Study on the characteristics of friction resistance and the mechanism of sudden sinking in the middle and late sinking stages of super large caisson foundation
SHI Zhou1，LI Siyang1，YANG Shili1，FENG Chuanbao2
(1. School of Civil Engineering，Southwest Jiaotong University，Chengdu，Sichuan 610031，China；2. Construction Headquarters of Nanjing Railway Terminal Project，Chinese Shanghai Railway Bureau Group Co.，Ltd.，Nanjing，Jiangsu 100142，China)
Abstract：According to the problems such as sinking lag，transient sudden sinking and so on of caisson foundations caused by the increasing frictional resistance in the middle and late period of sinking construction due to the increasing plane area，the theoretical formula of static and dynamical friction coefficients were proposed based on the theoretical study of the force composition of the bottom resistance，the friction resistance on the cutting edges and the lateral wall friction resistance during the sinking of the caisson. Taking the caisson foundation of Wufengshan Changjiang River Bridge as example，the friction resistance characteristics and the mechanism of the transient sudden sinking were investigated based on the measured data and the theoretical calculation results in the middle and late stages of sinking. The further control countermeasures of caisson sinking were analyzed. The results show that the lateral wall friction increases with the increasing sinking depth and accounts for more than 70% of the total resistance in the middle and late stage of sinking，which is regarded as the dominant factor of sinking stagnation. The force difference of instantaneous static and dynamical friction is the key factor causing the sudden sinking when the basement excavation is uneven and with local over excavation. The static and dynamical friction coefficients calculated from measured data of several cases of sudden sinking were between 0.444–0.525，0.245–0.401 respectively. And the dynamical friction coefficients were 0.56–0.77 times of corresponding static friction coefficients，which produced significant unbalanced force causing accelerative sinking of the caisson. The friction coefficient was effectively reduced to 0.225–0.325 with the sinking assistant methods such as air curtain，water level lowering，and the sinking coefficient was increased over 1.10，which are critical measures for avoiding sinking lag and sudden sinking of the caisson.
施 洲1，李思阳1，杨仕力1，冯传宝2. 超大型沉井基础下沉中后期摩阻力特性及突沉机制研究[J]. 岩石力学与工程学报, 2019, 38(S2): 3894-3904.
SHI Zhou1，LI Siyang1，YANG Shili1，FENG Chuanbao2. Study on the characteristics of friction resistance and the mechanism of sudden sinking in the middle and late sinking stages of super large caisson foundation . , 2019, 38(S2): 3894-3904.
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2019, Vol. 38 
