Abstract: This deep excavation for a raft foundation is located at the northwest side of Yaoshan Mountain in Jinan City. The excavation included many components, which possesses the characteristics of large scale, deep dewatering depth, and short construction duration, etc. During the support of excavation and dewatering period, several construction difficulties were encountered and were resolved successfully. These challenges included excavation difficulties in the several soil strata, such as, silty fine sandy layers, the thick-bedded miscellaneous soil and the hard rock at the bottom of some cast-in-situ concrete piles; the conflict between the constructed raft foundation and dewatering well points, etc. For the first time, the concept of perched groundwater in depressed soil layer is proposed in this study. This paper summarizes potential factors that might results in groundwater leakage in the waterproof cut-off wall formed by jet grout method. And the solutions to the groundwater leakage are suggested. It is very beneficial for making use of the exploration data from the dewatering well points. The ground anchors with casing pipe were used with satisfactory results. The rotary drilling and the long all-flight bored technics were used flexibility in the soldier pile construction. During the construction of the raft foundation, a new dewatering device for the submersible pump left-in-place was invented, which can solve the contradiction between the dewatering devices for the foundation pit and the completed raft foundation. By utilizing this new method, the raft foundation and other structure were installed satisfactory. 

Key words: silty fine sand layer, perched groundwater in depressed area, deep excavation for a raft foundation, submersible pump left in place, ground anchor with casing