通过分析松散地层条件下地表点沉降规律和Knothe 时间函数模型在预测松散地层条件下的不足，在原时间函数中增加了表达松散地层下沉的时间影响参数c2，构成了双因素时间函数模型；理论分析结果表明，双因素时间函数模型具有收敛慢，对参数值变化适应性强的特点，但并不完全符合地表点动态下沉的全过程；为此结合双因素时间函数的特点对其进行改进，并在薄松散、厚松散和特厚松散地层3种不同条件下对改进后的双因素时间函数进行了验证计算。结果表明：改进后的双因素时间函数能较好的预测赋存不同厚度松散地层条件下地表点的动态沉降全过程。研究成果可为“三下”采煤提供参考。

In this study, we studied the surface subsidence law and the shortcomings of predicting surface subsidence by Knothe time function model under loose formation conditions. To express the loose formation subsidence, a time impact factor c2 is introduced into the original time, and a two-factor time function model is developed. Theoretical analysis results indicate that although the two-factor time function has characteristics of slow convergence and strong adaptability to parameter change, it is not complete in accordance with the dynamic process of the surface subsidence. Hence, we improve the two-factor time function，and then verify the applicability of improved two-factor time function for three different thickness (i.e., thin, thick and extremely thick) of loose strata. The results show that the improved function can predict the whole dynamic process of ground point subsidence under the conditions of different thickness of loose strata. The results performed in the study can provide reference for coal mining under building, railway and water body.