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 Shearing with Infiltration Tests to Study Mechanical Behavior and Failure Mechanism of Shallow Slopes

2019 ◽  
Author(s):  
Ali Murtaza Rasool ◽  
Jiro Kuwano
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Optimum Moisture Content ◽  
Deviatoric Stress ◽  
Water Infiltration ◽  
Degree Of Saturation ◽  
In Series ◽  
Infiltration Tests

An experimental series of shearing tests with water infiltration were performed on compacted unsaturated soil to simulate the behavior of shallow slope failures. Soil samples were compacted at moisture contents from dry to wet of optimum moisture content with the degree of saturation varying from 24.0% to 59.5% while maintaining the degree of compaction at 80%. Two series of shearing with infiltration tests were performed in this study. In Series-I, just before the start of shearing, matric suction was decreased by increasing pore water pressure to start water infiltration i.e. shearing is carried simultaneously with water infiltration. In Series-II, the soil was first sheared with drained pore air and undrained pore water to pre-defined value of deviatoric stress, after which matric suction was decreased by increasing pore water pressure to start water infiltration and shearing is performed by keeping deviatoric stress constant on the specimen. The test results showed that the decrease in matric suction has an effect on the volume of infiltrated water and degree of saturation. The soil slopes compacted on the dry side of optimum moisture content showed better performance than other soils, they require more decrease in matric suction to start water infiltration and showed higher deviatoric stress. In addition to this, water infiltration alone can cause the failure of shallow slopes without having to have any further loading.

scholarly journals Effect of Reduced Zone on Time-Dependent Analysis of Tunnels

2011 ◽  
Vol 2011 ◽  
pp. 1-12
Author(s):  
Mohammed Y. Fattah ◽  
Kais T. Shlash ◽  
Nahla M. Salim
Keyword(s):  
Finite Element ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Outer Diameter ◽  
Transient Effects ◽  
Excess Pore Water Pressure ◽  
Modified Cam Clay ◽  
Tunnel Diameter ◽  
Excess Pore

The problem of the proposed “Baghdad metro line” which consists of two routes of 32 km long and 36 stations is analyzed. The tunnel is circular in cross-section with a 5.9 m outer diameter. The finite element analyses were carried out using elastic-plastic and modified Cam clay models for the soil. The excavation has been used together with transient effects through a fully coupled Biot formulation. All these models and the excavation technique together with Biot consolidation are implemented into finite-element computer program named “Modf-CRISP” developed for the purpose of these analyses. The results indicate that there is an inward movement at the crown and this movement is restricted to four and half tunnel diameters. A limited movement can be noticed at spring line which reaches 0.05% of tunnel diameter, while there is a heave at the region below the invert, which reaches its maximum value of about 0.14% of the diameter and is also restricted to a region extending to 1.5 diameters. The effect of using reduced zone on excess pore water pressure and surface settlement (vertical and horizontal) was also considered and it was found that the excess pore water pressure increases while the settlement trough becomes deeper and narrower using reduced .

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

Earthquake-induced deformation analyses of the Upper San Fernando Dam under the 1971 San Fernando Earthquake

2001 ◽  
Vol 38 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Guoxi Wu
Keyword(s):  
Finite Element ◽  
Pore Water ◽  
Effective Stress ◽  
Pore Water Pressure ◽  
Ground Deformation ◽  
Water Pressure ◽  
Soil Liquefaction ◽  
Shear Stresses ◽  
Cyclic Shear ◽  
San Fernando

A nonlinear effective stress finite element approach for dynamic analysis of soil structure is described in the paper. Major features of this approach include the use of a third parameter in the two-parameter hyperbolic stress-strain model, a modified expression for unloading–reloading modulus in the Martin–Finn–Seed pore-water pressure model, and an additional pore-water pressure model based on cyclic shear stress. The additional pore-water pressure model uses the equivalent number of uniform cyclic shear stresses for the assessment of pore-water pressure. Dynamic analyses were then conducted to simulate the seismically induced soil liquefaction and ground deformation of the Upper San Fernando Dam under the 1971 San Fernando Earthquake. The analyses were conducted using the finite element computer program VERSAT. The computed zones of liquefaction and deformation are compared with the measured response and with results obtained by others.Key words: effective stress method, finite element analysis, Upper San Fernando Dam, earthquake deformation, VERSAT.

scholarly journals Finite Element Analysis of Vertical and Horizontal Drainage Structures under Vacuum Combined Surcharge Preloading

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Daqing Wang ◽  
Dong Wei ◽  
Guoyi Lin ◽  
Jiannan Zheng ◽  
Zhiting Tang ◽  
...  
Keyword(s):  
Finite Element ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Horizontal Displacement ◽  
Reinforcement Effect ◽  
Vacuum Suction ◽  
Prefabricated Vertical Drains ◽  
Surcharge Preloading ◽  
Prefabricated Vertical Drain

Combined vacuum and surcharge preloading has gradually been widely used because of its advantages of low cost, green environmental protection, and good treatment effect. The conventional prefabricated vertical drain presents obvious defects in vacuum preloading treatment, such as obvious silting, serious bending of the drainage board, large attenuation of vacuum degree of drainage board along the depth, long construction period, and so on, which affect the final reinforcement effect. In this paper, the MIDAS finite element simulation of combined vacuum and surcharge preloading of prefabricated vertical drains (PVDs) and prefabricated horizontal drains (PHDs) is established through the comparative experiment of the engineering field. The comparative experimental study is carried out from the aspects of the vertical settlement, horizontal displacement, and pore water pressure. The results show that under combined vacuum and surcharge preloading, the consolidation effect of soft soil with PHDs is better than that with PVDs. When PHDs are used, the vertical settlement increases by 7.2% compared with PVDs; the horizontal displacement is larger; and the pore water pressure dissipates faster. This is because when the PHDs are adopted, the consolidation direction of the soil is consistent with the direction of the vacuum suction, which is mainly caused by vertical settlement. With the consolidation, the spacing between PHDs is gradually shortened, and the drainage distance is reduced, which can effectively reduce the consolidation time and improve the reinforcement effect of the soil. In addition, the PHDs can move downward uniformly with the soil during the consolidation process and have almost no bending deformation, which makes the vacuum transfer more uniform and effective.

The Finite-Element Analysis of Characteristics of Soil Slope Seepage Field Change in Rainstorm Condition

2012 ◽  
Vol 204-208 ◽  
pp. 50-53
Author(s):  
Zhong Ming He ◽  
Wei Wu ◽  
Ling Zeng ◽  
Zhong Xin Cai
Keyword(s):  
Finite Element ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Element Analysis ◽  
Finite Element Software ◽  
The Finite Element Analysis ◽  
Pressure Region ◽  
Pressure Area ◽  
Depth Of Infiltration

A numerical model was built by Finite Element software,discussed the effect of rainfall on slope pore water pressure、volatile water content and depth of infiltration in rainstorm condition. The results indicated that: (1)the variation of slope surface pore water pressure is more significant and the depth of infiltration is larger with the increase of rainfall intensity on the condition of fixed rainfall duration;(2)The slope section appears three pore water pressure divisions: transient saturated zone、negative pressure region and hydrostatic pressure area after the rainfall.

The Finite-Element Analysis of Characteristics of Soil Slopeseepage Field Change in Continuous Rain Condition

2012 ◽  
Vol 238 ◽  
pp. 451-454
Author(s):  
Zhong Ming He ◽  
Wei Wu ◽  
Ling Zeng ◽  
Zhong Xin Cai
Keyword(s):  
Finite Element ◽  
Ground Water ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Element Analysis ◽  
Finite Element Software ◽  
The Finite Element Analysis ◽  
Pressure Area ◽  
Depth Of Infiltration

A numerical model is built by Finite Element Software, discussed the effect of rainfall on slope pore water pressure, volatile water content and depth of infiltration in continuous rain condition. The result indicated that when the rainfall intensity and rainfall duration reach a certain condition, the ground water table rises slowly, and mostly, the spill points of ground water locate in the foot of slope. The slope section appears three pore water pressure divisions: transient saturated zone, negative pressure region and hydrostatic pressure area after the rain.

scholarly journals Evaluasi Tekanan Air Pori dan Rembesan Pada Bendungan Panohan

2019 ◽  
Vol 4 (2) ◽  
pp. 26
Author(s):  
Adib Lathiful Huda ◽  
Sri Prabandiyani Retno Wardani ◽  
Suharyanto Suharyanto
Keyword(s):  
Finite Element ◽  
Water Level ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
The Body ◽  
Reservoir Water ◽  
Planning Stage ◽  
Fem Method ◽  
Comparison Results

Salah satu penyebab kegagalan struktur bendungan adalah terjadinya rembesan yang dipicu oleh tingginya tekanan air pori yang terjadi pada tubuh bendungan. Pada Bendungan Panohan, kebocoran rembesan terjadi hingga memotong lereng hilir bendungan yang dapat mengganggu stabilitas tubuh bendungan. Tujuan dari penelitian ini adalah untuk mengevaluasi tekanan air pori dan rembesan di tubuh Bendungan Panohan menggunakan metode analisis instrumentasi piezometer dan v-notch yang kemudian dibandingkan dengan analisis metode elemen hingga (finite element method / FEM) menggunakan program perangkat lunak SEEP/W. Metode FEM menggunakan parameter desain material selama tahap perencanaan bendungan. Kedua analisis dilakukan pada section C - C Bendungan Panohan menggunakan beberapa variasi ketinggian muka air waduk. Hasil perbandingan menunjukkan bahwa nilai tekanan air pori dan rembesan pada metode FEM lebih besar dari hasil analisis dengan metode pembacaan instrumentasi pada kondisi muka air minimal dan normal. Kondisi sebaliknya terjadi pada kondisi ketinggian air banjir, yaitu nilai tekanan air pori dan rembesan dari pembacaan instrumentasi lebih besar dari hasil analisis metode FEM. Seiring dengan naiknya ketinggian muka air waduk, terjadi kenaikan nilai tekanan air pori dan rembesan dari kedua hasil analisis. Kondisi rembesan yang terjadi pada  Bendungan Panohan saat ini tidak aman pada kondisi muka air banjir, karena memiliki nilai debit rembesan 0,38 ltr/det melebihi dari yang disyaratkan yaitu sebesar 0,35 ltr/det.Kata kunci : bendungan panohan; tekanan air pori; rembesan; FEM ABSTRACTOne of the causes of the failure of a dam structure is the occurrence of seepage triggered by high pore water pressure that occurs in the body of the dam. In the Panohan Dam, seepage occurs on the downstream slope of the dam which can disturb the stability of the dam body. The purpose of this research is to evaluate the pore water pressure and seepage in the Panohan Dam body using the piezometer and v-notch instrumentation reading method which is then compared with the finite element (FEM) method using SEEP/W software program. FEM method uses material parameters during the dam planning stage. Both analyses were carried out on the C – C section of the Panohan Dam using several variations of reservoir water level. The comparison results show that pore water pressure in the FEM method is greater than the pore water pressure value based on the piezometer method at the minimum and normal water level conditions. The opposite condition occurs in maximum water level conditions. The seepage value of the v-notch reading is greater than the seepage value from the FEM method. Seepage that occurs in the Panohan Dam is currently unsafe under the maximal water level conditions.

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