Design optimization of a reinforced concrete slab in weak clay

Abstract

The objective of this Bachelor’s thesis is to design a slab in weak clay. The load bearing capacity of clay is 100kPa while slab will be a support system for municipal sewage pipe system. Due to the low load-bearing capacity of clay, it can’t hold all the loads that come from the top i.e. the traffic load and the earth load. There are different methods to design a slab when there is enough load bearing capacity of soil but due to the diverse and heterogeneous nature of the soil, the load bearing capacity of soil varies and it is very difficult to design the structure when the load bearing capacity of soil is less.

Similarly, this thesis is also part of a recommendation for SWECO Oy Finland for the design of a ground slab to support a municipal sewage pipe system in weak clay in an economic and effective way. In order to provide the support to the slab, a column with a compressive strength of 400kPa and radius of 400mm was designed using Deep soil mixing method with c/c distance of 1700mm. The value of moment and other necessary calculations were calculated using Robot Structural Analysis (FEM).

Firstly, the slab was placed in weak clay assuming clay as a support system where the elastic coefficient of clay (ks), was calculated and later the value was used in Robot Structural Analysis to calculate the moment and deflection. The deflection of the slab was very high so it was decided to provide supports to the slab using columns created from deep soil mixing method. Finally, in total, 14 columns of 400mm radius were used to achieve the suitable design condition.