Supernormal fluid pressures in sedimentary rocks of southern Ontario-western New York State

342A 926021 Subsidence due to pumping from layered soil - a perturbation theory Fallou, S N; Mei, C C; Lee, C K Int J Num Anal Meth Geomech V16, N3, March 1992, P157187 Groundwater pumping is a known cause of subsidence. Starting from a basis of Hantush's approximation for well hydraulics in a leaky aquifer, subsidence due to pumping for a system of three layers of comparable thickness, an aquitard sandwiched between two aquifers, is examined using a perturbation analysis. The upper aquifer is taken as phreatic, the lower artesian. The aquitard has much lower permeability and higher compressibility than the aquifers, and a vertical line pump withdraws water from the bottom of the lower aquifer. Soil subsidence is largely due to deformation of the aquitard layer. Effects of compressibility contrast are examined. 926022 Elevation changes associated with groundwater withdrawal and reinjection in the Wilmington area, Los Angeles coastal plain, California Testa, S M Proc 4th International Conference on Land Subsidence, Houston, 12-17 May 1991 P485-502. Publ IAHS Press: Wallingford, 1991 Subsidence in the Wilmington area due to oil production led to measured decreases of elevation up to 9m in the period 1928-1974, although water injection, commenced in 1953, stabilised most areas by 1966. Subsidence prior to significant oil production and subsequent uplift have been observed in adjacent areas. Strong correlation is seen between these movements and the changes in piezometric head. Localised movement is the sum of individual pumping and injection influences. The primary factor reflects movement of piezometric head in the three principal aquifers. Elevation changes attributable to the various factors are estimated. 926023 Land subsidence due to thermal water withdrawal: the case of Abano Terme, Northern Italy Brighenti, G Proc 4th International Conference on Land Subsidence, Houston, 12-17 May 1991 P515-523. Publ IAHS Press: Wailing)Cord, 1991 Abano Terme is the main centre of the Euganean thermal basin. Thermal waters, at up to 86 deg C, circulate freely in fractured carbonate rock. The main aquifer is a limestone complex, with Quarternary alluvial aquifers superincumbent. Excessive withdrawal of thermal waters led to rapid fall in the piezometric level (2.5m/yr in 1970-73). Management of the volume pumped has allowed water table stabilisation. Surface subsidence still occurs, at 20mm/yr in 1989 but at a decreasing rate, with no major structural damage reported.

Measurement of water pressure and its effects 926024 Supernormal fluid pressures in sedimentary rocks of southern Ontario-western New York State Raven, K G; Novakowski, K S; Yager, R M; Heystee, R J Can Geotech J I/'29, N1, Feb 1992, P80-93 Fluid pressures up 1.7 times hydrostatic have been measured at depths 50-310m in low permeability argillaceous Paleozoic rock around the Canada-USA border. Submersible pressure

transducers with straddle packers and multiple-packer casings were used in the measurement. Possible explanations for these supernormal pressures are examined in the light of available geological information and field test data. Gas migration and accumulation from deep distant sources via permeable vertical pathways is considered the most likely cause. Implications for regional groundwater flow and underground waste disposal are briefly discussed.

926025 Teosiometers - theory, construction, and use Stannard, D I Geotech Test J VI5, NI, March 1992, P48-58 The tensiometer, used to measure matric potential in a soil has the basic components of a porous surface (usually a ceramic cup) connected to a pressure sensor via a water filled conduit. The porous cup, buried in the soil, transmits soil water pressure to a measuring device. Measurement theory is outlined and construction, applications, and installation of tensiometers discussed. Variations in design allow optimisation of particular characteristics, such as accuracy, response time, cost, ruggedness, extent of data collection, or range of measurement conditions.

Properties of Rocks and Soils Composition, structure texture and density See also." 926206

926026 Porosity and packing of Holocene river, dane, and beach sands Atkins, J E; McBride, E F Bull Am Assoc Petrol Geol V76, N3, March 1992, P339-35~ Porosity and packing were determined for 174 samples ol surficial and shallow buried (up to 17m) unconsolidated Holocene sands by examination of thin sections. Deposition porosity, porosity size distribution, and packing are described for sands of beach, river point or braid bar, and eolian dune origin. Porosity does not decrease significantly with depth over the interval examined. Correlation is seen been grain size and oversized pores but not between total porosity and oversized pores. Variations in the measured parameters are discussed considering the depositional environments.

926027 Total stress probe determination of clay slurry density Tan, S A; Liang, K M; Tan, T S; Karunaratne, G P Geotech Test J V15, N1, March 1992, P59-64 Results of slurry consolidation tests in the laboratory indicated that above t.5 times the liquid limit, horizontal and vertical total stresses are equal. On this basis, an attempt was made to estimate the density profile in a hydraulic fill from the gradient of total stress with depth, obtained using a vertically inserted total stress probe. Field measurements at a reclamation site are presented. The calculated density profile is in good agreement with that obtained using a gamma backscatter density gauge.

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