Load Plate Test with Gripper Tunnel Boring Machine

The documentation requirements for tunneling have steadily increased due to the progressive digitisation of tunnel construction sites. The current tunnel boring ma-chines are equipped with a large number of sensors that continuously collect data such as gripper pressures and gripper paths and store them in databases. So to speak, there is a continuous measurement of the interaction between the mountain and the tunnel boring machine (TBM). So far, however, the measured values from the machine tunneling have not been used for a technical description of the ground conditions encountered.
Stephan Sprinkart, Dr. Christoph Niklasch, Ivo Banjan
Stephan Sprinkart, Dr. Christoph Niklasch, Ivo Banjan

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 PPresse = 148 bar results in a contact pressure of the gripper plate on the ground of PGripper= 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.

Figure 1: Example of the pressure — deformation relationship for a bracing process

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.

Figure 2: Representation of the results of the deformation mode measurements Em along the examined tunnel section. The horizontal lines represent the fluctuation range of the deformation module, which was the basis for the respective mountain class.

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.

Figure 3: Gripper tunnel boring machine

Project Partners:

  • Projekt 5th Waterline to Jerusalem

Duration of the project:

January 2017-December 2020