scholarly journals Study on Electroosmosis Consolidation of Punctiform Electrode Unit

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Xiaoyu Yang ◽  
Yongbin Xie ◽  
Jianhua Dong ◽  
Guosheng Liu ◽  
Yalin Zheng
Keyword(s):  
Finite Element ◽  
Pore Water ◽  
Potential Field ◽  
Potential Distribution ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Two Dimensional ◽  
Dimensional Model ◽  
One Dimensional ◽  
Electric Potential Field

In the electroosmosis method, when the distance between the opposite electrode and the same electrode is equal, the two-dimensional effect of electroosmotic consolidation is significant, and the use of one-dimensional model will overestimate the potential gradient, making the calculated pore pressure value too large. Aiming at this problem, according to the electrode arrangement rule and the minimum composition, a punctiform electrode unit model is proposed, and electroosmotic experiments are carried out on the symmetric and asymmetric unit models. The two-dimensional electroosmotic consolidation governing equation of the punctiform electrode unit is established. The electric potential field of the electrode unit and the finite element form of the electroosmotic consolidation equation are given by the Galerkin method. The PyEcFem finite-element numerical library is developed using Python programming to calculate. The research results show the following: (1) The two-dimensional effect of the potential field distribution of the punctiform electrode unit is significant. The reduction of spacing of the same nature electrode in the symmetrical unit can make the potential distribution close to a uniform electric field. The asymmetry prevents the electric potential field distribution from being reduced to a one-dimensional model. (2) The number of anodes will affect the electroosmosis effect of the soil. The more the anodes, the better the electroosmosis reinforcement effect of the soil, and the distribution of negative excess pore water pressure will be more uniform. (3) In the early stage of electroosmosis, the more the drainage boundaries, the faster the generation of negative pore pressure, but in the middle and late stages of electroosmosis, the potential value becomes the decisive factor, and the amplitude of negative pore water pressure in asymmetric units is higher than that in symmetric units. The potential distribution will not affect the degree of consolidation but will affect the extreme pore water pressure.

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 .

Vacuum and surcharge combined one-dimensional consolidation of clay soils

2002 ◽  
Vol 39 (5) ◽  
pp. 1126-1138 ◽  
Author(s):  
E Mohamedelhassan ◽  
J Q Shang
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Clay Soils ◽  
Soil Consolidation ◽  
Excess Pore Water Pressure ◽  
One Dimensional ◽  
Consolidation Model ◽  
The One ◽  
Excess Pore

In this study, a vacuum and surcharge combined one-dimensional consolidation model is developed. Terzaghi's consolidation theory is revisited by applying the initial and boundary conditions corresponding to combined vacuum and surcharge loading on a soil. A test apparatus is designed, manufactured, and assembled to verify the model. The apparatus has the capacity of applying designated vacuum and surcharge pressures to a soil specimen, and it allows for the measurement of the excess pore-water pressure, settlement, and volume change during the consolidation process. Two series of tests are performed using the apparatus on two reconstituted natural clay soils, namely, the Welland sediment at water contents close to its liquid limit and the Orleans clay, reconstituted and consolidated under an effective stress of 60 kPa. The former test series mimics the strengthening of a very soft soil, such as the hydraulic fill used in land reclamation. The latter test series is designed to study vacuum–surcharge combined strengthening of a consolidated soil. It is demonstrated from the experiments that the one-dimensional vacuum-surcharge consolidation model describes the consolidation behaviour of both soils well. The consolidation characteristics of the soils show no discrimination against the nature of the consolidation pressure, namely, whether they are consolidated under the vacuum pressure alone, under the surcharge pressure alone, or under a pressure generated by the combined application of vacuum and surcharge. The study concluded that the soil consolidation characteristics obtained from the conventional consolidation tests can be used in the design of vacuum preloading systems, provided that the one-dimensional loading condition prevails.Key words: consolidation, soil improvement, vacuum pressure, surcharge pressure, excess pore-water pressure, soil consolidation parameters.

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.

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.

A steady state model for flow in saturated–unsaturated soils

1984 ◽  
Vol 21 (3) ◽  
pp. 419-430 ◽  
Author(s):  
A. T. Papagianakis ◽  
D. G. Fredlund
Keyword(s):  
Finite Element ◽  
Steady State ◽  
Pore Water ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Pressure Head ◽  
Flow Equation ◽  
Coefficient Of Permeability ◽  
Steady State Model

A model is proposed describing continuous flow between saturated and unsaturated soil. The flow is assumed to be two dimensional and under steady state conditions. In the unsaturated zone, the coefficient of permeability is treated as a function of pore-water pressure head. The nonlinear differential equation governing the flow is solved using an iterative finite element scheme. The flow equation for an element is derived using the Galerkin weighed residuals method. Several example problems are solved and compared with flow net solutions. The proposed flow model is superior to traditional models, which consider flow only in the saturated zone. The results show that the zero pressure isobar is not an upper flow boundary. The finite element solution is shown to be relatively insensitive to the function used to express the relationship between the coefficient of permeability and the pore-water pressure head. Key words: saturated–unsaturated, pore-water pressure, head, phreatic line.

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