Identification of the actual excess excavation ratio (Stakhanovskaya street – Nizhegorodskaya street site)

Introduction. Redundant strain arises in buildings and structures in areas of construction work influence caused by the deep bore tunneling performed by tunnel boring machines. The strain analysis must include an excess excavation ratio that depends on the structural features of the shield, the technology of grouting mixture injection outside the lining, the counterweight pressure applied to the shield face and geotechnical conditions so that excessive settlement could be taken account of. The purpose of the article is to identify actual values of the excess excavation ratio to raise excavation and determine the values of standard averaged excess excavation to be further applied in design. Materials and methods. This paper focuses on tunnel driving between “Stakhanovskaya Street” and “Nizhegorodskaya Street” stations. The project excess excavation ratio was applied pursuant to the regulatory documents in order to perform the analysis using PLAXIS 2D and PLAXIS 3D software packages. The method of sequential iteration was applied to identify the value of excess excavation in line with the actual settlement of buildings and structures obtained by means of monitoring. Results. The analysis has shown that the actual excess excavation ratio varies between 0.1 and 1.2 % for this construction site which is below the values required by the regulatory documents. As for the 3D setting, the values of actual excess excavation ratios are 2 to 4 times higher than those obtained for the 2D setting, although the value of the actual building settlement remains the same. Conclusions. Since the actual building settlement is smaller than the projected one, the cost of deep bored tunneling can be reduced by cutting the cost of protection of nearby buildings and structures within the area of tunneling influence without violating any safety requirements and also by reducing the number of buildings withing the projected area of influence, and respectively, by reducing the cost of geodetic monitoring over their displacements.