Showing papers on "Embedment published in 2017"

Analytical analysis of fracture conductivity for sparse distribution of proppant packs

Abstract: Conductivity optimization is important for hydraulic fracturing due to its key roles in determining fractured well productivity. Proppant embedment is an important mechanism that could cause a remarkable reduction in fracture width and, thus, damage the fracture conductivity. In this work a new analytical model, based on contact mechanics and the Carman–Kozeny model, is developed to calculate the embedment and conductivity for the sparse distribution of proppant packs. Features and controlling factors of embedment, residual width and conductivity are analyzed. The results indicate an optimum distance between proppant packs that has the potential to maintain the maximum conductivity after proppant embedment under a sparse distribution condition. A change in the optimum distance is primarily controlled by closure pressure, the rock elastic modulus and the proppant elastic modulus. The proppant concentrations and the poroelastic effect do not influence this optimum distance.

Embedment Effects on Vertical Bearing Capacity of Offshore Bucket Foundations on Cohesionless Soil

Abstract: This paper presents the results from a series of physical modeling and three-dimensional finite-element (FE) analyses in which the authors examined the uniaxial vertical capacity of suction caissons for offshore wind turbines. The experiments were carried out in quartz sand and involved monotonic application of vertical load. It was found that the drained capacity of suction caissons is dependent on embedment ratio. In contrast, predictions from conventional semiempirical depth factors were found to somewhat underestimate when applied to rough foundations. On the basis of the tests and FE analyses, new expressions for the depth factor of shallow foundations were validated for embedment ratios (aspect ratios) up to unity, calibrating the fitting parameters by using data from a range of soil profiles.

Finite Element Investigation of the Bearing Capacity of Square Footings Resting on Sloping Ground

Abstract: The ultimate bearing capacity of foundation placed on a slope is significantly affected by its vicinity to the slope face, which offers substantially lesser passive resistance as compared to a footing resting on a semi-infinite medium. Conventional bearing capacity theories fail to address the behavior of such foundations. Few existing theories predict the bearing capacity of foundations on slopes considering stress-based failure approach. However, deformation along the slope plays a major role in governing the failure of such foundations, thus requiring a coupled stress-deformation based failure analysis. With the aid of 3-D finite element modelling, employing coupled stress-deformation analysis, this study addresses the failure mechanism and the bearing capacity (q u ) of a square footing located on a dry cohesionless slope. The effect of various parameters, namely the angle of internal friction of soil, setback distance, slope inclination, footing width and the depth of embedment of the footing, have been investigated. Variations parameters are found to noticeably alter the bearing capacity estimate and the observed failure mechanism. A critical setback distance is obtained [(b/B)critical = 3] beyond which the failure mechanism resembles the same obtained for a footing resting on horizontal ground. The unit weight and modulus of elasticity of the soil material is found to have negligible effect on the bearing capacity.

The evolution of seabed stiffness during cyclic movement in a riser touchdown zone on soft clay

Abstract: Steel catenary risers are pipelines that convey fluids from the seabed to floating structures. The stiffness of the pipe–seabed response, which is the ratio between soil resistance and pipe embedment, in the touchdown zone strongly affects the fatigue accumulation rate, so is an important design parameter. This paper reports a centrifuge modelling study into the long-term pipe–seabed interaction forces on soft clay seabeds, with tests representing many months of behaviour at prototype scale. The results show that the penetration and extraction resistance during large-amplitude cycles degrades during the initial few tens of cycles, in the same way that cyclic penetrometer tests capture the fall in soil strength from the intact to the remoulded state. Calculations using bearing capacity factors for a cylinder provide good predictions of this response, although if the cycles of movement involve the pipe breaking away from the soil then the resistance reduces by more than the ratio of intact to remoulded stre...

Load-Carrying Mechanism of Vertical Plate Anchors in Sand

Abstract: An experimental study on the load-carrying mechanism of vertical plate anchors is presented and discussed. It was found that, with a shallow anchor, the rupture surface reached the ground surface, leading to a general shear failure, whereas with deeper embedment, the rupture surface was localized around the anchor. Anchors placed close to the ground surface failed in linear rupture but, when embedded within the failure mechanism, were very close to the polar curve of a logarithmic spiral, which, however, tends to be nearly circular for deeper depths of embedment. The size of rupture surface increases with an increase in density of fill soil that mobilizes higher resistance, leading to enhanced anchor capacity. The critical embedment depth beyond which the anchor breakout factor does not change much is found to be approximately 7 times the anchor height for dense soil, whereas it is approximately 5 times the anchor height for loose soil. The anchor when placed below the critical depth, settlement, ...

Tensile Capacity of Anchor Bolts in Uncracked Concrete: Influence of Member Thickness and Anchor’s Head Size

Abstract: This study evaluated the influence of concrete member thickness and size of anchor head on the tensile capacity and performance of anchor bolts in concrete. Anchor bolts at various embedment depths ...

Assessing the penetration resistance acting on a dynamically installed anchor in normally consolidated and overconsolidated clay

Abstract: Predicting the final embedment depth of a dynamically installed anchor is a key prerequisite for reliable calculation of anchor capacity. This paper investigates the embedment characteristics of dynamically installed anchors in normally consolidated and overconsolidated clay through a series of centrifuge tests involving a model anchor instrumented with a microelectric mechanical system (MEMS) accelerometer, enabling the full motion response of the anchor to be established. The data are used to assess the performance of an anchor embedment model based on strain-rate-dependent shearing resistance and fluid mechanics drag resistance. Predictions of a database of over 100 anchor installations — formed from this study and the literature — result in calculated anchor embedment depths that are within ±15% of the measurements. An interesting aspect, consistent across the entire database, relates to the strain rate dependence on frictional resistance relative to bearing resistance. The predictions reveal that str...

State of the art: interface shear resistance of asphalt surface layers

Abstract: Interface shear resistance is a measure of the bonding between two layers under shear loading. Adequate interface shear resistance and long-term bonding of the surface to the underlying pavement are critical to the performance of pavement structures. Interface shear strength is a function of adhesion, friction and aggregate embedment or interlock and is commonly modelled as a Mohr–Coulomb type envelope. Measurement of interface shear resistance can be performed in the field on full-scale pavements, in the laboratory on cores recovered from the surface or in the laboratory using samples prepared in the laboratory. However, laboratory testing of cores recovered from the field is likely to be more reliable and repeatable than field testing. There is a large range of test methods and procedures for the measurement of interface bond. These test methods are generally grouped into three main loading mechanisms; axial tension, torsional shear and direct shear. Direct shear tests offer a more comprehensive...

Dynamic Response of Saturated Soil - Foundation System Acted upon by Vibration

Abstract: In this study, the response and behavior of machine foundations resting on dry and saturated sand was investigated experimentally. In order to investigate the response of soil and footing to steady state dynamic loading, a physical model was manufactured to simulate steady state harmonic load at different operating frequencies. Total of 84 physical models were performed. The footing parameters are related to the size of the rectangular footing and depth of embedment. Two sizes of rectangular steel model footing were tested at the surface and at 50 mm depth below model surface. Meanwhile the investigated parameters of the soil condition include dry and saturated sand for two relative densities 30% and 80%. The response of the footing was elaborated by measuring the amplitude of displacement by the vibration meter. The response of the soil to dynamic loading includes measuring the stresses inside the soil using piezoelectric sensors as well as measuring the excess pore water pressure using pore water pressu...

Seismic performance of embedded steel beam connection in cross-laminated timber panels for tall-wood hybrid system

Abstract: Recent developments in novel engineered mass timber products and connection systems have created the possibility to design and construct tall timber-based buildings This research presents the experiments conducted on the steel-wood connection as main energy dissipating part of a novel steel–timber hybrid system labelled Finding the Forest Through the Trees (FFTT) The performance was investigated using quasi-static monotonic and reversed cyclic tests The influence of different steel beam profiles (wide flange I-sections and hollow rectangular sections) and the embedment approaches (partial and full embedment) was investigated The test results demonstrated that appropriate connection layouts can lead to the desired failure mechanism while avoiding excessive crushing of the mass timber panels The research can serve as a precursor for developing design guidelines for the FFTT system as an option for tall wood-hybrid building systems in seismic regions

Bearing Capacity of Embedded Strip Footings on Cohesionless Soil Under Vertical and Horizontal Loads

Abstract: In the last decades a few attention was given to the evaluation of the bearing capacity of embedded footing under inclined loads on a frictional soil. This paper focuses on a numerical study using the finite-difference code Fast Lagrangian Analysis of Continua (FLAC), to evaluate the bearing capacity of embedded strip footing on a frictional soil. The soil is modeled by an elasto-plastic model with a Mohr–Coulomb yield criterion and associative flow rule; the effect of non-associativity of the soil on the bearing capacity is also investigated. The effect of the embedment is estimated though a depth factor, defined as a ratio of the bearing capacity of a strip footing at a depth D to that of a strip footing at the ground surface. The inclination effect is estimated by inclination factors, defined as the ratio of the limit vertical load for a footing under inclined loading to that of the vertically loaded footing. Both swipe and probe analyses were carried out to identify the vertical force–horizontal force (V–H) failure envelope. The results have been compared with those available in the literature.

Permeability Evolution of Propped Artificial Fractures in Green River Shale

Abstract: This paper compares the evolution of permeability with effective stress in propped fractures in shale for native CH4 compared with that for sorbing CO2, slightly sorbing N2 and non-sorbing He. We examine the response for laboratory experiments on artificial propped fractures in Green River Shale to explore mechanisms of proppant embedment and fracture diagenesis. Split cylindrical specimens sandwich a proppant bead-pack at a constant confining stress of 20 MPa and with varied pore pressure. Permeability and sorption characteristics are measured with the pulse transient method. To explore the effect of swelling and embedment on fracture surface geometry, we measure the evolution of conductivity characteristics for different proppant geometries (single layer vs. multilayer), gas saturation and specimen variation in order to simulate both production and enhanced gas recovery. The resulting morphology of embedment is measured by white light interferometry and characterized via surface roughness parameter of mean, maximum and root-mean-square amplitudes. For both strongly (CO2, CH4) and slightly adsorptive gases (N2), the permeability first decreases with an increase in gas pressure due to swelling before effective stress effects dominate above the Langmuir pressure threshold. CO2 with its highest adsorption affinity produces the lowest permeability among these three gas permeants. Monolayer propped specimens show maximum swelling and lowered k/k 0 ratio and increased embedment recorded in the surface roughness relative to the multilayered specimens. Permeabilities measured for both injection and depletion cycles generally overlap and are repeatable with little hysteresis. This suggests the dominant role of reversible swelling over irreversible embedment. Gas permeant composition and related swelling have an important effect on the permeability evolution of shales.

Effect of embedment on consolidated undrained capacity of skirted circular foundations in soft clay under planar loading

Abstract: The effect of foundation embedment ratio and soil–skirt interface roughness on the consolidated undrained capacity of skirted circular foundations under planar loading in normally consolidated clay...

Tensile and fatigue investigations of timber joints with glued-in FRP rods

Abstract: Glued-in rods are an effective method to form timber connections that are increasingly in the focus of research. Compared to steel rods, fibre-reinforced polymer (FRP) bars provide higher resistance against corrosion, reduced weight, and lower heat conductivity. Despite excellent mechanical performance, high fire resistance, and improved aesthetics, they are, however, not yet widely used due to lack of design regulation. This is particularly true for cyclic loads, where determination of fatigue characteristics depends upon time-intensive experimental procedures. In this research, 50 glued-in FRP rod specimens with different embedment lengths were manufactured and tested in uniaxial tension: a first set under quasi-static load and a second set under cyclic load. For the fatigue tests, a new approach based on a stepwise load increase was used to estimate fatigue strength, a method that aims at reducing the experimental effort usually associated with Woehler curves. Experimental results indicated tha...

Event-based lattice modeling of strain-hardening cementitious composites

Abstract: This paper presents novel developments in the lattice modeling of fiber reinforced cement composites, in which the individual fibers are explicitly represented. Attention is given to the modeling of strain-hardening cement composites under tensile loading. The pullout forces of fibers are derived from micromechanical bases and distributed along the fiber embedment lengths. This spatial description of the fiber bridging forces provides realistic representations of stress transfer between the fiber and matrix, which is essential for simulating crack openings and crack spacing. Stress transfer is modified to account for multiple cracks intersecting individual fibers, which is typical for materials with closely spaced cracks. Multiple cracking generates islands of material interconnected by fiber bridges, which places extraordinary demands on the solution procedure. An event-by-event solution strategy is developed for this reason. Comparisons with test results demonstrate the model’s ability to simulate global and crack-local features. In particular, simulated histograms of crack opening displacement compare favorably with those measured experimentally.