Deficiencies of the vertical slice method in assessment of the seismic earth pressures
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RESEARCH PAPER
Deficiencies of the vertical slice method in assessment of the seismic earth pressures Shi-Yu Xu1
•
Abiodun Ismail Lawal1
Received: 24 September 2019 / Accepted: 13 July 2020 Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Conventionally, when the method of slice is adopted to assess the earth pressures behind the retaining wall considering a curvilinear failure surface, the mobilized soil mass usually is discretized into vertical slices. The point of application of the resultant earth thrust predicted using this technique (implemented in a recently published analytical approach, the logspiral-Rankine (LSR) method) is reported to be insensitive to the magnitude of the horizontal seismic force. This result conflicts with those observed/suggested in several experimental tests and design guidelines, which state that the point of application will raise considerably toward the midpoint of wall as the horizontal seismic force increases. This study revealed the errors introduced by the vertical slice method and proposes to use the inclined slices (parallel to the effective gravitational field) as the remedy. The LSR method is thus re-formulated and also extended to the more general scenario in which a non-vertical wall supports an inclined frictional-cohesive backfill under seismic condition. The proposed inclined slice method is found to be more conservative than the conventional vertical slice method. The results obtained from the two methods of slices are compared and verified with those yielded by a few existing advanced analytical/numerical approaches. Keywords Inclined slices Inclined wall Limit equilibrium Log-spiral-Rankine Method of slices Sloping ground
1 Introduction The evaluation of active and passive earth pressures behind retaining walls is a complex subject, especially with the presence of earthquake forces, because the problem is statically indeterminate in nature, the failure surface within the soil medium is not pre-determined, the response of soil is highly nonlinear, and the soil’s shear strength is pressure dependent. Depending on the background physics/concepts used in the analysis, the assessment approaches can generally be classified into three categories, viz. the forcebased, stress-based, and energy-based methods. The analytical models commonly adopted by the researchers to
& Shi-Yu Xu [email protected] Abiodun Ismail Lawal [email protected]; [email protected] 1
Architecture and Civil Engineering Department, City University of Hong Kong, Kowloon, Hong Kong SAR
quantify the magnitude of lateral earth pressures include the limit-equilibrium, limit-analysis, and slip line method. The limit-equilibrium approaches [6, 19, 21] inspect the equilibrium conditions of the mobilized soil mass at the moment when the sliding (i.e., failure) surface forms within the backfill to determine the ultimate earth thrust. To improve the prediction of passive earth force, the limitequilibrium concept has
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