Application possibilities of on-line rock pressure measurement with the tunnel construction
The instrumentation use of the akusto elastic effect makes qualitatively and quantitatively new safeguards methods possible with the building and with the enterprise of tunnel. When example of possible applications know tunnel-build with high overlays and/or large rock pressure features are called, with those already during the construction period, which can be measured force application of the working forces of the tunnel drilling machine into the mountains surrounding the tunnel.
1.Application fields of on-line rock pressure measurement
Proof for the static group between Tubbings and mountains with the later compressed concrete (backfill) annular gap with long tunnel drivings. As example of possible applications of on-line ground pressure measurement with tunnel and/or shaft lining are mentioned pits and lugs with high overlays and/or large ground pressure features with alpine transit routes. Measurement very slowly itself developing mountain printings in rocks with high ductility and pore water printing. With the impact of such rocks very large and long lasting deformations can occur with the tunnel construction. If one tries to restrain these deformations by a rigid development, then develops a high, so-called genuine ground pressure in superposition with pore water printing, which can destroy the development.
The long, low-lying tunnels by the alps lend special meaning to the problem of the tunnel construction in printingful mountains. The measurement principle of on-line ground pressure measurement is independent of the water saturation of the environment. Long-term observation of the load admission of the tunnel tube with redistributions of stress in the mountains.
Conventional observations of the tunnel tube seize only deformations of the building. This geotechnical deformation or shift measurement can be determined only over the relative changes of position of individual often partially not visible points among themselves. In addition these geodetically determined points must be attached on. With on-line ground pressure measurement the stress measurement cannot only take place in the mountains, but directly the load creation can independently be based on each measuring point on the Tubbing, furnished for it.
Measurement of the forces between the Tübbings and mountains and the Tubbings. With the tunneling with a Gripper TBM the propulsion press strength and the torque of the drilling head are cleared away over the spanning of the Gripper Pratzen into the rock. This brackets for example equipped with measuring bodies for load measurement is directly measurable the force application into the mountains in the brackets. Possible flexiblenesses in the load-absorbing mountains can be measured so directly. The arrangement of measuring bodies between the Tubbings makes the measurement for the demolition possible of the forces of a TBM with sign, necessary for the feed motion.
The feed press strength can be cleared away thereby over the timbering of Tubbings already finished. The orientation of the plates of the measuring bodies is turned thereby around 90°. If the admission of the transverse forces is to be supervised, the installation of the measuring bodies in the annular gap between the timbering of Tubbings and the excavated cross-section presents itself.
Thereby if Tubbings with connections for pressure sensors are used for the measurement of the injection pressure of the filling medium, the connecting cable for the measuring bodies can be laid by this opening. Likewise the force application can be supervised into the mountains with driving along curves of the TBM with on-line ground pressure measurement.
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2. View for the application of on-line rock pressure measurement as a component of a tunnel monitoring
In the tunnel construction the monitoring the all possible effect and structural parameter forms the basis for the condition and safety analysis of the building during the building phase and the enterprise. The data seized with different geotechnical methods represent the basis for numeric and mechanical concept. The determining values of the parameters flowing into the concept can be won only from rock-mechanical values. On-line measuring procedures to force and load measurings, particularly stress measurements, do not have to be replaced in its force of expression and topicality. The most firmness and deformation from laboratory tests are linked so far insufficiently only with current deformation. With on-line ground pressure measurement the so far only modelful parameters can, as are measured the influence of the viscosities of the surrounding mountains on the stability of the development, with small expenditure and thereby the verification of all past models can improve substantially. From instrumentation view also the employment of RFI technology is conceivable. So measuring bodies with planar antennas or induction pick-up coils could be attached for the power supply of the ultrasonic units behind the Tubbings. Thus the installation is made possible for on-line rock pressure measurement without injury of the pressure water-close tunnel tube.