Title

Active earth pressure from c-Ø soil subjected to surcharge and seismic loadings

Date of Award

2010

Degree Type

Thesis

Degree Name

Master of Engineering Science

Faculty

Faculty of Computing, Health and Science

Abstract

Construction of retaining structures to support soils at slopes steeper than their angle of repose has been a routine practice in most civil engineering projects. The successful design of such structures depends greatly on the calculation of total active force from the soil backfills, which has been a topic of research since the early development of analytical expressions presented by Coulomb (1776) and Rankine (1857). Mononobe-Okabe equation was developed during 1926-1929 for calculating total active earth pressure from cohesionless soil (f soil) backfills.

In recent past, attempts have been made to develop analytical expressions for the total seismic active force on retaining structures from the c-f soil backfills considering both horizontal and vertical seismic coefficients. However, an effort still requires presenting an analytical expression for a generalised case. Therefore, in this thesis, an attempt is made to extend the earlier expression (Shukla et al., 2009) for incorporating the effect of surcharge so that the newly developed expression can be used to estimate the total dynamic active force under both surcharge and seismic loading conditions.

The newly developed analytical expression results in several simplified expressions for static/dynamic cases, which have been presented by earlier researchers. A parametric study has been carried out to investigate the effect of surcharge and seismic loadings on the active earth pressure considering practical ranges of field parameters. It is observed that the total seismic active force increases linearly as the surcharge increases for any value of angle of shearing resistance and cohesion of the soil backfill; the rate of increase remains independent of the cohesion. As the horizontal seismic coefficient increases towards the wall, the total seismic active force increases nonlinearly, but it decreases with its increase towards the backfill for any value of shear strength parameters of the backfill. As the vertical seismic coefficient increases downwards, the total dynamic active force increases linearly, but it decreases for an upward increase. It is also noted that the critical value of the inclination to the horizontal of the failure plane decreases with an increase in surcharge. As the horizontal seismic coefficient increases towards the wall, the critical angle of inclination decreases nonlinearly, whereas it increases for an increase towards the backfill. Additionally, it has been noticed that the critical angleof inclination increases nonlinearly as the vertical seismic coefficient increases downwards, but it decreases with an increase in the upward direction.

Design charts have been presented for several possible cases. A numerical example is illustrated to explain the design steps so that practising engineers can design the retaining structures conveniently under surcharge and seismic loadings.

LCSH Subject Headings

Engineering geology.

Soil mechanics -- Mathematical models.

Soil stabilization.

Foundations

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