The lateral earth pressure coefficient is taken into account in the design of earth support structures. Depending on the lateral movement of the soil and structure, they are divided into three types.
This is done mainly taking into account the rotation of the structure in relation to the existing soil profile.
There are the following three categories of land coefficients.
1. Earth pressure coefficient at rest
2. Active earth pressure coefficient
3. Passive earth pressure coefficient
There are several methods for determining these coefficients. There is relevant literature for calculating earth pressure coefficients. The following images show some of the methods that can be used to find the coefficients.
Figure 01: Variation of lateral earth pressure coefficients
Figure 01 and Figure 02 were taken from different publications. Figure 02 is located at EM 1110 – 2 – 2502.
Both publications provide methods for determining earth pressure coefficients. However, Figure 01 clearly shows the fluctuations in the earth's pressure coefficient at rest.
Figure 02: Variation of lateral earth pressure coefficients
In addition to the methods mentioned above, there are other methods for calculating earth pressure coefficients. Depending on the type of soil (sand and clay), we can find each coefficient using the Coulomb method or the Rankine method.
The Rankine method is simple compared to the Coulomb method. The calculation of earth pressure coefficients using the Rankine method is more complex.
In rest
Ko = 1-sinφ
The problem most engineers face is deciding when to apply sleep mode.
Simply put, if the structure does not rotate or we do not want to allow the structure to rotate, we must orient the structure to rest.
Furthermore, if the structure cannot move (rotate) due to an obstacle (from the ground, supports or any other reason), we must take into account the state of rest at the time of design.
Active pressure
Ka = (1-sinφ) / (1+sinφ)
When the wall is in an active state, we can apply this pressure coefficient to the design.
Passive pressure
Kp = (1+sinφ) / (1-sinφ)
If the wall is in a passive state, we can use this coefficient to calculate the earth pressure.
It should be noted that the designer must ensure full mobilization of passive pressure.
As shown in Figure 01 and Figure 02, rotation must occur to mobilize pressure.
Depending on the rotation of the wall, the pressure coefficient varies.
Therefore, we must be very careful when using the values obtained in the above equation.
If there is uncertainty, a certain reduction in the Kp value is advisable.
