The stability of shallow tunnels excavated in full face has been a major challenge to the scientific community for a long time. In recent years, new techniques based on the installation of a pre-reinforcement system a...The stability of shallow tunnels excavated in full face has been a major challenge to the scientific community for a long time. In recent years, new techniques based on the installation of a pre-reinforcement system ahead of the tunnel face were developed to control the deformations and surface settlements induced by the excavation and to ensure the sustainability of the tunnel in the long term. In this paper, a finite difference numerical simulation was conducted to study the behaviors and effects of two pre-reinforcement systems, i.e. the face bolting and the umbrella arch system installed in a section of southern Toulon tunnel in France. For this purpose, two approaches were taken and compared： a two-dimensional （2D） approach based on the convergence–confinement method, and a three-dimensional （3D） approach taking into account the complete modeling of the tunnel. A 2D numerical back-analysis was performed to identify the geomechanical parameters that offer satisfactory agreement with the measurement results. The limit of this method lies in the exact choice of the stress relaxation ratio λ. To overcome this uncertainty, a 3D model was developed, which permitted to study the influence of different pre-support systems on the reaction of ground mass. Both 2D and 3D numerical approaches have been fitted to measurements recorded in a section of the Toulon tunnel and the very satisfactory correspondence has allowed validating the simulations. The results show that the 3D numerical analysis with a full discretization of the inclusions seems unquestionably the most reliable approach.展开更多
Densification of agricultural residues into briquettes as the alternative renewable feedstock can improve their physico-mechanical and storage properties as solid fuels.This paper presents the physico-mechanical prope...Densification of agricultural residues into briquettes as the alternative renewable feedstock can improve their physico-mechanical and storage properties as solid fuels.This paper presents the physico-mechanical properties of the composite briquettes made from corncob and rice husk.Raw samples of corncob and rice husk were collected,sorted and pulverised into fines of 0.25,1.00 and 1.75 mm particle sizes.The fines were blended at mixing ratios of 80꞉20,70꞉30,60꞉40,and 50꞉50,bonded with 5%starch on weight percentage basis and compressed at compaction pressures of 25,50,and 65 kPa to produce the briquette samples.The briquette made from 80:20 ratio of corncob to rice husk,0.25 mm particle size and 65 kPa pressure exhibited the highest compressive strength of 111 kN/m2 and the least of 39 kN/m^(2) from briquette with 50꞉50 ratio of corncob to rice husk,1.75 mm particle size and 25 kPa pressure.The briquette made from 50꞉50 ratio of corncob to rice husk,0.25 mm particle size and 65 kPa pressure had the highest water resistance capacity,and the least from briquette of 80꞉20 ratio of corncob to rice husk,1.75 mm particle size and 25 kPa pressure.The resulting physico-mechanical qualities of the produced corncob and rice husk briquettes suggested that they could be used as the solid fuels for domestic and industrial applications.展开更多
文摘The stability of shallow tunnels excavated in full face has been a major challenge to the scientific community for a long time. In recent years, new techniques based on the installation of a pre-reinforcement system ahead of the tunnel face were developed to control the deformations and surface settlements induced by the excavation and to ensure the sustainability of the tunnel in the long term. In this paper, a finite difference numerical simulation was conducted to study the behaviors and effects of two pre-reinforcement systems, i.e. the face bolting and the umbrella arch system installed in a section of southern Toulon tunnel in France. For this purpose, two approaches were taken and compared： a two-dimensional （2D） approach based on the convergence–confinement method, and a three-dimensional （3D） approach taking into account the complete modeling of the tunnel. A 2D numerical back-analysis was performed to identify the geomechanical parameters that offer satisfactory agreement with the measurement results. The limit of this method lies in the exact choice of the stress relaxation ratio λ. To overcome this uncertainty, a 3D model was developed, which permitted to study the influence of different pre-support systems on the reaction of ground mass. Both 2D and 3D numerical approaches have been fitted to measurements recorded in a section of the Toulon tunnel and the very satisfactory correspondence has allowed validating the simulations. The results show that the 3D numerical analysis with a full discretization of the inclusions seems unquestionably the most reliable approach.
文摘Densification of agricultural residues into briquettes as the alternative renewable feedstock can improve their physico-mechanical and storage properties as solid fuels.This paper presents the physico-mechanical properties of the composite briquettes made from corncob and rice husk.Raw samples of corncob and rice husk were collected,sorted and pulverised into fines of 0.25,1.00 and 1.75 mm particle sizes.The fines were blended at mixing ratios of 80꞉20,70꞉30,60꞉40,and 50꞉50,bonded with 5%starch on weight percentage basis and compressed at compaction pressures of 25,50,and 65 kPa to produce the briquette samples.The briquette made from 80:20 ratio of corncob to rice husk,0.25 mm particle size and 65 kPa pressure exhibited the highest compressive strength of 111 kN/m2 and the least of 39 kN/m^(2) from briquette with 50꞉50 ratio of corncob to rice husk,1.75 mm particle size and 25 kPa pressure.The briquette made from 50꞉50 ratio of corncob to rice husk,0.25 mm particle size and 65 kPa pressure had the highest water resistance capacity,and the least from briquette of 80꞉20 ratio of corncob to rice husk,1.75 mm particle size and 25 kPa pressure.The resulting physico-mechanical qualities of the produced corncob and rice husk briquettes suggested that they could be used as the solid fuels for domestic and industrial applications.
