Table 7. 10. 1 monitoring type monitoring project monitoring instrument displacement surface subsidence surface horizontal displacement vault foundation settlement surrounding rock displacement (radial) surrounding rock displacement (horizontal) convergence horizontal hole around theodolite level, electronic level, electronic level single-point and multi-point displacement meter, three-dimensional displacement meter inclinometer, three-dimensional displacement meter convergence meter, Bassett system pressure surrounding rock pressure lining concrete pressure lining reinforcement stress surrounding rock contact lining pressure anchor axial force steel arch pressure groundwater seepage pressure box, pressure pillow, strain gauge pressure box, pressure pillow, strain gauge, pressure pillow reinforcement stress gauge, strain gauge, ring dynamometer reinforcement stress gauge, strain gauge, axial dynamometer osmometer Other physical quantities are acoustic emission elastic wave of blasting vibration in front of surrounding rock loose area, elastic wave of deformation resistance method, pre-drilling and measurement. It is the most intuitive method to judge the safety of surrounding rock, anchor rod, lining and tunnel with naked eyes without any measuring instruments, which is especially important for the discovery of individual phenomena and special circumstances.
Its purpose is to check geological data, judge the stability of surrounding rock and supporting system, provide basis for construction management and process arrangement, and test supporting parameters. Therefore, before monitoring with instruments, the monitoring personnel should first carefully observe the changes of geological conditions in the tunnel, the development and expansion of cracks, water leakage, whether there are loose rocks on both sides and the top of the tunnel, whether there are loose bolts, whether there are cracks in the spray layer, and whether there are cracks in the middle wall lining, especially whether there are cracks in the middle wall lining. If cracks are found, they should be closely observed and recorded with a crack observer. The observation in the cave should be carried out with the cooperation of the engineering and technical personnel of the construction unit, and the information and data should be exchanged in time. This work runs through the whole process of tunnel construction and provides intuitive information for construction.
7. 10.2, displacement monitoring In a certain range of tunnel entrance and shallow tunnel, it is necessary to monitor surface settlement and horizontal displacement. The vault settlement is generally monitored by a level, and the vault of a tunnel is generally high, so it cannot be measured by a common ruler. The vault can be monitored by setting a hook with a short anchor, hanging an indium steel wire with a length slightly less than the height of the tunnel, and hanging a ruler below.
1. Single-point displacement meter The single-point displacement meter is actually an anchor rod with one end fixed at the bottom of the borehole and a reading device with an orifice plate. The displacement meter is installed in the borehole, and the anchor rod body can be made of steel bar with a diameter of 22mm. The anchor end is wedged tightly with the borehole wall, and the free end is equipped with a probe, which can be freely extended and contracted, and the probe is flat and smooth. The locator is fixed on the drilled casing. When measuring, the measuring ring is inserted into the positioner. Both the measuring ring and the positioner are scored. When inserting and measuring, their notches are aligned. The measuring ring is equipped with a micrometer, a micrometer or a depth micrometer to read the reading. The probe, positioner and measuring ring are made of stainless steel. The invention has the advantages of simple structure, easy manufacture, high testing accuracy and small drilling diameter. It is less affected by external factors, easy to protect, and can be installed close to the blasting excavation face. At present, it is widely used.
The displacement measured by single-point potentiometer is the relative displacement between the hole wall and the anchor fixing point. If the hole is deep enough, the hole bottom can be regarded as a fixed point with small displacement, so the measured value can be regarded as absolute displacement. The depth of the fixed point is related to the engineering geological conditions, section size, excavation method and support time of surrounding rock. At the same measuring point, if displacement meters with different depths are set, the displacement of rock strata with different depths relative to the cave wall can be measured, and the displacement curves with different depths from the cave wall can be drawn accordingly. Single-point displacement meters are usually used in conjunction with multi-point displacement meters.
2. Multi-point displacement meter There are two kinds of multi-point displacement meters, mechanical and electronic, depending on the displacement monitoring instrument. Mechanical displacement meters generally use depth micrometer, dial gauge or dial gauge, and displacement sensors commonly used in electric displacement meters include resistance type, inductance type, differential type, variable pressure type and steel string type.
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