Frictional behaviour of three critical geosynthetic interfaces

This paper’s scope is the shear interaction mechanisms of three critical geosynthetic interfaces (geotextile/geomembrane; drainage geocomposite/geomembrane and soil/geomembrane) typically used for lined containment facilities such as landfills. A large direct shear machine was used to carry out 159 geosynthetic interface tests. The results showed strain softening behaviour, a very small dilatancy, 0.1–1 mm, and non-linear failure envelopes at normal stress range of 25–500 kPa. The three types of interfaces present the same main interaction mechanisms: interlocking and friction. For geotextile/geomembrane and drainage geocomposite/geomembrane interfaces, the higher the asperity height, the higher the interface shear strength.Whereas for soil/geomembrane interfaces, the higher the soil shear strength, the higher the interface shear strength. The drainage geocomposite/geomembrane interface showed the lowest friction angles, followed by the geotextile/geomembrane and the soil/geomembrane interfaces

The role of rock joint frictional strength in the containment of fracture propagation

The fracturing phenomenon within the reservoir environment is a complex process that is controlled by several factors and may occur either naturally or by artificial drivers. Even when deliberately induced, the fracturing behaviour is greatly influenced by the subsurface architecture and existing features. The presence of discontinuities such as joints, artificial and naturally occurring faults and interfaces between rock layers and microfractures plays an important role in the fracturing process and has been known to significantly alter the course of fracture growth. In this paper, an important property (joint friction) that governs the shear behaviour of discontinuities is considered. The applied numerical procedure entails the implementation of the discrete element method to enable a more dynamic monitoring of the fracturing process, where the joint frictional property is considered in isolation. Whereas fracture propagation is constrained by joints of low frictional resistance, in non-frictional joints, the unrestricted sliding of the joint plane increases the tendency for reinitiation and proliferation of fractures at other locations. The ability of a frictional joint to suppress fracture growth decreases as the frictional resistance increases; however, this phenomenon exacerbates the influence of other factors including in situ stresses and overburden conditions. The effect of the joint frictional property is not limited to the strength of rock formations; it also impacts on fracturing processes, which could be particularly evident in jointed rock masses or formations with prominent faults and/or discontinuities

Numerische Simulationen in der Geomechanik mittels expliziter Verfahren

SIGLEAvailable from TIB Hannover: RR 8917(2001,2) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Instrumented failure of hillslope models with soil-pipes

Soil-pipes (porous pipes inside a hillslope) are often detected in collapsed slopes indicating their influence on slope failure processes. Only limited studies can be found regarding the impacts of soil-pipes on landslide mechanisms. Hillslope models prepared in a flume are experimented with different soil-pipe configurations: a) no pipe, b) closed pipe and c) open pipe. Pore-water pressures were measured at six different locations along a slope. Discharges at the outlet of soil-pipe and groundwater seepage were also recorded. For the above mentioned pipe configurations two types of experiments were conducted: a) rainfall-induced failure and b) seepage-induced failure. Experimental results show that a closed pipe accumulates water around its lower end and continuously increases pore-water pressure till a failure. An open pipe works as a means of hillslope drainage and reduces the pore-water pressure of an entire slope. However, if open pipe is blocked, pore-water pressure close to its lower end rises rapidly, leading to immediate soil mass movement. For both seepage and rainfall-induced failure experiments, the maximum pressure before the failure was larger at a slope with an open pipe (once it is closed) than a slope with a pipe closed from the beginning or that without a soil-pipe. This indicates that the blockage of soil-pipes makes a slope more susceptible to failure. Displacement vectors show that soil movement velocity close to the surface was highest at slopes with open pipes after closure and lowest at slopes without pipes because of a higher degree of saturation and pore-water pressure at the time of failure of the former. Before a large failure, small fluctuations in pore-water pressure were also observed which can be an indicator of impending failure

A study of geogrid-reinforced ballast using laboratory pull-out tests and discrete element modelling

This paper presents an evaluation of the behaviour of geogrid-reinforced railway ballast. Experimental large box pull-out tests were conducted to examine the key parameters influencing the interaction between ballast and the geogrid. The experimental results demonstrated that the triaxial geogrid outperforms the biaxial geogrid and the geogrid aperture size is more influential than rib profile and junction profile. The discrete element method (DEM) has then been used to model the interaction between ballast and geogrid by simulating large box pull-out tests and comparing with experimental results. The DEM simulation results have been shown to provide good predictions of the pull-out resistance and reveal the distribution of contact forces in the geogrid-reinforced ballast system. Therefore, the calibrated geogrid model and the use of clumps to model ballast particles hold much promise for investigating the interaction between geogrids and ballast and therefore optimising performance

Experimental study on effects of soil pipe on hillslope water dynamics and slope failure

Soil pipes (porous pipes inside a hillslope) are often detected in collapsed slopes indicating their influence on slope failure. Flume tests were conducted to see the impact of soil pipes on a slope failure. Three different soil pipe configurations: a) no pipe, b) closed pipe and c) open pipe that are common in the field were conducted. Two types of tests were conducted for each of the pipe configurations: a) rainfall induced failure test and b) seepage induced failure tests. Experimental results show that a closed pipe accumulates water around its lower end and continuously increasespore-water pressure till a failure. Open pipes if are blocked, raises pore-water pressure more rapidly than other cases leading to immediate soil mass movement. This indicates the blockage of open soilpipes makes a slope more susceptible to a failure. The result also showed sudden increase in discharge before the slope failure. Such an increase in hillslope discharge can be taken as an indication of increment in potentiality of slope failure in real hillslopes. Before a large failure small fluctuations in pore water pressure were also seen in the experiments. This can also be used as an indicator of impending failure in an instrumented hillslopes

Coupled finite element and discrete element method for underground blast in faulted rock masses

10.1016/j.soildyn.2008.11.002Soil Dynamics and Earthquake Engineering296939-94

Instrumented failure of hillslope models with soil-pipes

Soil-pipes (porous pipes inside a hillslope) are often detected in collapsed slopes indicating their influence on slope failure processes. Only limited studies can be found regarding the impacts of soil-pipes on landslide mechanisms. Hillslope models prepared in a flume are experimented with different soil-pipe configurations: a) no pipe, b) closed pipe and c) open pipe. Pore-water pressures were measured at six different locations along a slope. Discharges at the outlet of soil-pipe and groundwater seepage were also recorded. For the above mentioned pipe configurations two types of experiments were conducted: a) rainfall-induced failure and b) seepage-induced failure. Experimental results show that a closed pipe accumulates water around its lower end and continuously increases pore-water pressure till a failure. An open pipe works as a means of hillslope drainage and reduces the pore-water pressure of an entire slope. However, if open pipe is blocked, pore-water pressure close to its lower end rises rapidly, leading to immediate soil mass movement. For both seepage and rainfall-induced failure experiments, the maximum pressure before the failure was larger at a slope with an open pipe (once it is closed) than a slope with a pipe closed from the beginning or that without a soil-pipe. This indicates that the blockage of soil-pipes makes a slope more susceptible to failure. Displacement vectors show that soil movement velocity close to the surface was highest at slopes with open pipes after closure and lowest at slopes without pipes because of a higher degree of saturation and pore-water pressure at the time of failure of the former. Before a large failure, small fluctuations in pore-water pressure were also observed which can be an indicator of impending failure