1. Preparation before trench excavation:
(1). Measure and set out according to the design requirements of the design drawings, and determine the center pile and groove edge.
(2) First, find out the underground pipelines and other underground structures, and properly handle them together with relevant departments to ensure construction safety.
(3) Before trench excavation, drainage around the trench should be well done to ensure that off-site surface water does not flow into the trench.
(4) According to the requirements of engineering monitoring, various types of observation points should be arranged before excavation, and the original data should be measured.
(5) Prepare all mechanical equipment and transportation roads inside and outside the site to facilitate the continuous and rapid completion of earthwork excavation.
2. Trench excavation method:
(1). Natural slope excavation is adopted for earthwork excavation, with slope coefficient of 1: 0.5, and plain concrete with thickness of 10cm is sprayed to harden the slope surface.
(2) The excavation method is mainly mechanical excavation, supplemented by manual excavation. Earthwork shall be excavated by sections and layers. Excavators shall be used for excavation within the range of 3.0m to 20.0cm from the bottom of the ditch, and excavators shall be used for excavation within the range of 3.0m to 20.0cm above, and the excavated earthwork shall be transported to the designated mud yard by dump trucks.
(3) The soil layer 20cm above the elevation of the trench basement should be excavated, cleaned and leveled manually, so as to avoid disturbing the basement soil. Overexcavation is strictly prohibited.
(4) During trench excavation, the elevation of different soil layers shall be submitted for inspection and confirmation by the supervisor and the owner, and records shall be made.
(5) When the soil layer does not conform to the design, the design and supervision unit shall be informed in time, and the design, supervision and construction unit shall discuss the treatment methods together.
3. Drainage measures for ditches:
(1). A drainage ditch and a collecting well are set outside the ditch to prevent surface water from flowing into the ditch, and the sewage in the collecting well is discharged after precipitation.
(2) During excavation, a temporary drainage ditch is set in the basement, and the section size of the drainage ditch is 200mm×300mm. A 600mm×600mm×800mm collecting well is set every 20m along the temporary drainage ditch, and the water in the collecting well is pumped out of the groove by submersible pump.
(3) The leakage during trench excavation shall be handled in time, and the treatment methods are as follows:
A. When there is little water leakage, directly block it;
B. When the water leakage is large, swing spraying or grouting shall be carried out on the outside of the groove to stop water.
4. After excavation, if the earthwork meets the backfill quality requirements and is confirmed by the supervisor, it will be used as a filler, and the earth materials unsuitable for backfilling will be abandoned at the place designated by the owner and the supervisor.
5. When the trench is excavated, its section size must be accurate, the trench bottom should be straight, without landslide, water, oil pollution and sundries, and the corner should meet the design requirements.
6. Earthwork shall be transported by car and transported to the spoil ground along the temporary construction road on the construction site.
7. In this project, C 15 shotcrete is used to support the groove slope. Before slope protection construction, manual tamping and trimming must be carried out to avoid slope instability. Shotcrete shall be carried out from bottom to top, and the construction shall be carried out in strict accordance with the shotcrete technology, and the mix design shall be strictly implemented.
8. When excavating at night, there should be enough lighting facilities, and the excavation sequence should be arranged reasonably to prevent wrong excavation or overbreak.
Second, the earthwork backfill:
1. Earthwork backfilling can only be carried out after the pipeline installation is completed and qualified.
2. Backfill materials shall be selected from suitable excavated materials confirmed by the Supervisor or materials that have passed the test. Before backfilling, make sure there is no water in the trench. Silt, humus, frozen soil and organic matter shall not be backfilled.
3. The earthwork backfill adopts the method of layered symmetrical backfill and layered compaction, and the backfill thickness of each layer is not more than 300 mm ..
4. When the compactness of backfill soil can't meet the required density, appropriate amount of lime soil, sand, gravel or other materials that can meet the required density can be added according to specific conditions.
5. When backfilling the earthwork on both sides of the pipeline, collision with the pipeline should be avoided to avoid damage. After each layer is backfilled, it should be tamped with a rammer.
6. When backfilling the earthwork on the pipe top, the compaction degree below the subgrade surface shall be not less than 95% in the range of 0 ~ 800 mm, not less than 93% in the range of 800 ~ 1500mm and not less than 90% in the range of 1500mm. ..