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Shear rupture behaviors of intact and granulated Wombeyan marble with the flat-jointed model

Li Kaihui, Han Dongha, Fan Xiang, Yang Yi, Wang Fei

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 1

art. no. e51, 2022

Many large hydropower projects have been constructed in the highly interlocked and non-persistently jointed rock mass (e.g., the columnar jointed basalt). Regarding the granulated Wombeyan marble as an analog of such rock mass, a series of direct shear test simulations under constant normal loading (CNL) and constant normal stiffness (CNS) boundary conditions were performed to better understand its shear rupture behavior using the flat-jointed model based on the discrete element method. The results show that the shear process under the CNS condition can be divided into four stages: linear-elastic stage, yielding stage, shear wear stage and shear sliding stage. The strain-strengthening in the shear wear stage is evident due to the feedback normal stress provided by the cap induced by shear dilation. As the initial applied normal stress increases, the peak shear strength point of specimens under CNL approaches the yield point of specimens under CNS. Additionally, the shear rupture process under CNS is strain controlled in granulated specimens but stress controlled in intact specimens. Correspondingly, the shear rupture zone creation in granulated specimens is not but that in intact specimens is dependent on the initial applied normal stress. Finally, it is demonstrated that the CNS condition can improve the stability of rock slopes or underground excavations embedded in such rock mass and its improvement effect increases with the normal stiffness.

Scale effect in shaft friction from the direct shear interface tests

Bałachowski L.

Archives of Civil and Mechanical Engineering

2006

Vol. 6, no 3

13-28

The thickness of the shear band mobilized on the pile shaft subjected to loading is practically the same for a small model and a large-diameter prototype. At the same normal stress applied to the shaft of the model and of the prototype pile, the normal stiffness of the interface and so the shear conditions are different for both cases. Lateral friction measured for the model and the prototype will differ. This scale effect in shaft friction related to the ratio of the diameter of the model to a mean grain size is studied with the direct shear interface tests, where the pile diameter is modeled with a constant normal stiffness applied to the shear box. The scale effect whose value is lower than unity is obtained for the dilative soil behaviour within the interface. The value of the scale effect smaller than unity is deduced from the direct shear interface tests with the soil contractancy.

Przy tym samym naprężeniu normalnym na pobocznicy modelu pala o małej średnicy i prototypu o dużej średnicy zjawisko mobilizacji tarcia przebiega w innych warunkach brzegowych. Zjawisko to może zostać odzwierciedlone w badaniu bezpośredniego ścinania w kontakcie ze stałą sztywnością normalną, odwrotnie proporcjonalną do rozpatrywanej średnicy pola. Przeanalizowano wartości maksymalne tarcia uzyskane w aparacie bezpośredniego ścinania dla piasków kwarcowych i węglanowych oraz gładkiego i szorstkiego kontaktu przy różnym zagęszczeniu piasku. Określono efekt skali jako stosunek tarcia mobilizowanego na modelu do tarcia mobilizowanego dla pala o dużej średnicy. Efekt skali mierzony w aparacie bezpośredniego ścinania w kontakcie przy stałej sztywności normalnej ma wartość większą od jednego w przypadku dylatacji w kontakcie lub wartość mniejszą niż jeden dla kontraktacji na styku konstrukcja-grunt.