ABSTRACT
The phenomenon of hydraulically fracturing soils was initially observed as an undesirable by-product of traditional grouting measures. The uncontrolled propagation of soil cracks which were rapidly filled with suspension did not achieve the objective of homogeneously filling cavities in unfixed soils. In the past, high-suspension pumping rates which no longer allowed the suspension to penetrate the pore system of the soil continuously were regarded as a grouting defect. It was crude oil technology using hydraulic soil fracturing for increasing the permeability and thus the yield of oil fields that provided the impetus for systematically applying geotechnical methods for utilising deliberately produced cavities in the soil. In the meantime, fracture grouting has been used for systematically improving soil properties. The load-bearing capacity and permeability of both granular and cohesive soils can be modified by incorporating a cement or solid matter skeleton. The repeated application of this method also permits the controlled raising of buildings with very different support systems. The most spectacular use of the method is found in connection with the complex tasks of compensating for settlements which, as a result of tunnel driving, endanger the continued existence of buildings above the tunnel.
