Showing papers on "Pore water pressure published in 1968"

Permeability of granite under high pressure

Abstract: The permeability of Westerly granite was measured as a function of effective pressure to 4 kb. A transient method was used, in which the decay of a small incremental change of pressure was observed; decay characteristics, when combined with dimensions of the sample and compressibility and viscosity of the fluid (water or argon) yielded permeability, k. k of the granite ranged from 350 nd (nanodarcy = 10−17 cm2) at 100-bar pressure to 4 nd at 4000 bars. Based on linear decay characteristics, Darcy's law apparently held even at this lowest value. Both k and electrical resistivity, ρs, of Westerly granite vary markedly with pressure, and the two are closely related by k = Cρs−1.5±0.1, where C is a constant. With this relationship, an extrapolated value of k at 10-kb pressure would be about 0.5 nd. This value is roughly equivalent to flow rates involved in solute diffusion but is still a great deal more rapid than volume diffusion. Measured permeability and porosity enable hydraulic radius and, hence, the shape of pore spaces in the granite to be estimated. The shapes (flat slits at low pressure, equidimensional pores at high pressure) are consistent with those deduced from elastic characteristics of the rock. From the strong dependence of k on effective pressure, rocks subject to high pore pressure will probably be relatively permeable.

Influence of Temperature Variations on Soil Behavior

Abstract: Volume and pore water pressure variations that develop in saturated soils due to temperature changes are expressed in terms of the thermal expansion of the soil components, compressibility of the soil and physico-chemical effects. While the compression index of remolded illite was found independent of temperate, the higher the temperature the lower the void ratio at any given consolidation pressure. The magnitude of pore pressure change accompanying temperature change under undrained conditions is controlled primarily by the compressibility of the soil and thermal expansion of pore water. Results are useful for assessing the effects of temperature variations on properties of soils, the assessment of necessary laboratory temperature control during undrained tests, and the study of physico-chemical phenomena in soils.

Electrical resistivity changes in saturated rocks during fracture and frictional sliding

Abstract: Changes in electrical resistivity were observed as a function of compressive stress in a variety of crystalline rocks that were subjected to confining pressure of up to 5 kb and to pore pressure of water of 500 bars In the majority of the rocks, resistivity increased slightly up to about half the fracture stress; just the reverse effect has been noted elsewhere for rocks that were apparently partially saturated Beyond half and particularly within about 20 per cent of the fracture stress, resistivity dropped typically by an order of magnitude This sharp decrease corresponded closely to an increase in porosity, or dilatancy, which took place under compressive stress Detailed study of one rock, Westerly granite, showed that changes in resistivity and, hence, porosity with stress were insensitive to effective pressure, when stress was normalized with respect to fracture stress This suggests that fracture occurred at a critical crack porosity that was pressure independent The changes in resistivity with stress that accompany frictional sliding on a fault are insignificant when the measurement volume contains the fault, even though faulted rock under pressure can support high stress

Pore Pressures, Consolidation, and Electrokinetics

Abstract: The pore-water pressures that develop when an electric field is introduced into a soil mass are shown to depend upon the voltage distribution and the ratio of the electrokinetic and hydraulic permeabilities of the soil. Thus, the magnitude of the pressures at a point depends upon electrode geometry. The time necessary for the development of these pore-water pressures is shown to be predictable by use of the theory of consolidation. The rate of pore-pressure development is dependent upon the hydraulic permeability of the soil and not upon its electrokinetic permeability. Whether soil stabilization occurs as a result of the development of negative porewater pressures or destabilization occurs due to positive pore water pressures, depends upon the boundary conditions at the electrodes. Secondary effects, from the point of view of large-scale engineering works, are associated with alterations in soil pH and conductivity. Laboratory and field test data are presented to substantiate the arguments presented.

Summary. the influence of geological features of clay deposits on the design and performance of sand drains.

Abstract: SAND DRAINS HAVE BEEN USED TO ACCELERATE THE CONSOLIDATION OF SOFT CLAY FOUNDATIONS OF EMBANKMENTS FOR OVER 30 YEARS. DURING THIS PERIOD MANY OBSERVATIONS OF FIELD RATES OF SETTLEMENT AND AN INCREASING NUMBER OF PORE PRESSURE MEASUREMENTS HAVE LED TO INCONCLUSIVE OPINIONS AS TO THE EFFICIENCY OF SAND DRAIN INSTALLATIONS. FOLLOWING A REVIEW OF THE LITERATURE, THE RESULTS OF RECENT FIELD MEASUREMENTS OF RATES OF SETTLEMENT AND PORE PRESSURE DISSIPATION OF CLAY FOUNDATION FOR EARTH EMBANKMENTS WITH AND WITHOUT SAND DRAIN INSTALLATIONS ARE COMPARED WITH PREDICTIONS BASED ON LABORATORY AND IN SITU TESTS. IT IS SHOWN THAT THE REAL DRAINAGE BEHAVIOR OF A DEPOSIT AS A WHOLE DEPENDS ON THE GEOLOGICAL DETAILS OF ITS FORMATION. QUITE SMALL LAYERS, VEINS OF SILT ALONG FISSURES, OR ORGANIC INCLUSIONS CAN TRANSFORM THE PERMEABILITY OF THE MASS COMPARED WITH THAT OF SMALL SAMPLES. /A/RRL/

Soil mechanics and foundations

Abstract: SOIL MECHANICS IS DISCUSSED IN RELATION TO STRUCTURES FABRICATED OF SOIL MATERIALS, AND TO STRUCTURES BUILT ON OR SUPPORTED BY SOIL DEPOSITS. DETAILED INFORMATION IS GIVEN ON MEASURING SETTLEMENT AND PORE PRESSURES, TYPES OF FOUNDATIONS, SEEPAGE AND FLOW THROUGH SOILS, SETTLEMENT OF FOUNDATIONS, BEARING CAPACITY OF FOUNDATIONS, EARTH PRESSURES, AND SLOPE STABILITY. /RRL/

Development of equipment for studying pore pressure effects in rock.

Abstract: : Evidence is presented that pore pressure has a measurable effect on rock strength and must be considered in any carefully conducted laboratory testing program for rock properties. It is not entirely clear, however, to what extent pore pressure affects test results for various rocks nor is it known how significant its effects might be in the design of structures founded in or upon rock. Thus the need for equipment to study pore pressure in rock is recognized. The report discusses the development of such equipment, its construction details, and operation. The pore pressure triaxial compression chamber is designed to accommodate 2 1/8-inch diameter specimens and operate at pressures up to 10,000 psi. Procedures relative to specimen preparation and saturation are described. Typical results are presented to demonstrate the reliability of the apparatus. The relationship among volumetric strain, pore pressure, and axial and diametric strain is discussed with regard to the mechanism of brittle fracture of rock. (Author)

The Effect of Pressure, Temperature, and Loading Rate on the Mechanical Properties of Rocks

Abstract: The influence of confining pressure, pore-fluid pressure, temperature, and rate of loading on the strength and ductility of rocks is reviewed in this paper. Effects of pressure and temperature on the mechanical behavior of a large variety of rock types have been studied by means of triaxial compression tests, and indentation experiments have been used to evaluate the influence of loading rates at ambient temperature and pressure. Data relating the combined effects of all of these variables over a wide range of values are not available; therefore. the effects of independent variations of pressure, temperature, and loading rate are considered in detail and interactions between these parameters are evaluated under limited conditions.

Letters: Piezometer for Monitoring Rapidly Changing Pore Pressures in Saturated Clays

Abstract: A modified Imperial College Piezometer incorporating a differential pressure transducer is a highly sensitive pore pressure measuring device unaffected by the total pressure of the environment in which it is placed. It is sufficiently rugged for field installation and provides the option of field calibration in situ.

Strain rate influence on shear strength characteristics of a saturated kaolinitic clay

Abstract: STRAIN RATE EFFECTS ON SHEAR STRENGTH CHARACTERISTICS OF SATURATED KAOLINITIC CLAY IN RELATION TO ITS INITIAL SOIL STRUCTURE ARE STUDIED. SAMPLES EXHIBITING DIFFERENT INITIAL SOIL STRUCTURE HAVE BEEN OBTAINED BY ELECTROCHEMICAL TREATMENT. THE RATES OF STRAIN ADOPTED IN THIS INVESTIGATION ARE 0.03 (0.762), 0.0012 (0.03), 0.0006 (0.015), AND 0.00024 IN./MIN (0.006 MM/MIN). THIS INVESTIGATION MAINLY ATTEMPTS TO FOCUS ITS EFFECT ON RATE OF STRENGTH DECREASE WITH RESPECT TO SLOWER RATES OF DEFORMATION, EFFECTIVE PRINCIPAL STRESS RATIOS, STRAIN AT FAILURE, STRENGTH PARAMETER, AND PORE PRESSURE DEVELOPMENT. SINCE SOIL MASS DEFORMATION INVOLVES THE MICROSCALE MOVEMENTS AT A RATE COMMENSURATE WITH STRUCTURAL STATE OF SOIL, DISTINCTLY DIFFERENT BEHAVIOR IN RELATION TO INITIAL SOIL STRUCTURE HAS BEEN OBSERVED. A METHOD BASED ON SENSITOMETRY TO NUMERICALLY RATE THE STRUCTURAL DIFFERENCE IS ALSO DESCRIBED. /ASTM/

Embankment Pore Pressures During Construction

Abstract: Theoretical methods for predicting pore pressures in earth dams are reviewed, and observed pore pressure data from selected dams constructed by the Corps of Engineers (CE) and other agencies are summarized to indicate the development and magnitudes of construction pore water pressures in earth dams. Construction characteristics and pore pressure data from 10 CE dams, 24 USBR dams, and 9 foreign dams are summarized and compared. The study determined that because of the numerous factors which influence pore pressure buildup, broad conclusions for all earth dams are difficult to make and each dam must be treated individually with respect to predicting construction pore pressures. It is concluded that: (1) Provisions for internal drainage effectively relieve construction pore pressures in earth embankments; (2) pore-pressure ratios in embankment materials increase rapidly as placement-water content increases, especially above optimum water content; and (3) pore pressures increase with increasing dam height, but even low dams (less than 100-ft high) can develop large pore pressures.

Review of measurement of soil water variables and flow parameters

Abstract: SOIL WATER VARIABLES, PARTICULARLY IN PARTIALLY SATURATED SOILS, ARE AMONG THE MOST DIFFICULT SOIL MECHANICS VARIABLES TO MEASURE IN BOTH THE LABORATORY AND THE FIELD. PROBABLY AS A CONSEQUENCE OF THIS, THEIR USE IN SOIL MECHANICS HAS BEEN RATHER NEGLECTED. HOWEVER, NEW TECHNIQUES WHILE STILL BEING CRUDE, ARE ENABLING ADVANCES TO BE MADE IN THE INVESTIGATION OF THE ROLE OF SOIL WATER IN SOIL MECHANICS. THE COMMONLY USED VARIABLE OF WATER CONTENT IS DISCUSSED AND AN EFFECTIVE VALUE IS SHOWN TO BE DIFFICULT TO MEASURE IN THE FIELD IN MOST NATURAL SOILS. ON THE OTHER HAND, PORE WATER PRESSURE OR SOIL WATER POTENTIAL IS ENVIRONMENTALLY CONTROLLED AND IS AT LEAST THEORETICALLY EASIER TO DETERMINE, FURTHERMORE, WATER FLOW IN SOIL IS CONTROLLED BY POTENTIAL GRADIENTS AND CONSEQUENTLY CHANGES IN MOISTURE STATUS OF SOILS CAN ONLY BE PREDICTED IN TERMS OF POTENTIAL. ALSO, EFFECTIVE STRESS CONCEPTS FOR PARTIALLY SATURATED SOILS SUGGEST THAT SOIL WATER EFFECTS ON SOIL ENGINEERING PARAMETERS ARE BEST STUDIED IN TERMS OF SOIL WATER POTENTIAL. SOIL WATER POTENTIAL CAN BE MEASURED IN THE FIELD BY PIEZOMETERS OR TENSIONMETERS, POROUS BLOCKS (E.G. GYPSUM BLOCKS) AND VAPOUR PRESSURE TECHNIQUES SUCH AS HUMAN HAIR HYGROMETERS AND THERMOCOUPLE PSYCHROMETERS. THE RANGE OF EACH TECHNIQUE AND THE ADVANTAGES AND DISADVANTAGES OF EACH ARE BRIEFLY DISCUSSED. FUTURE DEVELOPMENTS OF THESE TECHNIQUES ARE ALSO SUGGESTED. FLOW PARAMETERS, E. G. PERMEABILITY AND WATER CAPACITY FUNCTIONS ARE ALSO REQUIRED FOR WATER FLOW STUDIES IN SOILS. IN PARTIALLY SATURATED SOILS, THESE CANNOT BE CONSIDERED TO BE CONSTANTS, BUT FUNCTIONS OF THE SOIL WATER POTENTIAL. THESE FUNCTIONS CAN NOW READILY BE DETERMINED IN THE LABORATORY, BUT THE TRUE REPRESENTATIVE FUNCTIONS CAN ONLY BE DETERMINED IN THE FIELD. WHILE NO TECHNIQUES OF FIELD DETERMINATION HAVE BEEN ADEQUATELY DEVELOPED, OBVIOUS METHODS DO SUGGEST THEMSELVES. /AUTHOR/

The effects of tides on sub-soil pore-water pressures at a site on the proposed shoreham by-pass

Abstract: MEASUREMENTS ARE DESCRIBED MADE AT THE SITE OF THE SHOREHAM BY-PASS, CLOSE TO THE RIVER ADUR, TO EXAMINE THE EFFECTS OF TIDAL VARIATIONS IN RIVER LEVEL ON THE PORE-WATER PRESSURES IN THE NEARBY SUBSOILS. THE PERIOD OF OBSERVATION INCLUDED SPRING TIDES WHICH WERE CLOSE TO THE HIGHEST TIDE EVER RECORDED AT SHOREHAM. APPARATUS ASSEMBLED TO OBTAIN AUTOMATIC CONTINUOUS RECORDS OF PORE-WATER PRESSURES AND TIDAL LEVEL IN THE RIVER USING CONVENTIONAL FIELD PIEZOMETERS IS DESCRIBED. AT A DISTANCE OF SOME 80 M (250 FT) FROM THE RIVER IT WAS SHOWN THAT THE EFFECTS OF THE FLUCTUATING TIDAL LEVEL WERE SMALL. CHANGES IN RIVER LEVEL OF 3.81 M (12FT 6IN) RESULTED IN CHANGES OF UP TO 5.51 M (1FT 8IN) HEAD OF WATER IN SUBSOIL PORE-WATER PRESSURES. THE MEAN PORE-WATER PRESSURE PROFILE REPRESENTED A NORMAL HYDROSTATIC CONDITION IN CLOSE AGGREMENT WITH THE MEASURED STANDING WATER TABLE. TIDAL DATA IS GIVEN WHICH MAY BE OF ASSISTANCE DURING THE CONSTRUCTION OF THE NEW RIVER ADUR BRIDGE. THE RESULTS OF IN-SITU PERMEABILITY TESTS HAVE BEEN USED TO CALCULATE VALUES OF THE COEFFICIENTS OF CONSOLIDATION FOR THE CLAY STRATA. FROM THESE COEFFICIENTS A MODIFIED SETTLEMENT-TIME RELATION HAS BEEN OBTAINED FOR A SECTION OF THE BRIDGE APPROACH EMBANKMENT WHICH INDICATES THAT SETTLEMENT MAY OCCUR 3 OR 4 TIMES MORE RAPIDLY THAN CALCULATED FROM THE RESULTS OF NORMAL LABORTARY CONSOLIDATION TESTS. ON THE BASIS OF EXPERIENCE AT OTHER SITES, THE MODIFIED CALCULATIONS MAY STILL UNDERESTIMATE THE ACTUAL RATE OF CONSOLIDATION IN THE FIELD. /A/RRL/