一种模拟原状泥岩动力打桩与静载试验装置的研制及应用

Development and application of a test device for simulating pile driving and static load in undisturbed mudstone

针对泥岩地基打入桩贯入困难、承载力不足现象及软岩易扰动难以制备模型地基的特点,通过原状软岩约束单元、锤击贯入单元、导轨支架单元、静载单元4部分的设计与联系,初步研制了基于原状软岩的模拟打桩与静载试验装置,进行标定及验证性试验、应用试验,验证装置的可行性、稳定性,分析打入桩的沉贯与承载特性,明确桩周泥岩力学特征,提出进一步研究展望与工程应用建议。研究表明:(1)验证性试验、应用试验结果与现场试验结果一致,沉贯特性、承载特性与现场试验相同,验证了试验装置的可行性;(2)荷载传递相关因子α稳定性好,进一步证实了试验装置的荷载传递稳定可靠;(3)泥岩软硬互层严重,每10 mm贯入度通过锤击数表征的贯入阻力差异性大,低强度软夹层发生的静载破坏呈现出沉降急剧增大的陡降特征;(4)打桩对桩周2d(d为桩径)范围内的泥岩造成不同梯度的损伤,每间隔0.5d,强度损失66.0%、40.5%、17.0%、7.0%,弹性模量损失80.5%、54.5%、26.5%、11.0%;(5)完善取样技术,加强泥岩软硬互层的勘察判定,增强控制贯入度的施工措施,泥岩地基打入桩承载力的理论分析、数值计算及设计施工,应按损伤梯度合理选取原状力学参数折减后的数值。试验装置具有稳定、可靠、可控等优点,可为泥岩地基动力打入桩的相关研究提供支撑。

In response to the difficulties in driving piles into mudstone foundation,insufficient bearing capacity,and the difficulty in preparing a model foundation due to the disturbance of soft rock,a simulation pile driving and static load test device based on undisturbed soft rock was preliminarily developed.The device mainly includes undisturbed soft rock constraint model box unit,hammer-driven unit,guide rail support unit and static load unit.Calibration tests and application tests were carried out to verify the feasibility and stability of the device.The penetration and bearing characteristics of driven pile were analyzed,the mechanical characteristics of mudstone around pile caused by pile driving damage were defined,and further research prospect and engineering application suggestions were put forward.The study shows that:1)The results of tests are consistent with that of field test,and the penetration characteristics and bearing characteristics are both the same as those of field test,which verifies the feasibility of the test device.2)The stability of the load transfer factor α further proves that the load transfer of the test device is stable and reliable.3)As mudstone has intensive soft and hard interbedding,as a result,there is a significant difference in penetration resistance represented by the number of blows per 10 mm of penetration,and the static load failure of low strength soft interlayers presents a precipitously increasing settlement.4)The mudstone within 2d(d is the pile diameter)around the pile is damaged by pile driving;for every 0.5d interval,the strength loss is 66.0%,40.5%,17.0%,7.0%and the elastic modulus loss is 80.5%,54.5%,26.5%,11.0%,respectively.5)The reduced values of the undisturbed mechanical parameters should be selected according to the damage characteristics induced by pile driving in the design and bearing capacity evaluation of mudstone.The test device has the advantages of stability,reliability and controllability,which can provide support for related research on pile driving in mudstone.