In Figure 1 active earth pressure for partially submerged sand and surcharge is shown. The height of the wall is Z and the position of the water table is at a depth of Z_{1} and the surcharge acting at the top of horizontal surface of the wall is q. The height of the wall below water table is Z_{2}. The unit weight of the sand above water table is and that below water table is _{.}

**CASE 1**

Consider a depth z, such that z is less than Z_{1}. Then the earth pressure at depth z is given by:

When,

**Case 2**

Consider a depth z, such that z is greater than Z_{1}. Then the earth pressure at depth z is given by:

When,

When,

As shear strength of water is zero, then value of K_{a} in the third term of the above equation is unity. Hence,

The following condition can exist.

**Soil is dry or moist and no surcharge**

In this case, depth Z_{2} = 0, Z_{1} = Zand q = 0. Hence,

**Soil is completely submerged and no surcharge**

In this case, depth Z_{1} = 0, Z_{2} = Z and q = 0. Hence,

**Soil is dry or moist and carries surcharge**

In this case, depth Z_{2} = 0 and Z_{1} = Z. Hence,

**Soil is completely submerged and no surcharge**

In this case, depth Z_{1} = 0, Z_{2} = Z and q = 0. Hence,

**Effect of soil stratification**

If the backfill comprises two or more soil strata, then the top strata acts as a surcharge for the subsequent lower strata.