Cut blasting is one of the most essential processes to reduce blast-induced vibration in tunnel blasting. The long and large-diameter uncharged hole boring (LLB) method is an example of one of the cut blasting methods, which utilizes large-diameter uncharged holes drilled in the tunnel face. In this study, blasting simulations were performed to analyze its blasting mechanism, and the LLB method and the traditional burn-cut method were simulated to compare their blasting efficiency. A 3D numerical analysis using LS-DYNA code, a highly non-linear transient dynamic finite element analysis using explicit time integration, was used to simulate the blasting process, and a Johnson–Holmquist constitutive material model, which is optimal for simulating brittle materials under dynamic conditions, was used to simulate the rock behavior under blasting. The modified LLB method showed a 3.75-fold increase in the advance per round compared to the burn-cut method, due to the increased formation of long and large-diameter uncharged holes compared to blast holes. This modified LLB method used 30% less explosives, so its failure range was approximately 1.25 times less than that of the burn-cut method, but its advance was approximately 4 times larger than the burn-cut method, which was similar to the original LLB method. This confirmed that the modified LLB method is significantly more efficient in terms of increased blasting efficiency (particularly the advance per round) as well as reduced blast-induced vibration, compared to the traditional cut blasting method.

The new Austrian tunnelling method (NATM) and tunnel boring machine (TBM) are methods for excavating underground spaces. The NATM construction method has noise and vibration problems, and excavation using TBM has the disadvantage of high initial cost and is limited by ground conditions. A parallel TBM and NATM construction method has been developed to overcome these limitations. However, research on the TBM and NATM parallel construction method is lacking, and it is crucial to identify the applicability of the TBM and NATM parallel construction method in advance by applying it to various ground and blasting conditions. In this study, based on the vibration measurement data of the excavation site using the NATM construction method, the vibration measurement values generated when excavating the top surface using the existing NATM construction method and the TBM and NATM parallel construction methods were compared. Lastly, the vibration reduction effect of the two construction methods was analysed according to the tunnel excavation depth and tunnel size through 3D numerical analysis. As the depth of tunnel excavation increases, the vibration at the ground surface is reduced by up to 83%. In addition, as the ratio of the size of the blasting surface with NATM and the excavation surface with TBM is closer to 1.0, the vibration decreases.

Vital underground structures such as sewers, power transmission lines, subways, and underpasses are potentially vulnerable to adverse effects from aboveground construction. In this study, the influence of pile installation on nearby existing tunnels was investigated. Both a laboratory model test and finite-element numerical analysis were conducted. Twelve different combinations of horizontal and vertical offsets between the pile and the tunnel were investigated. Different surcharge loads (allowable and ultimate) were also considered. In this way, the appropriate separation distance between the existing tunnel and the piles was established for sandy, medium-compaction soil. Although this study considers simple ground conditions, it facilitates safe construction by confirming the appropriate separation distance and comparing the areas that cannot be penetrated by the structures of each standard.

In this study, a series of rock cutting tests was conducted using a conical pick to investigate the effect of joints on roadheader performance. Tests were performed on intact rock and jointed rock mass specimens with three different joint spacings. The results indicate that cuttability is enhanced in jointed rock mass compared to intact rock due to the influence of joints on fracture mechanics. When cutting perpendicular to the joint plane, joints shorten the fracture path for rock chip formation, reducing the cutting force (FC). In parallel cutting, the joint plane acts as a barrier to side-crack propagation, leading to a further reduction in FC. The FC and specific energy (SE) were generally lower in parallel cutting than in perpendicular cutting. However, when the cutting depth exceeded 0.2 times the joint spacing and the line spacing surpassed 0.4 times the joint spacing, this trend reversed. This occurred because joints hindered the interaction between adjacent cuts, causing a transition to an unrelieved cutting mode. Additionally, FC and SE increased with joint spacing. When joint spacing reached ten times the cutting depth, their values approached those of intact rock. This suggests that the joint effect becomes negligible. These findings provide a better understanding of the effect of joints on roadheader performance.

This study introduces a simplified method for predicting the optimal cutting conditions to maximize excavation efficiency based on tool forces. A laboratory-scale linear rock-cutting test was conducted using a conical pick on Finike limestone. The tool forces and their ratios were analyzed in relation to cutting parameters such as penetration depth and spacing. While the cutting force (FC) and normal force (FN) increased with the penetration depth and spacing, this relationship could not predict the optimal cutting conditions. The ratio of the mean normal force to the mean cutting force (FN_m/FC_m) increased with the penetration depth and the ratio of spacing to penetration depth (s/d). However, even while including this relationship, predicting optimal cutting conditions remained challenging. The ratio of the peak cutting force to the mean cutting force (FC_p/FC_m) reached a maximum value at a specific s/d, which is similar to the relationship between the specific energy (SE) and s/d. The optimal s/d obtained through the SE methodology was found to be between 3 and 5, and FC_p/FC_m reached a maximum at s/d. The error between the optimal s/d and the s/d in which FC_p/FC_m was maximized was less than 5%. Therefore, it was confirmed that the optimal cutting conditions could be predicted through the relationship between FC_p/FC_m and s/d. Additionally, by using the results from previous studies, the optimal cutting conditions obtained from the SE methodology and the proposed methodology were found to agree within a margin of error of 20%. The proposed methodology can be beneficial for the design of cutter heads and the operation of excavation machines.

The long and large-diameter uncharged hole-boring (LLB) method is a cut-blasting method used to reduce vibration induced by blasting. This method typically involves creating an uncharged hole with a 382 mm diameter and drilling 50 m in the tunnel excavation direction at a time. This method is reported to provide relatively good vibration reduction and with high blasting efficiency through short hole blasting compared to traditional cut methods. In this study, an advanced LLB method incorporating deck charge blasting was investigated to improve the blasting efficiency during long hole blasting. Numerical analysis was performed via ANSYS LS-DYNA to investigate the effectiveness of the deck charge technique. In the original LLB method, explosives were used to break the rocks more finely, and the fragmented rocks were concen trated at the end of the blast holes. On the contrary, the modified LLB, in which two-part explosives were loaded into the blast holes, is expected to push the fragmented rocks to the tunnel face more effectively than the original LLB method. Therefore, it is expected that the proposed LLB method combined with a deck charge technique can achieve superior blasting efficiency.