支盘桩外轮廓跨孔超声波检测现场试验研究

In-situ Experimental Study on Squeezed Branch Pile Outer Profile Cross-hole Ultrasonic Detection

目前有关定量评价支盘桩支盘/星支外轮廓检测方法局限于可行性研究,未有系统的、考虑实际工况的现场试验研究,无法为建立标准的支盘桩外轮廓检测提供有力支持。本研究开展支盘桩现场检测试验和理论研究,建立超声波透射法检测的技术工艺。首先,二次利用桩芯钻孔和打设桩周测斜管建立检测通道,通过地表管口建立直角坐标系并利用测斜数据进行测管定位以消除测管误差。其次,在混凝土内及桩周土内分别进行透射试验,测得超声波在混凝土和桩周土中的传递速度;利用跨孔超声波获得桩体超声波首波图,建立首波到达时间与桩身轮廓尺寸关系式,假设声波直线传播路径推导支盘轮廓尺寸。最后,考虑超声波在不同介质中的折射现象,依据Snell定律建立超声波透射法检测数据修正方法,并利用支盘桩几何关系计算出实际轮廓尺寸,形成支盘桩外轮廓跨孔超声波检测技术。研究表明超声波在桩身内传递的平均速度为4.24~4.36 km/s,与现场桩芯的平均速度4.27 km/s吻合;超声波在桩周土中传递速度随土层在1.65~1.8 km/s之间,与实际吻合。依据波列图计算的支盘位置和大体轮廓与设计相符,轮廓图显示桩身存在变形,基于Snell定律的修正算法可以更合理地计算支盘的实际轮廓尺寸。

The quantitative detection methods for squeezed branch pile(SBP) profile are limited to feasibility study by using model tests.There is a lack of systematic in-situ experimental study considering real working conditions for establishing standardized ultrasonic method.The in-situ tests and theoretical studies on SBP were conducted.The technical process for crossing-hole ultrasonic detection was established.Firstly,the detection channels were set up by reusing pile core boreholes and 3 inclinometers at periphery.The Cartesian coordinate system was established through surface openings,and the inclinometer data were used for tube positioning to eliminate tube errors.Subsequently,the crossing-hole ultrasonic tests were conducted within the concrete and surrounding soil to measure the propagation velocity of ultrasonic waves.The ultrasonic first wave diagram of pile body was obtained by using cross-hole ultrasonic method.The relation between first wave arrival time and pile body profile size was established.The linear propagation path was assumed to derive pile profiles.Finally,considering refraction phenomena in different media and Snell's Law,the data correction method was established.The actual contour dimensions were calculated by using SBP geometric relation.The cross-hole ultrasonic detection technique for SBP profile was formed.The result indicates that the ultrasonic velocity in pile body is 4.24-4.36 km/s,which is consistent with 4.27 km/s from in-situ pile core sample.The ultrasonic velocity in surrounding soil of ranges between 1.65 km/s and 1.8 km/s,which is consistent with the tested values.The position and general outline of braches calculated according to the wave diagram are in agreement with the design.The profile diagram reveals pile deformation.The correction algorithm based on Snell's Law enables the more accurate calculation on actual profile.