Mechanical and fracture behavior of rock mass with parallel concentrated joints with different dip angle and number based on PFC simulation

Zhao, Weihua,Huang, Runqiu,Yan, Ming Techno-Press 2015 Geomechanics & engineering Vol.8 No.6

Rock mass is an important engineering material. In hydropower engineering, rock mass of bank slope controlled the stability of an arch dam. However, mechanical characteristics of the rock mass are not only affected by lithology, but also joints. On the basis of field geological survey, this paper built rock mass material containing parallel concentrated joints with different dip angle, different number under different stress conditions by PFC (Particle Flow Code) numerical simulation. Next, we analyzed mechanical property and fracture features of this rock mass. The following achievements have been obtained through this research. (1) When dip angle of joints is $15^{\circ}$ and $30^{\circ}$, with the increase of joints number, peak strength of rock mass has not changed much. But when dip angle increase to $45^{\circ}$, especially increase to $60^{\circ}$ and $75^{\circ}$, peak strength of rock mass decreased obviously with the increase of joints number. (2) With the increase of confining stress, peak strengths of all rock mass have different degree of improvement, especially the rock mass with dip angle of $75^{\circ}$. (3) Under the condition of no confining stress, dip angle of joints is low and joint number is small, existence of joints has little influence on fracture mode of rock mass, but when joints number increase to 5, tensile deformation firstly happened at joints zone and further resulted in tension fracture of the whole rock mass. When dip angle of joints increases to $45^{\circ}$, fracture presented as shear along joints, and with increase of joints number, strength of rock mass is weakened caused by shear-tension fracture zone along joints. When dip angle of joints increases to $60^{\circ}$ and $75^{\circ}$, deformation and fracture model presented as tension fracture zone along concentrated joints. (4) Influence of increase of confining stress on fracture modes is to weaken joints' control function and to reduce the width of fracture zone. Furthermore, increase of confining stress translated deformation mode from tension to shear.

Advanced discretization of rock slope using block theory within the framework of discontinuous deformation analysis

Wang, Shuhong,Huang, Runqiu,Ni, Pengpeng,Jeon, Seokwon Techno-Press 2017 Geomechanics & engineering Vol.12 No.4

Rock is a heterogeneous material, which introduces complexity in the analysis of rock slopes, since both the existing discontinuities within the rock mass and the intact rock contribute to the degradation of strength. Rock failure is often catastrophic due to the brittle nature of the material, involving the sliding along structural planes and the fracturing of rock bridge. This paper proposes an advanced discretization method of rock mass based on block theory. An in-house software, GeoSMA-3D, has been developed to generate the discrete fracture network (DFN) model, considering both measured and artificial joints. Measured joints are obtained from the photogrammetry analysis on the excavation face. Statistical tools then facilitate to derive artificial joints within the rock mass. Key blocks are searched to provide guidance on potential reinforcement measures. The discretized blocky system is subsequently implemented into a discontinuous deformation analysis (DDA) code. Strength reduction technique is employed to analyze the stability of the slope, where the factor of safety can be obtained once excessive deformation of slope profile is observed. The combined analysis approach also provides the failure mode, which can be used to guide the choice of strengthening strategy if needed. Finally, an illustrated example is presented for the analysis of a rock slope of 20 m height inclined at $60^{\circ}$ using combined GeoSMA-3D and DDA calculation.

Effects of Particle Shape on Shear Strength of Clay-gravel Mixture

Yanrong Li,Runqiu Huang,Lung S. Chan,Jun Chen 대한토목학회 2013 KSCE JOURNAL OF CIVIL ENGINEERING Vol.17 No.4

Soils containing gravel-sized particles attract much less attention from researchers than clay and sands, though they may be the most commonly encountered materials in geotechnical engineering practice, especially in mountainous area. Large direct shear tests are carried out in this study to investigate the shear behavior of such soil mixtures, with emphasis on influences of shape properties (symmetry and smoothness) of gravel particles. The tested samples are prepared by mixing kaolin and gravel-sized particles (2.0 mm < d < 15 mm) of different shapes at various volumetric proportions (40, 70 and 100%). Three types of gravel are used, i.e., glass beads, river cobbles and crushed granite fragments. The applied normal stresses is 150 kPa and the shearing rate is 0.006 mm/min. Results are presented in terms of shear dilatancy, and peak and constant volume friction angle. Based on the analysis of the test results, it is found: (1) increasing gravel content increases both peak and constant volume friction angle; (2) both particle symmetry (quantified by elongation) and surface smoothness (quantified by convexity) play an important role in peak and constant volume friction, though they work in different ways; (3) increasing convexity decreases constant volume friction angle, while increases peak friction angle; and (4) increasing elongation increases constant volume friction angle, but decreases peak friction angle.

Deformation History Tacking of Typical Large-scale Rocky Landslides in China

( Weile Li ),( Qiang Xu ),( Huiyan Lu ),( Runqiu Huang ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

Large-scale rocky landslides usually have the characteristics of high-altitude, strong concealment, high-speed and long-runout, which often cause serious casualties and property losses. Revealing its deformation history and evolution rule can provide a reference for early detection of similar landslide disasters. Five typical large-scale rocky landslides in China in recent years were studied. Through visual interpretation of multi-temporal high-resolution remote sensing images, their deformation signs were identified and their evolution rules were analyzed. It is found that large-scale rocky landslides will produce significant surface deformation signs in the process of development and evolution. This deformation information can be identified by high-resolution (sub-meter level) optical remote sensing images. The incubation and evolution time of deformation can reach several years or even decades. Large-scale rocky landslides often do not have the "chair-like" geomorphological characteristics. The early identification signs of the landslides using optical remote sensing images are mainly whether there are tension cracks at the back of the slope and whether there are local slides at the front of the slope.

Effect of Glutinous Rice Slurry on the Unconfined Compressive Strength of Lime-Treated Seasonal Permafrost Subjected to Freeze-Thaw Cycles

Jie Deng,Jianjun Zhao,Xiao Zhao,Jianle Yu,Chun Lei,Minlee Lee,Runqiu Huang 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.4

It is important to account for the poor ecological environment of weak seasonal permafrost regions while developing a suitable ground improvement technique. As an organic non-polluting material, glutinous rice slurry improves the unconfined compressive strength of the soil through induction and synergy with lime. The Qinghai-Tibet Plateau has cold weather, large temperature differences between day and night, and a fragile ecological environment. Once damaged, it is extremely difficult to recover. This study investigates the effects of glutinous rice slurry on the unconfined compressive strength (UCS), failure mode, and microstructure of lime-treated seasonally frozen soil subjected to freeze–thaw cycles. Organic glutinous rice slurry with concentrations of 0, 2, 4, 6, and 8% was added to soil specimens that were treated with 10% lime and subjected to 0, 1, 3, 6, and 10 freeze–thaw cycles. In tests, the addition of glutinous rice pulp could increase the UCS of the soil by up to 40%. The first freeze-thaw cycle has the greatest impact on the UCS of the soil sample, with a decrease of 6 – 15%. Glutinous rice slurry can reduce the degradation effects of freeze-thaw cycles by increasing the contact area between soil particles. In a comprehensive evaluation under test conditions, a glutinous rice slurry concentration of 4% led to optimal results. It revealed the change characteristics of the microstructure under the action of freeze-thaw cycles, which has a good corresponding relationship with the macroscopic mechanical properties. The results can provide reference value for the application of glutinous rice slurry in the modification of subgrade soil in seasonal permafrost areas.