1.Introduction Shallow Overburden (Sauer Mergelsberg,2003) 百年问濟 4 TONGILUNIVERSITY 4 Shallow Overburden K < K 0 cr MODO I (K <1) 0 K > Kcr 0 0 0 K < K 0 cr MODO I (K <1) 0 K > Kcr 0 0 0 (Sauer & Mergelsberg, 2003) 1. Introduction