Abstract: In order to find out the supporting effect of advanced support in silty clay tunnel, the ground settlement, crown settlement, surrounding rock pressure, concrete shotcrete stress and grid steel frame stress are studied by the methods of field test and numerical simulation with the third-phase project of Harbin Metro Line 1 as the engineering background. The conclusions of the study are as follows: (1) Grout diffusion range is too small and uneven, the improving effect of current grouting capacity for soil is poor; the mechanical parameters of the slurry soil have not been raised too much; and its indexes are no different from those of the ordinary soil mass. (2) Silty clay stratum has a certain resistance to the deformation caused by tunnel excavation; the tunnel deformation can reach stability in a short time whether or not the advanced support exists or not. (3) There are obvious differences in lateral stress distribution of surrounding rock; and the grid steel stress increases rapidly in accordance with the increase of the surrounding rock pressure, illustrating that the time and spatial effects of the advanced support which improve uneven surrounding rock load and delay the release of surrounding rock pressure in the silty clay tunnel is not existent. (4) As the range of plastic zone is 1.5-3.0 m roughly and the small pipe do not go beyond the plastic zone on the radial, the supporting effect of them is actually the compaction effect they have on the surrounding soil, which increases its density but cannot reach the effect of arousing the self-supporting capacity of surrounding rocks. (5) The maximum stress of the grid steel frame is only about 30% of its yield strength and the concrete shotcrete layer maximum stress is only about 13.6% of its axial compressive strength, which means it has a sufficient strength reserve to ensure a greater safety.

Key words: silty clay, advanced support, small pipe grouting, field tests, numerical simulation