反压土及注浆对重庆深基坑的影响研究

Research on the Influence of Earth Berm and Grouting on Deep Foundation Pit in Chongqing

为提高基坑数值模拟的准确性,利用Plaxis里的Hardening Soil Model,对7种不同反压土宽度条件下,重庆某悬臂式桩板挡墙支护的深基坑进行数值计算分析,研究表明反压土宽度的增加可有效减少支护桩桩顶水平位移、坑后地表沉降及桩身最大弯矩;随着反压宽度增大,这种效果大多逐渐被削弱。随后,对支护桩周边土体“注浆”与“不注浆”两种情况下,该基坑的数值计算结果进行对比分析,研究表明坑底注浆加固后,桩顶水平位移、坑后地表最大沉降及桩身最大弯矩能减小17%~25%,效果显著。最后,对坑底反压及注浆的最优策略进行了探讨,研究表明,坑底注浆且反压土宽度不超过0.64H(H为基坑开挖深度)时,桩顶水平位移、坑后地表最大沉降及桩身最大弯矩随反压土宽度增大的减少量最明显。对于类似工程,建议对反压土顶面以下支护桩周边土体进行注浆加固,且反压宽度不宜超过0.64H。

In order to improve the accuracy of numerical simulation of foundation pit,the Hardening Soil Model in Plaxis is used to carry out finite element numerical calculation for a deep foundation pit supported by a cantilever pile-sheet retaining wall in Chongqing.Seven different width of the earth berm remained are compared.The study shows that,with height and slope ratio of the earth berm remained unchanged,the increase of the earth berm width can effectively reduce the horizontal displacement of the supporting pile top,the maximum ground settlement after the pit,and the maximum bending moment of the pile.As the earth berm width increases,this effect is gradually weakened.Subsequently,the numerical calculation results of the foundation pit excavation are compared between the"grouting"and"no grouting"of the soil below the top surface of the earth berm.The study shows that after grouting at the bottom of the pit,the horizontal displacement of the pile top,the maximum ground settlement after the pit,and the maximum bending moment of the pile can be significantly reduced by 17%~25%.Finally,the optimal strategy for earth berm and grouting is discussed.The study shows that when the bottom of the pit is grouting and the width of the earth berm remained does not exceed 0.64H(H is the foundation pit excavation depth),the horizontal displacement of the pile top,the maximum ground settlement after the pit,and the maximum bending moment of the pile decrease most obviously with the increase of the earth berm width.For similar projects,it is recommended that the soil around the supporting piles below the top surface of the earth berm be reinforced with grouting,and the earth berm width should not exceed 0.64H.