Development of method for evaluation of three dimensional distribution of in situ stress state and preliminary estimation of applicability

The in-situ stress condition in the rock mass is influenced by both tectonic and geological environment, such as faulting and shearing in the rock mass. This influence is of considerable magnitude in the Himalayan region where the tectonic movement is active, resulting periodic dynamic earthquakes. Each large-scale earthquake causes both accumulation and sudden release of strain energy instigating changes in the in-situ stress environment in the rock mass. This paper evaluates the influence of local shear fault on the in-situ stress state along the shot crete lined high pressure tunnel of Upper Tamakoshi Hydroelectric Project, 456 MW in Nepal. A detailed assessment of the in-situ stress state is carried out by using both; measured data and three-dimensional numerical analysis using FLAC3D. The analysis includes evaluation on the possible changes in the in-situ stress state in the rock mass caused by seismic activities (dynamic loading). HYDRO Nepal JournalJournal of Water, Energy and Environment Issue: 23Year: 2018

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3D in-Situ Stress Model of Upper Tamakoshi Hydroelectric Project Area

Hydro Nepal Journal of Water Energy and Environment ◽

10.3126/hn.v21i0.17819 ◽

2017 ◽

Vol 21 ◽

pp. 34-41

Author(s):

Chhatra Bahadur Basnet ◽

Krishna Kanta Panthi

Keyword(s):

Stress State ◽

Three Dimensional ◽

Tectonic Stress ◽

In Situ Stress ◽

Tectonic Activity ◽

Hydroelectric Project ◽

Headrace Tunnel ◽

Detailed Assessment ◽

Area Of Concern

Reliable estimation of in-situ stress state is very important in implementing the shotcrete lined/ unlined tunnels and shafts. The in-situ stress state of the area of concern is mainly governed by the gravity-induced stress, tectonic activity of the earth’s crust and topographic condition of that area. The local tectonic and geological environment such as faulting and shearing activities in general influences the magnitude of tectonic stress level. The Himalayan region is renowned with its active tectonic movement (earthquake activities), which causes accumulation and sudden release of strain energy instigating changes in the stress environment. This paper aims to evaluate in-situ stress state at the Upper Tamakoshi Hydroelectric Project, where shotcrete lined/ unlined headrace tunnel with considerable hydrostatic head is being implemented. A detailed assessment of the in-situ stress state is carried out by using both measured data and three-dimensional numerical analysis using FLAC3D. HYDRO Nepal JournalJournal of Water Energy and EnvironmentIssue: 21, July, 2017Page: 34-41Upload Date: July 18, 2017

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The Influence Mechanism of In Situ Stress State on the Stability of Deep-Buried-Curved Tunnel in Qinghai-Tibet Plateau and Its Adjacent Region

Shock and Vibration ◽

10.1155/2021/9955497 ◽

2021 ◽

Vol 2021 ◽

pp. 1-18

Author(s):

Huiqing Wang ◽

Chengxuan Tan ◽

Chengjun Feng ◽

Peng Zhang ◽

Bangshen Qi ◽

...

Keyword(s):

Stress State ◽

Pressure Coefficient ◽

Three Dimensional ◽

Multivariate Regression Analysis ◽

In Situ Stress ◽

Tibet Plateau ◽

Adjacent Region ◽

The Stability ◽

Qinghai Tibet Plateau

In China, rockburst disaster occurs mostly in construction of underground engineering in Qinghai-Tibet Plateau and its adjacent region. Previous research on deep-buried tunnels has indicated that tunnels stability is related to in situ stress state. To quantify these relationships, three-dimensional finite element modeling was done to analyze the influences that the angle φ between the maximum horizontal principal stress orientation and tunnel axis, and the lateral pressure coefficient KH, had on the tangential stress σ θ in a deep-buried-curved tunnel. Based on the in situ stress condition in Qinghai-Tibet Plateau and its adjacent region, 50 different simulation conditions were used to analyze the relationship that φ and KH had on σ θ for the rock mass surrounding the tunnel. With the simulation data produced, predictive equations were generated for σ θ as a function of φ and KH using multivariate regression analysis. These equations help estimate σ θ at various key positons along the tunnel boundary at Qinghai-Tibet plateau and its adjacent region. The equations were then proved by a set of typical tunnels to ensure validity. The results concluded that the change in φ has a significant impact on σ θ , and thus, the stability of the tunnel, when 30° < φ < 60°, with the most obvious influence being when φ is about 45°. With the equations, the rockburst potential at a certain location within a curved tunnel can be quickly estimated by calculating φ and KH on σ θ , without need of geo-stress background knowledge and heavy simulation, allowing for the practical value in engineering at design phase for the projects in Qinghai-Tibet Plateau and its adjacent region.

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