1.1 INTRODUCTION

In the construction and design of many structures, a thorough knowledge of the earth pressure to which these structures will be subjected is required. Important among these structures are retaining walls, sheet pile bulkheads, temporary sheathings for supporting vertical or near-vertical cuts in soils, and earth anchors. The earth pressure to which the above types of retaining structures are subjected is commonly referred to as lateral earth pressure. The lateral earth pressure on an earth-retaining structure can generally be divided into three major categories. They are

1. Earth pressure at rest

2. Active earth pressure

3. Passive earth pressure

The above-stated earth pressure conditions can be explained by means of Fig. 1.1, in which AB is a retaining wall supporting soil at its left. The backfill soil has a horieontal ground surface. If the retaining wall does not yield at all from its original position, the horizontal lateral earth pressure at any depth to which the wall will be subjected is called the lateral earth pressure at-rest. The total force per unit length of the wall is equal to P. This type of condition is shown in Fig. 1.1a. However, if the wall tends to yield away from the soil sufficiently to create a plastic state of equilibrium in the soil mass located immediately behind it, the lateral earth pressure at any depth to which it will be subjected is called the active earth pressure. The conditions for development of active earth pressure are shown in...