Study on the Mechanical Characteristics and Optimization of Composite Lining Structure Under High Geostress

Abstract

ABSTRACT Aiming at the problem of high geostress faced by deep buried tunnel, the mechanical characteristics and optimization of composite lining structure are studied. The influence of consolidation grouting ring and backfill grouting measures on the mechanical characteristics of composite lining structure are studied based on the three-dimensional finite element calculation theory, so as to determine the optimal thickness of concrete lining. The maximum tensile stress of 20cm lining during operation is about 8.73MPa, and that of 120cm lining during operation is about 4.68MPa. The maximum pressure stress during the construction period of 20cm lining is about −13.47MPa, and the maximum pressure stress during the construction period of 120cm lining is about −4.95MPa. After the pre-consolidation grouting of class IV surrounding rock, the maximum tensile stress during the operation period decreases. If backfill grouting is not carried out within 120° of the top arch of the lining, the maximum tensile stress during the operation period and the maximum compressive stress during the maintenance period are significantly increased, so the backfill grouting of the lining and its grouting quality have a significant role in improving the bearing capacity of the composite lining structure. INTRODUCTION With the continuous construction of water conservancy and hydropower projects in China, a number of deep-buried, long and large diversion tunnels crossing high altitude and high mountain areas have emerged, which are significantly different from the diversion tunnels of conventional power stations. The lining structure of deep-buried, long and large diversion tunnel is affected by many adverse factors, such as large burial depth, long tunnel line, large section, rich groundwater, high water head and high geostress level. The design and construction of lining structure is very difficult. The geological conditions in the western mountainous areas are complex, and the construction of deep-buried large-section tunnels is very easy to cause engineering accidents such as landslides, water inrush, mud inrush, etc. The main reason is the lack of understanding of the stress of such tunnel lining structures.