Values Of Pore Water Pressure Research Articles

Soil physical properties related to soil structure

The aim of this paper is to clarify the effect of soil aggregation on soil physical and chemical properties of structured soils both on a bulk soil scale, for single aggregates, as well as for homogenized material. Aggregate formation and aggregate strength depend on swelling and shrinkage processes and on biological activity and kinds of organic exudates as well as on the intensity, number and time of swelling and drying events. Such aggregates are, most of all, more dense than the aggregated bulk soil. The intra-aggregate pore distribution consists not only of finer pores but these are also more tortuous. Thus, water fluxes in aggregated soils are mostly multidimensional and the corresponding water fluxes in the intra-aggregate pore system are much smaller. Furthermore, ion transport by mass flow as well as by diffusion are delayed, whereby the length of the flow path in such tortuous finer pores further retards chemical exchange processes. The chemical composition of the percolating soil solution differs even more from that of the corresponding homogenized material the stronger and denser the aggregates are. The rearrangement of particles by aggregate formation also induces an increased apparent thermal diffusivity as compared with the homogenized material. The aggregate formation also affects the aeration and the gaseous composition of the intra-aggregate pore space. Depending on the kind and intensity of aggregation, the intra-aggregate pores can be completely anoxic, while the inter-aggregate pores are already completely aerated. The higher the amount of dissolved organic carbon in the percolating soil solution, the more pronounced is the difference between the gaseous composition in the inter- and in the intra-aggregate pore system. From the mechanical point of view, the strength single aggregates, determined as the angle of internal friction and cohesion, depends on the number of contact points or the forces, which can be transmitted at each single contact point. The more structured soils are, the higher the proportion of the effective stress on the total stress is, but even in single aggregates positive pore water pressure values can be revealed. Dynamic forces e.g. due to wheeling and/or slip processes can affect the pore system as well as the composition of the soil by: (1) a rearrangement of single aggregates in the existing inter-aggregate pore system resulting in an increased bulk density and a less aerated and less rootable soil volume, (2) a complete homogenization, i.e. aggregate deterioration due to shearing. Thus, the smaller texture dependent soil strength coincides with a more intensive soil compaction due to loading. (3) Aggregate deterioration due to shearing results in a complete homogenization, if excess soil water is available owing to kneading as soon as the octahedral shear stresses and the mean normal stresses exceed the stress state defined by the Mohr-Coulomb failure line. Consequently, normal shrinkage processes start again. Thus, the rearrangement of particles and the formation of well defined single aggregates even at the same bulk density of the bulk soil both affect, to a great extent, various ecological parameters. Environmental aspects can also be correlated, or at least explained with the processes in soils, as a major compartment of terrestial ecosystems, if the physical and chemical properties of the structure elements and their composition in the bulk soil are understood.

Evalution of Function Assessment Methods for Ground Water Drainage Facilities of Sarukuyoji Landslide Area

This report presents the methods of quantitative assessment for the function decrease of ground drainage facilities with the progress of time after completion of them by using data of pore water pressure and drain water volume which change depending on time series.For development of the methods, we used data which were observed at Sarukuyoji Landslide area. Two methods are considered in this study. At the tension zone where has sliding mass of high permeability, the method involves estimating the value of rain sensitive pore water pressure and drain water from horizontal drainage boring by using equation (2), (3), and comparing to this with the value of the reference period. At the compression zone water has sliding mass of low permeability, the method is to evaluate yearly changes of the observed data of pore water pressure just before the snowfoll.

A finite element model for the analysis of wave induced stresses, displacements and pore pressures in an unsaturated seabed I: theory

This paper presents the theoretical development of the differential equations governing wave induced stresses, displacements and pore pressures in an unsaturated seabed. These governing coupled flow and deformation equations are presented for plane strain conditions subject to a sinusoidal wave loading on the seabed. The finite element formulation of the resulting equations is also presented. The governing flow and deformation equations, reduced by assuming that all variables behave in simple harmonic form, are discretized in one-dimensional vertical space using the Galerkin finite element method. Simple linear two-noded elements are used to which closed form solutions of the element stiffness matrices and load vectors are presented. Solution algorithms for the flow and deformation equations are described. Nodal values of horizontal displacement, vertical displacement and pore water pressure are output in simple harmonic form, as are the total and effective components of stress at the element centroids.

Pore Water Pressures and Ground Motions Monitored During the 1985 Chiba-Ibaragi Earthquake

Following the successful measurements of accelerations and pore water pressure rise during the 1980 September 25 earthquake, a set of piezometers embedded in the sand deposit on the Owi No. 1 Island in Tokyo Bay became out of order. A new set of piezometers was again installed at the same site in a bid to monitor pore water pressures awaiting a reasonably large earthquake to come. On October 4, 1985, an earthquake of magnitude of 6.2 shook the area of Tokyo Bay and pore water pressure rise was again monitored, together with the accelerations on the ground surface and in the deposit at a depth of 10 m. The maximum ground surface acceleration recorded was 71 gal and the pore water pressure increase at depths of 6 m and 14 m was 4.5% and 5.3% of the mean effective confining pressure, respectively. On the basis of the laboratory test results performed previously on undisturbed soil specimens, an estimate was made of the pore water pressures that might be produced in the deposit by the seismic shaking with a maximum acceleration of 71 gal. The estimated values of pore water pressure at the depths of 6 m and 14 m were shown to be somewhat larger than that registered during the earthquake.

Pore Water Pressures Measured in Sand Deposits During an Earthquake

A set of piezometers was embedded in sand deposits on a reclaimed island in Tokyo Bay and a seismograph was placed on the ground surface nearby in order to monitor simultaneously in-situ pore water pressures and horizontal accelerations during earthquakes. During the September 25, 1980 earthquake, the instruments registered increases in pore water pressures corresponding to 19% and 16% of the effective overburden pressure at depths of 6.0 M and 14.0 M, respectively. At the same time, a maximum horizontal acceleration of 95 gal was registered at the ground surface. Laboratory cyclic triaxial tests had been performed on undisturbed soil specimens obtained from this site using a large diameter sampler. Based on the laboratory test data, an estimate was made of the pore water pressures that might be produced in the deposit by seismic shaking of a maximum acceleration of 95 gal. The estimated values of pore water pressure were shown to be in good agreement with the pore water pressures registered during the earthquake. (Author/TRRL)

Fundamentals of Liquefaction under Cyclic Loading

The mechanism of progressive pore pressure increase during undrained cyclic simple shear tests on saturated sands has been examined in detail. The concepts developed provide a better understanding of the physical processes leading to liquefaction of horizontal sand deposits during earthquakes. A quantitative relationship between volume changes occurring during drained cyclic tests and the progressive increase of pore water pressure during undrained cyclic tests has been developed. The use of this relationship enables the build-up of pore water pressure during cyclic loading to be computed theoretically using basic effective stress parameters of the sand. The application of the theory to the case of undrained cyclic simple shear tests with uniform stress controlled loading is illustrated. Values of progressive pore water pressure increases predicted theoretically agree reasonably well with the nature of pore water pressure increases observed experimentally.