Horizontal pressure on barricades for backfilled stopes. Part II: Submerged conditions

2009 ◽  
Vol 46 (1) ◽  
pp. 47-56 ◽  
Author(s):  
Li Li ◽  
Michel Aubertin
Keyword(s):  
Pore Pressure ◽  
Pore Water Pressure ◽  
Experimental Testing ◽  
Water Pressure ◽  
Companion Paper ◽  
Simple Method ◽  
Horizontal Pressure ◽  
Undrained Conditions ◽  
Backfilled Stopes ◽  
Submerged Conditions

This paper presents a method to calculate the pressure generated by submerged backfill on barricades (or bulkheads) located in drifts at the base of mine stopes. The paper complements Part I (see companion paper, this isue), which presents an analytical solution for the pressure on barricades when the backfill is in drained conditions (after the pore-water pressure has dissipated). The solution presented here applies shortly after backfill deposition, for undrained conditions. In this case, the effect of pore pressure cannot be neglected as it may be critical for the response of barricades. The solution is developed for totally or partly submerged backfill (with the water table at various elevations). Experimental testing and numerical modelling results are used to validate the proposed equations. Both numerical and analytical results show that the total pressure on barricades can be significantly increased by pore pressure, while the effective stress is decreased in the access drifts (compared to dry or drained conditions). The proposed solution provides a simple method to obtain a realistic estimate of the total and effective stresses, and can thus be used as a basis for barricade design.

Type of Slope Failure Identified from Pore Water Pressure and Moisture Content Measurements

2015 ◽  
Vol 744-746 ◽  
pp. 690-694
Author(s):  
Muhammad Rehan Hakro ◽  
Indra Sati Hamonangan Harahap
Keyword(s):  
Moisture Content ◽  
Pore Pressure ◽  
Slope Failure ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Failure Process ◽  
Small Scale ◽  
Content Increase ◽  
Sudden Increase ◽  
Model Slope

Rainfall-induced landslides occur in many parts of the world and causing a lot of the damages. For effective prediction of rainfall-induced landslides the comprehensive understanding of the failure process is necessary. Under different soil and hydrological conditions experiments were conducted to investigate and clarify the mechanism of slope failure. The failure in model slope was induced by sprinkling the rainfall on slope composed of sandy soil in small flume. Series of tests were conducted in small scale flume to better understand the failure process in sandy slopes. The moisture content was measured with advanced Imko TDR (Time Domain Reflectrometry) moisture sensors in addition to measurements of pore pressure with piezometers. The moisture content increase rapidly to reach the maximum possible water content in case of higher intensity of rainfall, and higher intensity of the rainfall causes higher erosion as compared to smaller intensity of the rainfall. The controlling factor for rainfall-induced flowslides was density of the slope, rather than intensity of the rainfall and during the flowslide the sudden increase in pore pressure was observed. Higher pore pressure was observed at the toe of the slope as compared to upper part of the slope.

scholarly journals A modified tank model including snowmelt and infiltration time lags for deep-seated landslides in Alpine Environments (Aggenalm, Germany)

2016 ◽  
Author(s):  
W. Nie ◽  
M. Krautblatter ◽  
K. Leith ◽  
K. Thuro ◽  
J. Festl
Keyword(s):  
Pore Water ◽  
Relative Error ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Snow Accumulation ◽  
Time Lags ◽  
Simple Method ◽  
Tank Model ◽  
Groundwater Supply ◽  
Alpine Environments

Abstract. Deep-seated landslides are an important and widespread natural hazard within alpine regions, and can have a massive impact on infrastructure. Pore water pressure plays an important role in determining the stability of hydro-triggered deep-seated landslides. We improve current methods of groundwater level prediction by introducing a means to account for time lags associated with groundwater supply caused by snow accumulation, snowmelt, and infiltration in deep-seated landslides. In this study, we demonstrate a simple method to improve the estimation of these time lags using a modified tank model to calculate groundwater levels. In a deep-seated landslide in Bavaria, Germany, our results predict daily changes in pore water pressure ranging from -1 to 1.6 kPa depending on daily rainfall and snowmelt. The inclusion of time lags improves the results of standard tank models by ~36% (linear correlation with measurement) after heavy rainfall and, respectively, by ~82% following snowmelt in a 1-2 day period. For the modified tank model, we introduced a representation of snow accumulation and snowmelt, based on a temperature index and an equivalent infiltration method, i.e. the melted snow water equivalent. This compares well to the in situ measurement for the same time interval which reflect changes of pore water pressure with 0-8% relative error in rainfall season (standard tank model: 2-16% relative error) and with 0-7% relative error in snowmelt season (standard tank model: 2-45% relative error). Here we demonstrate a modified tank model for deep-seated landslides that includes snow and infiltration effects and can effectively predict changes in pore water pressure in alpine environments.

scholarly journals Mechanical response and pore pressure generation in granular filters subjected to uniaxial cyclic loading

2018 ◽  
Vol 55 (12) ◽  
pp. 1756-1768
Author(s):  
Jahanzaib Israr ◽  
Buddhima Indraratna
Keyword(s):  
Cyclic Loading ◽  
Pore Pressure ◽  
Pore Water ◽  
Mechanical Response ◽  
Pore Water Pressure ◽  
Axial Strain ◽  
Water Pressure ◽  
Internal Erosion ◽  
Excess Pore Water Pressure ◽  
Excess Pore

This paper presents results from a series of piping tests carried out on a selected range of granular filters under static and cyclic loading conditions. The mechanical response of filters subjected to cyclic loading could be characterized in three distinct phases; namely, (I) pre-shakedown, (II) post-shakedown, and (III) post-critical (i.e., the occurrence of internal erosion). All the permanent geomechanical changes such, as erosion, permeability variations, and axial strain developments, took place during phases I and III, while the specimen response remained purely elastic during phase II. The post-critical occurrence of erosion incurred significant settlement that may not be tolerable for high-speed railway substructures. The analysis revealed that a cyclic load would induce excess pore-water pressure, which, in corroboration with steady seepage forces and agitation due to dynamic loading, could then cause internal erosion of fines from the specimens. The resulting excess pore pressure is a direct function of the axial strain due to cyclic densification, as well as the loading frequency and reduction in permeability. A model based on strain energy is proposed to quantify the excess pore-water pressure, and subsequently validated using current and existing test results from published studies.

An effective stress model for creep of clay

1995 ◽  
Vol 32 (5) ◽  
pp. 819-834 ◽  
Author(s):  
Mohammed M. Morsy ◽  
D.H. Chan ◽  
N.R. Morgenstern
Keyword(s):  
Finite Element ◽  
Pore Pressure ◽  
Effective Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Surface Model ◽  
Interpolation Technique ◽  
Stress Integration ◽  
Integration Algorithms ◽  
Double Yield

An effective stress constitutive model to study the problem numerically of creep in the field is presented. A double-yield surface model for the stress–strain–time behaviour of wet clay is described. The model adopts the concept of separating the total deformation into immediate and delayed components. The yield surfaces employed are the modified Cam-clay ellipsoid and the Von Mises cylinder inscribed in the ellipsoid. The proposed numerical scheme incorporates the pore pressure based on field observations into a finite element analysis. An interpolation technique is used to determine the pore pressure at every element. A field example is presented to illustrate the interpolation technique procedure. The scheme not only avoids the complexity of making predictions of pore-water pressure, but also allows the analysis to be carried out in terms of effective stresses based on the actual observed pore pressure. Two stress integration algorithms based on the implicit calculation of plastic strain are implemented and tested for the double-yield surface model. A numerical simulation of stress-controlled drained creep tests confirms the numerical procedure. Key words : constitutive equations, creep, finite element, stress integration algorithms, effective stress approach, pore-water pressure.

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 ANALISIS PENURUNAN PADA TIMBUNAN DENGAN PREFABRICATED VERTICAL DRAIN (PVD) MENGGUNAKAN DATA HASIL UJI CPTu

2020 ◽  
Vol 3 (1) ◽  
pp. 69
Author(s):  
Tomy Gunawan ◽  
Alfred Jonathan S ◽  
Ali Iskandar
Keyword(s):  
Pore Pressure ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soil Parameters ◽  
Cone Penetration ◽  
Vertical Drain ◽  
Prefabricated Vertical Drain ◽  
Soil Settlement ◽  
Hydrostatic Level ◽  
Settlement Analysis

Investigation of soil is important to do in the planning of building construction such as foundations, piles, roads, etc. To find out the bearing capacity and parameters of the soil where a building will be built. Investigation of the soil can be done in various ways, one of which uses an electrical cone penetration test with pore water pressure. In the embankment project for the calculations on the soil so that it can be known about the settlement in soil and the length of time it reaches the hydrostatic level. Cone penetraton test is reqired and the results produce data in the form of cone resistance (qc), blanket friction (fs) and pore pressure (u) which will be processed in the CPET-IT program in order to produce soil parameters that will be used for soil settlement analysis. To find out the settlement of embankment soil, it will be supported by finite difference program. Results of studies on general is to find the effectiveness of embankment using prefabricated vertical drain (PVD) and without prefabricated vertical drain (PVD).AbstrakPenyelidikan terhadap tanah penting untuk dilakukan pada perencanaan konstruksi bangunan seperti pondasi, timbunan, jalan, dll. Untuk mengetahui daya dukung dan parameter-parameter tanah tempat akan dibangunnya sebuah bangunan Penyelidikan tanah dapat dilakukan dengan berbagai macam cara salah satunya adalah menggunakan  uji sondir elektrik dengan tekanan air pori. Pada proyek timbunan memerlukan perhitungan pada tanahnya agar dapat diketahui besarnya penurunan pada tanah dan lama waktu tanah mencapai keadaan hidrostatis. Sehingga dilakukan uji sondir secara elektrik dan dari hasil uji sondir menghasilkan data berupa tahanan konus (qc), gesekan selimut (fs) dan pore pressure (u) yang akan diolah kedalam program CPET-IT agar menghasilkan parameter-parameter tanah yang akan digunakan untuk analisis penurunan pada tanah.Untuk mengetahui besarnya penurunan pada tanah timbunan maka akan dibantu program berbasis elemen higga. Hasil studi secara umum menunjukkan seberapa besar efektivitas pada timbunan dengan menggunakan prefabricated vertical drain (PVD) dan tanpa prefabricated vertical drain (PVD).

scholarly journals Total and Effective Stresses in Backfilled Stopes during the Fill Placement on a Pervious Base for Barricade Design

Minerals ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 38 ◽  
Author(s):  
Jian Zheng ◽  
Li Li ◽  
Yuchao Li
Keyword(s):  
Analytical Solution ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
The Self ◽  
Underground Mines ◽  
Filling Rate ◽  
Effective Stresses ◽  
Arching Effect ◽  
The Stability ◽  
Backfilled Stopes

Backfill is increasingly used in underground mines worldwide. Its successful application depends on the stability of the barricades built at the base of the stopes to hold the backfill in place, which in turn depends on the knowledge of the pore water pressure (PWP) and stresses during, or shortly after, the placement of the slurried backfill. Until now, self-weight consolidation is usually considered for the estimation of the PWP. There is no solution available to evaluate the total and effective stresses during, and shortly after, the filling operation. As excess PWP can simultaneously be generated (increased) and dissipated (decreased) during the backfilling operation, effective stresses can develop when the filling rate is low and/or hydraulic conductivity of the backfill is high. The arching effect has to be considered to evaluate the effective and total stresses in the backfilled stopes. In this paper, a pseudo-analytical solution is proposed to evaluate the effective and total stresses in backfilled stopes during the backfill deposition on a permeable base, by considering the self-weight consolidation and arching effect. The proposed solution is validated by numerical results obtained by Plaxis2D. A few sample applications of the proposed solution are shown.

Excess Pore Pressures During Undrained Clay Creep

1973 ◽  
Vol 10 (1) ◽  
pp. 12-24 ◽  
Author(s):  
Thomas L. Holzer ◽  
Kaare Höeg ◽  
Kandiah Arulanandan
Keyword(s):  
Pore Pressure ◽  
San Francisco ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Excess Pore Pressure ◽  
Time Behavior ◽  
Pore Pressures ◽  
Undrained Creep ◽  
Excess Pore

The objective of this presentation is to examine experimentally how the excess pore-water pressure is related to the mechanism for undrained creep of San Francisco Bay mud. The results are discussed in the context of creep mechanisms previously suggested in the literature and based on laboratory testing.It is found that shear strains occurring during undrained creep are directly related to a gradual but significant increase in excess pore pressure and, hence, reduction in effective stresses. The increase in magnitude of the pore pressure is, except immediately after the creep shear stress is applied, solely a function of the initial consolidation stress and consolidation period. The magnitude of the long-term build-up may be related to the amount of secondary compression which would occur during drained conditions. It increases with the organic content of the soil and decreases with the degree of remolding. The mechanism for the increase in pore-water pressure may be explained by drainage of water from micropores in the microstructure into the macrostructure.Unless one accounts for the increase in pore pressures during undrained creep, it is unlikely that one will be successful in formulating a generally valid mathematical model for stress–strain–strength–time behavior based on laboratory testing.

scholarly journals Pore Pressure Response to Groundwater Fluctuations in Saturated Double-Layered Soil

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Hongwei Ying ◽  
Lisha Zhang ◽  
Kanghe Xie ◽  
Dazhong Huang
Keyword(s):  
Pressure Distribution ◽  
Pore Pressure ◽  
Dimensionless Parameter ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Layered Soil ◽  
Excess Pore Pressure ◽  
Groundwater Fluctuation ◽  
Excess Pore Pressures ◽  
Excess Pore

Analytical solutions are developed for one-dimensional consolidation of double-layered saturated soil subjected to groundwater fluctuations. The solutions are derived by an explicit mathematical procedure using Duhamel’s theorem in conjunction with a Fourier series, when groundwater fluctuation is described by a general time-dependent function and assumed to be the pore water pressure variations at the upper boundary. Taking as an example the harmonic groundwater fluctuation, the relevant response of the excess pore water pressure is discussed in detail, and the main influencing factors of the excess pore pressure distribution are analyzed. A dimensionless parameterθhas been introduced because it significantly affects the phase and the amplitude of excess pore pressures. The influences of the coefficients of permeability and compressibility of soil on the excess pore pressure distribution are different and cannot be incorporated into the coefficient of consolidation in double-layered soil. The relative permeability ratio of two clayey soils also plays an important role on the curves of the distributions of the excess pore pressures. The effects of the thickness of the soil layer on the excess pore pressure distribution should be considered together with the dimensionless parameterθand the permeability and compressibility of the double-layered soil system.

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