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Embankment design on soft clays
162A 923184 Anisotropie stress influence on the permeability of weaklyeemented sandstones Bruno, M S; Bovberg, C A; Nakagawa, F M Rock Mechanics as a M~tidisciplinary Science: Proc 32nd U S Symposium, Norman, 10-12 July 1991 P375-383. Publ Rotterdam: A A Balkema, 1991 The influence of anisotropic stress on the permeability of weakly-cemented sandstone is described. Sandstone samples were subjected to triaxial stress conditions of up to 15MPa. Results show that the permeability reduction is strongly influenced by the direction of the applied loading with respect to the direction of fluid flow, and suggest that the magnitude of permeability reduction is related to the amount and strength of intergranular cementation. Axial loading alone on the cylindrical rock samples produced relatively little change in longitudinal permeability. Subsequent radial loading, however, reduced the permeability more significantly. These results suggest that horizontal permeability anisotropy in the field, even within some unfractured formations, may be strongly influenced by the direction of maximum compressive stress.
Compressibility, swelling and consolidation See also: 923003, 923335, 923371 923185 CoUapse behaviour of a compacted soil during inundation Tadepalli, R; Fredlund, D G Can Geoteck J 1/28, N4, Aug 1991, P477-488 The collapse behaviour of a compacted, unccmented soil is examined from the viewpoint of unsaturated soil mechanics. Two sets of experiments were carried out, the first to relate the amount of collapse to dry density and water content, the second to study the effect of matrix suction (pore air pressure minus pore water pressure) on collapse. A unique relation is observed between changes in matric suction and resultant volume change during inundation. The theory of transient flow through unsaturated soil predicts behaviour in general agreement with that seen. 923186 Some engineering eharacteristies of a compacted laterie residual soil lndraratna, B; Nutalaya, P lmt J Geoteek Geoi Engug V9, N2, June 1991, P125-137 Mineralogy, gradation, compaction, CBR, and permeability characteristics were examined for a lateritic soil from Thailand in order to evaluate its potential as a constructional material. Good shear strength and CBR values were found, but with a tendency to brittleness and tensile cracking on the dry side of optimum moisture content or if excessively compacted. At 2% wetter than optimum, this mode of failure is suppressed and the material is suitable for embankments or dam cores. 923187 Smear effect of vertical drains on soft Bangkok clay Bergado, D T; Asakami, H; Alfaro, M C; Balasubramaniam, A S J Gemeeh E:q:q Div A S C E 1/117, NIO, Oct 1991, 1"15091530 The effects of smearing during installation of prefabricated vertical drains were examined in a full scale test embankment and in the laboratory, using a special apparatus. In the field, drains were installed using mandrels of two different sizes. Results indicate the smear zone is about twice the equivalent mandrel diameter. Horizontal permeability in the smear zone
is approximately equal to vertical permeability in the undisturbed zone. In the small mandrel area the settlement rate and final settlement were greater than in the large mandrel area. Predictions of the methods of Skempton and Bjerrum (1957) and of Aoka (1978) are compared to observed settlements. 923188 Embankment design on soft clays Ciniciogiu, S F; Togrol, E J Geoteeit Engng Di~ ASCE Vl17, N i l , Nov 1991, P16911705 t A design procedure for staged construction of embankments is presented in which critical state theory is employed and the plastic behaviour of normally consolidated clays taken into account. An intermediate line is constructed below the critical state line and effective stress states achieved by the soil element during the undrained loading stage are kept below this line, ensuring control of shear stresses induced in the soil body and maintaining an adequate factor of safety against shear failure. The procedure enables optimisation of length of consolidation pause periods. Results are presented for both isotropically and anisotropically normally consolidated soft clays. 923189 Hyperbolk method for consolidation analysis Tan, T S; Inoue, T; Lee, S L J Geoteelt E~fftg Div ASCE VII7, N i l , Nov 1991, P17231737 The hyperbolic method, based on the assumption that settlement versus time behaviour approaches a straight line in t/s v t diagrams after some period, has been recognised to work for consolidation estimation under infinitesimal strain conditions. Analytical and numerical approaches with both field and laboratory data are used to demonstrate that the method can be extended to conditions including finite strain and material nonlinearity or inhomogeneity. The method is simple and accurate to use in the field and where material properties are difficult to quantify. 923190 3D reservoir simulation of Ekofisk compaction drive Sulak, R M; Thomas, L K; Boade, R R J Pet Teclmoi V43, NIO, Oct 1991, P1272-1278 Unexpected subsidence of 3m of the seafloor of the Ekofisk reservoir was discovered in 1984. Procedures developed to describe the phenomenon are illustrated. The model uses the finite element code D Y N A F L O W to describe the subsidence and a 3D three phase model to simulate the reservoir. Compressibility of the chalk as a function of porosity, rock type, reservoir pressure, and position in the reservoir is included together with the arch effect, which depends on mechanical properties of overburden and reservoir rock, porosity and pore pressure distribution in the reservoir, and reservoir geometry. 923191 Impo~ of a desiccated crust on d a y settlements Duncan, J M; Javette, D F; Stark, T D Soils Fmmd V31, N3, Sept 1991, P77-90 Differential settlements have been observed at clay sites with a desiccated crust even when there is no apparent systematic diffe~euce in clay thickness or induced stress. Investigations at sites in San Francisco Bay Mud and Boston Blue Clay suggest that where this behaviour is observed, spatial variation in preconsolidation pressure is the most important cause of differential settlement. A simple probabilistic method is presented for settlement prediction under the conditions
© 1992 Pergamon Press Ltd. Reproduction not permitted
Compressibility, swelling and consolidation See also: 923003, 923335, 923371 923185 CoUapse behaviour of a compacted soil during inundation Tadepalli, R; Fredlund, D G Can Geoteck J 1/28, N4, Aug 1991, P477-488 The collapse behaviour of a compacted, unccmented soil is examined from the viewpoint of unsaturated soil mechanics. Two sets of experiments were carried out, the first to relate the amount of collapse to dry density and water content, the second to study the effect of matrix suction (pore air pressure minus pore water pressure) on collapse. A unique relation is observed between changes in matric suction and resultant volume change during inundation. The theory of transient flow through unsaturated soil predicts behaviour in general agreement with that seen. 923186 Some engineering eharacteristies of a compacted laterie residual soil lndraratna, B; Nutalaya, P lmt J Geoteek Geoi Engug V9, N2, June 1991, P125-137 Mineralogy, gradation, compaction, CBR, and permeability characteristics were examined for a lateritic soil from Thailand in order to evaluate its potential as a constructional material. Good shear strength and CBR values were found, but with a tendency to brittleness and tensile cracking on the dry side of optimum moisture content or if excessively compacted. At 2% wetter than optimum, this mode of failure is suppressed and the material is suitable for embankments or dam cores. 923187 Smear effect of vertical drains on soft Bangkok clay Bergado, D T; Asakami, H; Alfaro, M C; Balasubramaniam, A S J Gemeeh E:q:q Div A S C E 1/117, NIO, Oct 1991, 1"15091530 The effects of smearing during installation of prefabricated vertical drains were examined in a full scale test embankment and in the laboratory, using a special apparatus. In the field, drains were installed using mandrels of two different sizes. Results indicate the smear zone is about twice the equivalent mandrel diameter. Horizontal permeability in the smear zone
is approximately equal to vertical permeability in the undisturbed zone. In the small mandrel area the settlement rate and final settlement were greater than in the large mandrel area. Predictions of the methods of Skempton and Bjerrum (1957) and of Aoka (1978) are compared to observed settlements. 923188 Embankment design on soft clays Ciniciogiu, S F; Togrol, E J Geoteeit Engng Di~ ASCE Vl17, N i l , Nov 1991, P16911705 t A design procedure for staged construction of embankments is presented in which critical state theory is employed and the plastic behaviour of normally consolidated clays taken into account. An intermediate line is constructed below the critical state line and effective stress states achieved by the soil element during the undrained loading stage are kept below this line, ensuring control of shear stresses induced in the soil body and maintaining an adequate factor of safety against shear failure. The procedure enables optimisation of length of consolidation pause periods. Results are presented for both isotropically and anisotropically normally consolidated soft clays. 923189 Hyperbolk method for consolidation analysis Tan, T S; Inoue, T; Lee, S L J Geoteelt E~fftg Div ASCE VII7, N i l , Nov 1991, P17231737 The hyperbolic method, based on the assumption that settlement versus time behaviour approaches a straight line in t/s v t diagrams after some period, has been recognised to work for consolidation estimation under infinitesimal strain conditions. Analytical and numerical approaches with both field and laboratory data are used to demonstrate that the method can be extended to conditions including finite strain and material nonlinearity or inhomogeneity. The method is simple and accurate to use in the field and where material properties are difficult to quantify. 923190 3D reservoir simulation of Ekofisk compaction drive Sulak, R M; Thomas, L K; Boade, R R J Pet Teclmoi V43, NIO, Oct 1991, P1272-1278 Unexpected subsidence of 3m of the seafloor of the Ekofisk reservoir was discovered in 1984. Procedures developed to describe the phenomenon are illustrated. The model uses the finite element code D Y N A F L O W to describe the subsidence and a 3D three phase model to simulate the reservoir. Compressibility of the chalk as a function of porosity, rock type, reservoir pressure, and position in the reservoir is included together with the arch effect, which depends on mechanical properties of overburden and reservoir rock, porosity and pore pressure distribution in the reservoir, and reservoir geometry. 923191 Impo~ of a desiccated crust on d a y settlements Duncan, J M; Javette, D F; Stark, T D Soils Fmmd V31, N3, Sept 1991, P77-90 Differential settlements have been observed at clay sites with a desiccated crust even when there is no apparent systematic diffe~euce in clay thickness or induced stress. Investigations at sites in San Francisco Bay Mud and Boston Blue Clay suggest that where this behaviour is observed, spatial variation in preconsolidation pressure is the most important cause of differential settlement. A simple probabilistic method is presented for settlement prediction under the conditions
© 1992 Pergamon Press Ltd. Reproduction not permitted