge Seismic Test on Seismic Behavior of Pile Group in Liquefiable Soil

2015 ◽  
Vol 764-765 ◽  
pp. 1041-1045
Author(s):  
Meng Hsiu Hsieh ◽  
Wen Yi Hung ◽  
Chung Jung Lee
Keyword(s):  
Water Table ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Bending Moment ◽  
Pile Group ◽  
Shaking Table ◽  
Bending Moments ◽  
Saturated Sand ◽  
Pressure Transducers ◽  
Pile Cap

A series of grouped-model piles (2×2) centrifuge shaking table tests at an acceleration of 80 g was conducted to simulate seismic responses of a grouped-piles embedded in liquefiable sandy soil subjected to different magnitudes of earthquake loading. The tested grouped-piles connected with a pile cap are used to support 4 sets of model dry storage tank.Different test conditions including elevations of pile cap, elevations of ground water table, and dry and saturated sand beds all are reported in the study. Sensors (i.e., strain gauges along the depths of pile for measuring the bending moments, accelerometers for measuring the accelerations at different depths, LVDTs and pore water pressure transducers) densely instrumented in the piles and the surrounding soils provide valuable information for examining their evolution at various degrees of liquefaction. The magnitudes of bending moment along pile depths would increase with the increases of base shaking. The lowest bending moments were measured for the grouped–piles with the pile cap embedded in the dry sand bed while the largest lowest bending moments for the grouped–piles with the pile cap embedded in the saturated sand bed with the water table at the surface. The test results can be used to validate the results derived from the numerical simulation.

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