Pore water pressure

About: Pore water pressure is a research topic. Over the lifetime, 11455 publications have been published within this topic receiving 247670 citations. The topic is also known as: pwp.

Regional sand injectite architecture as a record of pore-pressure evolution and sand redistribution in the shallow crust: insights from the Panoche Giant Injection Complex, California

Abstract: Observations on outcrop of a regionally developed sand injectite are used to infer and estimate the pore-pressure conditions in the shallow crust that caused the fluidization and injection of tens of cubic kilometres of sand. The estimated pore-fluid pressures at the base of the injection complex (at 1500 m burial depth, below a regionally developed shale-dominated seal) are from 22.26 to 25.08 MPa, which respectively correspond to 0.81 and 0.95 lithostatic pressure. A theoretical basis for prediction of sand injection is defined and applied to the prediction of pore pressure at the time of sand injection, the depth at which seal failure occurred, and the density and granular content of the fluidized flow. Lateral variations in the style and abundance of sandstone intrusions are described and these all fit into a remarkably uniform tripartite division of parent units, an intrusive complex and an extrusive complex. A sill zone (intrusions are dominated by sills) occurs in a restricted stratigraphic interval 200–270 m thick. Location of the base of the sill zone is directly related to the thickness of the overburden, and an isobaric surface at the time of sand injection, the lithostatic equilibrium surface, is defined at the base of the sill zone. When the sills formed an extended period of supra-lithostatic pressure occurred within the sill zone.

Introduction and digest to the Special Issue on Chemical Effects of Water on the Deformation and Strengths of Rocks

Abstract: The important role of pore pressure in promoting such brittle processes as cataclasis, hydraulic fracturing, large-scale faulting, and earthquakes within the crust is widely accepted in geology and geophysics [Hubbert and Willis, 1957; Hubbert and Rubey, 1959; Handin, 1958; Handin et al., 1963; Brace and Martin, 1968; Healy et al., 1968; Raleigh et al., 1976; Sibson, 1973, 1980; Raleigh and Evernden, 1981]. Provided that fluid pressure is fully communicated with rock pore space, the effective normal stresses that control crack growth, macroscopic fracture, and friction are reduced by the magnitude of the fluid pressui'e. Beyond this physical effect of pore fluids, there are chemical effects of water on the strength of rocks that are also important in governing differential stresseg and flow in the continental crust. Some of these chemical effects of water on rock deformation have long been recognized.

Pore pressure measurement in saturated stiff soils

Abstract: Errors associated with the measurement of pore water pressures in saturated cemented soils during undrained triaxial shear are presented. Methods of modifying standard testing equipment to minimize these errors are described and experimentally evaluated. Replacing the null indicator with a pressure transducer of low compressibility and minimizing the volume of water in the pore water lines will reduce the error in measuring pore pressures from over 15% to less than 3%. Volume changes due to leakage and operation of the drainage valves can significantly alter the measured pore pressures. However, the volume changes can be minimized by enclosing the test specimens in thick rubber membranes and by using no-volume change ball type valves. In undrained triaxial compression at low consolidation pressures cemented soils create a film of water between the sample and membrane, and the lateral effective stress becomes zero.

Influence of shear and deviatoric stress on the evolution of permeability in fractured rock

Abstract: [1] The evolution of permeability in fractured rock as a function of effective normal stress, shear displacement, and damage remains a complex issue. In this contribution, we report on experiments in which rock surfaces were subject to direct shear under controlled pore pressure and true triaxial stress conditions while permeability was monitored continuously via flow parallel to the shear direction. Shear tests were performed in a pressure vessel under drained conditions on samples of novaculite (Arkansas) and diorite (Coso geothermal field, California). The sample pairs were sheared to 18 mm of total displacement at 5 mm/s at room temperature and at effective normal stresses on the shear plane ranging from 5 to 20 MPa. Permeability evolution was measured throughout shearing via flow of distilled water from an upstream reservoir discharging downstream of the sample at atmospheric pressure. For diorite and novaculite, initial (preshear) fracture permeability is 0.5–1 � 10 � 14 m 2 and largely independent of the applied effective normal stresses. These permeabilities correspond to equivalent hydraulic apertures of 15–20 mm. Because of the progressive formation of gouge during shear, the postshear permeability of the diorite fracture drops to a final steady value of 0.5 � 10 � 17 m 2 . The behavior is similar in novaculite but the final permeability of 0.5 � 10 � 16 m 2 is obtained only at an effective normal stress of 20 MPa.