Showing papers on "Pore water pressure published in 1972"

Expansion of Cavities in Infinite Soil Mass

Abstract: A GENERAL SOLUTION IS PRESENTED TO THE PROBLEM OF EXPANSION OF SPHERICAL AND CYLINDRICAL CAVITIES IN AN INFINITE SOIL MASS. THE SOIL IS ASSUMED TO BEHAVE AS AN IDEAL ELASTIC-PLASTIC SOLID, FOLLOWING THE COULOMB-MOHR FAILURE CRITERION AND EXHIBITING VOLUME CHANGES IN A PLASTIC REGION SURROUNDING THE CAVITY. BEYOND THE PLASTIC REGION THE SOIL IS ASSUMED TO BEHAVE AS AN ISOTROPIC, LINEARLY DEFORMABLE SOLID. IT IS SHOWN THAT THE PRINCIPAL PARAMETERS AFFECTING THE ULTIMATE CAVITY PRESSURE ARE: THE INITIAL GROUND STRESS, STRENGTH AND VOLUME CHANGE CHARACTERISTICS OF THE SOIL, AND AND THE RIGIDITY INDEX OF THE SOIL (DEFINED AS THE RATIO OF SHEAR MODULUS TO INITIAL SHEAR STRENGTH). NUMERICAL EXAMPLES SHOW THE USE OF THE DERVIED SOLUTIONS FOR COMPUTATION OF ULTIMATE CAVITY PRESSURE, EVALUATION OF PRESSUREMETER TESTS AND COMPUTATION OF POREWATER PRESSURE CAUSED BY PILE DRIVING. /ASCE/

Aftershocks caused by pore fluid flow

Abstract: Large shallow earthquakes can induce changes in the fluid pore pressure that are comparable to stress drops on faults. The subsequent redistribution of pore pressure as a result of fluid flow slowly decreases the strength of rock and may result in delayed fracture. The agreement between computed rates of decay and observed rates of aftershock activity suggests that this is an attractive mechanism for aftershockss.

Dilatancy, pore fluids, and premonitory variations of ts/tp travel times

Abstract: Nerseov et al. (1969) found that the travel-time ratio of shear and compressional waves, ξ = t s /t p varies prior to the occurrence of earthquakes in the Garm region, USSR. Laboratory results indicate that the decrease of ξ can result from dilatancy of rocks around the focal zone. The subsequent increase of ξ, which terminates with an earthquake, can be caused by the flow of ground water into the dilated zone. The increasing pore pressure weakens the rock and leads to the observed failure.

Hydraulic fracturing and mineralization

Abstract: The factors relevant to the mechanism of normal faulting and brecciation are discussed. Normal faults develop as the consequence of an increase in the magnitude of the differential stress above the critical limit under the prevailing pore water conditions. The accumulation of a body of hydrothermal solution on the fault zones under pressures greater than the pore water pressure, results in the extension of the faults by hydraulic fracturing. The abrupt drop in the pressure of the hydrothermal solution when fracturing occurs, causes the bursting apart of the rock into which the hydrothermal solution has permeated under high pressure, thus forming angular breccias. The fracture may be extended by hydraulic fracturing even though the differential stress decreases, provided the pressure of the hydrothermal solution on the fracture plane exceeds the pore water pressure by increasing amounts. Under these conditions the dip of each extension of the normal fault increases, and eventually the fracture develops as a vertical breccia zone.

Effect of pore pressure on the velocity of compressional waves in low‐porosity rocks

Abstract: The velocity V sub p of compressional waves has been measured in rock samples of low porosity to confining pressures P sub c of 2 kb for a number of different constant pore pressures P sub p. An effective pressure defined by P sub e = P sub c-nP sub p, n less than or equal to 1, is found to be the determining factor in the behavior of V sub p rather than an effective pressure defined simply by the differential pressure Delta P = P sub c-P sub p. As pore pressure increases at constant effective pressure, the value of n increases and approaches 1, but as effective pressure increases at constant pore pressure, the value of n decreases. These observations are consistent with Biot's theory of the propagation of elastic waves in a fluid-saturated porous solid.

Freezing and heaving of saturated and unsaturated soils

Abstract: ANALYSIS OF THE BEHAVIOR OF AIR--WATER, ICE--WATER, AND AIR--ICE INTERFACES SHOWS THAT THE APPARENT CONTACT ANGLE BETWEEN AN AIR--ICE INTERFACE AND THE WALL OF A SOIL PORE OUGHT TO VARY RAPIDLY WITH CHANGES IN PORE WATER PRESSURE AND ICE PRESSURE. THIS PAPER GIVES THE EXPECTED RELATIONSHIP AND SHOWS THAT COOLING OF FAIRLY DRY SOIL, WITH FREEZING NUCLEATED AT ONE SPOT, SHOULD CAUSE CERTAIN PORES TO FILL ABRUPTLY WITH ICE, THUS DEPLETING THE WATER CONTENT OF THE SURROUNDING SOIL. THIS CONCLUSION AGREES WITH AVAILABLE DATA. IT IS SUGGESTED THAT THE ICE PRESSURE IS SLIGHTLY GREATER THAN ATMOSPHERIC PRESSURE WHEN PORES FILL. LIMITED DATA AVAILABLE IN THE LITERATURE INDICATE THAT A GIVEN MOIST SOIL MAY OR MAY NOT HEAVE; WHEN IT DOES, THE ICE LENSES APPARENTLY FORM SOME DISTANCE BEHIND THE FREEZING FRONT. TO EXPLAIN THIS, THE CONCEPTS OF PRIMARY AND SECONDARY HEAVING ARE PROPOSED FOR SATURATED SOIL. PRIMARY HEAVING OCCURS WHEN THE BASE OF THE GROWING ICE LENS COINCIDES WITH THE LIMIT OF FREEZING, AND THE RATE OF HEAVING IS LIMITED BY THE RATE OF HEAT EXTRACTION. SECONDARY HEAVING IS BELIEVED TO OCCUR WHEN THE FREEZING EXTENDS BELOW THE NOMINAL BASE OF THE (VISIBLE) ICE LENS. ICE IN THE FROZEN PORES CAN MOVE, RELATIVE TO THE PARTICLES, AS AN INTEGRAL PART OF THE GROWING LENS. A SOLUTION MODEL OF SECONDARY HEAVING IS USED TO ILLUSTRATE AN INCREASE OF ICE PRESSURE FROM THE FREEZING FRONT TO THE BASE OF THE ICE LENS, WHICH WILL OCCUR AT A POINT WHERE ICE PRESSURE IS EQUAL TO THE OVERBURDEN PRESSURE. IT IS CONTENTED THAT SECONDARY HEAVING PRODUCES LARGER HEAVING PRESSURES THAN PRIMARY HEAVING AND EXPLAINS WHY PREVIOUS THEORIES UNDERSTIMATED THE MAXIMUM HEAVING PRESSURE OF SATURATED SOIL. IT IS INFERRED THAT WHENEVER HEAVING OCCURS AS THE FREEZING FRONT IS DESCENDING THROUGH THE SOIL, THE PROCESS MUST BE SECONDARY HEAVING. IT IS SUGGESTED THAT THE DEVELOPMENT OF SIGNIFICANT HEAVING PRESSURES BY UNSATURATED SOIL WILL ORDINARILY INVOLVE SECONDARY HEAVING AND THAT THE PRESSURE DEVELOPED IS LESS THAN THAT DEVELOPED BY THE SAME SOIL WHEN IT IS SATURATED. /AUTHOR/

The mechanical strength of unsaturated porous granular material

Abstract: Summary The influence of pore-water suction on the strength of a porous material is that it contributes a compressive load which increases the shear strength. When the material is unsaturated, the normal load or effective stress is due, in part to the continuous water at measured suction in unemptied pores, and in part to isolated bodies in nominally emptied pores at suctions approximating to the suction at emptying. When the material is draining from saturation, the effective stress σ is where S is the fraction of saturation, α is the fraction of the initial water content drained at the maximum suction, Psd is the prevailing pore water suction, and Psd is a suction passed through in reaching pSd at which the reduction of S is dS. When the material is rewetting, the relationship becomes where psw is now the prevailing suction during wetting and f is a distribution function of the degree of saturation such that δS is the fractional saturation removed in the suction range δsd at sd and regained in the suction range δsw at sw. msd is the maximum suction attained. The effective stress is revealed experimentally by unconfined compression tests on samples with imposed pore water suctions, and the dependence on this suction confirms reasonably that which is predicted by the theoretical formulas.

The freezing point of water in porous glass

Abstract: IT WAS EXPECTED THAT CAPILLARY THEORY WAS APPLICABLE TO WATER CONTAINED IN CONSOLIDATED POROUS MATERIALS AND THAT WATER IN BUILDING MATERIALS FROZE OVER A RANGE OF TEMPERATURES DETERMINED BY THEIR POROUS STRUCTURE AND BY THERMODYNAMICS. LOWERING OF THE FREEZING POINT OF WATER IN POROUS GLASS WAS STUDIED BY A DTA TECHNIQUE. THE SAMPLES CONAINED A SPECTRUM OF AVERAGE PORE SIZES. THE FREEZING-POINT LOWERINGS MEASURED FROM MELTING AND FREEZNG CURVES CORRELATED, AS PREDICTED BY SIMPLE CAPILLARY THEORY, WITH THE AVERAGE PORE SIZE OF THE SAMPLE. THIS RESULT IS DISCUSSED IN TERMS OF CAPILLARY-CONDENSATION THEORY AND THEORIES OF FROST DAMAGE IN POROUS MATERIALS. /AUTHOR/

Pore fluid and mineralogical studies of recent marine sediments; Bauer Depression region of East Pacific Rise

Abstract: Geochemical studies of sediments and pore fluids of recent deep sea sediments in the vicinity of the equatorial East Pacific Rise were carried out to delineate diagenetic and hydrothermal activity. Pore fluids were extracted onboard ship at in situ temperatures to yield the pore water data free of thermal artifacts. Dissolved Cl SO4, Mg, Ca, and K display remarkably few variations from bottom water concentrations even through various sediment types from CaCO8 ooze to siliceous ooze, red clay, and "hydrothermal" heavy metal muds. However, a few examples of enrichment of K were noted. Dissolved Mn and SiO2, in contrast, displayed marked enrichments, with solubilities likely controlled by rhodochrosite and sepiolite, respectively. No evidence for removals of dissolved components was found.

The Behavior of Piles Driven in Clay. I. An Investigation of Soil Stress and Pore Water Pressure as Related to Soil Properties

Abstract: THIS PAPER OUTLINES RESEARCH ON LARGE MODEL PILES AND SOME FULL-SCALE PILES DRIVEN INTO INSENSITIVE CLAY TO STUDY THE PHENOMENA OF LOAD TRANSFER AND THE EFFECT OF PILE DRIVING ON THE SOIL. IT IS DIVIDED INTO TWO PARTS. PART I DEALS WITH THE STRESS FIELD SET UP BY DRIVING A LARGE MODEL PILE INTO AN INSTRUMENTED CLAY BED AND THE STRESSES MEASURED FOR SOME FULL-SCALE TIMBER PILES. PART II PRESENTS AN EVALUATION OF THE LOAD CARRYING CAPACITY OF THE MODEL PILE AND COMPARES THE RESULTS WITH FULL-SCALE PILE LOAD TESTS. THE SOIL PROPERTIES ARE EVALUATED IN TERMS OF EFFECTIVE STRESS FOR AN ESTIMATE OF THE BEARING CAPACITY OF THE PILES. THE MEASURED SOIL DISPLACEMENTS NEAR THE SHAFT AND BASE AGREE WELL WITH PLASTIC THEORY, WHILE THE OBSERVED MAGNITUDE OF THE PORE PRESSURES IN THE CLAY DUE TO DRIVING ARE SMALLER AND THE RATE PORE PRESSURE DISSIPATION IS GREATER THAN EXPECTED THEORETICALLY. THE MAGNITUDE OF THE TOTAL AND EFFECTIVE RADIAL STRESSES SURROUNDING THE PILE IS MAINLY RELATED TO THE STRESS CHANGES IN THE SOIL DUE TO PLACING THE PILE, AND SUBSEQUENT STRESS CHANGES ARE RELATIVELY SMALL. ON THE OPTHER HAND, THE TANGENTIAL AND VERTICAL STRESSES VARY APPRECIABLY WITH TIME AND THE LATTER STRESSES DEPART CONSIDERABLY FROM ESTIMATES BASED ON ELASTIC THEORY, DUE TO LOCK-IN-SOIL STRESSES. AN APPROXIMATE THEORY IS PRESENTED TO ESTIMATE THE AVERAGE EFFECTIVE RADIAL STRESS ON THE PILE SHAFT IN CONNECTION WITH THE ULTIMATE SHAFT CAPACITY. THIS PROPOSED APPROACH IS SUPPORTED BY OBSERVATIONS IN SOME CLAYS OF LOW SENSITIVITY, BUT REQUIRES FURTHER RESEARCH IN OTHER TYPE OF CLAYS.

Primary Migration of Petroleum from Clay Source Rocks

Abstract: An important difficulty in explaining primary migration from compacting source rocks concerns timing. The commonly accepted compaction curves for clay rocks imply maximum fluid expulsion early in a clay's compaction history, whereas most accumulations clearly have been formed later, after burial to depths of several thousands of feet. It was shown recently that abnormally pressured clays have been abnormally pressured since burial to a shallow depth. It was concluded that the thicker clays in most sedimentary basins have been abnormally pressured to some extent. If this conclusion is correct, the expulsion of petroleum becomes reconcilable with the time of entrapment because (a) thicker source clays, e.g., more than 200 ft, or 60 m, initial thickness) are probably more important than thinner source clays, and (b) mean fluid expulsion from the thicker clays is retarded. In addition, most of the fluid in a thin clay is expelled under geothermal temperatures and essentially hydrostatic pressures (implied in early migration) over a small depth range, whereas fluid in a thick clay is exposed to geothermal temperatures and near-geostatic pressures over a much greater depth range. The protopetroleum thus may be subjected to higher temperatures and much higher pressures for a longer time, thereby facilitating its solution in the pore water. The pressure decrease that necessarily accompanies expulsion may lead to the release of petroleum from solution in the outer, compacting layer of clay, and the accumulation of a slug that could be expelled by capillary force aided by the fluid potential gradient.

Chemical Effects of Pore Fluids on Rock Properties

Abstract: Disposal of waste fluids into the subsurface may affect the mechanical properties and strength of the rock mass in two important ways When fluid is chemically inert, strength and ductility are reduced by increasing pore pressure When fluid is chemically active, the strength of the rock mass is further reduced through modification of the cohesive strength of its constituent grains in contact with the fluid Several experiments reveal that the strength of rocks and propagation of minute surface cracks are highly dependent on the moisture content of the rock Dilute solutions of aluminum and ferric iron salts, in addition to water, react with the surface structure of quartz and silicates and weaken the surface silicon-oxygen bonds by hydrolysis The result is a reduction in surface energy, surface cohesion, and breaking strength The coefficient of internal friction, however, remains unaltered The frictional characteristics of already-broken rocks may be significantly altered by the introduction of chemically active fluids Because of such manmade earthquakes as those near Denver and Rangely, Colorado, it is obvious that more sophisticated tests of rock properties should be made, particularly regarding the influence of pore-fluid pressure and chemistry, if problems caused by unexpected rock failure are to be eliminated

Earthquake Related Stresses At Rangely, Colorado

Abstract: The investigation of the Rangely oil field has shown that artificially raised reservoir pressure in the neighborhood of a fault could initiate sliding and trigger earthquakes. The pore pressure along the fault at the site and depth where most earthquake foci were located has been monitored. Knowledge of the local stress configuration was needed, however, to confirm the type and direction of slip along the fault, establish the critical pore pressure necessary for an unstable equilibrium, and provide a basis for critical pore pressure estimates in future research of earthquake control. The hydraulic fracturing method was used to determine the in situ stresses in the vicinity of the fault at a depth of more than 6,000 ft below surface. A newly drilled and cased well was extended by diamond coring and an appropriate 12-ft interval of solid rock was selected. The interval was packed-off and pressurized until fracture. Additional pumping extended the artificial fissure away from the well. With some limitations, the method of hydraulic fracturing appears to be suitable for stress measurements along other active faults where critical pore pressures could thus be predicted and hopefully prevented. (12 refs.)

Vertical and Horizontal Laboratory Permeability Measurements in Clay Soils

Abstract: Publisher Summary This chapter discusses the vertical and horizontal laboratory permeability measurements in clay soils The direct measurement of vertical k v and horizontal permeability, k h , of clay soils and the validity of Darcy's law in the materials may be of considerable importance in estimating pore water pressure dissipation, and settlement rates, few measurements with this as the specific purpose have been made The direct laboratory measurement of k h and k v may enable a better estimate of field consolidation behavior to be made in soils with either marked creep properties or a more pervious macro structure This first effect is clearly demonstrated by tests on one undisturbed and three remolded clays Tests to demonstrate the effect of the second point are, at present, being made Darcy's law was generally valid, the exception occurring in organic clay where the permeant was not in chemical equilibrium with the pore fluid and a changing k under constant hydraulic gradient occurred, possibly as a result of particle migration The new permeameter systems functioned well throughout the tests A possible difficulty in the interpretation of radial flow test results because of the smearing at the drains It can be solved by measuring the seepage pressure distribution across the sample base

A stochastic model for predicting seismic failure in a soil deposit

Abstract: Liquefaction of saturated sand deposits under seismic excitation is studied on the basis of a fatigue failure approach. The model includes a stochastic treatment of the input, of the soil response and of the cumulative pore pressure effects produced by cycling stresses in the soil. A method of establishing safety factors against liquefaction is also considered. Results obtained from analysis of a case history confirm the applicability of the model for engineering purposes.

Earth pressure measurement on a braced slurry-trench wall in soft clay

Abstract: EARTH PRESSURE CELLS WERE PLACED ON THE OUTSIDE OF A FOUNDATION WALL, 20 M HIGH AND 1 M THICK, THAT WAS CONSTRUCTED BY THE SLURRY-TRENCH METHOD IN SOFT CLAY. THE MAGNITUDE AND DISTRIBUTION OF TOTAL EARTH PRESSURE ON THE WALL WERE MEASURED BEFORE, DURING, AND AFTER EXCAVATION OF THE SOIL ON ONE SIDE OF THE WALL. DURING EXCAVATION THE WALL WAS SUPPORTED AT THREE LEVELS AND AT THE BOTTOM WHERE IT WAS KEYED INTO THE BEDROCK. THIS ARTICLE SUMMARIZES THE EARTH PRESSURE MEASUREMENTS AS WELL AS RELATED OBSERVATIONS OF GROUND SETTLEMENT, DEFLECTION OF THE WALL, PORE PRESSURE CHANGES AND STRESSES IN THE REINFORCING STEEL IN THE INSTRUMENTED PANEL. /AUTHOR/

The measurement of pore pressure during sampling

Abstract: A METHOD FOR MEASURING THE PORE PRESSURE CHANGES IN A SOFT CLAY DURING SAMPLING IS DESCRIBED A HYPODERMIC NEEDLE PIEZOMETER CONNECTED TO A VIBRATING-WIRE PORE PRESSURE TRANSDUCER IS BUILT INTO THE PISTON OF AN NGI FIXED PISTON SAMPLER THE RESULTS OF TWO TESTS CARRIED OUT DURING SAMPLING OF ONE PLASTIC CLAY AND OF ONE QUICK CLAY ARE GIVEN IN THE QUICK CLAY THE PORE PRESSURE IN THE SAMPLE ONE HOUR AFTER IT IS CUT IN THE GROUND IS SLIGHTLY NEGATIVE, AND BECOMES ZERO WITHIN A FEW HOURS THE CONSEQUENT SWELLING CAN EXPLAIN THE DISTURBANCE OF A MECHANICALLY UNDISTRUBED QUICK CLAY /AUTHOR/

Interstitial water studies on small core samples, Leg 22

Abstract: Interstitial waters from Leg 22 in the Indian Ocean revealed two unique results: Site 214, on the Ninetyeast Ridge, penetrated through a 30-meter sequence of fine-grained basalt and reentered hard, silty clay containing carbonate skeletal debris. Such a basalt layer may well have been impervious and extensive enough to seal off underlying (fossil) seawater of Paleocene age. However, except for a marked increase in calcium and a slight increase in chloride, no appreciable changes in pore fluid chemistry could be confirmed. Site 217, at the northernmost end of the Ninetyeast Ridge, demonstrated record concentrations of interstitial calcium in clayey nannofossil oozes and a relatively small but significant increment in chloride with depth. Presumably, these increments signal the existence of evaporitic sediments or evaporiteinfluenced brines at considerably greater depth than penetrated. INTRODUCTION A total of 125 sediment samples collected from eight Leg 22 sites was squeezed for interstitial water. Sediment samples were collected immediately following the recovery of the core by the removal of discrete segments of sediment-filled plastic liner (mini-cores). This sampling method is essentially the same as was used for the special geochemical studies carried out on Leg 15 (Horowitz et al., in press). In most instances a 10-cm mini-core was cut from the top end of a 150-cm core section. This sample was first used for the resistivity measurements reported elsewhere in this volume (Chapter 32). Mini-cores were split lengthwise and one-half the available sediment was squeezed. All samples were squeezed at ambient room temperature. When soft sediments were encountered, two contiguous minicores were removed in order to make punch-in electrode pH measurements. pH measurements were also made on the squeezed, unfiltered pore water immediately following recovery. The fluid was injected directly from the receiver syringe into an Orion miniature flow-through electrode. The water content of all samples was determined from weight loss upon oven drying of approximately 1 -g portions of sediment taken from the mini-cores prior to processing. Analytical methods were identical to those outlined in earlier volumes of this series. Most of the analyses and data reduction were performed by John Mahoney. The analytical data are summarized in Tables 1 and 2. 1 Contribution No. 3100 of the Woods Hole Oceanographic Institution. RESULTS AND DISCUSSION Rather than cover sites comprehensively, as in previous interstitial water studies, effort was concentrated on a few sites, from which a number of samples were analyzed to provide continuity of information. A total of 41 samples as selected from Site 212 in the Wharton Basin, about 1500 km northwest of Australia; Sites 214 and 217 on the Ninetyeast Ridge; and Site 218 in the southern portion of the Central Bengal Fan. A greater effort was made on this leg to squeeze pore fluid from consolidated sediment than previously. Sufficient water for analysis was obtained from moderately lithified sediments (water content as low as 18%). This may help account for the more marked evidence of diagenetic reactions, as discussed below. Site 212 At this site, in the Wharton Basin, clayey nannofossil oozes showed moderate depletion in K, Mg, and SO4 and a 2.5-fold increase in Ca. Alkalinity remained roughly constant at values little higher than in seawater when corrected for a systematic analytical error. The mean rate of accumulation for this site was 0.65 cm/1000 years. Site 214 Located on the crest of the Ninetyeast Ridge, in water depth of 1655 meters, this site revealed an upper sequence of foraminiferal and nannofossil ooze, becoming glauconitic toward the base of the Eocene at about 330 meters depth below the sea floor. A remarkable series of increasingly shallow water to possibly lagoonal sediments culminated in lignitic and volcanoclastic sediments interbedded with igneous extrusive rock. Interestingly, one sample was

Observed and predicted behavior of two embankments on clay

Abstract: FOR TWO EMBANKMENTS CONSTRUCTED ON DEEP DEPOSITS OF CLAY, COMPARISONS ARE MADE BETWEEN PREDICTED AND MEASURED SETTLEMENT, RATE OF SETTLEMENT, HORIZONTAL MOVEMENT AND EXCESS PORE PRESSURE DISSIPATION IT IS FOUND THAT DESPITE THE APPARENT ONE-DIMENSIONAL GEOMETRY OF THE EMBANKMENTS A ONE-DIMENSIONAL ANALYSIS UNDERESTIMATES THE SETTLEMENT, WHEREAS THREE-DIMENSIONAL ANALYSIS GIVE REASONABLE AGREEMENT BETWEEN MEASURED AND PREDICTED SETTLEMENT, RATE OF SETTLEMENT AND EXCESS PORE PRESSURE DISSIPATION HOWEVER, EVEN SUCH RELATIVELY REFINED ANALYSES DO NOT GIVE GOOD CORRELATION BETWEEN MEASURED AND PREDICTED HORIZONTAL MOVEMENTS /AUTHOR/

Consolidation of Clay Layer in Two Dimensions

Abstract: The consolidation of a clay layer in two dimensions is analyzed and a numerical method of solving the governing equation is described. The technique is tested by comparing values with results from a closed form solution and they agree well. However, substantial differences exist between previously published data on the dissipation of pore pressure from the core of an ideal dam obtained with an electrical analogy and new numerical results for the same problem. The influence of impeded drainage on the dissipation of pore pressure from a rectangular section of soil is studied in detail.

Field and laboratory studies of 'short-term' earthworks failures involving the Gault Clay in West Kent.

Abstract: An investigation into the factors involved in the pore water pressure and stability of earthworks in the Gault is presented The study is based on field measurements in cuttings and natural slopes, and on instrumented full scale embankment and cutting trials many of the characteristics displayed by the Gault is attributed to its sedimentary and postdepositional history and so an outline of the geologic history of the strata and its engineering significance is presented, Details are given of the nature and widespread occurrence of Pleistocene periglacial discontinuities and their implications on the stability of earthworks are discussed The trial embankment data includes the pore water pressure details before and during construction and the results of insitu permeability tests The embankment failed during construction as expected and the contribution towards instability made by pre-existing slip surfaces in the foundation are elucidated The cutting trial data includes the pore water pressure and ground displacement measurements made before, during and after the excavation of the cutting Details are given of the stability of the steeply inclined section of the slope which failed 15 weeks after construction Examples of cutting failures which occurred after a much longer period are presented in the discussion of the Maidstone By-Pass investigations The analyses of these failures and the recorded lateral slope displacements give an insight into the significance of progressive failure in the stability of the slopes, Post-failure movement of the slipped masses provide some data, on the shear strength mobilized along slip surfaces under low effective normal stresses