During the development blasting of circular tunnels, the detonation of multiple blastholes arranged on concentric circles induces a complex dynamic response in the surrounding rocks. This process involves multiple blast loadings, static stress unloadings, and stress redistributions. In this study, the dynamic stresses of the surrounding rocks during development blasting, considering multiple blasting-unloading stages with exponential paths and triangular paths (linear simplified paths of exponential paths), are solved based on the dynamic theory and the Fourier transform method. Then, a corresponding discrete element model is established using particle flow code (PFC). The multiple-stage dynamic stress and fracture distribution under different in situ stress levels and lateral coefficients are investigated. Theoretical results indicate that the peak compressive stresses in the surrounding rocks induced by both triangular and exponential paths are equal, while the triangular path generates greater additional dynamic tensile stresses, particularly in the circumferential direction, compared to the exponential path. Numerical results show that the exponential path causes less dynamic circumferential tensile damage and forms fewer radial fractures than the triangular path in the first few blast stages; conversely, it exacerbates the damage and instability in the final blasting-unloading stage and forms more circumferential fractures. Furthermore, the in situ stress determines which of the two opposite effects is dominant. Therefore, when using overly simplified triangular paths to evaluate the stability of surrounding rocks, potential overestimation or underestimation caused by different failure mechanisms should be considered. Specifically, under high horizontal and vertical stresses, the static stress redistribution with layer-by-layer blasting suppresses dynamic circumferential tensile and radial compressive damage. The damage evolution of surrounding rocks in multi-stage blasting under different in situ stresses is summarized and classified according to the damage mechanism and characteristics, which can guide blasting and support design. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The injection of large volumes of natural gas into geological formations, as is required for underground gas storage, leads to alterations in the effective stress exerted on adjacent faults. This increases the potential for their reactivation and subsequent earthquake triggering. Most measurements of the frictional properties of rock fractures have been conducted under normal and shear stresses. However, faults in gas storage facilities exist within a true three-dimensional (3D) stress state. A double-direct shear experiment on rock fractures under both lateral and normal stresses was conducted using a true triaxial loading system. It was observed that the friction coefficient increases with increasing lateral stress, but decreases with increasing normal stress. The impact of lateral and normal stresses on the response is primarily mediated through their influence on the initial friction coefficient. This allows for an empirical modification of the rate-state friction model that considers the influence of lateral and normal stresses. The impact of lateral and normal stresses on observed friction coefficients is related to the propensity for the production of wear products on the fracture surfaces. Lateral stresses enhance the shear strength of rock (e.g. Mogi criterion). This reduces asperity breakage and the generation of wear products, and consequently augments the friction coefficient of the surface. Conversely, increased normal stresses inhibit dilatancy on the fracture surface, increasing the breakage of asperities and the concomitant production of wear products that promote rolling deformation. This ultimately reduces the friction coefficient. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Integral bridges have been proposed as a jointless design alternative to the traditional counterparts, possessing copious potential economic and structural advantages. However, due to the monolithic connection at the girder- abutment interface, longitudinal deformations from the superstructure must now be accommodated by the stiffness of the approach backfill and soil surrounding the foundation. Consequently, in addition to traffic loads, integral bridge approaches are subjected to long-term, cyclic loading due to diurnal and seasonal thermal variations. This has resulted in two progressive geotechnical phenomena: an escalation of lateral passive pressures at the abutment-soil interface and accumulated deformations near the bridge approach. Over the last two decades, several investigations on the approach backfill-abutment interaction have been carried out. However, previous reviews on integral bridges have not comprehensively discussed the theoretical aspects of these two complex geotechnical issues. Hence, this paper presents a discussion on the long-term response of stress ratcheting observed from controlled analyses, along with a comparison to that from field monitoring data. Subsequently, the occurrence of accumulated deformations, along with a correlation to the mechanism of the cyclic interaction is explored. The effects of foundation design choice and skew angle on the passive pressure accumulation and soil deformation behavior are then presented. Subsequently, approaches used to mitigate the effects of the backfillabutment interaction are compared. From this review, it is apparent that outcomes based on available experimental and field investigations are yet inadequate to develop analytical models required to predict the long-term response of integral bridge approach backfills under various loading conditions.

Although the internal stress state of soils can be affected by repetitive loading, there are few studies evaluating the lateral stress (or K0) 0 ) of soils under repetitive loading. This study investigates the changes in K0 0 and directional shear wave velocity (Vs) s ) in samples of two granular materials with different particle shapes during repetitive loading. A modified oedometer cell equipped with bender elements and a diaphragm transducer was developed to measure the variations in the lateral stress and the shear wave velocity, under repetitive loading on the loading and unloading paths. The study produced the following results: (1) Repetitive loading on the loading path resulted in an increase in the K0 0 of test samples as a function of cyclic loading number (i), and (2) Repetitive loading on the unloading path resulted in a decrease in K0 0 according to i. The shear wave velocity ratio (i.e. Vs(HH)/Vs(VH), s (HH)/V s (VH), where the first and second letters in parentheses corresponds to the directions of wave propagation and particle motion, respectively, and V and H corresponds to the vertical and horizontal directions, respectively) according to i supports the experimental observations of this study. However, when the tested material was in lightly over-consolidated state, there was an increase in K0 0 during repetitive loading, indicating that it was the initial K0, 0 , rather than the loading path, which is responsible for the change in K0. 0 . The power model can capture the variation in the K0 0 of samples according to i. Notably, the K0 0 = 1 line acts as the boundary between the increase and decrease in K0 0 under repetitive loading. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).