DHARM460 GEOTECHNICAL ENGINEERINGPp =1
2KH^2
p..γ ...(Eq. 13.11)
This may be taken to act at a height of (1/3)H above the base as shown, through the
centroid of the pressure distribution diagram. The appropriate value of γ should be used.13.6.4 Effect of Submergence
When the backfill is fully saturated/submerged, the lateral pressure will be due to two compo-
nents:
(i) Lateral earth pressure due to submerged unit weight of the backfill soil; and
(ii) Lateral pressure due to pore water.
This is shown in Fig. 13.9 (a).KHag¢Cohesionless
soil (buoyant
unit weight : )g¢Hz WaterKHag¢Cohesionless
soil (buoyant
unit weight : )gHgwz
Kzag¢gwHW.T.(a) Submerged backfill (b) Wall with submerged backfill
and water on the other side
Fig. 13.9 Effect of submergence on lateral earth pressure
At any depth z below the surface, the lateral pressure, σh, is given by:
σh = Ka.γ ′z + γw.z
The pressure at the base is obtained by substituting H for z.
In case water stands to the full height of the retaining wall on the other side of the
submerged backfill, as shown in Fig. 13.9 (b), the net lateral pressure from the submerged
backfill will be only from the first component, i.e., due to submerged unit weight of the backfill
soil, as the water pressure acting on both sides will get cancelled.
In the case of passive earth pressure, the coefficient of passive earth pressure Kp, has to
substituted for Ka; otherwise, the treatment will be the same.
If the backfill is submerged only to a part of its height, the backfill above the water table
is considered to be moist. The lateral pressure above the water table is due to the most unit
weight of soil, and that below the water table is the sum of that due to the submerged unit
weight of the soil and the water pressure. This is illustrated in Fig. 13.10 (a).
Lateral pressure at the base of wall,
= KaγH 2 + Kaγ ′H 1 + γwH 1 , as shown in Fig. 13.10 (b),where H 1 = depth of submerged fill,
Ka = active earth pressure coefficient,