Showing papers on "Pore water pressure published in 1974"

Theory of consolidation for clays

Abstract: A large strain theory of one-dimensional consolidation for normally consolidated and overconsolidated or aged clays which considers the changes in compressibility and permeability during the consolidation and includes secondary compression, shows that the consolidation process in clays is controlled by indexes of compression, recompression, secondary compression, permeability, and the critical pressure ratio, load-increment ratio, and the magnitude of total compression. A decreasing compressibility during the consolidation process accelerates the rates of compression and the excess pore pressure dissipation, whereas a decreasing permeability retards them. The influence of the load-increment ratio on the rate of consolidation depends on the ratio of permeability index to compression index. The secondary compression has a significant influence on the compression curves; however, it does not affect the dissipation of pore-water pressure appreciably. A fraction of the excess pore-water pressure equal to the critical pressure ratio dissipates at a rapid rate; the remaining pore pressure dissipates at a slower rate.

Lake Kinneret sediments: Nutrient composition of the pore water and mud water exchanges1

Abstract: Various elements of the pore water of Lake Kinneret scdimcnts have been analyzed and their fluctuations observed during 20 months at four stations, with concomitant measurements of bottom currents, temperature, and benthic flora. Dissolved iron reaches its maximum solubility at the beginning of turnover. The exchangeable phosphorus stems to be the iron-bound fraction and its concentration in the pore water increases simultaneously with the reduction of sulfates and precipitation of iron sulfide, but its release is controlled by the calcium phosphate equilibria. This mechanism explains how the rate of release of phosphorus is only 0.8 mg m-2day-” and how the Kinneret sediments play the role of a sink as far as phosphorus is concerned. Ammonia is produced by an intense process of ammonification and its rate of release reaches 25 mg mM2 day-l. The internal nutrient load is compared to the external one. Since there is evidence that the winter-spring Peridinium bloom can be supported solely by the internal load, working hypotheses are provided concerning the relationshiD between the release of nutrients from the mud and the nature of the Goom. The importance of regeneration of nutricnts in the epilimnion of lakes has been noted ( Klccrckopcr 1953; Lawacz 1969). However, a certain amount of trypton reaches the bottom and undergoes additional mineralization. In stratified and productive lakes, the “internal nutrient load” due to bottom regeneration may compctc with the amount of nutrients brought to the lake from the drainage area (Bachofen 1960; B urns and Ross 1971) and the qualitative composition of the internal load certainly plays a role in algal productivity and the predominance of certain species, The rcgcneration of nutrients in the sediments is a two step process: the first one, which includes bacterial activity an d physicochemical reactions, determines the concentration of nutrients in the pore water ’ Contribution of the Israel Oceanographic & Limnological Research Ltd., Kinneret Limnological Laboratory. (PW) ; the second one governs their release through the mud-water interface. Our purpose here is to show the fluctuations of nutrient concentration in pore water of Lake Kinneret sediments as a function of the bottom conditions, currents, temperature, flora, and of the sedimentation rate and composition of the trypton at different stations. We thank M. Hatab for his help in fieldwork. WC are grateful to H. L. Goltcrman for reviewing the manuscript. Methods and procedures The composition of the pore water of the sediments of four stations at different depths (A, 42 m; C, 30 m; F and G, 25 m: Fig. 1) was measured for 20 months (January 1971 to August 1972). Stations A, C, and G were sampled about twice a month ( 37 sets of data). Station F was sampled more frequently, especially at the turnover period ( 55 sets of data). The mud and water were sampled with LIMNOLOGY AND OCEANOGRAPI-IY 489 MAY 1974, V. 19(3)

Soil Motion Computations by Characteristics Method

Abstract: In this study the characteristics method is applied to wave propagation corresponding to earthquake intensities in models of unsaturated and saturated soils. Shear waves developed in linear, or in "strain-softening" materials, and pressure waves in viscoelastic materials are considered. One-dimensional transmissions in unsaturated layered systems are treated first, then the method is applied to two-dimensional simulations by the "lattice work" approach. The latter method may also be extended to treat three-dimensional problems. Pore pressure transients are investigated in a one-dimensional approach based on Darcy's law. By prescribing reductions of void ratios as a function of time, zones of potential liquefaction may be identified and their movement traced. By use of a lattice work representation, transient pore pressure within the upstream portion of an earth dam are investigated. /ASCE/

Time dependent strain following faulting of a porous medium

Abstract: A fracture that redistributes shear stress in a porous medium produces local fluid pore pressure changes. Decay of this pore pressure due to flow causes strain. Using the theory of Biot, I calculate the time dependent stress, strain, and pore pressure fields after a plane fracture whose offset varies sinusoidally in the direction of slip. The results permit construction of arbitrary one-dimensional slip functions by Fourier synthesis. In particular, I investigate the simple crack made from two edge dislocations. The fracture surface is slowly reloaded after an initial shear stress drop, and the shear strength of the material adjacent to the fracture varies with time. This behavior is useful in explaining earthquake foreshocks, aftershocks, and delayed creep. For the simple crack the frequency of aftershocks associated with the reloading decays like t−1.

Mass physical properties, sliding and erodibility of experimentally deposited and differently consolidated clayey muds (Approach, equipment, and first results)

Abstract: On experimentally deposited kaolinite, illite, and Ca-bentonite consolidated under their own load or by additional vertical pressure, the progress of compaction in relation to excess pore water pressure, mass physical properties, gravitational mass movements in a tilted tank, and erodibility under running water in a flume were studied. The very low consolidated sediments near the mud/water interface do not obey the generally used theory in soil mechanics. They show a different, non-linear relationship between void ratio or water content and depth below the sedimentary surface on the one hand, or effective overburden pressure and shear strength on the other. The same is true of other physical properties such as permeability, which changes considerably with depth and time of consolidation. High sedimentation rates on slopes induce shallow sediment flow, whereas at low rates and critical slope angles different types of slope failures including the breaking up of water-rich sediment into sharp boundered blocks are observed. Flume studies on soft clay muds show three different types of erosion: continuously suspending, discontinuous erosion of crumbs or shreds, and wavy deformation of the clay surface with disintegration of particles from the crests. The critical tractive stress depends not only on clay type, void ratio, and shear strength, but significantly also on the ‘geologic history’of the clay (i.e. deposition from thin suspension or dense slurry, fabric, consolidation and swelling generating minute inhomogeneities etc.). The experiments may lead to a better understanding of all mechanical processe's including pore-water flow taking place near or not far below the sediment/ water interface.

Second-order theory of flow in three-dimensional deforming media

Abstract: A basic assumption in groundwater flow theory is that consolidation occurs in the vertical direction only. In real three-dimensional media this condition is not satisfied a priori. In the present paper a second-order theory of flow is developed including the consideration of horizontal soil displacements. The ‘strain nucleus’ or ‘tension center’ approach, well-known in thermoelasticity, is used. The formulation of the theory shows that volume strain in a point P of the system may be viewed as being distinctly contributed by pore pressure variations in and outside P. The latter contribution, which vanishes identically in one-dimensional media, is called the ‘three-dimensional effect’. Solutions applied to a semi-infinite mechanically homogeneous medium show that the three-dimensional effect is negligible and the diffusion equation is good as long as the ratio W between the average depth and the thickness of aquifer is ≥2, whatever its areal exent. If W < 2 (shallow and thick aquifers), the above effect produces an additional compression of soil during an intermediate stage after pumping has begun and hence a slowing down of the rate of pressure head decline, as has been predicted by standard solutions. The most critical conditions occur for W=1/2, i.e., in unconfined aquifers. The present theory also allows for a short qualitative analysis of the ‘Noordbergum effect’ or reverse water level fluctuation.

Stability of Slopes in Frozen Soil, Mackenzie Valley, N. W.T.

Abstract: A field study of landslides has shown that certain types of mass movement in the Mackenzie Valley, N.W.T. are associated with shear failure in frozen soil. These land-slides have been classified on a descriptive basis as being block and multiple retrogressive slides. A detailed description of the characteristic morphology, and of the soil and permafrost conditions at these slides has been presented.Quantitative analysis of slides at a site on the Mountain River are consistent with the view that failure occurs through frozen soil with the base of the slide in unfrozen clay. It appears that high pore water pressures control the available shear strength in the unfrozen clay and that the long term strength of the permafrost soils is governed by a frictional resistance.

Apparatus for collecting deep-sea sediment pore water

Abstract: The collector filters and encapsulates pore water, in-situ, from unconsolted sediments. A pressure casing mounts a collection cylinder having a valved inlet opening for receiving the sediment pore water through a 1 micron filter. The valve is spring pressed to a closed position and opens in response to hydrostatic pressure. A second valve closes the inlet to the spring-pressed poppet valve. Trigger means initiate the opening of the second valve to expose the poppet valve to the hydrostatic pressure. Preferably, the exposure is accomplished in a delayed manner to assure proper positioning of the sampler before admission of the pore water to the cylinder.

Thaw–Consolidation Tests on Undisturbed Fine-grained Permafrost

Abstract: A series of thaw–consolidation tests on undisturbed frozen samples of Arctic soils is described. The tests were carried out in a special oedometer, and thawing was induced by the application of a sudden constant increase in surface temperature. Settlements, pore water pressures, and rates of thaw are measured, and interpreted in the light of current theories of heat transfer and thaw–consolidation. Excellent agreement is obtained between predicted and observed thaw rates, using published thermal properties. The observed pore pressures and settlements also are consistent with predicted behavior.These test results on a variety of undisturbed permafrost samples increase the level of confidence when applying the theory of consolidation for thawing soils to natural permafrost deposits.

Erosion of kaolinite clay by flowing water

Abstract: A set of experiments with a saturated kaolinite-water system is described in which the dependence of the erosion rate on the hydraulic bed shear, salinity (NaNO 3 ), temperature, zeta potential and ion-exchange capacity was studied. In all tests the eroding and pore water was the same, ranging from distilled deionized water to 0.100 M solution of NaNO 3 . The results indicate that temperature is an important variable in pure water. Its influence decreases rapidly with increasing salinity and decreasing particle size. The effect of sodium nitrate concentration was much more pronounced with finer fractions of kaolinite. No relation between erodibility and zero potential or cation and anion exchange capacity was found.

Strength and Stress-Strain Characteristics of Cemented Deep-Sea Sediments

Abstract: It has become increasingly apparent that the engineering properties of ocean sediments differ significantly from land sediments. The suspicion is that interparticle bonding may be the major cause of the difference.

Earthquake prediction and oriented microcracks in rocks

Abstract: VARIATIONS in the ratio of compressional wave velocities and shear wave velocities, presage some earthquakes1. The ratio first decreases, but just before the earthquake it returns to, or rises above, the original value. An attractive model has been proposed by Nur2. Briefly, he suggested that anelastic expansion of the rock (dilatancy) reduced the velocities. With the subsequent rise of the pore pressure of water, the velocity increases again. The increased pore pressure also weakens the rock, resulting in an earthquake. All that effects the velocity of compressional waves more than the velocity of shear waves, giving the apparent variation in their ratio.

Results of full-scale observations on the dam at the Serebrynka-I hydroelectric plant

Abstract: 1 The dam core, constructed from moraine soil placed in water, was homogeneous from the seepage standpoint and had a dense composition and a low permeability 2 When the moraine soil is placed in water, a small excess pore pressure develops (10–15% of the weight of the overlying soil), which is very quickly dissipated, within a period of 2–3 days This circumstance permits eliminating the control of the rate of raising the structure during construction 3 The rock-fill shells, placed in layers up to 18 m thick, without applying special compaction measures, during the period of dam construction and reservoir filling settled significantly, whose relative value can be estimated at 7–8%, of which 2–3% corresponds to the settlement caused by wetting of the rock fill The relative value of the settlement of the dam core during the same period was about 1% 4 Because of the significant difference between settlement of the core and of the shells, sliding of the latter with respect to the core took place This sliding occurred along the transition layers and was attended by formation of several longitudinal cracks in the shells, the transition layers, and the core 5 The three-year period of dam operation and the results of full-scale observations showed that the cracks formedin the dam did not cause any complications in the operation of this structure

Artificially Simulating the Geological History of Clay.

Abstract: : This report is concerned with the description of the development and research application of a high pressure consolidation cell, designed to simulate the progressive burial of clay sediments. The results of a series of 9 high pressure tests, 4 low pressure tests with elevated temperature and 4 constant rate of strain tests are presented. These results include information on the e-log p relationships, variations in pore pressure, and pore water chemistry and fabric changes; preliminary explanations of the observed phenomena are offered. Attention is drawn to geological implications and reference also made to future trends in the research program.

Nonlinear motion equations for a non-Newtonian incompressible fluid in an orthogonal coordinate system

Abstract: This paper describes the work carried out to investigate the pore pressures occurring in secondary consolidation. A theoretical approach and an experimental technique was developed in order to conduct the study. By considering compression to occur only due to water leaving the soil it was possible to derive an expression for the dissipation of pore pressure in the secondary phase. By further simplified assumptions which are based on experimental observations, the above general solution was reduced to a simple formula which predicted the observed behaviour of pore water pressures during secondary consolidation.

Rheology on the drawing zone in glass spinning

Abstract: This paper describes the work carried out to investigate the pore pressures occurring in secondary consolidation. A theoretical approach and an experimental technique was developed in order to conduct the study. By considering compression to occur only due to water leaving the soil it was possible to derive an expression for the dissipation of pore pressure in the secondary phase. By further simplified assumptions which are based on experimental observations, the above general solution was reduced to a simple formula which predicted the observed behaviour of pore water pressures during secondary consolidation.

Experimental study of clay deformability in terms of initial fabric and soil-water potential

Abstract: The energy of a clay-water system can be expressed as a function of its characteristic water retention curve, which represents the relationship between its water content and its total soil-water potential or soil-suction, where the latter is the difference between the free energy of the water in the soil and that of pure water in a free surface condition. Hence, the work required to remove an infinitesimal quantity of water from the soil is a measure of the combined effects of the forces holding the water in the soil, and, with the exception of cementation bonds, it can be considered to include implicitly the effects of the fundamental interaction forces that influence the deformation characteristics of the soil. The total soil-water potential of a soil varies with its water content, mineralogy, solutes present in the pore water, and soil fabric, as well as other parameters of the system. Soil fabric is taken herein to represent the geometrical arrangement of clay particles and their associated interparticle distances. This work is directed toward providing some indication of (a) the effect of fabric on the soil-water potential of a kaolinite clay and (b) the relationship between initial soil-water potential and the deformation characteristics of the soil.

Soil mechanics - new horizons. chapter 4: behaviour of unsaturated soils

Abstract: Chapter 4 is presented under the following sub-headings: introduction; retention of water by soils; flow of water through soils; prediction of pore pressures; immediate deformation under load; time-dependent deformations. The covering abstract for the book is IRRD no. 211916. /TRRL/

Influence of pore water pressure on the engineering properties of intact rock

Abstract: : The objective of this investigation was to determine the influence of pore water pressure on the engineering properties of rock. A series of drained triaxial compression tests were performed on Vermont marble in order to study strain rate effects. Isotropic compression and triaxial compression tests under drained and undrained conditions were performed on Berea sandstone, Salem limestone, Vermont marble, and Barre granite. The drained and undrained tests resulted in a single Mohr-Coulomb failure envelope in terms of effective stress for each rock type. In all cases the failure envelope was concave to the normal stress axis. The modified Mohr-Coulomb failure envelope plotted as a straight line for each rock type.