Effect of Arching on Passive Earth Pressure Coefficient. Rupa Sunil Dalvi

Department of Civil Engineering, Geotechnical Engineering Division, PIET’s College of Engineering, Pune – 411005,
Maharashtra, India.
Pise P.J.
Department of Civil Engineering, Geotechnical Engineering Division, PIET’s College of Engineering, Pune – 411005,
Maharashtra, India. (Former Professor, IIT Kharagpur )
Keywords: Arching, Passive earth pressure, Sandy soil, Wall friction, Retaining Wall
ABSTRACT : Analysis has been proposed by Paik & Salgado (2003) for the non linear distribution of active earth
pressure on a translating retaining wall considering arching effect. In the present paper, formulation is proposed for
calculating passive earth pressure on a rigid retaining wall undergoing horizontal translation based on his approach
(Paik & Salgado, 2003). It takes into account arching effect in the backfill. The proposed formulation is compared
with Coulomb’s results. The comparison between proposed and Coulomb’s values shows that the proposed equation
predict values of earth pressure much less than those of Coulomb’s values. In order to facilitate calculation of passive
earth pressures, using the proposed equation, a modified passive pressure coefficient is provided. It is a function of
soil friction angle φ and soil - wall friction angle, δ
1 Introduction
Arching is universal phenomena that involves transfer of pressure from the yielding part of soil to the adjoining part.
The soil is said to be arch over the yielding part of support. The state of stress within the zone of arching depends
upon the amount of yield. As yielding increases, arching effect is gradually reduced. However ,the effect of arching is
permanent in character as the shear strength property of soil .Arching effect is less if shear strength is less. Though
arching phenomenon occurs in number of geotechnical engineering problems, it has not received much attention.
Several researchers have attempted to estimate the active earth pressures exerted against rigid retaining walls
considering arching effect in the retained soil mass. Janssen (1895) set up the differential equation for pressures in
the silos by considering force equilibrium for any differential flat element in the silo. Based on Janssen’s arching
theory Spranglar & Handy (1984) and Wang (2000)suggested equations to estimate the non linear distribution of
active pressure on retaining walls. Handy (1985) and Harrop- Williams (1989) also proposed lateral active earth
pressure coefficients Kaw and equation for calculating non-linear active earth pressures. Dalvi et.al.(2005,2007) have
used approach similar to that of Handy and derived coefficient of passive earth pressure (Kpw).
Estimation of passive earth pressure acting on a rigid retaining wall is very important in the design of many
geotechnical engineering structures, particularly retaining walls. Civil engineers have traditionally calculated the
passive earth pressure against rigid wall using either Coulomb’s or Rankine’s formulation. Both assume that the
distribution of the passive earth pressure exerted against the wall is triangular. However, many experimental results
Naran et.al.(1969) and Fang & Ishibashi (1986) shows that the distribution of passive earth pressure on the face of
the rough wall depends on the wall movement (rotation about top, rotation about bottom, and horizontal
translation)and is non-linear. This is different from the assumption made by both Coulomb and Rankine.
1.1 Scope of Study
In this study the effect of arching on passive earth pressure in the non-cohesive backfill is considered. The backfill is
assumed to rise upward in a circular arc form due to arching. The vertical and lateral stress acting at arbitrary point
along a differential flat element in backfill is calculated. These stresses are the function of internal friction angle φ and
soil to wall interface friction angle δ. The ratio of lateral to vertical stress is denoted by Kpwn. A modified passive earth

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