研究目的: 《铁路工程基桩检测技术规程》(TB 10218—2019)的4.4.6条文说明:反射波法检测端承桩的桩底反射信号应为反向特征,可现场检测端承桩的桩底反射信号多为正向特征少为反向特征;以及石灰岩地区施工灌注桩的岩溶漏浆,导致浪费混凝土还影响桩的完整性, 由此就反射波法检测端承桩的桩底反射信号特征,以及如何控制岩溶漏浆浪费混凝土进行研究。
研究结论: (1)端承桩机械成孔施工桩端岩石面粗糙不平且残留少量沉渣,形成平均厚度约50 mm的低阻抗沉渣混凝土,使桩底反射信号呈正向特征,只有少数桩端岩层强度大于桩混凝土强度的人工挖孔桩,桩底清扫干净且无水,其灌注桩的桩底反射信号呈反向特征;(2)端承桩施工岩溶漏浆且浪费混凝土,还引起桩严重离析,返工费时又费料,可改设永久双笼或永久钢护筒灌注桩施工;(3)本研究成果可为铁路、公路等领域在岩溶地区施工灌注桩提供参考。

Research purposes: The article 4.4.6 of the Technical Specification for Testing of Railway Piles (TB 10218-2019) states that: the reflection signal from the bottom of end-bearing piles detected by reflected wave method should be reverse feature, which can be used to detect the reflection signal from the bottom of end-bearing piles in situ, the reflection wave method is used to detect the reflection signal characteristics of the bottom of the end-bearing pile, which is more positive than reverse, and the karst leakage of the cast-in-place pile in limestone stratum leads to waste of concrete and affects the integrity of the pile. Therefore, the reflection wave method is used to detect the reflection signal from the bottom of end-bearing piles, and how to control the waste of concrete karst slurry is studied.
Research conclusions: (1) The rock surface at the end of the end-bearing pile is rough and uneven, and a small amount of sediment remains, which forms a low impedance sediment concrete with an average thickness of about 50 mm, which makes the reflection of the bottom of the pile present a positive feature, there are only a few hand-dug piles whose rock strength is greater than the strength of pile concrete. The pile bottom is clean and has no water. (2) The end-bearing pile construction causes karst leakage and waste of concrete, and also causes serious segregation of the pile, re-work and time-consuming materials, which can be replaced by permanent double cage or permanent steel casing pile construction. (3) The research results can provide reference for the construction of cast-in-place pile in karst area of railway and highway.