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Landslide can be defined as the mass movement of rock, debris or earth down a slope [1,2,3]. It is currently one of the most common natural disasters in the world. Landslide causes and triggers have attracted the attention of researchers for centuries, most especially as early warning and mitigation measures. The causes of landslide are those factors that rendered slopes vulnerable to failure, while triggers are factors that initiate the downslope movement or slide. The major triggering factors include both natural and human activities [4]. The natural triggering factors include precipitation and slope instability, while landslides that are entirely due to or aided by human activities such as construction, mining, quarrying and excavations remain on the increase all over the world [4,5,6,7]. Slow and steady decrease in rock strength due to fracturing, water infiltration into cracks and pore spaces, weathering, etc., are some of the causes. The record of Fatal Landslides in America between 2002 and 2007 [8] and between 2004 and 2016 [9] exceeds forty thousand occurrences. The high incidence of fatal landslides may be accredited to an increase in water level due to global warming and climate change [10, 11], deforestation due to development and urbanization, etc.


The landslide in Agboona Hill, probably initiated with the development of parallel normal faults along the horst, further weakening of this zone by fracturing, water infiltration and gravity led to shattering of rocks along this zone. However, numerous open fractures joints, cracks, folds and high strain shears were encountered on the ruptured surfaces. Borehole and geophysical data that can help to verify the influence of earthquake were not available at the time of compiling this manuscript. However, most of the rock fragments displaced by the landslide show well-polished surfaces, suggesting that the dominant processes along this fault zone are bulk crushing, surface grinding and polishing.

Relic plumose structure preserved on the fracture surface (Fig. 4) shows a feathery Mode 1 (one) joint surface with E-W propagation direction. This is interpreted as the intermediate stress axis δ2. This structure reveals the direction of joint propagation to be E-W, and it was produced due to the changing intensity of the stress field at the tip during the growth of the joint. The stress intensity is proportional to the length of the crack. The Plumose structure is formed when an unexposed joint surface revealed a rough pattern resembling the imprint of a feather. The stress intensity is proportional to the length of the crack.

Generally, Yemen is located in the southwestern part of Arabian Peninsula, and it is affected by an active rifting zone of the Gulf of Eden and the Red Sea opening. This active (rifting) zone can cause the reactivation of the old fault systems and may create new faulting lines in the area. The active faults (such as, rock mass movements or sliding on the fault planes and bedrock lithologies cracking) may cause severe damages in some places, especially in urban or settlements areas. For example, bedrock cracking and rock mass sliding happened in the 2003 and 2010 in some places in Taiz city caused severe damages, and many houses, roads, and other infrastructures were destroyed.

The drainage pattern is apparently being controlled by structure and lithology in the study area. The lithologic variation has given a rise to different drainage patterns. For example, radial and dendritic drainage patterns are developed over granitic rocks. Moreover, the most important feature in the area is the presence of drainage lines patterns and fault lines. It is clearly to see that there is a good relationship between these fault lines and drainage pattern system distribution especially with third and fourth river orders in the area.

The stress-strain curve of the composite could be divided into four regimes: pore compaction (OA), a linear elastic section (AB), prepeak crack development (BC), and postpeak fracture development (CD). During the pore compaction stage, the preexisting cracks and pores in the coal and the rock parting were closed, and the AE activity was weak and fluctuated slightly. The AE activity in the composite remained basically stable over the linear elastic regime. However, there was some propagation of the preexisting cracks in the composite under compressive loading, and a small quantity of coal spalled off in the form of flakes. Consequently, a few AE peaks appeared, albeit with relatively small amplitudes. During prepeak crack development, the cracks inside the composite developed steadily, accompanied by the caving of small coal blocks. A small quantity of rock powder fell off, the coal failed in local areas, there were violent fluctuations in the AE activity, and multiple AE peaks appeared. During postpeak fracture development, small coal blocks erupted accompanied by a notable cracking sound and increasing AE activity. Each steplike sudden increase observed in the cumulative AE count curve corresponded to the initiation and development of microcracks in the composite, as well as the spalling of coal in the form of flakes. The cumulative AE count curve demonstrably corresponded to the stress-strain curve and could be approximately divided into four regimes: pore compaction and closure (during which the AE count increased slightly); a slowly ascending linear elastic section (during which the AE count increased steadily overall but suddenly increased to a relatively small extent at isolated points as a result of the propagation of the preexisting cracks); prepeak steady crack propagation (during which the propagation of the preexisting cracks intensified, new cracks were initiated, the AE activity increased, and the cumulative AE count curve exhibited a large rate of increase); and peak unsteady crack propagation (during which cracks developed unsteadily, and there was a sharp increase in the cumulative AE count curve).

High-speed photographs of the failure process of the composite showed that the coal failed first in the composite. This is primarily because of the large difference between the strengths of the coal and rock in the composite. The development of internal microcracks resulted in a relatively low coal strength. Consequently, under compressive loading, crack initiation and propagation occurred first in the coal, which spalled off in the form of flakes.

As D increased, the rock parting became the main load-bearing structure, and σu and Ke of the composite increased, as did the risk of bursting. Under uniaxial compressive loading, the rock parting was the key structure for accumulating energy due to its relatively high strength. The relatively low coal strength enabled micro- and macrocracks to develop in the coal before the ultimate failure strength of the rock parting was reached, causing a relatively large displacement in the coal and generating a relatively large vacated space. Under these conditions, the rock parting rebounded and released the accumulated elastic energy, which precipitated the violent bursting failure of the coal. Rebounding generated a tensile stress in the rock parting and caused similar splitting and tensile failure of the surfaces. However, premature crack propagation divested the rock parting of the preconditions for accumulating energy. The corresponding composite specimens in this study were found to exhibit static failure characteristics with a considerably lower risk of bursting. The larger the composite D was, the higher the capacity of the rock parting to accumulate elastic energy was. The release of elastic energy from the rock parting increased the extent of fragmentation of the coal. The larger D was, the more fragmented the coal was.

The experimental results were used to formulate two technologies for controlling the stability of the surrounding rock (Figure 14). (1) Excavation causes the surrounding rock stress at the free face of a roadway to transition from a three-dimensional stress state to a two-dimensional or unidirectional stress state, thereby decreasing the rock stability. The presence of partings increases the strength anisotropy of the coal-rock composite surrounding the roadway. Under the mining-induced surrounding rock stress, the coal ribs of a roadway significantly spall off. Consequently, an asymmetric strengthening support technology can be used to increase the strength of coal-seam support systems, reduce the difference between the strengths of the coal and rock in coal-rock composites, and maintain the stability of roadway surrounding rocks. (2) Under uniaxial compression, the initiation and propagation of microjoints and microcracks damages the coal in a coal-rock composite and thereby releases part of the accumulated elastic energy in the rock. Thus, the extent of damage sustained by the coal increases, and bursting is induced. It is necessary to reduce the extent of damage sustained by coal-rock composites, the bursting risk, and the coal cutting energy consumption. These goals can be achieved by using high-pressure fracturing to weaken and disrupt the integrity of rock partings, reduce the strength anisotropy of coal-rock composites, and decrease the risk of bursting in coal seams.

Wheel abnormality intensifies impact characteristics of train loads on railway concrete ties. Concrete ties are commonly prestressed with single or multiple tendons. This paper presents experimental studies on crack propagation of prestressed concrete ties with single steel tendons subjected to impact loads. The presented study includes the effect of supplementary fiber reinforcement using polypropylene fibers on crack arrest, in terms of fiber type and content by volume. Concrete ties are modeled as flexural beams subject to four-point loading system. A mass dropped from predetermined height simulated the wheel impact loads. Experimental results include crack patterns, dimensions, and accompanied loads. The concrete beams reinforced with fibers experienced a delay in crack growth in both length and width. Further, the fiber reinforced beams had smaller initial crack length in comparison to beams with no fiber reinforcement.

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