Mechanical Excavation Research Articles

Hard rock fragmentation by dynamic conical pick indentation under confining pressure

Mechanical mining and excavation in deep metal mines can be regarded as the process of crushing hard rock by conical pick indentation. In this study, a confining pressure loading device was designed and used to carry out dynamic conical pick indentation crushing tests under confining pressure conditions on three types of granite with varying strengths, using the Split Hopkinson Pressure Bar (SHPB). The objective was to quantitatively investigate the effect of confining pressure and rock strength on the indentation crushing characteristics of deep hard rocks. The results indicate that as the confining pressure increases from 5 MPa to 20 MPa, the dimensional parameters such as volume, diameter and depth of the impact groove decrease linearly, while parameters such as the specific energy, indentation force, indentation index and energy utilization rate progressively increase. The increase in the confining pressure inhibits the formation of internal cracks in the rock, enhancing its resistance to pick indentation, which in turn makes rock fragmentation more difficult. This creates unfavorable conditions for efficient rock breaking. Furthermore, rock strength plays a crucial role in the pick indentation process. The higher the rock strength, the greater its resistance to pick indentation, leading to increased energy consumption, accelerated wear of the conical picks, and reduced efficiency in rock breaking.

Size-Dependent Mechanical Properties and Excavation Responses of Basalt with Hidden Cracks at Baihetan Hydropower Station through DFN–FDEM Modeling

Basalt is an important geotechnical material for engineering construction in Southwest China. However, it has complicated structural features due to its special origin, particularly the widespread occurrence of hidden cracks. Such discontinuities significantly affect the mechanical properties and engineering stability of basalt, and related research is lacking and unsystematic. In this work, taking the underground caverns in the Baihetan Hydropower Station as the engineering background, the size-dependent mechanical behaviors and excavation responses of basalt with hidden cracks were systematically explored based on a synthetic rock mass (SRM) model combining the finite-discrete element method (FDEM) and discrete fracture network (DFN) method. The results showed that: (1) The DFN–FDEM model generated based on the statistical characteristics of the geometric parameters of hidden cracks can consider the real structural characteristics of basalt, whereby the mechanical behaviors found in laboratory tests and at the engineering site could be exactly reproduced. (2) The representative elementary volume (REV) size of basalt blocks containing hidden cracks was 0.5 m, and the mechanical properties obtained at this size were considered equivalent continuum properties. With an increase in the sample dimensions, the mechanical properties reflected in the stress–strain curves changed from elastic–brittle to elastic–plastic or ductile, the strength failure criterion changed from linear to nonlinear, and the failure modes changed from fragmentation failure to local structure-controlled failure and then to splitting failure. (3) The surrounding rock mass near the excavation face of underground caverns typically showed a spalling failure mode, mainly affected by the complex structural characteristics and high in situ stresses, i.e., a tensile fracture mechanism characterized by stress–structure coupling. The research findings not only shed new light on the failure mechanisms and size-dependent mechanical behaviors of hard brittle rocks represented by basalt but also further enrich the basic theory and technical methods for multi-scale analyses in geotechnical engineering, which could provide a reference for the design optimization, construction scheme formulation, and disaster prevention of deep engineering projects.

Mechanical properties and damage constitutive relationship of microwave irradiation of granite under uniaxial compression

Microwaves have great potential to increase the efficiency of hard rock breakage during mechanical excavation in engineering. This study conducted uniaxial compression tests on granite specimens after microwave irradiation at 4.85 kW. The results demonstrated a linear decrease in uniaxial compressive strength and elastic modulus correlating with increasing irradiation durations. Acoustic emission data indicated increased normalized crack closure stress and decreased normalized crack initiation and damage stress, suggesting complex crack propagation and evolution patterns under microwave influence. 3D Digital Image Correlation revealed that as heating time increased, the macrocrack leading to specimen failure shifted from being load-dominated to involving both load and microwave-induced thermal cracks. A simple four-parameter damage constitutive model for granite (a 1, r 1 , a 2, and r 2) effectively described the damage evolution under the coupling effect of microwave and uniaxial load. The model accurately characterized the complete stress–strain curves, including both microcrack compaction and post-peak stages, revealing that initial damage escalates with longer heating, though the progression rate decreases.

Microwave-assisted TBM cutter for efficient hard rock fracturing in high stress environments

Elucidating the effects and fundamental mechanisms of microwave-assisted mechanical excavation under high initial stress conditions is of paramount importance for enhancing the efficiency of deep resource extraction. In this study, indentation experiments were conducted on microwave-damaged rock under initial stress conditions using a tunnel boring machine (TBM) for the first time. By integrating acoustic emission, digital image correlation, and the discrete element method, we conducted a comprehensive analysis of the multifaceted effects of microwave irradiation and initial stress on rock fracturing. The rock-breaking efficiency was evaluated based on the volume of broken rock and the energy consumption. The indentation failure of the sample can be divided into three stages: microfracture closure, elastic deformation, and unstable crack propagation. The microwave irradiation reduced the peak load during the indentation process and simultaneously reduced the brittleness of the specimen. The experimental and simulation results jointly demonstrated the existence of an initial stress threshold in the rock fracturing process. When the initial stress is below the threshold, it suppresses the extension of rock fractures, which is unfavorable for rock fragmentation. When the initial stress exceeds the threshold, stress-induced rock failure occurs, which promotes rock fragmentation. A notable observation is that microwave irradiation alters the initial stress threshold of the rock, where a higher microwave power correlates with a lower initial stress threshold. This indicates that the optimal parameters for microwave equipment must be reconsidered when the initial stress changes. Methods for optimizing rock breakage at initial stress were suggested and examined.

Evaluation of rock cutting performance of conical cutting tool based on commonly measured rock properties

Efficiency of rock cutting process plays a critical role in performance of mechanical excavation units. The composition of cutting forces (normal and drag force acting on cutting tools) and the total force (FT), specific energy (SE), and percent of fine material (FM) produced in cutting process are important indicators of efficient cutting process. The other key factors in assessment of machine performance are tool wear, energy consumption, dust production, and machine maintenance, availability, and utilization. In this study, small scale linear cutting experiments were performed with a conical pick on thirteen sedimentary and metamorphic weak to medium strength rock samples at a range of 0.5 to 6 mm cutting depths in unrelieved cutting mode. FT was measured by using a 3D dynamometer and recorded by the data acquisition system, and FM was determined by sieve analysis. Finally, SE was calculated using both the cutting force signal and the volume of the cuttings for each test. Subsequently, an analysis of the effective cutting geometry was performed based on cutting depth, using the specific energy as an indicator of cutting efficiency. Statistical and regression analysis was used to correlate FT, SE, and FM with the rock properties and cutting geometry. The results revealed that the uniaxial compressive strength, Schmidt rebound number, and density are the main parameters that affect FT and SE, and the brittleness index is the main parameter that affects FM. A nonlinear predictive model is introduced that offers a reasonable estimate of FT, SE, and FM to assist engineers in determining the effective operational cutting geometry for a given rock type for unrelieved cuts.

True triaxial test and DEM simulation of rock mechanical behaviors, meso-cracking mechanism and precursor subject to underground excavation disturbance

Mechanical excavation or blasting generates stress waves that rapidly dissipate in the surrounding high-geostress rock, causing microdynamic disturbances. These disturbances trigger microcracks within the damaged rock, even inducing engineering disasters. However, the fracture behaviors and mechanisms of rockmass subjected to excavation disturbances under three-dimensional geostress remains unclear. Therefore, this study proposed a true triaxial static–dynamic combined loading method to capture the entire process of tunnel excavation damage and the continuous fracturing induced by microdynamic disturbances. True triaxial static–dynamic combined tests and numerical simulations using PFC3D-GBM were employed systematically to analyze the influence of principal stresses σ1, σ2, and σ3 on the disturbances mechanical behaviors of the gabbro. The disturbance failure under true triaxial stress indicated a three-stage pattern of deformation: deceleration, constant velocity, and acceleration. With increased σ1 or decreasing σ2 and σ3, the disturbance bearing capacity of the gabbro significantly decreased. Moreover, an increase in σ1 and σ3 corresponded to an increased proportion of intergranular shear cracks, whereas an increase in σ2 resulted in a notable increase in intragranular tensile cracks. Small-magnitude events tended to disperse during the deceleration and constant-velocity stages, whereas larger-magnitude events were concentrated during the acceleration stage. The AE parameter b-value initially increased and then decreased during disturbance fracture process. The excavation disturbance of the tunnel intensified the depth of the damage zone and the energy released, thereby increasing the risk of a catastrophic deep fracture.

Numerical and Preliminary In Situ Investigation on Roadway Excavation Using Static Expansion Mechanical Fracturing

This paper introduced a new nonexplosive roadway excavation method, combining the reserved free space technology and the static expansion mechanical fracturing technology, where the former is implemented by the gasbag, while the piston splitter is for the latter. The numerical model of roadway excavation was set up via PFC3D to investigate the mechanical fracturing performance, including the single-hole fracturing and the hole network fracturing. The results show that the reasonable hole margin is about 1.0–1.5 m, and the optimal column spacing of the hole network pattern is 1.0 m, after comprehensively analyzing the fracturing performance and the splitting force evolution. Moreover, the mechanical fracturing excavation method was applied to construct a parking chamber in the Kalatongke Mine, to preliminarily verify the feasibility of the static expansion mechanical fracturing technology. The in situ investigation results indicate that the excavation footage is about 0.8 m with the piston splitter when adopting a hole margin of 1.0–1.5 m. To sum up, the preliminary field application and the numerical simulation result both support the feasibility of mechanical fracturing, and the reasonable fracturing hole margin is about 1.0 m.

Effects of changing water content of clay-content rocks on field cutter consumption rate of roadheaders: a case study of porous ignimbrites

The changing formation characteristics during excavation can cause a higher cutter consumption rate (CCR) of mechanical excavators than theoretically estimated before the project begins. This study investigates the adhesive potential of clay-content porous ignimbrites in increasing water content and their effects on the CCR of roadheaders. For this purpose, the actual field CCR data of roadheaders were recorded for ten cold storage caverns (CSC) projects during the excavation in dry and wet conditions. Then, laboratory tests were carried out on the rock samples collected from project areas. CCRs of roadheaders were theoretically estimated based on the Cerchar abrasivity index of rocks using three different empirical models. The laboratory test results showed that increasing water content reduces the abrasivity and strength of the rocks. The theoretically estimated results also showed that CCR is to be less under saturated conditions. However, actual field data revealed higher CCRs for all CSC projects in wet conditions. Therefore, the adhesion potential of rocks in different water contents was analyzed, and positive relationships were obtained between the field CCR in wet conditions and the adhesion potentials of excavated rocks with 15%, 20%, and 25% water content. New equations were developed to estimate the CCR of roadheaders, especially in excavating rocks that have an adhesive potential to cutters, such as clay-content rocks. It has been concluded that for an accurate CCR estimation, more than theoretical calculations will be required, and changing formation conditions should also be analyzed in detail.

Optimization-based design support for engineer-to-order product quotation

AbstractQuotation of engineer-to-order products provides substantial challenges in effectively managing engineering resources. This paper describes an approach that rationalizes this process by integrating multi-disciplinary design analysis and optimization with a new open-source library for managing engineering knowledge before and after optimization. The approach is applied and evaluated on mechanical rock excavation machines. Adapting the approach and considering the user feedback gathered can lead to an enhanced design space overview during quotation and thus more competitive product offerings.

Optimization of blasting construction and vibration control technology of multi arch tunnels without central partition walls

The construction technology for multi arch tunnels without central partition walls is a new design method for multi arch tunnels. The construction technology of multi arch tunnels without central guide tunnels eliminates side and central guide tunnels, which not only accelerates construction progress but also ensures construction quality and safety. The excavation and support of the rear tunnel of a double-arch tunnel without a central partition are crucial to ensuring the overall stability of the tunnel structure. A combination of manual mechanical excavation and blasting excavation in some areas was used in the excavation and construction of the rear tunnel of the Chenjiachong Tunnel on the Chuyao Expressway in Yunnan in addition to damping materials and measures in the lining of the front tunnel, ensuring the safe excavation of the rear tunnel and the prevention of the lining of the front tunnel from cracking because of earthquakes, The on-site vibration monitoring results of the tunnel indicate that this technology has achieved good results. Overall, the optimized construction technology without a central partition greatly shortens the construction period and improves economic benefits. The construction method is simple and feasible and can be flexibly selected according to the surrounding rock conditions. This study can provide a reference for the construction of other highway tunnels in mountainous areas.

Mechanical excavation of wetland habitat failed to eradicate invasive American red swamp crayfish (Procambarus clarkii) in Malta

Abstract Invasive crayfish are an important ecological concern in many freshwater ecosystems. Many efforts have been made to eradicate them, but there is very little documentation of the effectiveness of these efforts. Between 2019 and 2020, a restoration project funded by the European Regional Development Fund tried to eradicate invasive American red swamp crayfish Procambarus clarkii from the Fiddien valley system in Malta by mechanically excavating the valley's stream bed and exporting contaminated debris securely off‐site to a dry quarry. Three years post‐intervention, we systematically surveyed the valley system to explore the distribution and relative abundance of the invasive crayfish population. We placed traps in a stratified random sample of stream segments (both those that were included in the original restoration project and those that were not) and recorded catch per unit effort (crayfish caught per trap night) and the size/frequency distribution of crayfish caught. The invasive crayfish were still abundant in the upper reaches of the valley system, and, despite the excavation effort, crayfish were present at the highest relative abundance (4.3–14.8 CPUE, median = 12.3) within the restored area. Despite substantial effort and spending of more than 700,000 €, mechanical excavation did not eradicate invasive crayfish populations. We urge caution for future projects planning to attempt crayfish eradication using this approach and call for much greater impact evaluation, and at the very least post‐project monitoring, to ensure lessons can be learnt from such failures in future.

TBM construction risk analysis based on fuzzy Bayesian network

ABSTRACT Aiming at the characteristics of various TBM construction risk factors, fuzzy and complex systems, and frequent shutdown accidents, a TBM construction risk analysis methodology based on a fuzzy Bayesian network is proposed. This method mainly selects eighteen risk factors to construct an interpretive structural model. These factors affect the TBM construction from the four aspects of the geological risk, equipment risk, management risk, and technical risk encountered during the construction of a full-face mechanical excavation of the tunnel. A five-level hierarchical directed graph is extracted by matrix operation to determine the relationship between factors. In the case of incomplete data, the Bayesian network model can be established by employing the prior probability to describe the state of the root node through expert scoring, ideal for system predictions lacking data. Finally, the main risk factors affecting the TBM construction are introduced and discussed, and the TBM construction of the West Second Tunnel of the Beijing Water Supply Phase II Project is taken as an example to compare the evaluation results with those of the actual construction status. The obtained results are not much different from those of the actual situation, which proves that the proposed method is scientific and can provide a reliable basis for analogous projects.

You Can’t Make an Omelette without Breaking an Egg. Surveying Submerged Paleo-terrains with a Mechanical Excavator

Abstract Preserved Stone Age sites and prehistoric landscapes under water can often be challenging to find and access for archaeologists. In consequence, the Viking Ship Museum has, within recent years, frequently used mechanical excavators in archaeological surveys to find and delineate Stone Age sites and prehistoric landscape features. In this article, the authors provide an overview of the introduction of mechanical excavators in maritime archaeology. The respective advantages and limitations of the method are then discussed in light of different scientific and practical considerations. Finally, as a case study, we present our proposed best practice for the method using the recent archaeological survey at the development-led project of Lynetteholmen, Copenhagen. The authors conclude that using mechanical excavators to survey paleo-landscapes is a very effective but potentially destructive method. Most importantly, the method provides access to sediment depths and areas that are inaccessible to divers alone.

Effect of Cyclic Loading on Mode I Fracture Toughness of Granite under Real-Time High-Temperature Conditions

Under hot dry rock development, rock formations undergo the combined challenges of cyclic loading and high temperatures, stemming from various sources such as cyclic hydraulic fracturing and mechanical excavation. Therefore, a fundamental understanding of how rocks fracture under these demanding conditions is fundamental for cyclic hydraulic fracturing technology. To this end, a series of three-point bending tests were conducted on granite samples. These tests entailed exposing the samples to cyclic loading under varying real-time high-temperature environments, ranging from 25 °C to 400 °C. Furthermore, different upper load limits (75%, 80%, 85%, and 90% of the peak load) obtained in monotonic three-point bending tests were used to explore the behavior of granite under these conditions. The analysis encompassed the study of load–displacement curves, elastic stiffness, and mode I fracture toughness under cyclic loading conditions. In addition, the microscopic features of the fracture surface were examined using a scanning electron microscope (SEM). The findings revealed notable patterns in the behavior of granite. Cumulative vertical displacement in granite increased with the growing number of cycles, especially at 25 °C, 200 °C, and 300 °C. This displacement exhibited a unique trend, initially decreasing before subsequently rising as the cycle count increased. Additionally, the critical damage threshold of granite exhibited a gradual decline as the temperature rose. As the temperature ascended from 25 °C to 200 °C, the damage threshold typically ranged between 80% and 85% of the peak load. At 300 °C, this threshold declined to approximately 75–80% of the peak load, and at 400 °C, it fell below 75% of the peak load. Within the temperature ranging from 25 °C to 300 °C, we noted a significant increase in the incidence of cracks, crystal microfracture zones, and the dislodging of mineral particles within the granite as the number of cycles increased.

Intermittent disturbance mechanical behavior and fractional deterioration mechanical model of rock under complex true triaxial stress paths

Mechanical excavation, blasting, adjacent rockburst and fracture slip that occur during mining excavation impose dynamic loads on the rock mass, leading to further fracture of damaged surrounding rock in three-dimensional high-stress and even causing disasters. Therefore, a novel complex true triaxial static-dynamic combined loading method reflecting underground excavation damage and then frequent intermittent disturbance failure is proposed. True triaxial static compression and intermittent disturbance tests are carried out on monzogabbro. The effects of intermediate principal stress and amplitude on the strength characteristics, deformation characteristics, failure characteristics, and precursors of monzogabbro are analyzed, intermediate principal stress and amplitude increase monzogabbro strength and tensile fracture mechanism. Rapid increases in microseismic parameters during rock loading can be precursors for intermittent rock disturbance. Based on the experimental result, the new damage fractional elements and method with considering crack initiation stress and crack unstable stress as initiation and acceleration condition of intermittent disturbance irreversible deformation are proposed. A novel three-dimensional disturbance fractional deterioration model considering the intermediate principal stress effect and intermittent disturbance damage effect is established, and the model predicted results align well with the experimental results. The sensitivity of stress states and model parameters is further explored, and the intermittent disturbance behaviors at different f are predicted. This study provides valuable theoretical bases for the stability analysis of deep mining engineering under dynamic loads.

Field test of high-power microwave-assisted mechanical excavation for deep hard iron ore

Microwave-assisted mechanical excavation has great application prospects in mines and tunnels, but there are few field experiments on microwave-assisted rock breaking. This paper takes the Sishanling iron mine as the research object and adopts the self-developed high-power microwave-induced fracturing test system for hard rock to conduct field experiments of microwave-induced fracturing of iron ore. The heating and reflection evolution characteristics of ore under different microwave parameters (antenna type, power, and working distance) were studied, and the optimal microwave parameters were obtained. Subsequently, the ore was irradiated with the optimal microwave parameters, and the cracking effect of the ore under the action of the high-power open microwave was analyzed. The results show that the reflection coefficient (standing wave ratio) can be rapidly (<5 s) and automatically adjusted below the preset threshold value (1.6) as microwave irradiation is performed. When using a right-angle horn antenna with a working distance of 5 cm, the effect of automatic reflection adjustment reaches the best among other antenna types and working distances. When the working distance is the same, the average temperature of the irradiation surface and the area of the high-temperature area under the action of the two antennas (right-angled and equal-angled horn antenna) are basically the same and decrease with the increase of working distance. The optimal microwave parameters are: a right-angle horn antenna with a working distance of 5 cm. Subsequently, in further experiments, the optimal parameters were used to irradiate for 20 s and 40 s at a microwave power of 60 kW, respectively. The surface damage extended 38 cm × 30 cm and 53 cm × 30 cm, respectively, and the damage extended to a depth of about 50 cm. The drilling speed was increased by 56.2% and 66.5%, respectively, compared to the case when microwaves were not used.

Enhancing rock breakage efficiency by microwave fracturing: A study on antenna selection

Microwave fracturing of rocks prior to mechanical breakage has the potential to significantly enhance rock breakage efficiency while reducing the wear of cutters/bits of mechanical excavators. However, rocks in nature require a vastly different microwave power intensity to be fractured, and they tend to fail in varying patterns under different power intensities. At present, there is no established suggest method for selecting the most suitable microwave antenna to fracture a specific rock in the field. In this study, we compared the technical characteristics of the four open-ended waveguide-based antennas: namely, the horn antenna, the standard waveguide antenna, the converging waveguide antenna, and the dielectric-loaded converging waveguide antenna. Using a 6 kW microwave source and these antennas, we treated four types of hard rocks. We investigated the impact of antenna type on rock fracturing and found that depending on the rock type and antenna used, rocks were typically fractured or weakened in the pattern of cracking, spalling, melting, or a combination thereof. Based on our observations, we have, for the first time, proposed a method for selecting the optimal antenna to fracture rocks with varying microwave fracturability indexes. This paves the way for the commercialization of microwave-assisted mechanical rock breakage.

Effect of water saturation on Cerchar abrasivity index (CAI) of clay-rich rocks at different scratch lengths

Predicting the cutter consumption rate of mechanical excavators using the Cerchar abrasivity index (CAI) results is possible. However, changing operational parameters in the field may cause differences between the estimated cutter consumption rate based on CAI test results and the real cutter consumption rate observed in the field. One of the essential parameters in the field that affects the cutter consumption rate is the increase in the water content of the excavated rocks. In theory, an increase in the water content of rocks is expected to reduce their abrasivity. In addition, the prediction of cutter consumption rate is based solely on CAI test results conducted on dry surfaces. However, especially during the excavation of low-strength clay-rich rocks, the excavated rock material can adhere to the cutters and block them, leading to a higher cutter consumption rate than initially predicted. This study aims to analyze the rock-pin interaction in CAI tests conducted on wet surfaces of clay-rich rocks and investigate the effect of water saturation on CAI at different scratch lengths. CAI tests were conducted on dry and wet surfaces of 20 clay-rich rocks with low strength at 10, 30, 50, and 70 mm scratch lengths, respectively. The relationships between the CAI test results obtained on dry and saturated rock surfaces were statistically analyzed for each scratch length. A positive linear correlation was found between CAI values obtained on dry (CAIDry) and saturated surfaces (CAISat) at each scratch length. The percentage variations in CAI values at each scratch length were analyzed in detail. It was found that 90 % of samples have higher CAIDry than CAISat at 10 mm scratch length. However, it was observed that as the scratch length increased, the relationship between the CAI values obtained in dry and saturated conditions changed, and the proportion of samples with CAIDry higher than CAISat decreased to 65 %, 55 %, and 25 % at scratch lengths of 30 mm, 50 mm, and 70 mm, respectively. In CAI tests conducted on saturated surfaces, it was observed that the excavated rock material adhered to the test pins, and as the scratch length increased, the increase in CAISat values was considered to be due to this situation. This study revealed the importance of considering the adhesion potential of rocks to cutters at water-saturated conditions for the accurate prediction of cutter consumption in the excavation of clay-rich rocks.

Research on Optimization Design of Tunnel Blasting Scheme Adjacent to Buildings

The section of Jialingjiang Road Station to Xiangjiang Road Station along Qingdao Metro Line 13 is located in Qingdao, China. All of them show obvious characteristics, being soft on the top and hard on the bottom, and the interval tunnel is faced with the problem of existing adjacent buildings. In order to ensure the smooth progress of construction, as well as minimize the damage to the buildings, a new mechanical excavation combined with a blasting construction scheme for the adjacent buildings is proposed. In this scheme, the step method is used for excavation. The upper step is in the weak stratum, and the mechanical method is therefore used for excavation; the lower step is in the hard stratum, and the drilling-and-blasting method is thus used for excavation. Using FLAC3D 5.0 finite difference software and the method based on blasting an equivalent load, the vibration velocity at adjacent buildings caused by the combined mechanical excavation and blasting scheme, as well as the traditional full-section blasting scheme, is compared and analyzed. Further, the construction parameters of the combined mechanical excavation and blasting scheme are compared and selected based on building settlement, the plastic zone of surrounding rocks, building vibration velocity and other factors. The results show that under the mechanical excavation blasting scheme, the peak particle velocity of each monitoring point decreases significantly compared with that under the full-section blasting scheme, with a maximum reduction of 61.1%, which is within the allowable range of the project, demonstrating the rationality of the new scheme. Finally, the mechanical excavation advance in the upper step is determined as 0.5 m. The optimized parameter construction effect is monitored and evaluated, the problems encountered in the project are successfully solved using the combined mechanical excavation and blasting scheme, and the expected construction period is shortened by 3 months, which shows the rationality of the blasting construction scheme proposed and its parameters, as well as the validity of the calculation results. The research results can be used as a reference for the construction scheme design of similar projects.

PRIMJENA KONTROLISANOG MINIRANJA PRI ISKOPU ULAZNOG PORTALA DESNE TUNELESKE CIJEVI TUNELA „VRANDUK“ NA KORIDORU VC

The height of the section of the right portal structure, Vranduk tunnel, starts at 337.24, while the height of the left side starts at 331.74. The projected level of the right tunnel pipe is at 315.24, which means that it is necessary to excavate 22m' of the right and 16.50m' of the left slope. Excavation work was carried out using a combination of mechanical excavation and blasting. Excavation with a hydraulic excavator to a height of 10-11m' to the level of the tunnel was not economically acceptable because it was a rock mass of considerable hardness with an average uniaxial strength of qu=45 MPa. The main task and the biggest challenge during the excavation by blasting the rock mass at the intersections is the determination of the drilling and mining parameters that will ensure as little damage as possible to the depth of the contour part of the rock mass, and reduce all potential harmful effects of blasting to a minimum. This paper describes the determination of drilling and mining parameters during the excavation of the entrance portal of the right tunnel pipe of the "Vranduk" tunnel on the Vc corridor.