Abstract
This work aims to characterize the in situ stress field along the Lijiang to Shangri-La railway and identify possible engineering geological problems when constructing tunnels along this railway on the margin of the Tibetan Plateau. The in situ stress measured at 76 points in 12 boreholes by the hydraulic fracturing method was analysed. A rose diagram of the maximum principal stress direction was plotted based on the measured in situ stress data. The results show that the measured in situ stress is mainly horizontal stress, corresponding to a strike-slip fault-related tectonic stress field with a moderate to high in situ stress value. The main stress values have a good linear relationship with the burial depth, and the maximum horizontal principal stress (σH) increases by 1.1–8.8 MPa per 100 m, with an average gradient value of 3.6 MPa per 100 m. The maximum and minimum horizontal principal stresses and the stress differences increase with depth, and the lateral pressure coefficient (σH/ σ v ) is generally 1–1.5. The ratio of the maximum and minimum effective stresses is less than the threshold at which faulting occurs, resulting in faults that are relatively stable at present. The direction of the maximum horizontal principal stress is oriented at a small angle to the axial direction of the deeply buried tunnel along the railway line; therefore, the tunnel sidewalls could readily deform during the construction process. Rock bursts are expected to occur in strong rock masses with high risk grades, whereas slight to moderate deformation of the rock surrounding the tunnel is expected to occur in weak rock masses. This study has significance for understanding the regional fault activity and issues related to the construction of deeply buried tunnels along the Lijiang to Shangri-La railway.
Highlights
In situ stress is a fundamental parameter in a wide range of endeavours in rock mechanics and engineering construction, and it is related to many engineering problems, such as rock bursts, rock slack, and rock deformation [1,2,3,4]
Erefore, the horizontal in situ stress is the dominant stress in the rocks along the Lijiang to Shangri-La railway, and this stress predominantly results from tectonic stress. is in situ stress field represents a typical tectonic stress field
There are still 56 points with σH > σv > σh, accounting for 73.6% of the total measured points and showing that the in situ stress field is conducive to the formation of strike-slip faults. e western boundary of the Zhongdian-Longpan-Qiaohou fault (No 23 in Figure 1(c)) presents dextral strike-slip offset features [30], and the horizontal displacement is larger than the vertical displacement, as determined with the Global Positioning System (GPS) technique. is GPS observation result is consistent with the results of the in situ stress measurement
Summary
In situ stress is a fundamental parameter in a wide range of endeavours in rock mechanics and engineering construction, and it is related to many engineering problems, such as rock bursts, rock slack, and rock deformation [1,2,3,4]. The in situ stress can be measured in the field or simulated by finite element models or other model codes. A series of in situ stress measurement techniques have been developed to interpret stress in different geological conditions at a given point [1, 2]. In situ stress measurement methods include the hydraulic fracturing method [2, 6,7,8,9], stress relief method [7,8,9,10], flat jacking method [9], borehole breakout method [9], drillinginduced tensile fracture method [11], acoustic emission method [12], strain recovery method [9], differential strain
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