# Research on the Stress Characteristics of Initial Tunnel Supports Based on Active Load Adjustment
###### Abstract
In the 1970s, [PERSON] and others put forward the energy support theory, and they believed that although the total energy contained in the surrounding rock was conserved, the surrounding rock released part of the energy in the process of interaction and synergistic deformation between the support structure and the surrounding rock; this part of the energy was absorbed by the support structure to achieve stability [18]. In the 1980s, Professor [PERSON] from Italy carried out theoretical and field test research on hundreds of tunnels and gradually established the geotechnical control deformation analysis method (ADECO-RS method). This new support method proposes that the load and deformation of the tunnel structure should be considered before the excavation stage [19]. At the end of 1990s, [PERSON] proposed the concept of \"yield control\" type support, i.e., the support is deformed altogether with surrounding rock before failure [20]. Subsequently, [PERSON] and [PERSON] highlighted that yield support can be achieved in two forms. One is to fill the compressible layer after rigid support, and the other is to use the combination of sliding steel frame and high compressibility shotcrete [21]. Yield support has been applied in a considerable number of tunnels. Different forms of fine control methods of load have been proposed as more insights have been gained relative to the interaction between the surrounding rock support. Numerous studies have been conducted worldwide on the stress characteristics of the initial support and how to adjust the support stress over the past few years. \"Flexible support\" and \"pressure-yielding structure\" have been proposed based on the concept of energy absorption and energy dissipation of surrounding rock to adjust and increase the support's force. For instance, lining supports, yielding anchor bolts, and retractable steel arches have been extensively used in the mining field [22; 23]. [PERSON] et al. systematically investigated the stress characteristics, failure process and evolution characteristics, ultimate bearing capacity, and deformation of different initial supports by conducting model experiments [24]. In accordance with different yield criteria, [PERSON] et al. investigated the entire process of support-surrounding rock interactions based on the ideal elastic plastic model [25]. [PERSON] et al. introduced the spatial effect of excavation surfaces into the interaction relationship between the support and surrounding rock and studied the entire process of dynamic interaction between support structure and surrounding rock at the early stage of deep buried tunnel [26; 27]. [PERSON] et al. proposed the \"limited support resistance damper\", and it is capable of effectively limiting the internal force of the support and controlling the stress release of the surrounding rock, which is used to solve the problem of tunnel support cracking caused by excessive stress [28]. [PERSON] et al. proposed a \"flexible support\" scheme (e.g., yielding support bolts) to control the continuous large deformation of surrounding rock [29]. Existing research has been essentially based on the support characteristic curve of the surrounding rock of tunnel. The purpose of adjusting and controlling the support load is achieved by adjusting support stiffness and support timing, which facilitates the development of the theoretical tunnel system. However, there are also some shortcomings. For instance, it is difficult to design different load distributions of the surrounding rock according to different tunnel cross-section forms for increasing the bearing capacity and long-term safety of the support structure; the bias load cannot be corrected. On the basis of previous research, this paper proposed a transfer and transmission method of tunnel surrounding rock load.