The purpose of foundation pit construction monitoring is to grasp the actual state of supporting structure and the changes of surrounding environment in the process of dewatering, foundation pit excavation and construction in time, provide monitoring data for the safety and stability of foundation pit construction and surrounding environment, make construction controllable in advance, nip in the bud, and take necessary engineering measures. In addition, the results of construction monitoring can guide on-site construction, determine and optimize construction parameters, and carry out information construction. The monitoring items of foundation pit construction include the monitoring of surrounding environment and the systematic monitoring of protected objects including surrounding buildings, important roads and underground pipelines.
Before excavation, details such as excavation section, excavation machinery and slope protection measures should be drawn up according to construction drawings, site soil quality, groundwater level, existing underground and above-ground facilities and nearby buildings. This paper mainly discusses the method of man-machine combined excavation and earth borrowing.
The excavation sequence is from inside to outside: first loosen the soil in the middle part, then dig out the soil in the middle part, and then take down the soil around the well to form a big flat bottom. If there is water in the well, dig a big puddle in the middle of the well. In order to ensure that the soil at the bottom of the foundation pit will not be disturbed or destroyed during excavation, and to prevent overbreak during mechanical excavation, manual excavation will be adopted when the excavation reaches 20 cm ~ 30 cm before the design elevation, and it will be smooth. The excavation shall ensure continuous operation, smooth connection process and subsection excavation.
Earthwork should be piled up on one side, and excavated soil should not be piled up within 5m of the edge of foundation pit. At the same time, the slope of the mound shall not be steeper than1:1.5, and the maximum height shall not endanger the adjacent buildings or cause any danger to the safety of the project or personnel. Earthwork shall be transported out in time or used for filling according to the soil conditions, so as to facilitate the construction of subsequent processes.
Monitor the surrounding buildings and structures, and keep abreast of the impact of earthwork excavation on the environment. During excavation, special attention should be paid to the silt or cohesive soil in the foundation pit. Because under certain conditions, this kind of soft soil layer is easy to collapse, so when this kind of soil layer appears, necessary measures should be taken, such as keeping the groundwater level low and reducing the drainage of collecting wells. When excavating, if you encounter bad substances, you should transport them out of the site and deal with them as required. These sundries include tree roots, organic matter, silt, residual building materials and toxic substances.
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