Preparation before subgrade excavation construction?

The following is the preparation work before subgrade excavation brought by Zhong Da Consulting for your reference.

1 survey lofting

Construction restoration alignment survey and construction lofting are the main technical work in the construction preparation stage. The contractor shall carry out retest according to the design drawings, coordinates of traverse points and elevation of leveling points provided by the supervision engineer in writing, and submit the retest data to the supervision engineer for review after closing. The contractor shall pay off the construction according to the pay-off data approved by the supervision engineer. According to the specification, before subgrade construction, the center line piles, boundary piles for subgrade land, cutting slopes, side ditches, borrow pits, berms, spoil piles, etc. Should be in accordance with the design drawings, construction technology and the relevant provisions of the recovery. The straight-line part of the road centerline pile is set every 20m, and the permanent fixed pile is set every 100m. The starting point, ending point, circular slow point and circular slow point of the curve are set with fixed piles. After measuring the centerline pile, measure the cross section, and then set out the side pile according to the subgrade cross section and the measured elevation. At the top of the slope in the excavation section, the side piles in the excavation section are generally set at a certain distance from the side piles to prevent the side piles from being lost and recovered in time.

2 Review and test before construction

Before subgrade construction, the constructors should make a detailed investigation on the geological and hydrological conditions of the subgrade engineering scope, determine its nature and scope through sampling tests, and understand the treatment methods of special soil by existing buildings nearby. We should master the degree of weathering and cracking, bedding, joints and schistosity of rock strata in rock areas, and pay special attention to faults and geological changes in areas prone to collapse.

Geotechnical test sampling should generally be based on the data provided by design documents, and each soil type should be sampled in not less than three groups; There are also geotechnical engineering routines or tests based on pile number sampling. According to Technical Specification for Highway Subgrade Construction (JTJ033-95), the test method of soil used as filler in excavation and borrow yard should be handled according to Standard for Highway Geotechnical Test (JTJ05 1-93).

3. Excavation of drainage facilities in front of the cutting

Because water is the main cause of cutting diseases, no matter what kind of excavation method is adopted, effective drainage should be ensured during excavation and after completion.

(1) Do a good job of intercepting ditch before cutting excavation, and build temporary drainage ditch when excavating in layers.

(2) Temporary drainage facilities should be combined with permanent drainage facilities, and running water should not be discharged into farmland and cultivated land, polluting natural water sources or causing siltation and erosion.

(3) During cutting construction, attention should be paid to maintaining drainage channels frequently to ensure smooth running water. Drainage ditches in permeable soil or rapids should be reinforced to prevent leakage and erosion. In areas with poor hydrogeological conditions, drainage at the top of cutting must be strictly done.

(4) Take away all the surface water and groundwater that may affect the slope stability, and keep a certain longitudinal slope (one-way or two-way) along the cutting line to facilitate drainage.

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