In order to improve the efficiency of the directional cracking of hard rocks, starting from the mechanism of cracking from hard rocks to breaking rocks, based on the empty hole effect theory, the stress variation law of the empty hole wall under the 200 mm、250 mm、300 mm、400 mm hole spacing and the 20 mm、40 mm、90 mm、120 mm hole radius is studied, and the theoretical calculation and numerical simulation are compared and analyzed to verify. The results show that the existence of empty hole makes the stress concentration near the expansion hole, with the increase of empty hole spacing and the decrease of empty hole radius, the stress concentration of empty hole effect becomes weaker. The maximum tensile stress appears on the connection line of the empty hole and the expansion hole. The maximum pressure stress appears near the empty hole circle 70°. The stress intensity factor of type I rock on the inter-hole connection line corresponds to the law of stress variation. When the hole spacing reaches 400 mm, the stress intensity factor K_I is smaller than the fracture toughness K_IC of rock and the condition for formation of through cracks cannot be reached. According to the research results, set the parameters of the empty hole and in Shenzhen Tiegang-Shiyan reservoir Shiyan North clear water diversion tunnel to carry out the rock breaking test. The test results show that empty holes play a guiding role in the direction of crack propagation, which can cause the main crack to form on the connecting line between the empty hole and the expansion hole and is beneficial to improving the efficiency of the breaking rocks in hard rocks, which can provide reference for similar projects.

Shallow hole blasting is com in roadway or tunnel excavation, which has the disadvantages of more work cycles, less footage per cycle and low excavation speed. Meanwhile, deep-hole blasting which is widely used in mining engineering usually adopts continuous charge structure. This brings problems such as high charge quantity per delay, significant blast-induced harmful effect and high boulder yield. To overcome these problems, it is effective to adopt the in-hole sectional blasting technique. Firstly, key factors such as charging structure, charging materials, decking length, sectional delay and charging method are emphatically introduced based on the patents of in-hole sectional blasting in recent years. Then, taking the open-pit bench blasting of a mine adjacent to a railway as an example, the new two-deck charge blasting technology with rock powder barrier as the decking material was presented and compared with the traditional continuous charge blasting technology. After application of the new technique, the boulder yield was reduced by 54%, preventing secondary blasting. At the same time, the explosive usage was saved by 20%. The blasting vibration at the nearest monitoring point to the railway was reduced by 7.62%, and the flying rocks were all within the allowable range. The new technical scheme can also make the bench surface smoother after loading and transporting, which is more conducive to the subsequent stage of blasting operations.

The dislocation and overbreak of tunnel inverted arch are serious when traditional blasting excavation technology is used. This is because traditional blasting technology does not adopt the smooth blasting method, and the angle of the perimeter holes is too large when drilled by manual rock drilling rigs. By therefore analyzing the traditional blasting excavation technique of invert, the cause of serious studiedthe smooth blasting technology for inverted arch is proposed based on the smooth blasting theory and a large quantity of engineering practice. Water decking charge structure is adopted in the perimeter holes, which can be adjusted according to the inverted arch shape. The spacing between the perimeter holes is 30~50 cm, and the thickness of the smooth blasting layer is greater than the perimeter hole spacing by 10~30 cm. Additionally, a drilling counterforce support is used to reduce the angle of the perimeter holes which can ensure each blast hole to be drilled to the design depth. After comparing the blasting effects of the proposed smooth blasting technology and traditional blasting technology for the inverted arch by field tests, the contour overbreak by the smooth blasting technology is far less than that of traditional blasting technology, and the cost of every 12 m tunnel excavation is reduced by 35.14%.

Aiming at the problem that the blasting effect is not good due to poor or even no stemming of blast holes in underground coal mine, numerical simulation was used to analyze the mechanism of rock breaking and stemming mechanism. A 3 m×3 m two-dimensional concrete model with blast hole diameter of 0.04 m and hole depth of 1m was established using the finite element analysis software. In addition, the continuous emulsion explosive charge was set as 0.3 kg, and the stemming material was set as sand. For the explosive simulation, concrete and sand were modeled by Lagrange grid, and the air was modeled by Euler grid. ALE algorithm was used to simulate the explosion stress nephogram and damage cloud maps with a single hole stemming length of 0 mm, 200 mm and 400 mm respectively under the blast load. The results show that the maximum stress around the hole with stemming is significantly higher than that without stemming. Meanwhile, the damage degree around the hole with stemming is more severe with smaller fragments than that without stemming. On the basis of analyzing the advantages and disadvantages of clay and water stemming structures commonly used in underground mines, a stemming structure by expansion-pipe water injection was designed, which can replace the clay and water stemming structure in underground coal mine blasting as a good field application.

The conclusions including: the Kuznetsov and kansake models are still applicable to the prediction of unit explosive consumption in bench blasting tunnel engineering, and the Kuznetsov model considers the influence of rock mass characteristics, which is more practical than the kansake model. In addition, the Kuznetsov model can predict the average blasting fragment as the basis of the distribution model of blasting fragment. Compared with the lower bench, the upper bench has higher single blasting consumption, higher content of fine particles and smaller fragments. The Kuz-Ram model has a good prediction effect for the small blasting fragments that below the average value. For the large blasting fragments that above the average value, the KCO model has a better prediction effect, and it has more accurate for the prediction of the largest blasting fragment. This paper analyzes the applicable conditions and scope of the prediction model for rock fragment, which provides a basis for the unit explosive consumption and fragment distribution of tunnel blasting. The methods for predicting the specific consumption of explosives and the fragmentation of rock mass during blasting originated from open-pit blasting. However, the stress state of the rock mass in stepped tunnels is different from that in open-pit mines, so it is unknown whether the above prediction methods are applicable to stepped tunnel blasting. Based on statistical data from the bench blasting in the Tianjiangli tunnel, several commonly used calculation methods in open-pit mines were used to predict the specific consumption of explosives and the distribution of fragments, and the predicted results were compared with the actual measurements. The results show that the Kuznetsov model and the Kansake model are still applicable to predicting the specific consumption of explosives in stepped tunnel blasting, and the Kuznetsov model takes into account the influence of rock mass characteristics, making it more practical than the Kansake model. In addition, the Kuznetsov model can predict the average value of the blasting fragmentation and serve as a basis for the fragmentation distribution model. The specific consumption of explosives is higher on the upper bench, resulting in a higher content of fine particles and smaller overall rock mass after blasting, while the specific consumption is lower on the lower step, resulting in a lower content of fine particles and a larger overall rock mass after blasting. The Kuz-Ram model is better in predicting the blasting fragmentation of small rock masses with a block size below the average value, while the KCO model is better for predicting the blasting fragmentation of large rock masses with a block size above the average value, and the KCO model can accurately predict the maximum blasting block. This article analyzes the applicable conditions and scope of the prediction models and provides a basis for the specific consumption and fragmentation distribution in tunnel blasting.

In order to comprehensively evaluate the effect of deep hole bench blasting in Weijiamao Coal Mine, considering the three objectives of blasting quality, safety and economy, eight parameters such as block rate, root rate, back crack distance, loose coefficient, unit consumption, long-meter blasting amount, vibration speed and flying distance were selected as evaluation indexes. Through UAV, high-speed photography, vibration monitoring and other technical means, the field monitoring of four production blasting flat plates in Weijiamao Coal Mine was carried out. In the meantime, the data analysis was carried out by Split-desktop, Motion studio and other software, and the quantitative indexes of the above parameters were obtained. The subjective and objective weights of evaluation indexes are obtained by using analytic hierarchy process and CRITIC method respectively, and then the combined weights of each index are determined based on the principle of maximum sum of squares of deviations. The grey clustering method is optimized by using the center point triangle whitening weight function, and the grey clustering evaluation model of blasting effect is established. The deep hole bench blasting effect of Weijiamao Coal Mine is comprehensively evaluated, and the order of blasting effect of four flat plates is obtained according to the comprehensive clustering coefficient. Finally, the main problems of the flat plate with the worst blasting effect are analyzed by comparing the index data. The results show that the combined weight of explosive unit consumption, bulk rate and base rate is greater than 0.15, which has a great influence on the blasting effect. The order of blasting effect of four flat plates is that 1080 flat plate > 1064 flat plate > 1096 flat plate > 1112 flat plate. The 1112 flat plate needs to be combined with geological conditions to optimize the bench blasting parameters for the problems of large back crack distance, high unit consumption, small blasting amount per meter and large flying distance.

The average lumpiness of ore rock is an important index to measure the blasting quality. The early research mainly relies on empirical formula summary, rock mechanics model calculation, which have shortcomings such as insufficient accuracy and strong subjectivity. Recently,, machine learning algorithm is applied for prediction, but still have problems such as empirical feature selection, insufficient model prediction stability, and poor generalization ability for the prediction of blasting material fragmentation. Aiming at above shortcomings, an extreme Gradient Boosting (xgboost) blasting fragmentation prediction model based on Feature Engineering is proposed. Taking Yuanjiacun Iron Mine in Taiyuan as the research area, engineering data are collected, Random Forest (RF) and Mutual Information (MI) are used for feature selection respectively, and the two feature subsets are integrated to obtain the best feature subset based on the value of MSE. XGBoost is used to predict the block size on the optimal feature subset, and the evaluation system is composed of two indexes: Mean Square Error (MSE) and Mean Absolute Error (MAE). The proposed method is compared with other traditional machine learning algorithms, and the results show that it is better than others. Furthermore, it can provide scientific guidance for the management and control of blasting.

The dynamic response characteristics such as deformation capacity, acceleration, and load transfer of high-rise frame structure buildings under the condition of single column failure in different parts were studied. Firstly, according to the Code for Design of Concrete Structure (GB50010), a 4×6 span 8-story reinforced concrete frame structure model was established by using PKPM design software. Secondly, based on the component removal method, the finite element software SAP2000 was used to calculate the dynamic response characteristics of the frame structure with the failure of different single columns at the first floor, including the center column, long side middle column, short side middle column and corner column. The results show that the plastic angle is less than 6 for all the four column failure conditions, and the structure will not collapse. When the central column fails, the structural stability is the worst, and the probability of continuous collapse is the highest, followed by that of the short side and long side middle columns, and the corner column has the least probability. Under the condition of center column failure, the dynamic impact of the load on the residual structure is the most significant, with a maximum negative acceleration of about 3 g, which is twice as high as that of the short side middle column and the long side middle column. After the failure of the columns, the loads will be redistributed. The axial force will be borne by the adjacent columns, while the stress form of the upper beam will also change from bending to tension, resulting in a catenary effect. In the scenario of the central column failure, the axial force of the adjacent columns will increase by nearly 20%.

In order to successfully demolish two brick chimneys and two reinforced concrete chimneys located in the same plant area where is a complex environment by blasting. The overall blasting scheme of “single cut, directional collapse” is determined to demolish the four chimneys at one time, by analyzing the surrounding environmental conditions and the structural characteristics. According to the engineering experience, it is determined that the bottom edge of the chimney cut is at the elevation of+0.5 m, the cut angle is 215°, the cut height, cut length and relevant blasting parameters are calculated by theoretical formula. The cut form is trapezoid like, and the initiation network uses the digital electronic detonator initiation system with higher accuracy to initiate in the way of parallel firing. Considering the different structural composition of the four chimneys, corresponding pretreatment schemes are formulated respectively. Through the safety check of the collapse reliability, blasting vibration and collapse vibration of the chimneys and the effective control of the flying debris and flying stones after blasting, the four chimneys collapse in the design direction and prevent harm to the surrounding protection targets. By using the finite element software LS-DYNA to simulate the collapse process of four chimneys, the results show that the simulated collapse process is almost the same as the actual process, and the collapse completion time is around 14 s. Moreover, by analyzing the displacement and velocity law of the top node, it can be judged that the chimney collapse effect is sufficient and the expected goal is achieved, which further shows a guiding significance of the numerical simulation for engineering practice and can provide reference for similar projects.

The inlet cofferdam of the expansion engineering of Wuqiangxi hydropower station consists of the reserved rock barrier, concrete, soil and stones. The rock barrier is a bedding slope with relatively developed soft interlayers, which results in a complicated geological condition and blasting demolition environment for the cofferdam. In the process of demolishing the bedding rock barrier, it is impossible to break the rock once in a large area according to the economic section of a conventional cofferdam due to the large engineering quantity of the underwater blasting excavation, high requirement of fragmentation, long construction time and high risk. Under the condition of ensuring the stability of the cofferdam, the method of vertical stratification, horizontal zoning and loosening bench blasting was adopted to implement land excavation as much as possible. For the underwater blasting, according to the geological conditions of rock barrier, the mechanical characteristics of rock mass, the water depth (20~37 m) and the fragmentation requirement, the powder factor of 0.9~1.1 kg/m³ and maximum charge per delay of 60 kg was adopted. Electronic detonators were used for blast hole initiation and a series of safety measures such as bubble curtains and flexible protective nets were set. The field monitoring results show that the effect of blasting vibration and water percussive wave on structures such as inlet gate has been effectively controlled, and the efficiency of underwater slag removal and transfer has been improved.