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.