| Protection of surrounding environment including roads, buildings, pipelines etc. is one of the major difficuties during the foundation pit construction in cities. Recognizing the main factors and effect way which affect the surrounding environment by foundation pit construction, it raises controlling standards and protective measures accordingly, which has important economic significance and social influence. In this thesis, according to the experiences in foundation pit construction in Nanjing Hexi area, and combine with laboratory experiments and numerical simulation, as well as engineering monitoring and other methods, it explains the geological characteristics in Hexi area and its influence on surrounding environments, and focus on the surrounding environment affect by some factors such as soil reinforcement of foundation pit, the quality of retaining structures, overloading nearby and gushing water and sand, then the engineering measures to control the surrounding environment are presented. The main conclusions can be drawn as follows:1.The deposited soils in Hexi area belong to typical deposited structure of river binary phase: the upper layer is soft soil of floodplain phase, the bottom layer is the sand layer of bed phase. Under the influence by the Yangtze River and its historical changes during the deposition process of deposits, it presents that the characteristics of large variation in thickness, and dramatic changes in local section. In which, soft soil of floodplain phase has the characteristics of high water content, high compressibility, high sensitivity and low strength. During excavation of the foundation pit, it easily to appear big lateral displacement of retaining structures and uplift of foundation soil, and results of settlement the surrounding strata. Sand layer is a major aquifer in the Hexi area, which has high permeability, high groundwater levels and hydraulic connection with the Yangtze River, so the foundation pit excavation is often caused by water gushing well dewatering failure or defect of waterproof curtain take the sand, which led to the settlement of the surrounding strata.2.Bottom soil reinforcement range, the quality of retaining strucures and overloading near the foundation pit is easily ignored factor in the foundation construction in the Hexi area, and it has an important impact on the surrounding strata deformation. Studies have shown that if the bottom soil reinforcement range more than3～4m, the inhibitory effect of the surrounding strata of settlement has been slowing, it is recommended that the depth of soil reinforcement can be selected as3～4m; In addition, the study also showed that:when the substrate is fully reinforced, the largest settlement of the surrounding strata than the existence of1m reinforcement defects area reduced by1/3; foundation pit overload is one of the important resasons leading to strata settlements, and it’s reconmended reducing the overloading and its time to reduce the sourrounding strata settlement.3. Based on the gound surface settlement monitoring data in pumping test, and combine with typical construction dewateringin Hexi area, it’s indicated that surrounding settlement caused by foundation pit dewatering is very small, when no large number of particles bring out from the groundwater. In addition, the gound surface settlement monitoring results also indicate that:sand take from the pit will cause serious settlement, even collapse, influence its radius greatly, perhaps even more than50m.4.By summarizing the project experience and analyzing cases, it arised the control standards and protection measures of surrounding environment that suitable to Hexi in Nanjing city. Focused on the application effect of the foundation grouting reinforcement,foundation underpinning and correction technique in Hexi.The conclusion can provide reference for the similar projects in Nanjing Hexi area. |
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