Bearing capacity of geocell reinforced foundation

- Jan 11, 2021-

 Improving the bearing capacity of the foundation is the earliest application field of geocells. The mechanism of improving the bearing capacity is that the friction and limiting force of the cell walls not only increase the confining pressure of the soil, but also make it obtain "quasi-cohesion".

The study found that the bearing capacity increases with the increase of the cell material strength, and the reinforcement effect is better when the height to width ratio of a single cell is within the range of 1.5 to 1.0. When the side wall of the cell has diagonal lines and perforations, the bearing capacity can be further improved. The perforation of the side wall has the effect of draining water and allowing the root system to develop laterally, while reducing material consumption.

R.M. Koerner, a well-known American scholar and geosynthetic material expert, proposed the calculation of the bearing capacity of geocell reinforced foundations based on the Vesi'c ultimate bearing capacity theory.

The damage surface of the foundation extends downwards, which enlarges the range of the sliding surface. The calculation formula of bearing capacity is formula (1) and formula (2)

Without geocell:

pu = cNcζc +qNqζq +0.5 γbNγζγ;             (1)

With geocell:

pu = 2 τ+cNcζc +qNqζq +0.5 γbNγζγ        (2)

In the formula: pu is the ultimate bearing capacity of the foundation;

c is cohesion;

q is the side load (q = γqDq); γq is the bulk density of the soil in the cell; Dq is the depth of the geocell;

γ is the bulk density of the soil in the damaged area;

b is the base width;

τ is the shear strength of the side wall of the geocell and the soil between them (τ=σh tanδ for coarse-grained soil);

σh is the average horizontal stress of the soil in the geocell (σh =pK a);

Ka is the active earth pressure coefficient;

δ is the friction angle between the soil and the side wall of the cell;

Nc, Nq, Nγ are the bearing capacity coefficients (related to the internal friction angle of the soil);

ζc, ζq, and ζγ are the correction coefficients for the shape of the bottom surface of the foundation considering the error of the assumption that the basis is a strip foundation. For foundations of other shapes, this article recommends the use of the basic shape factor calculation formula given in the A.S.Vesi'c foundation ultimate bearing capacity formula.

According to the formula, the effect of improving the ultimate bearing capacity of the geocell reinforced foundation is significant, which is about 4.9 times that without geocells.