Hainan plastic inspection well  

1. Well pit

The pit excavation shall be carried out at the same time as the pipe trench. During excavation, the main pipe of the well seat shall be on the same axis as the pipe in the pipe trench. During pit excavation, the foundation soil shall not be disturbed. If the foundation soil is disturbed, remedial measures shall be taken according to the soil quality of the foundation soil. During the manual excavation of the well pit, the temporary soil piling or other loads shall not affect the stability of the well pit. The height of soil piling and the distance between the soil piling and the edge of the well pit shall be in accordance with the relevant construction specifications. Drainage and water level lowering measures shall be taken in areas with high groundwater level or during construction in rainy season; During construction, the groundwater shall be lowered to 300mm below the lowest point of the well pit. After the installation and connection of the manhole, the dewatering can be stopped only after the manhole is backfilled to a height that meets the anti floating stability of the manhole. The well pit shall not be soaked in water. If the well pit is soaked in water during construction, the water shall be drained first, and then the soaked soil layer shall be removed, and replaced according to the design requirements. The compactness shall meet the design requirements. Safety warning signs such as safety rope or guardrail shall be provided after the excavation of well pit and pipe trench.

2. Foundation

The plastic inspection well must be installed on the foundation soil layer that meets the design requirements, or on the foundation that has been treated and compacted after the well pit is excavated. Requirements for foundation soil layer: 1. 100mm medium coarse sand cushion shall be laid in the well pit of sandy soil, rock and gravel soil; 2. 150 mm thick gravel (brick) or gravel (particle size 5 mm~40 mm) layer shall be laid in the well pit of soft soil, and the upper layer shall be paved with 50 mm medium coarse sand cushion after compaction; 3. The original soil in the well pit of collapsible loess soil shall be compacted and then paved with 37 lime soil (100mm~150mm) cushion, and then paved with 100mm medium coarse sand cushion. The compaction coefficient of sand gravel cushion should not be less than 0.95; 4. The well seat of municipal inspection well shall be poured and compacted with cast-in-place concrete foundation not lower than C15.

3. Connection between well base and pipeline

The connection and installation sequence between the well seat and the pipeline shall be noted: the installation shall start from the upstream section of the household pipe, and gradually extend to the downstream branch pipe and main pipe; Install in the sequence of well pipe well pipe; The center of the well seat shall be positioned first, the well seat and the lower cushion block shall be placed in the well pit, the elevation of the pipe bottom shall be adjusted, and then the connecting pipe shall be installed. If there is a flow arrow on the well seat of the plastic inspection well, it shall be consistent with the flow direction of the pipeline. The bottom of the plastic inspection well and the connected water inlet pipe must not be lower than the bottom of the pipe slot of the inspection well. When the whole drainage system is constructed, inspected and accepted by item (section), the interface connecting the next pipe section shall be temporarily blocked with pipe plugs. When the underground water level is high or during the rainy season construction, when the pipeline (including the plastic inspection well) is installed (but the water filling test has not been conducted), the technical measures to prevent the well body from floating shall be taken.

4. Backfilling

Backfilling shall be carried out after the drainage pipeline (including pipeline and inspection well) is accepted. The well pit shall be backfilled to the top of the cushion of the pressure bearing cover plate of the inspection well. The well pit shall be backfilled at the same time as the pipe trench, and shall be backfilled symmetrically from the circumferential bottom of the plastic inspection well. The lower part of the connecting pipe fittings must be compacted, and the backfill requirements of the lower part of the connecting pipe fittings shall meet the requirements of road subgrade compactness. During backfilling, there shall be no ponding in the well pit, no backfilling with water, and no backfilling with silt, organic matter and frozen soil. The backfill shall not contain stones, bricks and other hard sundries. Before backfilling, the well seat and shaft can be fixed with sand bags, steel drills and wooden supports. When the plastic inspection well is located in soft soil layer, low-lying, marshy and high groundwater level sections, the well pit shall be backfilled with medium roving to fill the bottom of the well pit tightly, and then backfilled with medium roving or sand gravel to 400mm above the bottom of the well in layers, and then backfilled with good soil upward. If the local maximum frozen soil depth is greater than or equal to 1.0m, medium roving shall be backfilled in the frozen layer within the range of not less than 100mm around the shaft.

During backfilling, manual layered and symmetrical backfilling shall be adopted to avoid damage, displacement and inclination of the shaft. When backfilling in layers, the thickness of each layer of dummy backfill shall not be greater than 300mm. Each layer of backfill shall be symmetrically compacted with light tamping tools such as wood tamper, and its compactness shall be consistent with that of pipeline backfill. When the inspection well on the road is backfilled to the upper part of the shaft, the foundation pit for the shaft cover foundation shall be reserved around the shaft according to the backfill soil texture and the characteristic value of the bearing capacity of the backfilled foundation.

5. Installation of pressure bearing ring

The inner diameter of the pressure ring shall be greater than the outer diameter of the wellbore, and a gap of 50mm~100mm shall be left between the pressure ring and the wellbore. The structure of the pressure bearing ring shall be designed according to the size of the wellbore and the size of the external load it is subjected to. Generally, 300 mm thick foundation cushion shall be laid under the pressure bearing ring, and the width of each side of the cushion shall be at least 200 mm greater than the outer diameter of the pressure bearing ring. The cushion material can be divided into two layers, gravel cushion and C20 concrete cushion. Before lifting the pressure ring, small wooden piles shall be used to position around the pressure ring to ensure the center of the circle. Before the pressure ring construction, the retaining ring shall be sleeved on the outer wall of the shaft; When no retaining ring is provided, ballast, concrete and shaft isolation measures shall be taken around the shaft wall.