Experimental Weathering of Weak Sandstone Without Direct Water Participation by Using Sandstone from the Yungang Grottoes in Datong, China

In this study an extensive experimental program has been carried out in order to characterize the mechanical behavior of two weak sandstone formations of an offshore field for application to sand production modeling. The experimental tests included Scratch tests, Triaxial tests and Advanced thick wall cylinder tests (ATWC) where the sand production initiation and the cumulative sand produced were registered. Numerical simulations of experimental tests were then performed using an advanced elasto-plastic constitutive model. Triaxial tests simulations allowed calibrating the constitutive model parameters. These parameters were employed for the numerical simulation of the ATWC in order to determine the equivalent plastic strain threshold required to the onset of sand production observed in laboratory for sanding assessment. Results obtained highlight the importance to use a realistic representation of the rock behavior focusing on post-yield behavior in order to build confidence in model predictions.

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Tunnel construction in very weak sandstone

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts ◽

10.1016/0148-9062(89)92651-x ◽

1989 ◽

Vol 26 (3-4) ◽

pp. A191

Keyword(s):

Tunnel Construction ◽

Weak Sandstone

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Experimental Research on Rheological Property of Water-Bearing Weak Sandstone in Large Cross-Section Tunnelling

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.256-259.1402 ◽

2012 ◽

Vol 256-259 ◽

pp. 1402-1405 ◽

Cited By ~ 1

Author(s):

Ye Zhou ◽

Peng Fei Li

Keyword(s):

Water Content ◽

Cross Section ◽

Rheological Characteristic ◽

Test Results ◽

Large Cross Section ◽

Rheological Equation ◽

Tunnel Face ◽

Water Bursting ◽

The Relationship ◽

Weak Sandstone

Various problems such as sand, mud and water bursting, unstability of tunnel face, large deformation of surrounding rock and severe cracking of primary support occurred in excavation of the water-bearing weak sandstone strata of Huma Ling Tunnel, Lan-Yu railway. Based on the uniaxial compressive strength tests and uniaxial compressive rheological tests on weak sandstone with water content of 0, 2%, 5%, 8% and 12%, the relationship between rheological characteristic and water content of water-bearing weak sandstone is obtained. According to results of tests, factors and water contents are fitted by applying generalized rheological equation of Kelvin. And the rheological equation of water-bearing weak sandstone with various water content is deduced. The test results and conclusion can offer reference for analyzing deformation characteristics and instability mechanism of water-bearing weak sandstone in large cross-section tunnelling.

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Study on the Seismic Performance of Small-diameter Bolts Reinforced in Grottoes

10.21203/rs.3.rs-117512/v1 ◽

2020 ◽

Author(s):

Ningbo Peng ◽

Bo Sun ◽

Jizhong Huang ◽

Yun Dong ◽

Ye Zhu

Keyword(s):

Rock Mass ◽

Seismic Performance ◽

Axial Force ◽

Small Diameter ◽

Vertical Direction ◽

World Heritage Site ◽

Dynamic Responses ◽

Structural Defects ◽

Seismic Capacity ◽

Yungang Grottoes

Abstract The Yungang Grottoes, a World Heritage Site in Datong, consist of 252 caves that are noted for their collection of 5th and 6th century Buddhist grotto sculptures and reliefs. Various diseases have appeared in the grottoes under the general influence of natural and artificial factors. Bolt support is a commonly employed method for grotto reinforcement and has been widely applied in many projects. Small-diameter bolts have also been used in the reinforcement projects at the Yungang Grottoes, but the corresponding effect on the seismic performance of grottoes is still unclear. In this paper, a dynamic analysis via the numerical modelling of an ear grotto of the 19th grotto in Yungang was established, and the rock displacement, acceleration and bolt axial force responses under a seismic wave are analyzed. The results show that the seismic dynamic responses of grottoes are greatly affected by the cliff structure. The displacement and acceleration responses of the cliff body vary greatly within the abrupt transition of the cliff structure. Based on this variation, the seismic capacity of small-diameter bolts in the vertical direction is greater than that in the horizontal direction. The axial force of a bolt is small at both ends of the bolt, large in the middle of the bolt, small on the top of a cliff and large at the bottom of the cliff. Although the axial force is small, the upper rock mass of the grotto has a tendency to undergo relative movement compared with the outer rock mass. The results also indicate that based on the structural defects in the vertical direction of the cliff body caused by grotto excavation, the inclined angle of the bolt should be increased as far as possible or vertical support should be adopted to enhance the stability of the rock mass at the top of the grotto.

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An adaptive prediction method for mechanical properties deterioration of sandstone under freeze–thaw cycles: a case study of Yungang Grottoes

Heritage Science ◽

10.1186/s40494-021-00628-8 ◽

2021 ◽

Vol 9 (1) ◽

Author(s):

Chenchen Liu ◽

Yibiao Liu ◽

Weizhong Ren ◽

Wenhui Xu ◽

Simin Cai ◽

...

Keyword(s):

Mechanical Properties ◽

Prediction Method ◽

Rock Properties ◽

Gradient Boosting ◽

Physical Factors ◽

Freeze Thaw ◽

Thaw Cycle ◽

Freeze Thaw Cycle ◽

Yungang Grottoes

AbstractDue to the location of the Yungang Grottoes, freeze–thaw cycles contribute significantly to the degradation of the mechanical properties of the sandstone. The factors influencing the freeze–thaw cycle are classified into two categories: external environmental conditions and the inherent properties of the rock itself. Since the parameters of rock properties are inherent to each rock, the effect of rock properties on freeze–thaw degradation cannot be investigated by the control variates method. An adaptive multi-output gradient boosting decision trees (AMGBDT) algorithm is proposed to fit nonlinear relationships between mechanical properties and physical factors. The hyperparameters in the GBDT algorithm are set as variables, and the Sequential quadratic programming (SQP) algorithm is applied to solve the hyperparameter optimization, which means finding the maximum Score. The case study illustrates that the AMGBDT algorithm can precisely determine the effect of each independent factor on the output. The patterns of mechanical properties are similar when the number of freeze–thaw cycles and porosity are used as variables separately and when both are used simultaneously. The uniaxial compressive strength decay rate is positively correlated with the number of freeze–thaw cycles and porosity. The modulus of elasticity is negatively correlated with the number of freeze–thaw cycles and porosity. The results show that the number of freeze–thaw cycles is the main factor influencing the freeze–thaw cycling action, and the porosity is minor. In addition, the fitting accuracy of the AMGBDT algorithm is generally higher than neural networks (NN) and random forests (RF). Studying the influence of porosity and other rock properties on the freeze–thaw cycle will help to understand the failure mechanism of rock freeze–thaw cycles.

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