Rock Mechanics and Rock Engineering

Steel wire meshes are a key component of rockfall protection barriers. The efficiency in reproducing the structure response with numerical methods relies upon the specific modelling technique employed to capture the wire mesh behaviour. The fabric of some rockfall meshes, such as chain-links is quite complex, which leads to sophisticated and costly numerical models, if modelled accurately. This paper presents an efficient approach to model the response of steel wire meshes to rockfall impacts by using shell elements to develop an equivalent continuum model. An elastoplastic behaviour is prescribed to the shell elements to reproduce the results of a set of experimental data, carried out on mesh portions under various load paths and boundary conditions. The idea is that simple laboratory tests can be used to calibrate an effective numerical model of the steel wire mesh with a significantly lower computational cost if compared to other effective solutions. The model’s ability in yielding consistent results when implemented at the structure scale is then assessed, based on the data of full-scale impact tests on a three-span low-energy rockfall barrier. The method can be extended to other wire mesh types and can find convenient application on exploring the response of a rockfall barrier with a cost-effective tool.

Fractures have significant impact on the stability of underground projects such as coal mining. The identification of geological features based on drilling parameters is a promising option for intelligent detection of rock formations. A series of studies conducted to identify fractures under unstable drilling conditions are presented in this paper. First, the forces acting around the drill bit are analyzed to further improve the force model of the two-wing PDC drill bit. Then, based on the self-developed borehole drilling device, the drilling parameters are collected in real time while drilling in concrete of different strengths and different fracture widths. Finally, the response characteristics of drilling parameters are analyzed, and the multi-parameter voting method is proposed for fracture identification. The experimental results show that when fracture width increases, the crushing area, which forms around the borehole when the drill bit encounters the fracture, tends to increase. The rate of penetration (ROP) increases suddenly, the revolution per minute (RPM) decreases, and the torque increases at fracture encounter. The sudden changes are recovered after passing the fracture. The multi-parameter voting method has a high recognition rate for fractures of width greater than 2 mm, but a relatively low recognition rate for fractures of 1 mm width. In addition to detecting fractures, the method performs well in predicting fracture location and fracture width.

The swelling characteristics of swelling soft rocks (SSRs) in the Yanji Basin, Northeastern China, have posed huge challenges to the construction of local highways. Based on the geological background, the swelling properties and strength characteristics of undisturbed and reconstructed SSRs, especially the constitutive relationship, are studied, which is of great significance to engineering practice. In this study, X-ray diffraction and scanning electron microscopy were used to determine SSRs’ mineral composition and microstructural characteristics. Swelling test, shear test, and unconfined compression test were used to identify the relationship between different water content of SSRs and free swell ratio (δe), swelling pressure (Pe), stress–strain characteristics, and strength, respectively. The results showed that (1) the mixed layer content of illite-montmorillonite in SSRs reached 95%. (2) δe and Pe were negatively linearly and exponentially related to the initial moisture content (ωs), respectively. Rapid and intense swelling mainly occurred at the initial swelling stage. (3) ωs were negatively linearly related to the shear stress (τ), cohesion (c) and the angle of internal friction (φ). In addition, SSRs with lower ωs suffered "strain softening" failure, while SSRs with higher ωs suffered "strain hardening" failure. (4) δe and the moisture content after swelling were both linearly related to the logc and logφ. Furthermore, the optimum moisture content (21–26%) of SSRs of the Yanji Basin’s project was determined for the first time. These results have already been applied to engineering practice in the Yanji Basin and other regions where SSRs are widely distributed.

Der seit Januar 1971 im Vortrieb befindliche Tauerntunnel liegt im Zentrum der ehemaligen „Alpenüberschiebung“, somit in einem geologisch-tektonisch äußerst interessanten, tunnelbautechnisch jedoch schwierigen Bereich. Die Tunnelbauarbeiten erfolgen nach den Prinzipien der Neuen Österreichischen Tunnelbauweise (NATM), welche sich bei den gegebenen geomechanischen Verhältnissen, die aus den gebirgsbildenden Vorgängen resultieren und durch tektonische Restwirkungen zu unerwarteten Gebirgsverhalten führten, bestens bewährten. Aus der Fülle interessanter Beobachtungen wird auf ein typisches Beispiel des Gebirgsverhaltens, vor allem aber auf den Bewegungsverlauf des den Hohlraum umgebenden Gebirges eingegangen, welcher mittels geomechanischer Messungen erfaßt und interpretiert wird. Schließlich wird durch Auswertung vergleichbarer Meßergebnisse aus den beiden Baulosen dieses Tunnels ein Vergleich versucht, der den tektonischen Einfluß der „Alpenüberschiebung“ herausarbeitet.