Observation Standard Nanping Observation Standard Specification

Description :

　　Observation Standard Nanping Observation Standard Specification

　　12*100mm,12*150mm,12*200mm,14*150mm,14*200mm,14*250mm,14*300mm,16*150mm,16*200mm,16*250mm,16*300mm,16*350mm,16*400mm,18*150mm,18*200mm,18*250mm,18*300mm,20*150mm,20*200mm,20*250mm,20*300mm,12*120mm,

　　material

　　stainless steel

　　Compared to other projects, tunnel construction has higher specificity and complexity. In order to improve the quality of the project, we should fully understand the hazards of common quality problems in tunnel engineering and take preventive measures.

　　Common quality problem 1: Delayed and inaccurate advance geological forecasting and measurement, discontinuous mileage, and inability to provide reliable basis for construction safety.

　　Preventive measures: (1) Advanced geological forecasting requires comprehensive exploration through various means, utilizing the characteristics of each exploration to complement each other's strengths and weaknesses for mutual verification, ensuring the accuracy of exploration;

　　(2) Special treatment should be given to special areas. For high-risk tunnels and special areas, detection should be strengthened to expose hidden dangers in advance, and corresponding measures should be formulated for prevention and control.

　　Common quality problem 2: Collapse of the tunnel entrance.

　　Preventive measures:

　　(1) Before excavating the inclined slope at the entrance of the tunnel, construct a top interception and drainage ditch to prevent surface water from washing away the slope;

　　(2) Strictly excavate the slope at the entrance of the cave according to the design requirements, protect while excavating, and do a good job in anchoring, netting, and spraying protection to prevent rainwater erosion;

　　(3) Develop corresponding construction plans based on the surrounding rock conditions at the entrance of the tunnel, provide advanced support for weak surrounding rock, and reserve core soil for excavation into the tunnel. If the surrounding rock is good, advanced small conduits can be used to enter the tunnel. Generally, construction should strictly follow the design support type, and local reinforcement should be appropriately strengthened before safe entry into the tunnel; (4) The settlement at the entrance of the tunnel is generally large, and the lining construction time is relatively late. During construction, the settlement reserve should be appropriately increased according to the surrounding rock conditions to prevent the invasion of the lining clearance due to deformation of the surrounding rock.

　　Quality common problem 3: Partial collapse during excavation of faults and fractured zones.

　　Preventive measures:

　　(1) Strengthen advanced detection, fully understand the lithology and hidden dangers of the surrounding rock ahead, formulate corresponding construction measures, and adopt a combination of multiple detection methods for mutual verification detection in special sections;

　　(2) Do a good job in settlement observation. The surrounding rock generally has significant deformation before collapse. Monitoring and measurement can timely detect changes in the surrounding rock and take corresponding measures to prevent collapse. At the same time, based on the results of monitoring and measurement, timely construction of lining can be carried out to prevent serious delays in lining construction and hidden dangers of collapse.

　　Quality common problem 4: Insufficient thickness of sprayed concrete, strength not meeting design requirements, and large rebound of sprayed concrete.

　　Preventive measures:

　　(1) Strictly control the concrete mix ratio during shotcrete construction. Different mix ratios seriously affect the strength of shotcrete and the amount of backfill. It is generally better to use cement with slightly higher strength grades for the mix ratio selection, which results in less rebound;

　　(2) The level of proficiency in spraying during concrete construction affects the effectiveness and rebound of the sprayed concrete. Generally, layered construction is used, with each layer having a thickness of about 3-5cm. The distance between the spray gun nozzle and the sprayed concrete surface should be 80-120cm;

　　(3) Winter concrete construction should develop corresponding winter construction measures according to different regions to ensure the temperature of concrete discharge and not affect the construction quality of concrete;

　　(4) Before spraying concrete, inspect the excavation section and promptly address any under excavation;

　　(5) The thickness control of sprayed concrete can be achieved through drilling or reserved hole inspection.

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