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Engineered piles to improve cyclic load capacity
48A 80mm. Finite element analysis indicated bending stresses induced in the unreinforced or lightly reinforced piles were insufficient to cause cracking. 921369 Modified Vlasov model for beams on elastic foundations Vallabhan, C V G: Das, Y C J Geotech Engng Dir ASCE Vl17, N6, June 1991, P956-966 The Vlasov and Leontev two parameter model of a beam on elastic foundations was developed as an improvement on the classical Winkler model. It requires the estimation of a parameter (gamma) which controls the decay of stress in the continuum and it has complex mathematical formulation. A method is shown which uses a unique iterative technique based on variational principles to solve for a consistent value of gamma, and the finite difference method to solve the fourth order differential equations. Results are available within 15-20 seconds on a PC, yet are consistent with those of sophisticated finite element solutions. 921370 Engineered piles to improve cyclic load capacity Poulos, H G; Sim, K B Marine Geotechnol V9, N2, April-June 1990, P131-140 Theoretical analysis using a boundary element approach was used to examine behaviour of five pile types (conventional, variable stiffness, variable diameter, belled base, belled insert) in soils representing uncemented and cemented calcareous sediments. Results indicate static and cyclic load performance is improved by altering the diameter and/or stiffness distribution along the pile. For cyclic loading conditions piles should be designed such that stress concentrations are minimised and the shape of the distribution of pile-soil shear stress is the same as that of the limiting skin friction. 921371 Effects of liquefaction-induced lateral spreading on pile foundations Miura, F; Stewart, H E; O'Rourke, T D Soil Dynam Earthq Engng VIO, N5, July 1991, P271-279 Pile failure during earthquakes often results from lateral ground movements due to soil liquefaction. Parametric studies are used to estimate maximum bending moment on piles subject to lateral ground displacement. Results suggest that the maximum bending moment on the pile is significantly affected by the presence of a non-liquefiable soil layer at the surface. If this is thick relative to the liquefiable layer, neither material nonlinearity nor stiffness of the liquefiable layer have significant effects on maximum bending moment on the pile. When this is not the case, stiffness of the liquefiable layer must be chosen with care when estimating bending moment.
921373 Settlement behaviour of non-linear soil around single piles subjected to vertical loads Kuwabara, F Soils Found II31, N1, March 1991, P39-46 Simplified nonlinear analysis is presented of distribution of vertical displacements in the soil around a pile whose end bearing contribution may be neglected. Nonlinearity of shear modulus and shear strain either based on laboratory data or according to a hyperbolic relation is assumed. Results are compared to those from a linear analysis using the boundary element method and field observations in published pile tests. Nonlinear analysis indicates greater shear strain concentration near the pile surface than in linear analysis. For practical application of theoretical elastic solutions, a shear modulus of 3 times that from conventional triaxial tests is recommended. 921374 Analysis of the interaction between a moderately thick circular plate and an isotropic elastic halfspace using a mixedvariational principle Faruque, M O; Zaman, M M Soils Found 1/31, NI, March 1991, P73-82 For many structural foundations, the plate is sufficiently thick that the effect of shear deformation on flexible response cannot be ignored, and thick plate theory must be used in analysis. This problem is tackled using a mixed variational approach, with which the plate deflection, plate bending moment, and shear forces are treated as independent variables and approximated using power series. Unknown coefficients associated with the approximation functions are evaluated by using the stationary properties of the variational functional. Numerical results are presented for a range of plate rigidities. 921375 Effect of construction on existing subway tunnels - a case study from Toronto Lo, K Y; Ramsay, J A Tunnlg Underground Space Technol V6, N3, 1991, P287-297 The case of the construction of the York Mills Centre Phase III over the Toronto subway is described. The soil is uniform dense grey silt. Large diameter caissons straddling the tunnel were used to transfer load to thesubsoil below the tunnel invert and minimise loading on the tunnels. Soil parameters were obtained by laboratory testing and back analysis of ground movements during excavation and construction. 2 and 3 dimensional finite element analyses were used to predict displacements along and around the tunnels. These data are compared to those measured.
921372 Analysis of foundation-elastic haifspace interaction using a mixed-variational approach Zaman, M; Faruque, M O; Uddin, N Soils Found V31, N1, March 1991, P27-38
921376 Edinburgh pile integrity testing technique McCavitt, N; Forde, M C; Batchelor, A J Proc 2nd International Conference on Foundations and Tunnels, London, 19-21 September 1989 V2, P293-299. Publ Edinburgh: Engineering Technics Press, 1989
Deflections, flexural moments, and contact stresses at the interface of a thin square or rectangular foundation resting in smooth contact with an isotropic elastic half space have been evaluated using a mixed-variational approach. Loading is uniform, symmetrically located concentrated, or a combination of these two. Contact stress distribution at the interface is expressed as a direct function of the assumed deflected shape of the foundation. Results are presented for several foundation rigidities. Good agreement is seen with finite element analyses. The method is computationally efficient.
Time domain (sonic echo) or frequency domain (transient dynamic response) methods are generally used for integrity testing of cast in situ concrete piles. The two techniques are basically similar but results are analysed in different ways. Damping of signals makes examination of long piles difficult. To overcome this, the Edinburgh technique uses advanced signal processing techniques, autocorrelation, cross correlation and Cepstrum and Liftered Spectrum processing. The ability to detect overbreak bulb, neck, and occluded void defects, including multiple defects, is demonstrated using field tests.
© 1992 Pergamon Press plc. Reproduction not permitted
921373 Settlement behaviour of non-linear soil around single piles subjected to vertical loads Kuwabara, F Soils Found II31, N1, March 1991, P39-46 Simplified nonlinear analysis is presented of distribution of vertical displacements in the soil around a pile whose end bearing contribution may be neglected. Nonlinearity of shear modulus and shear strain either based on laboratory data or according to a hyperbolic relation is assumed. Results are compared to those from a linear analysis using the boundary element method and field observations in published pile tests. Nonlinear analysis indicates greater shear strain concentration near the pile surface than in linear analysis. For practical application of theoretical elastic solutions, a shear modulus of 3 times that from conventional triaxial tests is recommended. 921374 Analysis of the interaction between a moderately thick circular plate and an isotropic elastic halfspace using a mixedvariational principle Faruque, M O; Zaman, M M Soils Found 1/31, NI, March 1991, P73-82 For many structural foundations, the plate is sufficiently thick that the effect of shear deformation on flexible response cannot be ignored, and thick plate theory must be used in analysis. This problem is tackled using a mixed variational approach, with which the plate deflection, plate bending moment, and shear forces are treated as independent variables and approximated using power series. Unknown coefficients associated with the approximation functions are evaluated by using the stationary properties of the variational functional. Numerical results are presented for a range of plate rigidities. 921375 Effect of construction on existing subway tunnels - a case study from Toronto Lo, K Y; Ramsay, J A Tunnlg Underground Space Technol V6, N3, 1991, P287-297 The case of the construction of the York Mills Centre Phase III over the Toronto subway is described. The soil is uniform dense grey silt. Large diameter caissons straddling the tunnel were used to transfer load to thesubsoil below the tunnel invert and minimise loading on the tunnels. Soil parameters were obtained by laboratory testing and back analysis of ground movements during excavation and construction. 2 and 3 dimensional finite element analyses were used to predict displacements along and around the tunnels. These data are compared to those measured.
921372 Analysis of foundation-elastic haifspace interaction using a mixed-variational approach Zaman, M; Faruque, M O; Uddin, N Soils Found V31, N1, March 1991, P27-38
921376 Edinburgh pile integrity testing technique McCavitt, N; Forde, M C; Batchelor, A J Proc 2nd International Conference on Foundations and Tunnels, London, 19-21 September 1989 V2, P293-299. Publ Edinburgh: Engineering Technics Press, 1989
Deflections, flexural moments, and contact stresses at the interface of a thin square or rectangular foundation resting in smooth contact with an isotropic elastic half space have been evaluated using a mixed-variational approach. Loading is uniform, symmetrically located concentrated, or a combination of these two. Contact stress distribution at the interface is expressed as a direct function of the assumed deflected shape of the foundation. Results are presented for several foundation rigidities. Good agreement is seen with finite element analyses. The method is computationally efficient.
Time domain (sonic echo) or frequency domain (transient dynamic response) methods are generally used for integrity testing of cast in situ concrete piles. The two techniques are basically similar but results are analysed in different ways. Damping of signals makes examination of long piles difficult. To overcome this, the Edinburgh technique uses advanced signal processing techniques, autocorrelation, cross correlation and Cepstrum and Liftered Spectrum processing. The ability to detect overbreak bulb, neck, and occluded void defects, including multiple defects, is demonstrated using field tests.
© 1992 Pergamon Press plc. Reproduction not permitted