Load Plate Test with Gripper Tunnel Boring Machine

The aim of the project was to measure the deformations of the mountains in the course of the TBM bracing processes using the gripper paths. The material properties of the deformation module should be determined from the relationship between the contact pressure and the measured deformation. In tunnel statics, the deformation module is the most important soil parameter that is included in the calculation.

In order to implement these plans, a tunnel drive with a gripper TBM was used, in which there is a concept for rock classification, a rock mechanical interpretation of the rock properties and a documentation of the actual geology encountered. All of these requirements were met for the 5th Waterline to Jerusalem project.

Since the TBM in this project dates from the 1980s and does not have the necessary measuring equipment, the gripper routes are conventionally recorded by hand. A commercially available digital caliper is used, which can measure from 0 to 500 mm with an accuracy of one hundredth of a millimeter. 

At the beginning of the computational evaluation, the gripper press pressure is converted to the contact pressure of the gripper plate. For example, a press pressure of P_Presse = 148 bar results in a contact pressure of the gripper plate on the ground of P_Gripper= 1.933 MPa.

The contact pressures can now be entered in a diagram together with the measured gripper paths (see Figure 1). With the help of the slope triangle, the deformation module at this point of the mountain range can be calculated from the two values.

A total of 22 gripper path measurements were carried out on the construction site. In order to confirm the plausibility of the results, the pierced mountains were mapped in parallel and evaluated according to the mountain classification of the RMR system.

Ideally, the measurements were carried out in two different mountain classes, so that in addition to the basic plausibility, the sensitivity of the methodology to changes in the nature of the mountains could be checked.

Figure 2 shows that the calculated values for the deformation module correlate well with the mountain classification from the RMR report.

The values from area A calculated using the gripper paths are 100% within the range of deformation module values of class II. So there is a very clear measurement technological confirmation of the mountain range.

In area B, approximately 86% of the calculated modules are within mountain class III.

With regard to the mountain classification, area C lies in the transition between classes II and III: approx. One third of the values lie within class III and two thirds within class II.

The research project has proven that TBM machine data can be used to measure mountain properties. This ensures continuous, reliable verification of the geological and mountain mechanical properties encountered during tunneling. The results can be used in addendum management, contract design (billing according to mountain quality) and in the construction of pressure tunnels.