On some uncertainties related to static liquefaction triggering assessments

2022 ◽  
pp. 1-53
Author(s):  
David Reid ◽  
Simon Dickinson ◽  
Utkarsh Mital ◽  
Riccardo Fanni ◽  
Andy Fourie
Keyword(s):  
Principal Stress ◽  
Stress Ratio ◽  
Slope Failure ◽  
Potential Effect ◽  
Intermediate Principal Stress ◽  
In Situ Test ◽  
Current State ◽  
Static Liquefaction ◽  
In Situ Conditions

Static liquefaction has been identified as the cause of several recent tailings storage facility (TSF) failures. Partially based on the investigations carried out, significant advances on the analysis of static liquefaction triggering have been made. This includes application of critical state-based models in a stress-deformation framework to identify if in situ conditions are approaching a level where triggering could occur. However, several important uncertainties remain. The current work investigates three of these uncertainties and their effect (both independently, and in conjunction) on the identification of static liquefaction triggering and slope failure: geostatic stress ratio K0, intermediate principal stress ratio, and principal stress angle from vertical. These uncertainties are examined through a series of numerical analyses of an idealised TSF. Various values of K0 are used to examine their effect on triggering, while different approaches to the potential effect of intermediate principal stress ratio and principal stress angle from vertical on instability are taken. This work shows that current state of knowledge in these areas is such that significant uncertainty seems unavoidable in attempting to identify exactly when a particular slope may undergo static liquefaction triggering. Experimental and in situ test programs that may be useful in reducing this uncertainty are outlined.

Dynamic Impact Measurements on Crossings, in Free Floating and In-Situ Conditions

2014 ◽  
Author(s):  
M. A. Boogaard ◽  
A. L. Schwab ◽  
Z. Li
Keyword(s):  
Finite Element ◽  
Condition Monitoring ◽  
Impact Loading ◽  
Dynamic Behaviour ◽  
Element Model ◽  
Mode Shapes ◽  
Dynamic Impact ◽  
In Situ Test ◽  
In Situ Conditions

As vibration based condition monitoring requires a good understanding of the dynamic behaviour of the structure, a good model is needed. At the TU Delft a train borne monitoring system is being developed which currently focusses on crossings. Crossings are prone to very fast degradation due to impact loading. In this paper a finite element model of a free floating frog is presented and validated up to a 100 Hz using dynamic impact measurements. The mode shapes of the free floating frog are then also compared to some preliminary results from an in-situ test. This comparison shows that the in-situ frequencies can be up to twice the free floating frequency.

scholarly journals Numerical Investigation of a Hydrosplitting Fracture and Weak Plane Interaction Using Discrete Element Modeling

Water ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 535
Author(s):  
Shuaiqi Liu ◽  
Fengshan Ma ◽  
Haijun Zhao ◽  
Jie Guo ◽  
Xueliang Duan ◽  
...  
Keyword(s):  
Shear Stress ◽  
Principal Stress ◽  
Stress Ratio ◽  
Water Pressure ◽  
Maximum Shear Stress ◽  
Water Inrush ◽  
Discrete Element ◽  
Maximum Principal Stress ◽  
In Situ Stress

Water inrush caused by hydrosplitting is an extremely common disaster in the engineering of underground tunnels. In this study, the propagation of fluid-driven fractures based on an improved discrete element fluid-solid coupling method was modeled. First, the interactions between hydrosplitting fractures (HFs) and preexisting weak planes (WPs) with different angles were simulated considering water pressure in the initial fracture. Second, the influence of the in situ stress ratio and the property of WPs were analyzed, and corresponding critical pressure values of different interactions were calculated. Lastly, the maximum principal stress and maximum shear stress variation inside the pieces were reproduced. The following conclusions can be drawn: (1) Five different types of interaction modes between HFs and natural WPs were obtained, prone to crossing the WPs under inclination of 90°. (2) The initiation pressure value decreased with an increased in situ stress ratio, and the confining stress status had an effect on the internal principal stress. (3) During HFs stretching in WPs with a high elastic modulus, the value of the maximum principal stress was low and rose slowly, and the maximum shear stress value was smaller. Through comprehensive analysis, the diversity of the principal stress curves is fundamentally determined by the interaction mode between HFs and WPs, which are influenced by the variants mentioned in the paper. The analysis provides a better guideline for understanding the failure mechanism of water gushing out of deep buried tunnel construction and cracking seepage of high head tunnels.

scholarly journals The suction,yield and strength characteristics of unsaturated intact loess based on true tri-axial tests

2019 ◽  
Vol 7 (3) ◽  
Author(s):  
Jinjin Fang
Keyword(s):  
Principal Stress ◽  
Stress Ratio ◽  
Shear Failure ◽  
Confining Pressure ◽  
Intermediate Principal Stress ◽  
True Triaxial ◽  
Yield Stress Increase ◽  
Isotropic Consolidation ◽  
The Relationship ◽  
Intact Loess

To simulate the failure of loess under undrained condition in the actual engineering,a series of isotropic consolidation and shear tests with different intermediate principal stress ratio b under constant water content were performed on intact loess with various initial suctions using the true tri-axial apparatus for unsaturated soil. The relationship between the saturations and initial suctions,the characteristics of yield,suction and strength of unsaturated intact loess were studied. The results show that the initial suctions and the suctions after the isotropic consolidation decrease with the increase of saturations. The suctions increase with the increase of the intermediate principal stress ratio b at the true triaxial shear failure. The net mean yield stress increase with the increase of the initial suction. The yield suction is a constant,but not always equal to the maximum suction that the soil specimen experienced in the history. The strength of soil increase with the increase of the net confining pressure,initial suction and the intermediate principal stress ratio b.

Static liquefaction of sand in plane strain

2007 ◽  
Vol 44 (3) ◽  
pp. 299-313 ◽  
Author(s):  
Dariusz Wanatowski ◽  
Jian Chu
Keyword(s):  
Plane Strain ◽  
Laboratory Tests ◽  
Stress Ratio ◽  
State Parameter ◽  
Intermediate Principal Stress ◽  
Log P ◽  
Loose Sand ◽  
Static Liquefaction ◽  
Testing Data ◽  
Unique Relationship

Experimental results on the static liquefaction behaviour of sand under plane-strain conditions are presented in this paper. Undrained tests on very loose sand under both plane-strain and axisymmetric conditions were conducted and the results compared. The test data show that the undrained behaviour of sand under plane strain is similar to that under axisymmetric conditions. However, the critical-state line (CSL) on both the q–p′ and the e–p′ planes determined under plane-strain conditions is different from that under axisymmetric conditions. The slope of the CSL is different as a result of the influence of the intermediate principal stress. The state parameter (ψ), which is measured with reference to the CSL in the e – log p′ plane, is also different: the ψ value for plane strain is about 0.05 less than that for axisymmetric conditions for the sand tested. The instability behaviour of very loose sand under undrained plane-strain conditions is also studied. Based on the testing data, a unique relationship between the stress ratio of the instability line and ψ is established to enable the triaxial results to be used for plane-strain conditions.Key words: failure, sands, laboratory tests, liquefaction, shear strength.

scholarly journals Development of a polyaxial platen for testing true triaxial behavior of rocks

2021 ◽  
Author(s):  
Prasoon Garg ◽  
Bhardwaj Pandit ◽  
Brijes Mishra ◽  
G.L. Sivakumar Babu
Keyword(s):  
Stress State ◽  
Principal Stress ◽  
Axial Stress ◽  
Intermediate Principal Stress ◽  
Intact Rock ◽  
Triaxial Stress ◽  
Triaxial Tests ◽  
True Triaxial ◽  
True Triaxial Tests

Mining at greater depths can lead to stress-induced failure, especially in areas of high horizontal in-situ stress. The induced stresses around the opening are known to be in a poly-axial stress state where, σ_1≠ σ_2≠ σ_3 with special case of σ_3= 0 and σ_1, σ_2 ≠ 0 at its boundary. The conventional triaxial testing does not represent the actual in-situ strength of the rock in regions of high horizontal stress, as it ignores the influence of intermediate principal stress (σ_2). The typical poly-axial testing (biaxial and true-triaxial tests) of intact rock mostly requires sophisticated and expensive loading systems. This study investigated the mechanical behavior of intact rock under a poly-axial stress state using a simple and cost-effective design. The apparatus consists of biaxial frame and a confining device. The biaxial frame has two platens that apply equal stress in both directions (σ_1=σ_2) on a 50.8 mm cubical specimen when placed inside the uniaxial loading device. The confining device performed separate biaxial tests under constant intermediate principal stress (σ_2 = constant) and true-triaxial tests when used along with the biaxial frame. This study then compared the failure modes and peak strength of Berea Sandstone specimens with other biaxial/triaxial devices to validate the design of the poly-axial apparatus. We also performed uniaxial tests on both standard cylindrical samples and prismatic specimen of different slenderness ratios. These tests provided a complete understanding of the failure mode transition from standard uniaxial compressive tests to triaxial stress conditions on cubical specimen. Additionally, this study determined best-fitted strength envelopes for biaxial and triaxial stress state. Based on regression analysis, we found a quadratic polynomial to be a good fit to biaxial strength envelope. For true-triaxial strength envelope, we found the 3D failure criterion by Nadai (1950) to be a good fit with R^2 of 0.964

scholarly journals The Behavior of a Coarse Granular Material under Complex Stress Conditions

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Yuefeng Zhou ◽  
Jiajun Pan ◽  
Zhanlin Cheng ◽  
Yongzhen Zuo
Keyword(s):  
Granular Material ◽  
Principal Stress ◽  
Stress Ratio ◽  
Intermediate Principal Stress ◽  
Friction Reduction ◽  
Western China ◽  
Triaxial Tests ◽  
Confining Stress ◽  
True Triaxial ◽  
Prediction Approach

In recent years, dozens of high rockfill dams are under construction or planning for hydropower exploration in western China. In dam construction, the mechanical behavior of coarse granular material greatly affects the compatible deformation of dam body. In this article, an indirect in situ density prediction approach for coarse granular material is firstly proposed to solve the technical obstacle on prediction of the material density in thick overburden layer of a dam site in southwest China. Adopting a self-developed large-scale true triaxial apparatus with a special friction-reduction technique, four series of true triaxial tests were then performed to investigate the behavior of a coarse granular material with a maximum particle diameter of 60 mm. Test results show that the peak strength of the material increases together with the increasing confining stress and the increasing intermediate principal stress ratio. The material dilatancy is restricted by both the confining stress and the intermediate principal stress ratio. With the increase in intermediate principal stress ratio, the internal friction angle increases firstly and then decreases slightly, but the slope of stress path reduces gradually. The tested peak states were compared with several well-known strength criteria under the framework of generalized stress, showing a good fitness with the Lade–Duncan criterion and underestimation by the Mohr–Coulomb criterion and the Matsuoka–Nakai criterion. The strength envelope in the π plane shrinks with the increasing confining stress.

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