Description of the problem

To verify the consolidation settlement calculated by ELPLA, the final consolidation settlement of a clay layer under a rectangular raft calculated by Graig (1978) (Example 7.2, page 186) is compared with that obtained by ELPLA.

A building is supported on a raft 45 [m] × 30 [m] is considered. The contact pressure is assumed to be uniformly distributed and equal to q = 125 [kN/m²]. The soil profile is as shown in Figure 6. The coefficient of volume change for the clay is m_v = 0.35 [m/MN].

It is required to determine the final settlement under the center of the raft due to consolidation of the clay.

 Example 6: Consolidation settlement under a rectangular raft

Description of the problem

It is known that the modulus of subgrade reaction ks is not a soil constant but is a function of the contact pressure and settlement. It depends on foundation loads, foundation size and stratification of the subsoil. The main modulus of subgrade reaction ksm for a rectangular foundation on layered subsoil can be obtained from dividing the average contact pressure qo over the settlement so under the characteristic point on the foundation, which had been defined by Graßhoff (1955). Clearly, this procedure is valid only for rectangular foundations on a layered subsoil model. Determining the main modulus of subgrade reaction ksm for irregular foundation on an irregular subsoil model using another analysis is also possible by ELPLA.

In this example, settlement calculations at the characteristic point on the raft, using Steinbrener's formula (1934) for determining the settlement under the corner of a rectangular loaded area with the principle of superposition, are used to verify ELPLA analysis for determining the main modulus of subgrade reaction k_sm. Consider the square raft in Figure 17, which has area of A_f = 8×12 [m] and thickness of d = 0.6 [m].

 Example 13: Main modulus of subgrade reaction k_sm

Description of the problem

To verify the mathematical model of ELPLA for computing the immediate (elastic) settlement under a rectangular loaded area on layered subsoil, the immediate settlement of saturated clay layers under a rectangular loaded area calculated by Graig (1978) (Example 6.4, page 175) is compared with that obtained by ELPLA.

Janbu/ Bjerrum/ Kjaernsli (1956) presented a solution for the average settlement under an area carrying a uniform pressure q [kN/m²] on the surface of a limited soil layer using dimensionless factors. Factors are determined for Poisson’s ratio equal to ν_s = 0.5 [-].

 Example 4: Immediate settlement under a rectangular loaded area on layered subsoil

Description of the problem

A simple example was carried out to show the influence of load geometry on the values of settlements and internal forces for the different subsoil models. To carry out the comparison between the different soil models, three different soil models are used to analyze the raft. The three mathematical models Simple assumption, Winkler’s and Continuum models are represented by five calculation methods.

 Example 21: Influence of load geometry