Showing papers on "Embedment published in 2021"

Metal foam-phase change material composites for thermal energy storage: A review of performance parameters

Abstract: Many efforts have been made to improve the weak thermal performance of phase change materials (PCMs). Among the common methods of such, embedment of open-cell metal foams (MFs) into PCMs offer unique opportunities to overcome the issue. The composites made of PCMs and MFs (PCM-MFs) have been extensively studied while behaviour of such composites is yet to be fully understood. There are a variety of parameters affecting thermophysical performance of PCM-MFs, some of which are well-known to date, and some are a subject of controversy. This study provides a detailed review of the parameters affecting thermophysical performance of PCM-MFs. In doing so and directed by literature, the most effective parameters are identified, and all their possible effects are investigated. The common observations along with the contradicting reports are pointed out and discussed in detail. Finally, the current gaps in the field are identified and opportunities for further research work to address them are discussed.

Vertical Uplift Capacity of Circular Anchors in Clay by Considering Anisotropy and Non-Homogeneity

Abstract: New numerical analyses of the vertical uplift capacity of circular anchors embedded in anisotropic and non-homogenous clay are presented in this paper. These analyses are derived based on the lower bound and upper bound finite element limit analysis under an axisymmetric condition. The anisotropic undrained shear (AUS) failure criterion is applied in these analyses. The undrained shear strength of clay increases linearly with depth. The anisotropy is adopted by changing of the ratios between undrained shear strengths determined from triaxial compression test and extension test. The variation of uplift factor (Fc) and shape of failure pattern with three parameters including embedment ratio (H/B), ratio of increasing undrained shear strength with depth (m), and the ratio of anisotropic parameters (re) are verified and investigated. These analyses will provide reliable results in order to improve the engineering calculation for plate anchor embedded in anisotropic and non-homogenous clays.

Experimental and Numerical Investigations of the Role of Proppant Embedment on Fracture Conductivity in Narrow Fractures (includes associated Errata)

Abstract: With the advancement of drilling and completion technologies in unconventional reservoirs, more extended reach wells are developed, and narrow-fracture environments are created in these reservoirs. Proppant embedment in monolayer/thin-layer-propped fractures can be significantly different from multilayer-propped fractures. In this study, a comprehensive investigation combining laboratory experiments with numerical simulations was conducted to explore the factors affecting proppant embedment and induced fracture conductivity loss in narrow fractures. The fracture-conductivity experiments were performed using monolayers of sand and ceramic proppant particles sandwiched between Berea Sandstone and Eagle Ford Shale plates under different closure pressures. The experiment study demonstrated that the long-term rock/fluid interaction leads to significant proppant embedment, and the fracture having a rough rock surface has higher fracture conductivity in monolayer-propped fractures. To further quantify the influence of proppant layer number, size, distribution variations, and particle crushing on proppant embedment, a numerical modeling approach that coupled continuum mechanics, discrete element method (DEM), and the lattice Boltzmann (LB) method was developed. In the simulation, the fracture/proppant system was constructed by filling proppant, modeled by DEM, between two fracture surfaces that were modeled by FLAC3D (Itasca Consulting Group 2012); LB simulation was then performed on the changing proppant pack to compute its time-dependent permeability. The numerical model was validated by comparing numerical results with measured fracture conductivities in the laboratory experiment. The simulation results demonstrated a strong correlation between proppant embedment and rock mechanical properties. When the Young’s modulus of the rock plate is less than 5 GPa, large magnitudes of proppant embedment can be expected in fractures supported by monolayers of ceramic proppant particles. Moreover, large-size proppant particles are more sensitive to the variations of Young’s modulus of the rock plate. When the rock formation in a narrow fracture environment has a relatively high Young’s modulus, the proppant diameter distribution has a lesser effect on the fracture conductivity. The outcome of this study will provide insights into the role of reservoir rock characteristics, proppant properties, and closure pressure on proppant embedment in narrow fractures.

Cyclic response and modelling of special moment resisting beams exhibiting fixed-end rotation

Abstract: Rebar slippage in reinforced concrete (RC) elements results in concrete expansion, large cracks, and consequently, early deterioration of strength as well as premature stiffness degradation, particularly in the inelastic energy dissipating zones. Although design standards prescribe different minimum concrete compressive strength, seismic evaluation and retrofit standards, and guidelines permit the use of provisions regarding bond strength and bar slippage issues regardless of the minimum specified concrete strength postulated in design standards. To better understand the seismic behavior of special moment-resisting (SMR) beams exhibiting fixed-end rotation resulting from the rebars inelastic elongation and slip, quasi-static cyclic tests were performed on eight full-scale SMR beams. The chosen beams have longitudinal reinforcement ratios of 0.84% (Type-1) and 1.26% (Type-2) with a shear-span to depth ratio of 6.14 and detailed following the provisions of ACI-318-19. Two specimens were prepared for each reinforcement ratio using concrete with compressive strengths equal to 2000 psi (14 MPa, M14) and 3000 psi (21 MPa, M21). The specimens were tested under cyclic displacement protocols, exhibiting flexure yielding that was followed by diagonal shear cracking and, ultimately, bond failure at the beam–block interface. It is even though the beams fulfill the requirements of ACI 318-19 for steel bars embedment and end hooks for anchorage. Force–displacement hysteretic response curves were obtained revealing pinching behavior in the cyclic response. Both types of beams deformed up to maximum chord rotations of 5.22% and 5.73% in case of beams with M14 and M21 concrete, respectively, and experienced cover concrete crushing at the compressed toe. Representative numerical models were assembled implementing fiber-section force-based inelastic beam elements. Additionally, lumped inelastic rotational springs were added to the model for fixed-end rotation. A tri-linear moment-rotation hysteretic response curve has pinching behavior was used to simulate the reduction in re-loading stiffness. This was verified with the measured response of tested beams; excellently simulates the hysteretic response. Moreover, to examine the seismic response of a total structural system regarding these findings, several response history analyses were performed on capacity-designed five-story frames to demonstrate the importance of modeling beam element fixed-end rotation for predicting the story drift demands subjected to different earthquake ground motions. It was found that despite the bar-slip phenomenon the beams developed their yield capacities; however, the response of the frame was subjective depending on the characteristics of input motions, particularly the valleys and hills of the spectral shape.

Pull-out and Critical Embedment Length of Grouted Rebar Rock Bolts-Mechanisms When Approaching and Reaching the Ultimate Load

Abstract: Rock bolts are one of the main measures used to reinforce unstable blocks in a rock mass. The embedment length of fully grouted bolts in the stable and competent rock stratum behind the unstable rock blocks is an important parameter in determining overall bolt length. It is required that the bolt section in the stable stratum must be longer than the critical embedment length to ensure the bolt will not slip when loaded. Several series of pull tests were carried out on fully grouted rebar bolts to evaluate the pull-out mechanics of the bolts. Bolt specimens with different embedment lengths and water/cement ratios were installed in either a concrete block of one cubic meter or in steel cylinders. Load displacement was recorded during testing. For some of the bolts loaded beyond the yield load, permanent plastic steel deformation was also recorded. Based on the test results, three types of failure mechanisms were identified, corresponding to three loading conditions: (1) pull-out below the yield strength of the bolt steel; (2) pull-out between the yield and ultimate loads, that is, during strain hardening of the steel; and (3) steel failure at the ultimate load. For failure mechanisms 2 and 3, it was found that the critical embedment length of the bolt included three components: an elastic deformation length, a plastic deformation length and a completely debonded length due to the formation of a failure cone at the borehole collar.

Preliminary Studies on the Proppant Embedment in Baltic Basin Shale Rock

Abstract: Proppant embedment is a serious issue that reduces fracture width and conductivity. The paper presents the results of experiments on embedment phenomena on a shale rock from the region of the Baltic Basin, which is regarded as an unconventional gas deposit. A novel laboratory imaging procedure was implemented to the proppant embedment visualization. The tests were performed for conditions corresponding to the average reservoir conditions occurring in the studied deposit formation. The parameters characterizing damage of the surface of the fracture faces by the grains of proppant material, after the application of axial compressive stress to two shale core samples with proppant placed in between, are presented. The tests were carried out for rock samples pre-saturated with fracturing fluid. The obtained results of relatively low total effective penetration depth of proppant grains into the walls of the fracture (0.293 mm), and high effective width of fracture with proppant material after hydraulic fracturing (87.9%), indicate the proper selection of proppant and fracturing fluid for the properties of the rock and the reservoir conditions. The results of the experiments present a range of embedment parameters, that have not been widely described before. The test procedure presented in the article is a good method for assessing the vulnerability of a deposit rock to embedment phenomenon.

Interference of Surface and Embedded Three Strip Footings in Undrained Condition

Abstract: The closed-form solutions for the undrained bearing capacity of shallow footing have been derived considering only single footing due to difficulties associated with adding the effect of nearby footings. However, the footing, in reality, may be separated or bounded by other footings from one side or two sides, and hence, the interference effect should be considered. This study has been conducted to understand the influence of the presence of existed footings on the undrained bearing capacity of a new footing that is placed between the existed footings. Validated numerical analyses have been conducted for single and interference footings to clearly understand the effect of the spacing between the footings on the obtained bearing capacity and the associated failure mechanism. The influence of the embedment ratio and the undrained cohesion has also been considered in these analyses to illustrate the combined influence of all of the factors. It was found that the undrained cohesion does not remarkably influence the trend of the relationship of the bearing capacity ratio and the distance ratio between the old and the new footings, while the embedment ratio has been found to have a remarkable impact on the trend of the aforementioned relationship. The average maximum percentage increase of the bearing capacity of the new footing due to the interference effect is found to be ranged between 6% to 23% depending on the embedment ratio and the distance between the footings. Importantly, the embedment ratio is found to influence the critical distance at which the maximum bearing capacity of the new footing is achieved.

Nonlinear Seismic Performance of Nuclear Structure with Soil–Structure Interaction

Abstract: In the present study, the emphasis is made on the seismic performance of nuclear containment constructed on layered medium to dense silty sand soil considering the nonlinearity of the containment structure using the concrete damage plasticity (CDP) model and Drucker–Prager plastic model for soil. The finite element model is prepared using the ABAQUS. From the static pushover analysis, it is noticed that yielding force is reduced up to 8.37% and 2.37% in the case of with and without embedment, respectively, as compared to a fixed base. Furthermore, incremental dynamic analysis is performed for the motion range of 0.1 g to 0.6 g, corresponding to the fundamental frequency. For the dynamic analysis, Kelvin element is used at boundaries to incorporate the truncated soil mass. The results are shown in the form of base shear, base moment and displacement ductility, drift ratio, normalized peak settlement, and normalized peak foundation sliding. Moment demand is reduced up to 25.89% and 51.31% in the case of with and without embedment, respectively, as compared to a fixed base. Similarly, base shear demand is increased up to 21.85% in the case of with embedment. It may reduce up to 29.08% in the case of without embedment of foundation as compared to a fixed base. Drift demand of nuclear power plant (NPP) structure is increased up to 14.47% and 38.16% in the case of with and without embedment of foundation, respectively, as compared to a fixed base. In contrast, displacement ductility demand reduced up to 47.95% and 57.52% in the case of with and without embedment of foundation, respectively. Settlement demand is increased linearly in the case of with embedment with respect to ground motion intensity; however, it increases sharply for ground motion intensity > 0.3 g in the case of without embedment. The sliding demand of foundation increase with a low and fixed amount of sliding is examined in the condition of with embedment case; however, it rises steeply in the case of without embedment case, indicating that without considering the embedment effect may increase the design requirement and therefore lead to uneconomical designing. The effect of the CDP model shows the need to consider the nonlinearity of structure along with the nonlinearity of soil.

Pinching-Free Connector for Timber Structures

Abstract: In timber structures resisting earthquakes, slender steel fasteners are traditionally employed to provide ductility in the joints. However, this is associated with pinched hysteresis loops ...

Effect of the interfacial shearing stress of soil–geogrid interaction on the bearing capacity of geogrid-reinforced sand

Abstract: A transformed approach has been made to predict the impression of inclusion geogrid on the reinforced soil’s bearing capacity underneath the strip foundation. The influence of the friction factor of the tensile strength of the reinforcement element performs a significant purpose in estimating the tolerance of the strengthened soil. Analytical study and experimental tests have been performed to validate the proposed empirical approach. This study analyzed certain parameters that influence the efficiency of the strip footing placed on reinforced soil, such as effects of two geogrid layers, the efficacy of geogrid embedment depths, the distance between geogrid layers, the tensile strength of geogrid, the contact surface friction angle, and shear stress distribution along the interactions at the soil–geogrid interface. Consequently, a simple new equation was proposed to modify the reinforced soil’s increased bearing capacity, then a comparative study was executed by the analytical method of literature. Finally, the calculations confirmed a good agreement between laboratory and analytical results such that the error rate was less than 2%. It was found that the value of strain-induced at the midpoint of geogrid decreases with depth, and their magnitude is constant at a 0.5B embedment depth. The impact of geogrid with length ratio (L/B = 5–7) on the strain values has similar behavior, but it is a significant effect of shorter geogrid length layers.