1. What are the necessary items for tunnel construction survey?
Answer: Measurement of peripheral displacement, vault subsidence, observation of geological and supporting conditions, axial force and pullout resistance of anchor rods and cables.
2. Briefly describe the purpose and method of peripheral displacement measurement and the arrangement and application of data.
Answer: The peripheral displacement is the most intuitive reflection of the stress state change of tunnel surrounding rock, and the following purposes can be achieved by measuring the peripheral displacement; Judging the stability of surrounding rock and the reasonable time of secondary lining construction according to the deformation rate. Guide the construction. After each measurement, the original records should be sorted into official records in time. For each survey line of each survey section, the collated survey data should include: the original record table and the actually arranged survey points, the change of displacement with time and the distance of the excavation face, and the change of displacement speed and acceleration with time and the distance of the excavation face.
3. Briefly describe the purpose and content of geological and supporting observation.
Answer: tunnel face observation: mainly through visual investigation to understand the engineering geological and hydrogeological conditions of the excavation face.
The main contents include: rock type and occurrence. Lithologic characteristics: color, composition, texture and structure of rocks. Stratigraphic age attribution and occurrence. The nature, group number, spacing and scale of joints, the development degree and orientation of joints and cracks, the characteristics of section state, the type and occurrence of fillings, etc. The nature and occurrence of faults, the width and characteristics of fault zones. Groundwater type, water inflow, water inflow location, water inflow pressure, chemical composition of water, etc. The stability of the excavation surface, roof peeling phenomenon.
Observation of construction area: Understand the supporting state mainly through visual inspection. Mainly includes: water leakage (location, state, water volume, etc. ). Observe the surface of spray coating, and describe and record the crack situation (location, type, width, length and development). When sprayed concrete contacts with surrounding rock, whether cracks or spalling occur, special attention should be paid to whether shear failure occurs in sprayed concrete. Whether the anchor rod is damaged and whether the backing plate is stuck in the surrounding rock. Whether there is any quality problem of bolting and shotcreting construction. Whether the steel arch is buckled. Observe the secondary lining surface, and describe and record the cracks (location, type, width, length and development). Whether there is a bottom drum.
4. Briefly describe the purpose and method of vault subsidence measurement, and the arrangement and application of data.
Answer: The absolute subsidence of tunnel vault inner wall is called vault subsidence value, and the vault subsidence value per unit time is called vault subsidence speed. For shallow tunnels, holes can be drilled from the ground, and the displacement of the vault relative to the fixed point on the ground can be measured by deflectometer or other instruments. For deep-buried tunnels, there are two methods to measure vault subsidence: contact observation method (precision level) and non-contact observation method (total station).
The vault subsidence value is mainly used to confirm the stability of surrounding rock, especially to predict the vault collapse in advance; Its method is the same as convergence measurement, and generally speaking, their law of change with time is the same (except collapse or shallow burial).
5. Briefly describe the test method of anchor pull-out force.
Answer: According to the test purpose, anchor holes are drilled in the designated parts of tunnel surrounding rock. Install the anchor rod to be tested according to the normal installation process. The drawing time depends on the type of anchor and the purpose of the test. Pad the tail of the anchor rod, put on a hollow jack, fix the inner cylinder at the outer end of the anchor rod together, and install displacement measuring equipment and instruments. Pressurize with a manual hydraulic pump, read the oil pressure from the oil gauge, and convert the pull-up force of the anchor rod according to the piston area.