scholarly journals A method of estimating excess pore pressures beneath embankments on sensitive clays

1979 ◽  
Vol 16 (4) ◽  
pp. 691-702 ◽  
Author(s):  
K. T. Law ◽  
M. Bozozuk
Keyword(s):  
Pore Pressure ◽  
Plane Strain ◽  
Strain Curve ◽  
Elastic Response ◽  
Test Results ◽  
Pore Pressures ◽  
Laboratory Test Results ◽  
Pore Pressure Response ◽  
Excess Pore Pressures ◽  
Excess Pore

A laboratory testing program for predicting undrained excess pore pressures beneath embankments constructed on sensitive clays is reported. A study of the pore pressure response, based on Henkel's equation applied to triaxial and plane strain tests performed on marine clay from South Gloucester, Ontario, provides a basis for comparing behaviour under conditions of axisymmetry and plane strain. Comparison shows that (1) pore pressure is smaller in plane strain than in axisymmetric conditions; (2) a below-elastic response prevails at the prepeak stage of the stress–strain curve; and (3) there is an elastic response at the peak.Finite element and modified elastic methods are developed for estimating undrained excess pore-water pressures from laboratory test results. The estimated values are used to evaluate the effect of consolidation under the center of an embankment during construction. The procedure is illustrated with case records.

scholarly journals Incorporating chemical shrinkage volume into Gibson’s solution

2018 ◽  
Vol 55 (6) ◽  
pp. 903-908 ◽  
Author(s):  
Megan L. Walske ◽  
James Doherty
Keyword(s):  
Pore Pressure ◽  
Qualitative Assessment ◽  
Chemical Shrinkage ◽  
Cemented Paste Backfill ◽  
Pore Pressures ◽  
Pressure Development ◽  
Paste Backfill ◽  
Pore Pressure Response ◽  
Excess Pore Pressures ◽  
Excess Pore

Rapid filling of low-permeability cemented paste backfill (CPB) into underground stopes results in the generation of significant excess pore pressures. These are dissipated through conventional consolidation and shrinkage due to cement hydration. Gibson’s solution for excess pore pressures in an accreting sediment can be used to assess the self-weight consolidation of CPB in a stope. In this paper, numerical modelling is used to determine the chemical shrinkage–induced pore pressure response for hydration of CPB for an accreting material and the results presented in a series of dimensionless design charts. It is shown that superposition can be used to combine Gibson’s solution with the newly developed charts for chemical shrinkage–induced pore pressures. This allows a qualitative assessment of potential pore pressure development in a CPB backfilled stope.

Surpressions interstitielles développées par le fonçage dans les sols cohérents

1979 ◽  
Vol 16 (4) ◽  
pp. 814-827
Author(s):  
M. Peignaud
Keyword(s):  
Pore Pressure ◽  
Excess Pore Pressure ◽  
Overburden Pressure ◽  
Pore Pressures ◽  
Excess Pore Pressures ◽  
Plastic Clays ◽  
Excess Pore

The Laboratoire Régional des Ponts et Chaussées, Angers (France) has investigated the excess pore pressures developed during the driving of a piezometer probe at different rates on four sites. Attention is drawn to the important differences between the pore pressures measured during penetration and at rest.During driving, negative excess pore pressures are measured. When the piezometer is stopped the pore pressures become large and positive. For the soils tested, i.e., plastic to highly plastic clays, the maximum excess pore pressure at rest may be estimated from the total overburden pressure. [Journal translation]

A New Technique for Reduction of Excess Pore Pressures During Pile Driving

1974 ◽  
Vol 11 (3) ◽  
pp. 423-430 ◽  
Author(s):  
Robert D. Holtz ◽  
Per Boman
Keyword(s):  
Pore Pressure ◽  
Alternative Methods ◽  
New Technique ◽  
Excess Pore Pressure ◽  
Relative Reduction ◽  
Pile Driving ◽  
Pore Pressures ◽  
A New Technique ◽  
Excess Pore Pressures ◽  
Excess Pore

A new technique is described whereby excess pore pressures induced during pile driving in soft, varved silts and clays were economically reduced to a safe level. The technique was applied to piles at a bridge site south of Stockholm, Sweden, where a small slide had occurred during pile driving. A new paper–plastic drain was attached to the wood piles during driving, and two pulling tests indicated that the drain was undamaged under normal driving conditions. The excess pore pressure generated during the driving of some 13 test piles without drains and 48 piles with drains was measured. The data indicated at least a 50% relative reduction in excess pore pressure when the drain was used. In addition, the cost of the technique was considerably less than alternative methods for dealing with dangerous excess pore water pressures resulting from piling in similar soils. The technique has been successfully applied at two other piling sites in Sweden.

Analysis of the Pore Pressure Changes Following the Excavation of a Slope

1975 ◽  
Vol 12 (3) ◽  
pp. 429-440 ◽  
Author(s):  
Kurt D. Eigenbrod
Keyword(s):  
Pore Pressure ◽  
Field Data ◽  
Pressure Measurements ◽  
Pore Pressures ◽  
Field Evidence ◽  
Slope Excavation ◽  
Order Of Magnitude ◽  
Excess Pore Pressures ◽  
Pressure Changes ◽  
Excess Pore

In a numerical analysis the pore pressure changes due to excavation of a slope and the subsequent dissipation of excess pore pressures were calculated. The analytical results of the pore pressure changes due to unloading of a slope agree reasonably well with pore pressure measurements in comparable embankments. This suggests that pore pressures immediately after slope excavation can be predicted analytically in homogeneous materials.The results of an analysis dealing with the dissipation of excess pore pressures due to unloading can also be substantiated by field evidence; however, only few comparable field data are available. For many slopes it can be noted that the time for full dissipation is of the same order of magnitude as the time between excavation and failure. This suggests that many failures might be caused by the delayed equalization of pore pressures.

Evaluation of excess pore pressures and drainage conditions around driven piles using the cone penetration test with pore pressure measurements

1990 ◽  
Vol 27 (2) ◽  
pp. 249-254 ◽  
Author(s):  
P. K. Robertson ◽  
D. J. Woeller ◽  
D. Gillespie
Keyword(s):  
Pore Pressure ◽  
Large Diameter ◽  
Cone Penetration Test ◽  
Pressure Measurements ◽  
Penetration Test ◽  
Cone Penetration ◽  
Pore Pressures ◽  
Clayey Silt ◽  
Excess Pore Pressures ◽  
Excess Pore

Large-diameter steel pipe piles were driven as part of the foundations for the Alex Fraser Bridge near Vancouver, British Columbia. The piles penetrated through a normally consolidated marine clayey silt. As part of the geotechnical studies a multipoint piezometer was installed close to the pile group. A cone penetration test with pore pressure measurements (CPTU) was performed adjacent to one of the piles shortly after driving. During the CPTU through the clayey silt deposit, dissipation tests were performed to evaluate the pore pressures around the nearby pile. The CPTU results are compared with the pore pressures recorded at the multipoint piezometer, allowing for differences in radial distance from the piles. Excellent agreement was obtained between the CPTU and multipoint piezometer data, both showing large excess pore pressures around the piles. The CPTU dissipation data were also analyzed to evaluate the time required for dissipation of excess pore pressures around the piles. The upper half of the clayey silt deposit was inter bedded with thin sand and silt layers. The CPTU data showed that the thin sand layers were sufficiently large in extent to allow rapid dissipation of the pore pressures due to cone penetration but were not of sufficient extent to allow dissipation of the excess pore pressures from the much larger diameter piles. Key words: in situ, piles, pore pressures, CPT.

Consolidation of a soil layer subsequent to cessation of deposition

2005 ◽  
Vol 42 (2) ◽  
pp. 678-682
Author(s):  
Guofu Zhu ◽  
Jian-Hua Yin
Keyword(s):  
Pore Pressure ◽  
Soil Layer ◽  
Average Degree ◽  
Excess Pore Pressure ◽  
Triangular Distribution ◽  
Pressure Distributions ◽  
Pore Pressures ◽  
Degree Of Consolidation ◽  
Excess Pore Pressures ◽  
Excess Pore

It is necessary in certain cases to estimate the progress of consolidation in a soil layer that has ceased increasing in thickness over time. In this paper, the existing excess pore pressures for two time–thickness relations are used as the "initial" pore pressures for analysing the consolidation of soil subsequent to the cessation of deposition. Average degrees of consolidation of the soil layer are presented for one-way drainage and two-way drainage boundary conditions. The average degrees of consolidation are compared with those for uniform and triangular initial excess pore pressure distributions. It is found that the average degree of consolidation for one-way drainage boundaries can be estimated using the value for the triangular distribution. The average degree of consolidation for two-way drainage boundaries is bound by the averages for both the uniform and the triangular initial excess pore pressure distributions.Key words: consolidation, deposition, drainage, settlement, soil.

Effective-Stress Finite Element Analysis of Spudcan Penetration

2012 ◽  
Author(s):  
Jiang Tao Yi ◽  
Fook Hou Lee ◽  
Siang Huat Goh ◽  
Yu Ping Li ◽  
Xi Ying Zhang
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Analysis ◽  
Pore Pressure ◽  
Effective Stress ◽  
Excess Pore Pressure ◽  
Element Analysis ◽  
Pore Pressures ◽  
Excess Pore Pressures ◽  
Excess Pore

The numerical modeling of spudcan penetration involves technical challenges posed by large soil deformation coupled with significant material non-linearity. The Lagrangian approach commonly used for solid stress analysis often does not work well with large deformations, resulting in premature termination of the analysis. Recently, the Arbitrary Langrangian Eulerian (ALE) and the Eulerian methods have been used in spudcan analysis to overcome problems caused by the soil flow and large deformation. However, most of the reported studies are based on total stress analysis and therefore shed no light on the excess pore pressures generated during spudcan installation. As a result, much remains unknown about the long-term behaviour of spudcans in the ground, which is affected by the dissipation of excess pore pressures. This paper reports an effective-stress finite element analysis of spudcan installation in an over-consolidated (OC) soft clay. The Eulerian analysis was conducted using ABAQUS/ Explicit, with the effective stress constitutive models coded via the material subroutine VUMAT. The results demonstrated the feasibility of conducting effective-stress finite element analysis for undrained spudcan penetration in OC clays. The paper discusses the flow mechanism, stable cavity depths and bearing capacity factors when spudcan installation occurs in various OC soils. It was found that the pore pressure build-up concentrates in a bulb-shaped zone surrounding the spudcan. The size of the pore pressure bulb increases with increasing penetration. The maximum excess pore pressure, which is generated near the spudcan tip, is predominantly controlled by the undrained shear strength at the tip level.

scholarly journals A laboratory study of particle ploughing and pore-pressure feedback: a velocity-weakening mechanism for soft glacier beds

2008 ◽  
Vol 54 (184) ◽  
pp. 169-181 ◽  
Author(s):  
Jason F. Thomason ◽  
Neal R. Iverson
Keyword(s):  
Pore Pressure ◽  
Water Discharge ◽  
Fold Increase ◽  
Excess Pore Pressure ◽  
Measured Velocity ◽  
Pore Pressures ◽  
Pressure Diffusion ◽  
Pressure Feedback ◽  
Excess Pore Pressures ◽  
Excess Pore

AbstractIf basal-water discharge and pressure are sufficiently high, a soft-bedded glacier will slip over its bed by ploughing, the process in which particles that span the ice–bed interface are dragged across the bed surface. Results of laboratory experiments indicate that resistance to ploughing can decrease with increasing ploughing velocity (velocity weakening). During ploughing at various velocities (15–400 m a−1), till was compacted in front of idealized particles, causing pore pressures there that were orders of magnitude higher than the ambient value. This excess pore pressure locally weakened the till in shear, thereby decreasing ploughing resistance by a factor of 3.0–6.6 with a six-fold increase in ploughing velocity. Characteristic timescales of pore-pressure diffusion and compaction down-glacier from ploughing particles depend on till diffusivity, ploughing velocity and sizes of ploughing particles. These timescales accurately predict the ranges of these variables over which excess pore pressure and velocity weakening occurred. Existing ploughing models do not account for velocity weakening. A new ploughing model with no adjustable parameters predicts ploughing resistance to no worse than 38% but requires that excess pore pressures be measured. Velocity weakening by this mechanism may affect fast glacier flow, sediment transport by bed deformation and basal seismicity.

Effects of test procedure on flat dilatometer test (DMT) results in intermediate soils

2016 ◽  
Vol 53 (8) ◽  
pp. 1270-1280 ◽  
Author(s):  
F. Schnaid ◽  
E. Odebrecht ◽  
J. Sosnoski ◽  
P.K. Robertson
Keyword(s):  
Pore Pressure ◽  
Soft Clay ◽  
Test Procedure ◽  
Pressure Measurements ◽  
Dimensionless Velocity ◽  
Pore Pressures ◽  
Rate Effects ◽  
Excess Pore Pressures ◽  
Excess Pore ◽  
Flat Dilatometer Test

The evaluation of rate effects on the flat dilatometer test (DMT) can best be developed with some knowledge of the excess pore pressures generated during penetration, dissipation, and subsequent membrane expansion. While research that includes pore pressure measurements in the DMT has documented drainage conditions in clean sand and soft clay, further studies are required to determine the drainage conditions during the DMT in intermediate permeability soils, such as silts. For that purpose, a simple and inexpensive research device has been developed for monitoring pore pressures at the center of the DMT blade. Data using both a standard DMT and the modified research DMT from various tests in sand, silt, and clay have been compared in a space that correlates dimensionless velocity to degree of drainage. In this space, it is possible to evaluate whether partial drainage is taking place. Measurements indicate that the DMT is essentially undrained in soft clay and dominated by penetration pore pressures, is drained in clean sand and is partially drained in intermediate permeability soils, such as silt. A method is suggested to identify soils where partial drainage may influence the standard DMT results.

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