Numerical prediction of the optimal shield tunneling strategy for tunnel construction in karst regions

Shield tunneling in karst areas poses significant challenges, as vibration caused by the shield machine can disturb the stability of the karst caves, ultimately resulting in the collapse of a tunnel. In the present study, a numerical model involving an iteration process was developed based on the Mindlin solution scheme to identify the optimal shield tunneling speed for minimizing the disturbance to karst cave stability. The developed model was then implemented to investigate an underground tunnel constructed in a karst region with different shield tunneling strategies. By using the variation in the energy density of a karst cave as a performance index, the model predicts that when approaching the affected zone of a karst carve (e.g., approximately 5 m from the carve), the shield tunneling machine should be controlled within a certain speed (i.e., < 30 mm/min). Once the shield tunneling machine moves into the affected zone of the cave, the speed of the machine needs to be decelerated to 11 mm/min, and the speed of 30 mm/min can be restored when the shield machine moves out of the affected zone. This finding demonstrates that the developed model could potentially be used to identify the optimal shield tunneling speed to minimize the disturbance to karst cave stability and ensure the safety of tunnel construction in karst regions.

Numerical and Experimental Study of a Device for Electrical Power Lines Probing for a Tunnel-Boring Complex Control System

The article considers the problems of the magnetic field distribution, generated by a power electric cable at the micro-tunnel-boring shield arrangement site by numerical modeling with a further full-scale device model experiment. The impact of foreign magnetic field sources on readings of three-component sensors was established in the process of the study. The considerable existence of parasitic noises, conditioned by external magnetic fields and high sensitivity of the probes, which will require the use of additional filters, was established. When using three-component ferroprobes, the most informative is the probe component coinciding with the tunnel shield longitudinal axis Z. The study showed that with current values greater than 200 A and changes in cable location during the experiment, it is possible to record signals from other sensor components and subsequently determine the location and orientation of the current-carrying cable. The experimental results obtained confirm the feasibility of a multi-sensor probing device for the micro-tunneling machine shield movement control system.

Improvement of Safety for the Underground Vertical Workings

The main scientific and practical calculations used to increase the efficiency of vertical mine workings based on studying the operation of tunneling complexes and road-heading machines, as well as by sectional blasting of the deep wells are presented in the article. This will ensure high-quality mine workings in accordance with the design and improve the operational safety throughout the entire service life. The methods are used related to the complex generalization, analysis and assessment of the practical experience and scientific achievements in the field of the underground geotechnology, theory and practice of explosive destruction of the solid media, mechanics of continuous media, mathematical statistics, as well as studies of the wave processes according to the standard and new methods developed by the leading experts from the leading mining countries of the world, including with the authors participation. Technological audit of the vertical working drilling and blasting was conducted using KPV-4A tunneling complex and the tunneling machine Robbins 73R, as well as the efficiency of conducting them in the cycle of mining operations was established. Mathematical modeling and calculation of the parameters of drilling and blasting operations were carried out using the contour blasting of explosive charges when driving vertical mine workings. Rounder of RS-220 type for the hole boring was recommended (complete with machine tool NKR-100MPА) of the downward wells with a diameter of 220 mm in rocks with a coefficient of f = 8–14 according to the scale of M.M. Protodyakonov, which is already being used at the mines of Ukraine, Russia, the Republic of Kazakhstan, and other countries. The new device for the contactless transmission of electricity from the stationary object to a mobile one was proposed, which will allow to improve the operating conditions of KPV-4A tunneling complex, LMSh-1 mine type elevator used for lifting and lowering people, small equipment, and materials along the rise workings, which is achieved due to external location of the cable rewinding mechanism and the absence of complex, for example, planetary mechanisms. It will also improve the efficiency and safety of work for the vertical mine workings in the rock massifs.