不同开挖方式下基坑受力变形特性三维数值分析

THREE-DIMENSIONAL NUMERICAL ANALYSIS OF STRESS DEFORMATION CHARACTERISTICS OF FOUNDATION PIT IN DIFFERENT EXCAVATION METHODS

基坑在不同开挖卸荷方式下引起的受力变形效应不同。针对此问题,运用有限元软件midas GTS建立理想化的三维基坑模型,研究悬臂支护基坑在岛式、分层、盆式3种开挖方式下支护结构、坑底土体、周边地表、工程桩的变形规律。结果表明:3种工况下支护结构的位移随着开挖深度的增加而增加,最大位移出现在顶部,岛式开挖下支护结构的变形比分层、盆式降低了10.33%、6.23%。坑底土体隆起变形呈“拱”形,基坑中心土体隆起最大,分层和盆式最大隆起量分别是岛式的1.086倍和1.044倍。周边地表以沉降为主,分层开挖最大沉降是岛式和盆式的2倍。坑底工程桩会受到支护结构变形的影响,离支护结构越近桩位移越大,岛式开挖对工程桩的影响范围约为1.48 H,分层开挖和盆式开挖对工程桩的影响范围约为1.8 H;工程桩桩身下部位置受拉,最大拉力出现在桩身的0.6~0.7 H处。

The stress deformation effect of the foundation pit caused by different excavation unloading methods are different.To solve this problem,an idealized three-dimensional foundation pit model is established by using the finite element software midas GTS,and the deformation rules of supporting structure,soil at the pit bottom,surrounding surface and engineering pile of cantilever supporting foundation pit under the three excavation methods(namely the island type,layered type and basin type)are studied.Results showed:the displacement of the supporting structure increases along with the increase of the excavation depth under the three excavation methods,the maximum displacement appears at the top and the displacement of the supporting structure in the island excavation type is 10.33%and 6.23%lower than that in the layered type and the basin type respectively.Besides,the uplift deformation of the soil at the pit bottom is in a''arch''shape,among which the soil in the center of the foundation pit is uplifted most,while the maximum uplift of the layered type and basin type is 1.086 and 1.044 times that of the island type respectively.The surrounding surface is mainly settlement and the maximum subsidence of the layered excavation type is twice that of the island type and the basin type.The engineering piles at the pit bottom can be affected by the deformation of the supporting structure,the closer the engineering pile is to the supporting structure,the greater the displacement becomes;the impact area of the island excavation on the engineering pile is about 1.48 H,while that of the layered excavation and the basin excavation is about 1.8 H;the lower part of the engineering pile body is strained,of which the maximum tension occurs at 0.6~0.7 H of the pile body.