High pressure jets have already been widely used in many industries. Its most important application in geotechnical engineering is jet grouting, where high pressure jet is used to cut the soil for ground improvement. The understanding on jet grouting is limited because of the underground nature of the technique and the complexity of the process. It is difficult to control and predict the size of column formed by jet grouting.
Tank experiment is carried out to investigate the mechanism involved in jet grouting. The observation shows the existence of both seepage and erosion at the interface between the injected fluid and the intact soil. The movement of the erosion front, which defines the radius of influence by the jet, can be best described by an exponential function. The influences of various operating parameters are studied, which agree with field observations.
The pore water pressure profile measured during the experiment is closely linked with the progress of the erosion front. The pressure increases with the erosion distance, which is associated with the pressure required to drive the spoil back to the surface.
A new model is constructed to estimate the ultimate cutting distance by the jet. The proposed model takes the spoil backflow into account in addition to the injected fluid/soil interaction. The jet behaviour is derived from the hydrodynamic characteristics of submerged jet. Based on the jet grouting mechanism, the failure of soil is checked in terms of the horizontal effective stress. The new model gives a more accurate estimation comparing to current models that only consider the soil resistance against the jet action. The new model is developed to cover jet grouting cases using single fluid and double fluid jet grouting systems.