Selected problems connected with the use of the jet grouting technique

The paper presents selected problems connected with the use of the jet grouting technique. It is one of the most popular methods for subsoil strengthening, enhancement for existing foundation, vertical and horizontal waterproof cut-off walls. Columns made using this method feature a high bearing capacity (very high friction on the shaft). The newest achievements of the numerical explanation of the interaction between jet grouting columns and subsoil are presented in the paper. The created models will be used to verify engineering methods of jet grouting columns dimensioning. Computational analyses are conducted using software based on the finite element method (Z-Soil). The computational model describes the interaction between a group of jet grouting columns and soil. The main element of this analysis consists of selection and calibration of computational model of the "group of jet grouting columns-subsoil" interaction. The model space is divided into three zones: columns, soil and the contact layer formed between the columns and the soil massif. The computational model allows for a plastic character of deformation under load and especially for a non-linearity of contact zone. The description of shape of a shaft surface of jet grouting columns is very difficult, so the fractal theory is used to describe this shape. Fractal and box dimensions are used to estimate the irregular surface. This model allows a precise selection of formation parameters, like the injection rod pull out velocity and number of rotations, injection pressure and the water/cement ratio, which define the geometry of jet grouting columns.