Study on the Construction Mechanical Response during Tunneling in Artificially Frozen Sandy Pebble Stratum

The artificial freezing method is an effective technique for tunnel construction in water-rich sandy cobble strata. It is of great engineering significance to clarify the construction mechanical response when tunneling in frozen sandy cobble strata. Considering the complexity sandy cobble strata, the uniaxial compression indoor tests and numerical tests of frozen sandy cobble soil under different rock contents were conducted. The concrete plastic damage constitutive model was employed to describe the mechanical property of frozen sandy cobble soil, a numerical model and an analysis method for simulating tunnel excavation in artificially frozen sandy cobble soil were established. Then, the tunnel excavation simulations in frozen strata with different rock contents were carried out, and the construction mechanical responses of frozen strata and lining structure were analyzed. The results show that rock content has a significant impact on the stress-strain curve of frozen sandy cobble soil. The center of the lining bottom plate, the junction between the lining bottom plate and the straight wall are the dangerous locations. The plastic zone width in the center of the bottom plate increases gradually with increasing rock content. However, the stress distribution pattern of the lining is not affected by the rock content. The surface settlement curves under different rock contents all can be described by Peck's empirical formula. With the increase of rock content, the maximum value of ground surface settlement and the uplift of bottom plate all increase linearly, while the vertical displacement of arch shoulder and straight wall monitoring point increase firstly and then decrease.