Different Types of Earth Pressure Cells, Their Applications and Construction of Isobar Diagram Using Them-2

(2) Two-to-one Load Distribution Method:- The actual distribution of load with the depth is complex. However, it can be assumed to spread approximately at a slope of two (vertical) to (horizontal). Thus the vertical pressure at any depth z below the soil surface can be determined approximately by constructing a frustum of pyramid (or cone) of depth z and side slopes(2:1). The pressure distribution is assumed to be uniform on a horizontal plane at that depth.

The average vertical stress σ_z depends upon the shape of the loaded area, as given below( fig. 1.2).

Fig.1.2: Two-to-One Distribution.

(a)	Square Area (B × B)
(b)	Rectangular Area (B ×L)
(c)	Strip Area (width B, unit length)
(d)	Circular Area (diameter D)

The above method gives fairly accurate values of the average vertical stress if the depth z is less than 2.5 times the width of the loaded area. The maximum stress is generally taken as 1.5 times the average stress determined above.

(3) Sixty Degree Distribution:- This method is similar to the preceding method. In this case, the pressure distribution is assumed along lines making an angle of 60° with the horizontal instead of 63.5⁰ (2:1). The method gives approximately the same results.