In tunnel blasting excavation, it is important to clarify the attenuation law of blast wave propagation and predict the blast vibration velocity effectively to ensure safe tunnel construction and protection design. The effects of the free surface area its quantity on the blast vibration velocity are considered, and free surface parameters are introduced to improve the existing blast vibration velocity prediction formula. Based on the Tianhuan railway Daqianshiling tunnel project, field blast vibration monitoring tests are performed to determine changes in the peak blasting vibration velocity based on the blast distance and free surface area. LS-DYNA is used to establish tunnel blasting excavation models under three operating conditions; subsequently, the attenuation law of blast vibration velocity and changes in the vibration response spectrum are analysed. Results show that the free surface area and number of free surfaces enable the blast vibration velocity to be predicted under various operating conditions: a smaller free surface area results in a narrower frequency band range, whereas more free surfaces result in a narrower frequency band range. The improved blast vibration velocity prediction formula is validated using field and numerical test data. It is indicated that the improved formula is applicable to various tunnelling conditions.

In deep underground engineering, in a large spatial, high-stress environment, rapid excavation is likely to affect the loading rate of the fault structure and to cause stick-slip. In this study, an experiment was conducted to explore the stick-slip characteristics at different loading rates. A double-sided shear experiment and the digital speckle correlation method were used to analyze the evolution of the displacement field, the slip displacement, and the slip rate of the fault’s stick-slip activity at different loading rates as well as their correlation with the loading rate. The loading rate, moment magnitude, and stress drop of the fault’s stick-slip and their corresponding relationships were studied. The results show that the occurrence of stick-slip is inversely proportional to the loading rate. The evolution of the fault-slip displacement field at different loading rates is similar. At a given loading rate, the magnitude is positively correlated with the stress drop. The magnitude and stress drop are inversely related to the loading rate.

It is important to study the fracture mechanism of fractured rocks. Uniaxial compression tests and discrete element numerical simulations were conducted on sandstone specimens with fixed dip angles and parallel fractures. With the help of acoustic emission detection technology, the effects of different fracture spacings and number of fractures on the mechanical properties, fracture mechanism and acoustic emission full dynamic time-varying evolution of sandstone were investigated. The results show that: there is an obvious correlation between the number of fractures and elastic modulus and no obvious correlation with strength. There is no clear relationship between fracture spacing, elastic modulus, and peak strength. The fracture spacing determines the basic type of crack aggregation, and the number of cracks mainly affects the diversity of crack aggregation types. Spalling damage mainly occurs at the middle position of through-bridge shear cracks, and plate crack damage mainly occurs at the position on both sides of the specimen. Through-bridge shear cracks are a common type of crack in specimens containing parallel fractures, which influence the initiation location of the main shear crack and the damage mechanism of the specimen, and affect the overall strength of the specimen by changing the local narrowest width of the “column” structure. There is a mutual excitation between the tension and shear cracks, and each sudden increase in the shear-tension crack ratio corresponds to a macroscopic rupture of the specimen. The multifractal parameters of acoustic emission can provide a more detailed description of signal complexity. The abrupt changes in the time-varying multifractal parameters Δα and Δf(α) can serve as short-range prediction indicators for disaster occurrences.

The BeiDou navigation satellite system (BDS) provides precise positioning, navigation, and timing (PNT) services in the Asia-Pacific Region, but the BDS-based structural health monitoring (SHM) approach (SHM) is rarely studied, especially in civil engineering. Moreover, how BDS can be applied to complete the tasks of SHM in a real project is also not fully investigated, especially working in conjunction with other techniques. This study aims to propose a BDS-based approach for SHM in civil engineering. The performance of the proposed approach is investigated through a case study—the Tianhan Grand Theater (TGT). A specific Tianhan system corresponding to BDS is proposed to complete the SHM tasks of TGT. Based on the collected data, the trusses with maximum displacement and stress are found by BDS to evaluate structural health in the construction stage. The results show that the maximum displacement and stress have certain safety reserves and meet the requirements of the specifications and regulations. Thus, BDS can satisfactorily complete the tasks of SHM for Long-span steel structures. This study gives a clear view to engineers and researchers that how to apply BDS in structural construction and provides a valuable real case for evaluating the performance of BDS in SHM.

In this work, through the field monitoring and vibration signal analysis, we proposed a multi-parameters vibration assessment method for ground vibration induced by high-speed railway trains. And also, based on the assessment results, we developed a prediction model of z-vibration level, which is characterized with multiple piers vibration source and exactly applicable to the ground vibration prediction under the high-speed railway bridges. Firstly, by carrying out the field monitoring test, the ground vibration signals induced by high-speed railway trains were collected, with the ground vibration characteristics and influencing factors under the high-speed railway bridge are analyzed. Secondly, the ground vibration assessment was conducted by Peak Particle Velocity (PPV), Peak Particle Acceleration(PPA) and the z-Vibration Level (VL_Z) respectively, and on this basis, we proposed a multi-parameters vibration assessment method for ground vibration around the high-speed railways. Then, according to the assessment results, based on the vibration attenuation model under railway traffic load effect and the superposition feature of multi-piers vibration sources under high-speed railway bridges, we developed a ground vibration attenuation prediction model of VL_Z, which is characterized with multi-piers vibration sources and exactly applicable to the ground vibration prediction under the high-speed railway bridges. Besides, an application example of environment vibration prediction was given, and the site selection distance threshold away from the high-speed railways of different types of environmental vibration function areas were determined. The study showed that the proposed multi-parameters vibration assessment method was so comprehensive that it could take the vibration safety of building structures, human perception comfort and environmental vibration limit all into consideration. And meanwhile, by comparing the predicted VL_Z with the field monitored data and the empirical formula calculated value, the developed ground vibration attenuation prediction model was tested with better prediction accuracy and wider effective prediction range. As a result, the study was expected to provide a theoretical reference for the construction of ground vibration assessment system around high-speed railways, with potential engineering application value in ground vibration attenuation prediction and site selection of building structures under the high-speed railway bridges.

In order to investigate the energy attenuation of microseismic signal in the "three-zone" structure of goaf, a similar model test of the overburden of goaf is proposed to collect the artificially excited microseismic signals propagated through the structure of goaf. The relationship between the central frequency and energy of the mode components of the microseismic signal via variational mode decomposition (VMD) is analysed. The optimal number of mode components of the microseismic signal is determined according to the central frequency method, and the energy of each component is calculated for the under-decomposition, optimal decomposition and over-decomposition states of the microseismic signal. The relationship between the energy of each mode component and the central frequency distribution is fitted for the optimal decomposition state of the signal under each source, and the energy of each mode component is analysed for different propagation states of the microseismic signal in the "three-zone" structure. The effect of each structural layer on the energy of the microseismic signal under different propagation states of the "three-zone" structure is analyzed. The results of the study show that: (1) The number of effective modes of the artificially excited vibration signal in the VMD process ranges from 6 to 11, and the energy of the microseismic signal varies significantly with the number of modes. (2) The power function can be used to fit the mode energy versus frequency of the microseismic signal, and the fitting state is good (the coefficient of determination is greater than 0.9), in which the low-frequency mode component contains nearly 50% of the total energy of the signal. The Gaussian function can be used to fit the distribution performance of the energy of each component of the source in the frequency domain, and the fitting state is good and shows the Gaussian single-peak characteristic. (3) The microseismic signal traverses through the "three-zone" structure of goaf, and the energy of the microseismic signal decreases as the distance between the source location and the sensor increases. The collapse zone has a significant attenuating effect on the signal compared to the fracture zone and the bending zone. The energy of the microseismic signal does not change as it passes through the "three-zone" structure of goaf.