旋挖成孔方式下螺纹状围岩粗糙度量化分析

Quantitative Analysis of the Pile-rock Interface Roughness Due to Rotary Drilling

嵌岩桩是大跨径桥梁工程中常用的一种基础形式。由于钻孔工具等因素,桩-岩界面上会形成系列起伏的三维粗糙体,其对桩基承载性能至关重要。因此准确量化实际三维桩-岩粗糙体的粗糙度特征,是建立基于界面粗糙度的桩基承载力设计方法首先需要解决的问题。为此,依托于马鞍山长江大桥深嵌岩桩基工程,在现场钻取含三维粗糙体的砂岩试样,利用三维激光扫描重塑桩-岩界面数字化模型,对其粗糙度特征值,面积扩展率(S)、相对平均起伏度(R_(s))和桩-岩界面平均倾斜角(θ)等进行量化分析;而后构建桩-岩界面试样开展3组界面剪切试验和3组界面抗压试样以计算试样的结构面粗糙度系数JRC^(3D)(joint roughness coefficient)值,并基于试验结果验证已有JRC^(3D)经验计算方法对桩-岩界面的适用性。结果表明:实际桩-岩界面既有规则的螺纹状凹槽,也有起伏较低的相对平整面,而非室内试验中规则粗糙体或不规则孔洞;实际桩-岩界面粗糙度远大于岩体结构面和室内规则粗糙体,面积扩展率、相对平均起伏度和界面平均倾斜角均明显较大;桩-岩界面JRC^(3D)均值(26.15)大于岩体结构面(标准轮廓线上限值20)和室内规则粗糙体,可近似采用JRC=6.423+2.329×(100S)-0.187R_(s)-2.676 tanθ公式估算。研究成果可为建立基于界面粗糙度的深嵌岩桩设计方法提供科学依据。

Rock socketed pile is a common foundation in long-span bridge engineering.Due to the drilling tools,a series of undulating rough bodies will be formed on the pile-rock interface,which contributes to the pile bearing capacity.Therefore,it is quite important to accurately quantify the roughness characteristics of actual pile-rock rough interface in calculating the pile bearing capacity considering the interface roughness.For this aim,the sandstone samples containing rough interface were drilled in the rock socketed pile foundation of Maanshan Yangtze River Bridge,and the digital model of the pile-rock interface was reconstructed using three-dimensional laser scanning,aiming to calculate the roughness characteristic,including area expansion rate(S),relative average undulation(R_(s))and the average inclination angle(θ)for quantitative analysis.Then,three shear tests and compression tests were performed on pile-rock interface to calculate the JRC^(3D)(joint roughness coefficient),and the results were compared with three analytical models to check their applicability for actual pile-rock interface.The results show that the actual pile-rock interface has both regular threaded grooves and relatively flat surfaces with low undulation,rather than regular rough bodies or irregular holes in experimental tests.The roughness of the actual pile-rock interface is much greater than that of the rock mass structural plane and the indoor regular rough body,i.e.,the area expansion rate,relative average undulation and average inclination angle of the interface of pile-rock interface are obviously larger than those of rock structure surface and regular rough body.The average JRC 3D of rock-pile interface(26.15)is larger than those of rock structural interface(maximum value of 20)and the indoor regular rough body,which can be estimated using JRC=6.423+2.329×(100S)-0.187R s^(-2).676 tanθ.The research results can provide scientific basis for establishing design method of deep rock socketed pile based on interface roughness.