在经过大量有限元分析计算的基础上，论述了灰土井桩承载力随着桩长变化的规律性，提出了有效桩长的概念；并经过一些实测资料分析验证，证明了有效桩长存在的可靠性，同时指出深度效应问题是工程中值得注意的问题。 Based on a large number of finite element analysis calculations, the regularity of the change of pile bearing capacity with the length of piles is discussed. The concept of effective pile length is proposed. After some actual data analysis, it is proved that the effective pile length exists. Reliability, while pointing out that the depth effect problem is a noteworthy issue in engineering.