This paper, based on model and in-situ tests on tunnels supported by shotcreting and rockbolting, reveals the Carrying Capacity Rock Ring(CCRR). The methods to form the CCRR and its mechanism in difficult ground are discussed. According to CCRR theory and tunnel support experience in China, the support strategy in difficult ground is presented.
La presente these, basee sur le model et le teste sur place dans le tunnel supporte par l'injection de consolidation, demontre le phenomene de l'anneau de sotien de roche enveloppe dans les couches difficiles et sur son mechanism. Selon la theorie sur l'anneau de sontien de roche enveloppe et les experiences sur le support des tunnels en Chine, la strategie de support dans les couches difficiles est presentee.
Auf dem Modellversuche fuer stuetzung durch spruehrung unde Ankeilen im Tunnel sowie der Ergebnisse des Versuches an Ort und Stelle gegruendet, sind in diesem Schrifttum die Tragringe der Nebengesteine aufgezeigt, auBBerdem sind die Methode, nit der die Tragringe der Nebengesteine auf der schwierigen Erdshiche gebildet wurden, und ihr Mechanismus diskutiert werden. Gegruemdet sich auf die Theorie ueber die Tragringe der Nebengesteine und die Erfahrungen der Tunnelstuetsung bei und in China, sind die Gegenma- BBnahmen fuer Stuetung auf der schwierigen Erdschicht dargestellt werden.
Shotcreting and rockbolting as supporting means in underground engineering have fund wide application. Extensive theoretical and experimental studies on surrounding rock mechanical behavior and interaction between surrounding rock and support have been made. The author tries to explore the CCRR revealed by model tests and facilitated by shotcreting and rockbolting in tunnel engineering in order to get a deeper understanding for the essence of shotcreting and rockbolting and to discuss the methods for utilizing and bringing the carrying capacity of rock into full play.
Tests on round tunnels supported by shotcrete/rockbolt and supported by split- set rockbolt have been carried out on PYD 50 plane strain geomechanical model test unit. The test revealed that a reinforced zone can be formed around tunnel walls by shotcreting and rockbolting. In addition, with the increasing of external load, the rockmass out of reinforced zone was damaged, forming looseness. Tunnel was safe and reliable because loosened failure zone was far away from tunnel walls. In fact, it is mainly because of CCRR formed by shotcreting and rockbolting that has helped to bring about surrounding rock stable. The similar model design does not take any concrete project into consideration, but simulates the general rock conditions to make every effort to reflect the main features of support and to meet the similar needs. Assuming that the rock mass is a homogeneous medium and there are vertical principal stress and horizontal principal stress in ground stress field, then coeficient of side pressure λ=PH/PV, neglecting the effect of dead weight of rock mass. Test was conducted by method of exerting load at first and then excavating tunnel under plane strain conditions. Loading device is PYD-50 model test unit (Fig. 1). Main materials for making model are gypsum and sand. Tunnel excavation and support work were conducted under initial ground stress field. Overload test on model was made after the excavation and support were completely finished to investigate the condition of tunnel failure. Force-bearing condition of model tunnel is shown in Fig.2. It can be seen from Fig.3 that no failure occured on tunnel wall supported by shotcreting layer and rockbolt. In addition, reinforced zone of anchored body with thickness being same as rockbolt length was formed, while rock failure and loosening were produced out of reinforced zone of the anchored rock.