Back Issues 11-20

INFLUENCE OF STRAIN SOFTENING AND SHEAR-BAND TILTING EFFECTS ON THE ACTIVE EARTH PRESSURE ON RETAINING WALLS

Tse-Shan Hsu

President, Institute of Mitigation for Earthquake Shear Banding Disasters

Professor, Department of Civil Engineering, Feng-Chia University, Taiwan R.O.C.

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Yi-Ju Chen

Ph.D. Student, Ph.D. Program of Mechanical and Aeronautical Engineering, 

Feng-Chia University, Taiwan, R.O.C.

Zong-Lin Wu   Yi-Lang Hsieh

Directors, Institute of Mitigation for Earthquake Shear Banding Disasters, 

Taiwan R.O.C.

Jiann-Cherng Yang   Yi-Min Huang

Associate and Assistant Professors, Feng-Chia University, Respectively,

Taiwan, R.O.C.

Abstract

Local shear bands develop on highway slopes and river banks where retaining walls are located, and shear banding implies strain softening and shear-band tilting effects. However, the traditional theory of active earth pressure for retaining walls ignores the influence of shear-banding. As a result, design codes have not fortified against shear-banding, which has caused a large number of retaining walls under shear banding to collapse. In view of this, this paper explores the influence of strain softening and shear-band tilting effects on the maximum lateral earth pressure on a retaining wall. The results of this paper lead to the following four conclusions. (1) The main cause for collapse of shear-band retaining walls is that design codes do not fortify against shear banding. (2) Finite-element analysis results show that shear bands can only appear in the elastic-plastic strain softening model. The traditional active earth pressure theory for retaining walls assumes that a failure surface exists according to the elastic-perfectly plastic model. (3) Because piping failure in a retaining wall only occurs locally in the shear band, piping failure analysis for retaining walls should use unsteady-state pipe flow instead of steady-state seepage flow. (4) The case study results show that both strain softening and shear-band tilting effects increase the maximum lateral earth pressure on the retaining wall beyond the values calculated using the traditional active earth pressure method. The total increase can be as high as 148.6%, which shows that this calculation discrepancy is a key factor in the collapse of the shear-band retaining walls. Based on these four conclusions, it is suggested that strain softening and shear-band tilting effect should be included in retaining wall design codes, so as to ensure that retaining walls do not undergo local collapse.

Keywords: strain softening, shear-band tilting effect, piping failure, earth pressure, retaining wall.

Attachments:

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