The design of underground works, due to the uncertainties caused by the impossibility of investigating all points of the route and the anisotropic nature of the materials, is based on assumptions that must be validated during the excavation phase through monitoring.
This process is usually done using systems that allow continuous sampling of rock mass deformation data around the tunnel face. In this zone the deformation response is three-dimensional. In particular, if the crossed medium disturbed by the excavation activities reaches plasticization, it is possible to identify a reduction of the excavation section, a pre-convergence phenomenon in the advance core and a consequent extrusion of the face.
Obtaining data on the deformations in the advance core allows to preliminarily identify eventual deviations from the expected behavior and to make eventual modifications to the excavation stabilization systems.
The PreConv Array is an innovative system designed to measure pre-convergence in underground excavations with a high sampling rate. It consists of a sequence of IP69 epoxy resin nodes, joined together by a fiberglass rod and a four-pole signal cable. Each node contains within it a high-resolution MEMS 3D sensor and a thermometer.
Depending on the project requirements, it is possible to define the number of measuring sensors, the spacing and the length of the instrument. The PreConv Array instrument can be managed by the G802, G301 or any other Datalogger compatible with the RS485 Modbus RTU protocol.
The instrument is supplied in segments to be assembled by means of special connectors. The installation takes place inside advance perforations or steel pipes, in the case of pre-support with threading umbrellas, where it is subsequently cemented.
PRINCIPLE OF OPERATION
Knowing the distance between the nodes, the location of the sensors calculated using the data recorded by MEMS, through appropriate algorithms it is possible to identify the relative position of the instrument in space and consequently the trend of pre-convergence in the advancement core.
- Pre-convergence profile reconstructed from local displacements
- Pre-convergence profile reconstructed on cumulative displacements
- Local and cumulative displacements of calculation points over time
- Acceleration and velocity of displacements at calculation points in time
- Rolling nodes over time
- Node temperature over time
- Automatic pre-convergence monitoring in near real-time
- Data acquisition also during the excavation phases
- Automatic alerting based on multi-level and multi-parameter thresholds
- Automatic Monitoring Report