1. Foundation pit excavation and support
The trench excavation depth of this storm sewer is between 1.4~3m, and this project is located in farmland. Rainwater pipes with shallow ditch depth are excavated by large excavation, and the slope coefficient is 1: 0.33 ~ 0.5.
Before trench excavation, sample holes shall be excavated under the guidance of the Owner's representative, and the trench shall be explored, and the public pipelines in the construction area shall be clearly modeled. If yes, it should be marked in its position. In densely populated areas, public pipelines are exposed by manual excavation, and reinforcement measures such as hanging and supporting are taken. Where there is no underground pipeline, mechanical excavation is adopted. During mechanical excavation, there should be a special person to command and make a detailed disclosure of important parts.
Excavators adopt the method of reverse excavation when digging, and strictly control the elevation when digging mechanically to avoid overbreak or disturbing the base surface. The bottom surface shall be manually trimmed to 20cm above the bottom of the tank, and foundation construction shall be carried out after the foundation tank is qualified.
The bulldozing height on one side of the groove edge should be controlled at around 1.5m, and the distance from the groove edge should not be less than1.2m. When parking tools, there should be a 3.5m-wide entrance between two inspection wells, and the lifting position of construction tools should be stable. The distance from the tank edge shall be determined after calculation according to the self-weight of the equipment and the soil conditions, and shall be reinforced when necessary, generally not less than 0.8m 。
2. Pipeline foundation
Check the elevation of the elevation template before foundation construction. The subsoil of the foundation is excavated manually, the bottom of the trough is trimmed, and drainage ditches are excavated on both sides, with a depth and width of about 20cm. Remove silt and broken soil. If there is any overbreak, fill it with gravel. The thickness of gravel cushion is 10cm. The trench width shall be leveled, leveled and compacted.
When installing the transverse slab of concrete foundation in gravel cushion soil, according to the center position of the pipeline, pull out the center line on the elevation template. In order to fix the spacing between templates, a crosspiece buckle is set every 2.5m, which can only be removed after pouring.
During construction, attention should be paid to the side ditch not being blocked, and concrete cannot be poured when there is water on the gravel cushion. Concrete shall be vibrated and leveled with a flat vibrator. After the concrete foundation is poured, avoid flooding within 6~ 10 hours and maintain it properly. The formwork can only be removed when the concrete strength reaches above 2.5mpa.
3. Pipeline laying
Before pipeline laying, recheck the elevation template, clean the foundation surface, and eliminate the accumulated water in the tank. Ink lines in the pipes are popped up on the bottom plate, and the pipes are arranged in the well position, and sufficient net size is reserved in the inspection well. For the laying of tongue-and-groove and socket-type concrete pipes, the center position and elevation of pipe joints at both ends shall be determined according to the elevation template. On the outer wall of the socket of the horizontal centerline of the pipe joint, pull out a positioning sideline, which is about 10mm away from the outer wall of the socket. The exhaust pipe discharges from downstream to upstream, with the socket of the pipe joint facing upstream and the socket facing downstream. Before laying, clean the socket and socket with clean water.
At the bottom of the cushion block on the concrete foundation surface, cement mortar shall be applied first, and the distance between the cushion block and both ends of the pipe joint is about 15cm. When laying reinforced concrete, lead the center line of the pipeline vertically to the iron pillar, pull the center line and hang a vertical ball. When laying the pipe joint, use lifting equipment to hang the pipe vertically, use manual hoist or electric hoist to pull the pipe horizontally, and place the pipe pillow in advance. The distance between the pipe pillow and the end of the socket is 22-23 cm.
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