深基坑附近房屋出现裂缝的施工监测分析

ANALYSIS OF EXCAVATION MONITORING FOR HOUSE CRACKING NEARBY DEEP PIT FOUNDATION

针对明挖隧道深基坑旁6#房屋出现明显的墙体裂缝,结合施工设计开展相应的安全监测工作,监测内容主要有房屋裂缝、房屋沉降、土体深部位移、支护桩水平位移及爆破振动等。根据对典型裂缝测点和房屋周边环境的跟踪监测成果,对裂缝成因进行分析,推断出施工动荷载是房屋裂缝出现较快扩展的主要因素,冲孔桩施工使房屋墙体力学性能弱化,爆破开挖施工造成墙体出现裂缝,连续几天爆破振速超过1.0 cm/s时产生的已有裂缝将持续扩展;而环境温差对裂缝宽度变化有一定的影响。将分析成果应用于后续施工中,对7#房屋附近区域的爆破作业提出严格的振速控制要求,使7#房屋裂缝扩展速率得到很好的控制。

Obvious wall cracks appear on the house No.6 near the deep pit foundation of open-cut tunnel. With the characteristics of the cracks and construction design, safety monitoring in the area is conducted, which include house cracks, house settlement, displacements of deep soil, horizontal displacements of piles, blasting vibration, etc.. According to the numerical simulation and the monitoring results with rapid cracking in three stages, the causes of cracking are analysed, which exclude the factors such as uneven settlement, temperature difference, slope instability, anchor tension, etc.. The results show that dynamic load is the main factor which causes the rapid expansion cracks; and the mechanical properties of the wall are weakened by punch pile construction as well as cracks induced by blasting, and the original cracks will expand continuously if the vibration velocity of the wall is greater than 1.0 cm/s in several days. It is also shown that the temperature difference of environment has effect on expansion width of crack. Based on the above results, strict control measures for vibration velocity are adopted in blasting operation near the house No.7, making the original crack in house No.7 expand much slower than those in the house No.6 before being deal with, so that the cracks in the house No.7 are well controlled during the construction period, and the safety of the house is ensured.