62. Modelling the Boring of Curves in (very) Soft Soils During Microtunneling

In recent years the interest in microtunnelling has grown due to the fact that open trenching is an increasing undesired operation. However, microtunnelling encounters restrictions in expanding into new areas. In the Netherlands, and more general in (very) soft soils, one of the main problems is the controlled boring of curves. To better understand the behaviour of the tunnel boring machine (TBM) an analytical model has been developed that takes translation and rotation of the TBM into account. These movements can be superimposed to describe the complete movement of TBM. The model has been developed in an incremental fashion by first taking only the influence of a limited set of parameters into account. The first model takes the subgrade reaction modulus and the influence of the machine on the stiffness of the soil into account and is subsequently improved upon by taking the dead weight and eccentric jacking forces into account. This second model is validated with a case study, the installation of the KPE-pipe under the Hartel canal in Roterdam, and this shows reliable results. Using the model, the required position of the steering jacks in the tunneling machine can be determined, given that the required parameters are known. In addition, the ovalization of the bored hole can be forecast. With the variation in angular rotations and maximum rotation, the behaviour of the joints can be determined. In this way problematic situations can be prevented. Although the results of the validations are good, a number of aspects do need further research.