Numerical simulation study on shear resistance of anchorage joints considering tensile-shear fracture criterion of 2G-NPR bolt

2G-NPR bolt (the 2nd generation Negative Poisson’s Ratio bolt) is a new type of bolt with high strength, high toughness and no yield platform. It has signifcant efects on improving the shear strength of jointed rock mass and controlling the stability of surrounding rock. To achieve an accurate simulation of bolted joint shear tests, we have studied a numerical simulation method that takes into account the 2G-NPR bolt's tensile–shear fracture criterion. Firstly, the indoor experimental study on the tensile–shear mechanical properties of 2G-NPR bolt is carried out to explore its mechanical properties under diferent tensile–shear angles, and the fracture criterion of 2G-NPR bolt considering the tensile–shear angle is established. Then, a three-dimensional numerical simulation method considering the tensile–shear mechanical constitutive and fracture criterion of 2G-NPR bolt, the elastoplastic mechanical behavior of surrounding rock and the damage and deterioration of grouting body is proposed. The feasibility and accuracy of the method are verifed by comparing with the indoor shear test results of 2G-NPR bolt anchorage joints. Finally, based on the numerical simulation results, the deformation and stress of the bolt, the distribution of the plastic zone of the rock mass, the stress distribution and the damage of the grouting body are analyzed in detail. The research results can provide a good reference value for the practical engineering application and shear mechanical performance analysis of 2G-NPR bolt.

Compensation excavation method control for large deformation disaster of mountain soft rock tunnel

In recent years,the mine tunneling method and the new Austrian tunneling method have been considered the main theories of tunneling approaches in China.It is difficult for the traditional technique to overcome the large deformation problems imposed by complex geological conditions of mountain soft rock tunneling.Hence,the compensation excavation method has been proposed to solve this issue under the consideration that all damage in tunneling originates from the excavation.It uses supportive strategies to counteract the excavation effects successfully.This paper provides an overview of the fundamental ideas of the compensation excavation method,methodologies,and field applications.The scientific validity and feasibility of the compensation excavation method were investigated through the practical engineering study of the Muzhailing and Changning tunnels.

In vivo evaluation of urokinase-loaded hollow nanogels for sonothrombolysis on suture embolization-induced acute ischemic stroke rat model

The urokinase-type plasminogen activator(uPA)loaded hollow nanogels(nUK)were synthesized by a one-step reaction of glycol chitosan and aldehyde capped poly(ethylene oxide).The resultant formulation is sensitive to diagnostic ultrasound(US)of 2 MHz.Herein,we evaluated the in vivo sonothrombolysis performance of the nUK on acute ischemic stroke rat model which was established by suture embolization of middle cerebral artery(MCA).Via intravenous(i.v.)administration,the experimental data prove a controlled release of the therapeutic protein around the clots under ultrasound stimulation,leading to enhanced thrombolysis efficiency of the nUK,evidenced from smaller infarct volume and better clinical scores when compared to the i.v.dose of free uPA no matter with or without US intervention.Meanwhile,the preservation ability of the nanogels not only prolonged the circulation duration of the protein,but also resulted in the better blood-brain barrier protection of the nUK formulation,showing no increased risk on the hemorrhagic transformation than the controls.This work suggests that the nUK is a safe sonothrombolytic formulation for the treatment of acute ischemic stroke.