scholarly journals Model Experimental Study on Stress Transfer and Redistribution in a Clay Landslide under Surcharge Load

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Heng-Jun Hou ◽  
Bo Wang ◽  
Quan-Xiang Deng ◽  
Zheng-Wei Zhu ◽  
Feng Xiao
Keyword(s):  
Slip Surface ◽  
Process Analysis ◽  
Stress Transfer ◽  
Horizontal Stress ◽  
Vertical Stress ◽  
Transfer Efficiency ◽  
Stress Monitoring ◽  
Stress Growth ◽  
Stress Variation ◽  
Two Stages

Stress transfer and redistribution always accompany with the evolution of landslides. However, previous literature studies have mainly focused on stages of stress variation, and far too little attention has been paid to detailed transfer and redistribution process analysis on stress variation. In this paper, a large-scale clay model slope with masonry slide bed and prefabricated cambered slip surface was constructed. Earth pressure cells were embedded into slip mass to monitor vertical and horizontal stresses in different parts of the test soils under the set load sequence. Stress transfer efficiency (STE) indicators based on qualified stress monitoring datasets (tested by Shapiro-Wilk method) were established to quantify the stress transfer process. Staged development of stress inside the clay slope was analyzed through extracting slopes of stress curves and limit loads. The stress redistribution process was analyzed using STE and deflection of stress isolines derived from numerical simulation. Moreover, to study the influence of loading position on stress variation, geometry partitioning has also been discussed. Results showed that vertical and horizontal stresses had different growth trends on both sides of 80 kN and 60 kN, respectively. Horizontal stress growth has two stages; vertical stress growth has two stages in soils close to slope surface and shear outlet, while there are three stages in other soils. Vertical stress transfer efficiency (VSTE) and horizontal stress transfer efficiency (HSTE) are recommended to quantify stress transfer and redistribution process. Based on VSTEs and HSTEs, the slip mass could be partitioned into three parts: loading zone, transfer zone, and free zone. Deflecting amplitudes of stress isolines were in consistency with the results revealed by STEs.

scholarly journals A Review on Mechanical Properties of Natural Fibre Reinforced Polymer Composites under Various Strain Rates

2021 ◽  
Vol 5 (5) ◽  
pp. 130
Author(s):  
Tan Ke Khieng ◽  
Sujan Debnath ◽  
Ernest Ting Chaw Liang ◽  
Mahmood Anwar ◽  
Alokesh Pramanik ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Polymer Composites ◽  
Stress Transfer ◽  
Natural Fibre ◽  
Transfer Efficiency ◽  
Strain Rates ◽  
Reinforced Polymer ◽  
Fibre Reinforced Polymer ◽  
Fibre Matrix

With the lightning speed of technological evolution, the demand for high performance yet sustainable natural fibres reinforced polymer composites (NFPCs) are rising. Especially a mechanically competent NFPCs under various loading conditions are growing day by day. However, the polymers mechanical properties are strain-rate dependent due to their viscoelastic nature. Especially for natural fibre reinforced polymer composites (NFPCs) which the involvement of filler has caused rather complex failure mechanisms under different strain rates. Moreover, some uneven micro-sized natural fibres such as bagasse, coir and wood were found often resulting in micro-cracks and voids formation in composites. This paper provides an overview of recent research on the mechanical properties of NFPCs under various loading conditions-different form (tensile, compression, bending) and different strain rates. The literature on characterisation techniques toward different strain rates, composite failure behaviours and current challenges are summarised which have led to the notion of future study trend. The strength of NFPCs is generally found grow proportionally with the strain rate up to a certain degree depending on the fibre-matrix stress-transfer efficiency. The failure modes such as embrittlement and fibre-matrix debonding were often encountered at higher strain rates. The natural filler properties, amount, sizes and polymer matrix types are found to be few key factors affecting the performances of composites under various strain rates whereby optimally adjust these factors could maximise the fibre-matrix stress-transfer efficiency and led to performance increases under various loading strain rates.

Well Shear Associated with Conventional and Unconventional Operations: Diagnosis and Mechanisms

2021 ◽  
pp. 1-18
Author(s):  
Russell T. Ewy
Keyword(s):  
Cross Sections ◽  
Slip Surface ◽  
Bedding Plane ◽  
Vertical Stress ◽  
Natural Fracture ◽  
Shear Deformations ◽  
Horizontal Fracture ◽  
Bedding Planes ◽  
Shear Slip ◽  
Fluid Pressurization

Summary Wells are sometimes deformed due to geomechanical shear slip, which occurs on a localized slip surface, such as a bedding plane, fault, or natural fracture. This can occur in the overburden above a conventional reservoir (during production) or within an unconventional reservoir (during completion operations). Shear slip will usually deform the casing into a recognizable shape, with lateral offset and two opposite-trending bends, and ovalized cross sections. Multifinger casing caliper tools have a recognizable response to this shape and are especially useful for diagnosing well shear. Certain other tools can also provide evidence for shear deformation. Shear deformations above a depleting, compacting reservoir are usually due to slip on bedding planes. They usually occur at multiple depths and are driven by overburden bending in response to reservoir differential compaction. Shear deformations in unconventional reservoirs, for the examples studied, have been found to be caused by slip on bedding planes and natural fractures. In both cases, models, field data, and physical reasoning suggest that slip occurs primarily due to fluid pressurization of the interface. In the case of bedding plane slip, fracturing pressure greater than the vertical stress (in regions where the vertical stress is the intermediate stress) could lead to propagation of a horizontal fracture, which then slips in shear.

scholarly journals Stress transfer efficiency in aligned multi-wall carbon nanotubes sheet/epoxy composites

2014 ◽  
Vol 67 ◽  
pp. 16-21 ◽  
Author(s):  
Terumasa Tsuda ◽  
Toshio Ogasawara ◽  
Sook-young Moon ◽  
Kengo Nakamoto ◽  
Nobuo Takeda ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Stress Transfer ◽  
Epoxy Composites ◽  
Transfer Efficiency ◽  
Multi Wall Carbon Nanotubes

Numerical Simulation on Failure Mechanism of Rock Slope Using RFPA

2011 ◽  
Vol 50-51 ◽  
pp. 568-572 ◽  
Author(s):  
Nu Wen Xu ◽  
Chu Nan Tang ◽  
Chun Sha ◽  
Ru Lin Zhang
Keyword(s):  
Rock Slope ◽  
Slip Surface ◽  
Process Analysis ◽  
Failure Process ◽  
Numerical Code ◽  
Natural State ◽  
Left Bank ◽  
Good Tool ◽  
Deep Rock ◽  
The Stability

This research applied a numerical code, RFPA2D (Realistic Failure Process Analysis) to evaluate the stability and investigate the failure mode of the high rock slope during excavations based on Strength Reduction Method (SRM). The corresponding shapes and positions of the potential slip surfaces are rationally simulated in different stages, and the related safety coefficients are obtained, which agrees well with the allowable minimum safety factors of the slope. The numerical results show that the safety coefficient drops from 1.25 at the natural state to 1.09 after excavation, and then increases to 1.35 after slope reinforcement. Moreover, the potential slip surface of the left bank moves into deep rock mass after taking support measures, which demonstrates the reinforcement is reasonable and efficient. The study shows that cracks and faults will cause crucial influences on the slope stability, and RFPA2D is a good tool to directly display the potential slip surface of the slope, which will offer valuable guidance for bolt support.

Coefficient of earth pressure at rest for sands subjected to vibration

2007 ◽  
Vol 44 (10) ◽  
pp. 1242-1263 ◽  
Author(s):  
Barames Vardhanabhuti ◽  
Gholamreza Mesri
Keyword(s):  
Lake Michigan ◽  
Earth Pressure ◽  
Horizontal Stress ◽  
Vertical Vibration ◽  
Vertical Stress ◽  
Dynamic Changes ◽  
Shearing Resistance ◽  
Interparticle Contacts ◽  
Horizontal Pressure ◽  
Stress Ratios

An oedometer instrumented to measure horizontal pressure was used to examine the behavior of the coefficient of earth pressure at rest, Ko, of clean sands subjected to vertical vibration. Reconstituted specimens of Ottawa, Lake Michigan Beach, and Niigata sands were used in a comprehensive series of tests. The dynamic effort is defined by the ratio of dynamic increase in effective vertical stress to the static effective vertical stress, and frequency and duration of vibration. Dynamic changes in Koare referenced to a series of lines representing the ratio of the increase in effective horizontal stress to the increase in effective vertical stress corresponding to different void ratios or friction angles through the Jaky equation. An increase in Kooccurs when the combination of the initial sand state and dynamic effort results in periodic disengagement of interparticle contacts, producing a periodic decrease in interparticle shearing resistance and thus a periodic fluidization of the sand. The highest values of [Ko]maxas well as the lowest values of eminwere obtained with dynamic stress ratios equal to or greater than 3–4. Vibration of overconsolidated sands results in an initial Kodrop that increases with previbration density and overconsolidation ratio. Thereafter, the behavior of Koand void ratio with vibration depend on the potential for fluidization.

scholarly journals In Situ Stress and Stress Regime in the Onshore Part of the Northeast Java Basin

2021 ◽  
Vol 44 (2) ◽  
pp. 95-105
Author(s):  
Agus M. Ramdhan
Keyword(s):  
Petroleum Industry ◽  
Horizontal Stress ◽  
In Situ Stress ◽  
Vertical Stress ◽  
Stress Regime ◽  
Severe Erosion ◽  
Tectonically Active ◽  
Minimum Horizontal Stress ◽  
Maximum Horizontal Stress

In situ stress is importance in the petroleum industry because it will significantly enhance our understanding of present-day deformation in a sedimentary basin. The Northeast Java Basin is an example of a tectonically active basin in Indonesia. However, the in situ stress in this basin is still little known. This study attempts to analyze the regional in situ stress (i.e., vertical stress, minimum and maximum horizontal stresses) magnitude and orientation, and stress regime in the onshore part of the Northeast Java Basin based on twelve wells data, consist of density log, direct/indirect pressure test, and leak-off test (LOT) data. The magnitude of vertical (  and minimum horizontal (  stresses were determined using density log and LOT data, respectively. Meanwhile, the orientation of maximum horizontal stress  (  was determined using image log data, while its magnitude was determined based on pore pressure, mudweight, and the vertical and minimum horizontal stresses. The stress regime was simply analyzed based on the magnitude of in situ stress using Anderson’s faulting theory. The results show that the vertical stress ( ) in wells that experienced less erosion can be determined using the following equation: , where  is in psi, and z is in ft. However, wells that experienced severe erosion have vertical stress gradients higher than one psi/ft ( . The minimum horizontal stress ( ) in the hydrostatic zone can be estimated as, while in the overpressured zone, . The maximum horizontal stress ( ) in the shallow and deep hydrostatic zones can be estimated using equations: and , respectively. While in the overpressured zone, . The orientation of  is ~NE-SW, with a strike-slip faulting stress regime.

scholarly journals A Crack Propagation Control Study of Directional Hydraulic Fracturing Based on Hydraulic Slotting and a Nonuniform Pore Pressure Field

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Yugang Cheng ◽  
Zhaohui Lu ◽  
Xidong Du ◽  
Xuefu Zhang ◽  
Mengru Zeng
Keyword(s):  
Crack Initiation ◽  
Hydraulic Fracturing ◽  
Pore Pressure ◽  
Pressure Field ◽  
Process Analysis ◽  
Failure Process ◽  
Horizontal Stress ◽  
Directional Hydraulic Fracturing ◽  
Rock Failure Process ◽  
Initiation Pressure

Hydraulic fracturing techniques for developing deeply buried coal reservoirs face routine problems related to high initial pressures and limited control over the fracture propagation direction. A novel method of directional hydraulic fracturing (DHF) based on hydraulic slotting in a nonuniform pore pressure field is proposed. A mechanical model is used to address crack initiation and propagation in a nonuniform pore pressure field, where cracks tend to rupture and propagate towards zones of high pore pressure for reducing the effective rock stress more. The crack initiation pressure and propagation morphology are analyzed by rock failure process analysis software. The numerical results show that the directional propagation of hydraulic fracturing cracks is possible when the horizontal stress difference coefficient is less than or equal to 0.5 or the slotting deviation angle is less than or equal to 30°. These findings are in good agreement with experimental results, which support the accuracy and reliability of the proposed method and theory.

How many plates?

2020 ◽  
Author(s):  
Tiantian Chen ◽  
Chun‘an Tang ◽  
Yongyi Wang
Keyword(s):  
Thermal Expansion ◽  
Probability Distribution ◽  
Spherical Shell ◽  
Shell Model ◽  
Layer Thickness ◽  
Process Analysis ◽  
Failure Process ◽  
Three Dimensional ◽  
Stress Transfer ◽  
Global Scale

<p>The spacing of opening-mode fractures in layered materials, such as certain sedimentary rocks and laminated engineering materials, is often proportional to the thickness of fractured layers. Bai, Pollard & Gao (2000) investigated the full stress distribution between such fractures, from which they show that the spacing initially decreases as extensional strain increases in the direction perpendicular to the fractures. But at a certain ratio of spacing to layer thickness, no new fractures form and the additional strain is accommodated by further opening of existing fractures: the spacing then simply scales with layer thickness, which is called fracture saturation. Their conclusion is in marked contrast to existing theories of fracture, such as the stress-transfer theory, which predict that spacing should decrease with increasing strain ad infinitum. Here we show that the principle for 2D equal spaced fracture problem also applies to the 3D polygonal fracture problem. By using 3D mechanical modeling on a spherical shell model under interior expansion, we found that the modeled plate mosaic exactly follows the same principle that the size of formed plates is also proportional to the thickness of the fractured shell. By using a spherical shell model with isotropic, elastic two-layers, we numerically load the shell to fail under a quasistatical, slowly increasing interior pressure in a displacement controlling manner (induced, e.g., by gradual thermal expansion). The fractures only occur in the surface layer. The value at which a particular element breaks is random, but fixed at the start of the fragmentation process (i.e., the disorder is quenched). The probability distribution (PD) of breakdown thresholds is a material property and is known from the start. We account for this local randomness by assigning to each element a failure threshold taken from a Weibull probability distribution (PD), with a parameter defines the degree of material homogeneity, called the homogeneity index. We use a three-dimensional finite element code named RFPA (Rock Failure Process Analysis) to solve the problem. The modeling results show that, under conditions of uniform expansion force from inside the shell, the cracking pattern also follows a global scale law in terms of the thickness of the fractured layer. The numerical modeling demonstrates an important observation that, under conditions of uniform and layer-parallel tension induced by thermal expansion within the spherical shell, surface cracks spontaneously self-organize into quasi-hexagonal tessellations, following the mechanical principle that the hexagonal pattern relieves the greatest strain energy for the least work invested in nucleation and propagation of fractures. If this applies to the problems of Earth tessellations, called Platonics (Anderson, 2002), it implies that the thermal expanded Earth may breakup to form plate-like network as a consequence of thermal-expansion induced rift rather than mantle convective or plutonic causes, and the plate size may be proportional to the thickness of lithosphere. This provides a new explanation on how the plate number should be, and whether there is a pattern in the plate mosaic, issues related to the optimal sizes and shapes of plates in terms of fracture spacing.</p>

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