锤击打桩桩周岩土体力学特性试验研究

Experimental study on mechanical properties of rock and soil around hammer driven piles

为研究打桩前后桩周黏性土和泥岩力学性质的变化,在打桩前后分别进行标准贯入试验,分析了桩周黏性土与泥岩经打桩扰动后的力学特性,探讨了桩周岩土体力学性质变化的影响因素,提出了减小扰动、保证桩周岩土体力学性质的工程措施。研究表明:锤击打桩导致桩周泥岩力学性质降低,桩周泥岩产生损伤;黏性土随打桩产生的超静孔隙水压力逐渐消散,其力学性质28d后基本恢复,但不同黏性土的消散速率不同,力学性质恢复存在差异;泥岩打桩损伤后很难恢复,打桩前后同深度处以标贯锤击数表征的力学性质最大差异超过2倍;若存在软弱夹层,会加剧打桩对泥岩的影响;地下水、软弱夹层、打桩扰动是影响桩周泥岩力学性质的关键因素。

In order to study the changes in mechanical properties of cohesive soil and mudstone around piles before and after pile driving,standard penetration tests before and after pile driving are conducted.The changes in mechanical properties of cohesive soil and mudstone around the pile are analyzed after pile driving and the influencing factors leading to changes in the mechanical properties of the soil around the pile are discussed.Engineering measures to reduce disturbance and to ensure the mechanical properties of rock and soil around piles are proposed.The study shows that hammer driving reduces the mechanical properties of mudstone around the pile,mudstone around the pile is damaged;the excess pore water pressure generated by pile driving in cohesive soil gradually dissipates after 28 days,the mechanical properties of the soil are basically restored,but the dissipation rate of different cohesive soils is different,and the mechanical properties are different;it is difficult to restore the mechanical properties of mudstone after pile driving,the maximum difference in mechanical properties of mudstone characterized by standard penetration hammer blows at the same depth exceeds 2 times;if there is a weak interlayer,it will exacerbate the impact of pile driving on the strength of mudstone;groundwater,weak interlayers,and pile driving disturbance are key factors affecting the mechanical properties of mudstone around piles.