On the effect of confining pressure on fatigue failure of block‐in‐matrix soils exposed to multistage cyclic triaxial loads

In view of the limitations of several existing stress measurement methods under extremely high stress conditions ( stress − strength ratio σ / R c > 0.5 ), this paper proposes a slot relief method based on partial deformation recovery to measure rock mass surface stress under extremely high stress conditions and justifies its viability with the help of an infinite element model. This method is then used to measure and study a research tunnel in West China’s Jinping II Hydropower Station, where the maximum stress measured reached 80 MPa. In the process of measurement, this method needs neither complete borehole core nor ultrahigh pressure equipment. On the contrary, the test equipment is easy to carry and operate on, suitable for rock mass surface stress measurement under extremely high stress conditions, and able to provide in situ stress measurements for cavern rockburst prevention and slope management.

Section: Major Existing Methods For Measuring In Situ Stress and Thei...mentioning

confidence: 99%

Study on the Method for Measuring Stress on Rock Mass Excavation Surface under Extremely High Stress Conditions

Zhang

Chao

2022

“…Therefore, the landslide rock mass and internal structure can be viewed as a whole when judging the instability mechanism of the whole system. According to the variation trend of each data factor at different time nodes and the above-mentioned deformation characteristics, the system deformation can be divided into four stages: initial deformation stage I, uniform deformation stage II, accelerated deformation stage III (divided into the first accelerated deformation stage (1) and the second accelerated deformation stage (2)), and residual deformation stage IV [34]. In stage I, under the influence of external force, the soil stress behind the pile begins to rise and is transferred to the micropile.…”

Section: Comprehensive Analysis Of Multisource Datamentioning

confidence: 99%

Study on Interaction Mechanism of Natural Gas Pipe-Landslide System Reinforced by Micropile Groups Based on Model Test

Guan

et al. 2022

Natural gas pipeline projects in mountainous areas are inevitably affected by geological disasters such as landslides, which pose a serious threat to the safe operation of pipelines along the routes crossing landslide areas. In this paper, based on a pipe-landslide project in a mountainous area in southwest China, the interaction mechanism and failure evolution process of the landslide-pipeline system reinforced by two kinds of micropiles are studied through indoor large-scale physical model tests, and some suggestions on the support work of the pipe-landslide project are put forward according to the test results. It was found that the deformation process of the engineering system composed of landslide, micropile, and pipeline presents a high degree of synergy under the external force and mainly experiences four stages: initial deformation period, uniform deformation period, accelerated deformation period, and residual deformation period. The bending deformation of the perforated pipe micropile is large at the 1/4 position of the pile top from the pile bottom, and the deformation of the screw micropile near the sliding surface is serious. The pipeline welding port is the weak position of the pipeline; after the failure of the pile, the pipeline interface is first cracked, along the interface position along the two ends of the tear, and finally completely broken. The screw micropile cannot effectively resist the landslide thrust at a large load level, so the risk of pipeline damage is greater. The yield strength and ultimate strength of the perforated pipe micropile are greater than those of the screw micropile, and the perforated pipe micropile can still exert a certain residual resistance after reaching the ultimate bearing capacity, which has a beneficial effect on the reinforcement of the pipeline crossing the landslide system. The research results provide important reference value for landslide-pipeline treatment engineering.

“…The threedimensional stress is the occurrence condition of the fractured rock mass, and the fracture dip angle is the geometric state of the fracture itself. These two aspects have mutual influence on the slurry migration in the fracture and are a pair of coupling factors [39][40][41][42][43][44]. In a word, the slurry diffusion in the fractured rock body needs to consider the slurry diffusion mechanism in the fractured rock body with different dip angles under the three-dimensional stress environment, which is the research direction that meets the needs of the project.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on Grouting Seepage Characteristics of Single-Fractured Rock Masses with Different Inclination Angles under Three-Dimensional Stress

Zhu

Han

2022

In underground engineering, the fracture dip angle and three-dimensional stress have great influence on the permeability and mechanical properties of fractured rock mass. Firstly, single-fracture samples with similar three-dimensional fractal dimensions and different dip angles were selected by using CT scanning technology. Then, the grouting material seepage tests under different dip angles and different three-dimensional stresses were carried out by self-developed single-fracture stress-seepage coupling true triaxial test system. The experimental data of stress-strain curve, grouting pressure, and grouting material flow rate of single-fracture specimen under different fracture dip angles and three-dimensional stress were obtained. The results show that the three-dimensional fractal dimension can be used as an index to measure the influence of fracture factors on grouting seepage test. The third principal stress σ 3 had a greater influence on the fracture width than the first principal stress σ 1 . The larger the fracture inclination, the lower the strength of the single-fracture specimen. As the third principal stress σ 3 increases, the grouting pressure increased while the grouting flow decreased. With the increase of the fracture inclination angle, the influence of σ 1 on the hydraulic conductivity became larger, while the influence of σ 3 on the hydraulic conductivity became smaller. Moreover, the expression of hydraulic conductivity of single-fracture specimen with different dip angles under three-dimensional stress was obtained by nonlinear fitting of hydraulic conductivity data.