ABSTRACT
The consistency of a cohesive soil is an important parameter when driving with Earth Pressure Balance shields (EPB shields). It determines the flow behaviour of the excavated material or the support medium in the excavation chamber and the screw conveyor. Furthermore, depending on the consistency and other parameters of cohesive soils, e.g. the plasticity index, clogging can occur in front of the cutting wheel, which can cause high impacts on productivity and costs due to reduced excavation speed and downtime due to cleaning measures. A quick experimental identification of the consistency of the excavated material during the excavation process and an appropriately adjusted conditioning of the soil can help to make EPB excavations safer, more cost-efficient and easier to plan in the future. For this purpose, a new displacement-controlled penetration test for measuring the flow behaviour was developed for both cohesionless and cohesive soils. Initial test series show that there is a clear correlation between consistency and the corresponding penetration resistance of the new penetration test. Further, the penetration resistance also depends on the plasticity index of the soil. Numerous test series with the new penetration test show a high rate of reproducibility of 95 %. Thus, a quick determination of the consistency of the excavated muck will be possible in the future. The consistency can be checked and, if necessary, conditioning measures can be adapted. The risk of adhesion and clogging can thus be reduced and the support pressure transmission improved. Furthermore, tests with foam-conditioned cohesionless sands have shown that the resolution of the relevant measuring range is sufficiently large to quantitatively differentiate the foam injection rate (FIR). The developed test device is therefore a precise and more versatile alternative to the frequently used slump test, which is not suitable for cohesive muck.
