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1

Conventional triaxial loading and unloading test and PFC numerical simulation of rock with single fracture

Tang Yin, Chen Haijun, Xiong Liangxiao, Xu Zhongyuan

Archives of Civil Engineering

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2024

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Vol. 70, nr 2

233--254

EN

Take the metamorphic sandstone as the reference object, by making rock like samples with fractures, the conventional triaxial loading and unloading test and PFC numerical simulation of rock like sample with single fracture were conducted, and the effects of the loading path, inclined angle of fracture, axial stress level during unloading, initial confining pressure during unloading on the compressive strength, peak strain and crack propagation evolution of the samples were considered. The compressive strength of the specimen under triaxial unloading is smaller than that under triaxial loading. The peak strain of the specimen under triaxial unloading is also smaller than that under triaxial loading. The specimen is more prone to brittle failure. When the axial stress level is the same during unloading, with the increase of the initial confining pressure during unloading, the difference of the compressive strength of the specimens with different inclined angles of fracture gradually decreases. Under the condition of uniaxial compression and triaxial compression, the failure of all specimens is tensile failure, and the shear failure is the main one during unloading.

2

Experimental study on shear mechanical properties of cement mortar specimen with through-step joints under direct shear

Xiong Liangxiao, Chen Haijun, Guo Haogang, Mei Songhua, Xu Zhongyuan, Liu Bin

Archives of Civil Engineering

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2022

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Vol. 68, nr 4

45--61

EN

In this study, direct shear tests were carried out on cement mortar specimens with single-ladder, single-rectangular, and double-rectangular step joints. Consequently, the shear strength, and crack shape of specimens with these through-step joints were analyzed, for understanding the influence of the through-step joint’s shape on the direct shear mechanical properties. The results of the investigation are as follows: (1) Under the same normal stress, any increases in the height h of the step joint causes an initial-increase-decrease in the shear strengths of specimens with single-ladder and double-rectangular step joints, causing a type-W variation pattern for the specimens with single-rectangular step joint. More essentially, when normal stress and h are constant, the shear strength of specimens with a single-ladder step joint is the greatest, followed by specimens with a double-rectangular step joint, and then specimens with a single-rectangular step joint is the least. (2) Furthermore, given a small h and low normal stress, specimen with a single-ladder step joint mainly experiences shear failure, whereas specimens with single-rectangular and double-rectangular step joints mainly generate extrusion milling in the step joints.

3

Numerical simulations of horizontal bearing performances of step-tapered piles

Xiong Liangxiao, Chen Haijun, Xu Zhongyuan, Yang Changheng

Archives of Civil Engineering

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2021

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Vol. 67, nr 3

43--60

EN

In this study, we tried to understand the horizontal bearing performances of step-tapered piles using numerical simulations. The influence of the geometric parameters, e.g. the diameter (D) and the distance (L), and the length (H) of the pile were considered, and the soil distribution imposed on the horizontal bearing capacity of the piles was simulated. Numerical results show that when the other geometrical parameters of step-tapered piles are kept unchanged: (a) the increasing diameter (D) of the enlarged upper part of step-tapered piles improves the horizontal ultimate bearing capacity of step-tapered piles; (b) reduced distance (L) improves the horizontal ultimate bearing capacity of the step-tapered piles; (c) Increasing length (H) of the enlarged upper part of steptapered piles increases the horizontal ultimate bearing capacity; (d) the reduced length (H) decreases the bending moment of the pile body. Higher soil strength surrounding the enlarged upper part of step-tapered piles can increase the horizontal ultimate bearing capacity of step-tapered piles. The change of soil strengths at the end of the step-tapered piles does not influence the horizontal ultimate bearing capacity of step-tapered piles.