When the Holmquist-Johnson-Cook (HJC) constitutive model is used to simulate limestone under the impact load, problems of a compaction stage not being characterised and low dynamic peak stress prediction accuracy are observed. The numerical simulation and experimental results were inconsistent. In this study, we proposed a modified HJC constitutive model and parameter determination method. Based on the characteristics of the dynamic stress-strain curve of limestone and relationship between axial and volumetric strains, the linear elastic phase of the state equation of the original HJC constitutive model was modified, and a new state equation was proposed. The yield surface of the original HJC constitutive model was modified on the basis of the sensitivity analysis method and limit surface theory, and a method for determining the parameters of the modified HJC constitutive model of limestone was proposed. The modified model and parameter determination method were experimentally verified using the split Hopkinson pressure bar (SHPB) and a high-speed camera. The results showed that the state equation curve of limestone under the impact load was divided into compaction, linear elastic, and fully compacted stages. After the introduction of the pressure parameters M, P, and Q, the nonlinear change in the stress-strain curve during the compaction stage was highly consistent with the SHPB results. The strength parameters fc, A, B, and N exhibited the maximum impact on the dynamic strength of limestone. After the strength parameters A, B, and N were modified for the yield surface, the prediction accuracy of limestone dynamic peak stress was over 97%, the prediction error rate decreased by more than 10%, and the reliability of numerical simulation results improved. These results can provide a simple and feasible numerical simulation method for the dynamic analysis of rock materials.

Direct shear tests were carried out on nonthrough jointed rock masses (NTJRM) with three types of joints under five normal stresses. The strength characteristics of shear strength, initial crack strength, and residual strength and the deformation characteristics of tangential displacement and dilatancy displacement as well as the transformation of failure mode and the variation of shear parameters of rock mass with different joint morphology are studied. Under the same normal stress, with the increase of joint undulation, the shear strength of NTJRM increases, and the corresponding tangential displacement of NTJRM increases. Two typical failure modes are observed: TTTS mode and TSSS mode. TTTS model indicates that the initial failure, extension failure, and final failure of rock mass are caused by tensile action, while the failure mode of through plane is formed by shear action. The initial failure of TSSS mode rock mass is caused by tensile action, while the expansion and final failure are caused by shear action, and the failure mode of through plane is formed under shear action. When the joint undulation is small and the normal stress is small, NTJRM will fail in TTTS mode; when the joint undulation is large and the normal stress is large, NTJRM will fail in TSSS mode. The results show that the shear parameters of NTJRM are related to the joint morphology, the bond force increases with the increase of joint undulation, and the internal friction angle increases with the increase of joint undulation. The research results of direct shear test of nonthrough jointed rock mass can provide reference for related research.

In situ stress and joints have a significant impact on the propagation and attenuation pattern of blast stress waves, and they are two important factors that must be considered for tunnel blasting hole network deployment. This paper proposes a blast stress wave attenuation equation and a peripheral hole distance calculation method under the combined action of in situ stress and joints. First, the static and dynamic parameters of the jointed slate are obtained by drilling core samples in the field and conducting indoor tests. Next, considering the geometric and physical attenuation of the blast stress wave, the attenuation formula of the blast stress wave under the combined action of in situ stress and joints is derived. Based on the theory of the combined action of stress waves and explosive gas, a formula for calculating the peripheral hole distance that integrates the effects of in situ stress, joints, and tensile strength of the rock body is proposed. Finally, LS-PREPOST software is used to analyze the damage to the surrounding rock, verified by an on-site blasting test. The results show that the blast stress wave attenuation formula proposed in this paper can accurately predict the stress wave peak value under the combined action of in situ stress and joints. Combining the geological conditions and blasting parameters of the Bayueshan Tunnel study section, the optimal peripheral hole spacing is calculated to be 45 cm. The average over-excavation value of the grade IV surrounding rock is controlled within 22 cm and the over-consumption of concrete per linear meter is controlled within 100% using the peripheral hole layout method and the hole network layout parameters proposed in this paper. The research results provide a reference for the control of over-excavation and under-excavation in large-section tunnel blasting.

The traditional tunnel-drilling and blasting parameter design is based on the small-section roadway and involves many boreholes and conditions that require slow operation progress and thus cannot meet the rapid operation requirements of a large-span tunnel. Taking the Baizhushan Tunnel as the engineering background, this article put forward a theoretical basis for a hole-reducing layout method for large-section tunnel blasting. These parameters of the rock statics and dynamics were obtained through core-drilling sampling in the field and the development of static and dynamic tests. LS-DYNA software was used to establish the numerical model of large-span tunnel blasting. The method was verified through three aspects, namely, cavity effect, effective stress, and surrounding rock damage and was implemented in the field application. The results showed the following: the scheme for reducing-hole numbers used 26 fewer blast holes per cycle footage and saved 0.7 h of drilling time; the average effective stress of the retained rock was 0.6 times that of the original blasting scheme, which reduced the damage to the remaining rock; the maximum over-excavation thickness control was within 50 cm, which reduced over-break; in the field test, the utilization rate of cutting holes was 81.9%, the utilization rate of other blasting holes was 91.2%, the unit consumption of explosives was 0.72 kg/m3, the average over-excavation thickness control was within 20 cm, and the smooth blasting effect was superior.

To explore the dynamic mechanical properties and damage evolution law of the more common layered rock masses in geotechnical engineering, this paper determined the Holmquist–Johnson–Cook (HJC) constitutive model parameters of dolomite, gray sandstone, and limestone according to the static mechanical parameters of the rock mass. We used Hypermesh/ANSYS software to establish the numerical analysis model, carried out the dynamic impact numerical simulation of the layered rock mass, and analyzed the stress wave propagation characteristics, dynamic stress–strain relationship, energy dissipation, and damage evolution laws of layered rock masses under different combinations. At the same time, this paper analyzed the stress characteristics of the layered rock mass and studied its failure characteristics. The research results show that the wave impedance matching relationship alters the dynamic characteristics of the layered rock mass; however, with the increase in impact velocity, the difference gradually weakens. The difference in elastic modulus leads to different initial failure modes of layered rock masses, and the quality of the wave impedance matching relationship leads to differences in the law of damage evolution of layered rock masses. Under different combination forms, the failure degree and failure modes of the two parts of the layered rock mass are different.