Showing papers on "Embedment published in 2011"

Undrained failure envelope for skirted foundations under general loading

Abstract: Three-dimensional failure envelopes can be used to define the bearing capacity and proximity to failure of shallow foundations under general vertical, horizontal and moment loading (V, H, M/B). Different structures, and different load cases for the same structure, cover varying domains of (±V, ±H, ±M/B) load space; therefore, a fully encompassing failure envelope in (V, H, M/B) load space is a useful tool to define ultimate limit states for design. In this technical note, a closed-form expression is proposed that enables prediction of undrained bearing capacity of skirted foundations under general in-plane loading, valid for a range of embedment ratios and soil shear strength heterogeneities.

Slope Stabilizing Piles and Pile-Groups: Parametric Study and Design Insights

Abstract: This paper uses a hybrid method for analysis and design of slope stabilizing piles that was developed in a preceding paper by the writers. The aim of this paper is to derive insights about the factors influencing the response of piles and pile-groups. Axis-to-axis pile spacing (S), thickness of stable soil mass (Hu), depth (Le) of pile embedment, pile diameter (D), and pile group configuration are the parameters addressed in the study. It is shown that S ¼ 4D is the most cost-effective pile spacing, because it is the largest spacing that can still generate soil arching between the piles. Soil inhomogeneity (in terms of shear stiffness) was found to be unimportant, because the response is primarily affected by the strength of the unstable soil layer. For relatively small pile embedments, pile response is dominated by rigid-body rotation without substantial flexural distortion: the short pile mode of failure. In these cases, the structural capacity of the pile cannot be exploited, and the design will not be economical. The critical embedment depth to achieve fixity conditions at the base of the pile is found to range from 0:7Hu to 1:5Hu, depending on the relative strength of the unstable ground compared to that of the stable ground (i.e., the soil below the sliding plane). An example of dimensionless design charts is presented for piles embedded in rock. Results are presented for two characteristic slenderness ratios and several pile spacings. Single piles are concluded to be generally inadequate for stabilizing deep land- slides, although capped pile-groups invoking framing action may offer an efficient solution. DOI: 10.1061/(ASCE)GT.1943-5606.0000479. © 2011 American Society of Civil Engineers. CE Database subject headings: Slope stability; Embedment; Pile groups; Parameters. Author keywords: Slope stabilizing piles; Embedment depth; Simplified method; Dimensionless charts; Arching; Pile groups.

The Effects of Fracturing Fluids on Shale Rock Mechanical Properties and Proppant Embedment

Abstract: The development of shale reservoirs has grown significantly in the past few decades, spurred by evolving technologies in horizontal drilling and hydraulic fracturing. The productivity of shale reservoirs is highly dependent on the design of the hydraulic fracturing treatment. In order to successfully design the treatment, a good understanding of the shale mechanical properties is necessary. Some mechanical properties, such as Young’s modulus, can change after the rock has been exposed to the hydraulic fracturing fluids, causing weakening of the rock frame. The weakening of the rock has the potential to increase proppant embedment into the fracture face, resulting in reduced conductivity. This reduction in conductivity can, in turn, determine whether or not production of the reservoir will be economically feasible, as shale rocks are characterized by their ultra-low permeability, and conductivity between the reservoir and wellbore is critical. Thus, shale reservoirs are associated with economic risk; careful engineering practices; and a better understanding of how the mechanical properties of these rocks can change are crucial to reduce this risk. This paper discusses various laboratory tests conducted on shale samples from the Bakken, Barnett, Eagle Ford, and Haynesville formations in order to understand the changes in shale mechanical properties, as they are exposed to fracturing fluids, and how these changes can affect the proppant embedment process. Nanoindentation technology was used to determine changes of Young's modulus with the application of fracturing fluid over time and under high temperature (300 °F) as well as room temperature. Mineralogy, porosity, and total organic content were determined for the various samples to correlate them to any changes of mechanical properties. The last part of the experiments consisted of applying proppants to the shale samples under uniaxial stress and observing embedment using scanning acoustic microscope. The results of this study show that maximum reduction of Young’s modulus occurs under high temperature and in samples containing high carbonate contents. This reduction in Young’s modulus occurs in “soft” minerals as well as the “hard” rock-forming minerals. This reduction of modulus can cause the effective fracture conductivity to decrease significantly. Introduction In geology, shale has traditionally been defined as a sedimentary rock containing high percentages (more than 50%) of clays and lower percentages of silica or carbonate minerals (Britt and Schoeffler, 2009). However, many of the shale prospects that are currently being developed in the petroleum industry are not shales, as defined in geology. They are, instead, “prospective shale” reservoirs, which are fine-grained clastics that are characterized by their ultra low permeability and usually composed of silica and carbonate with a small amount of clay minerals (Britt and Schoeffler, 2009). Generally, shale rocks have been considered as source rocks for conventional oil and gas reservoirs. However, with technological evolution in the petroleum industry, such as hydraulic fracturing, the rising oil and gas prices, as well as the escalating demand for fossil fuels, these rocks are increasingly regarded as the source, the seal, and the reservoir. Subsequently, development of such reservoirs is becoming more and more technically and economically feasible. The reasons behind the success of these shale systems are largely dependent on excellent hydraulic fracturing designs that require a good understanding of the mechanical properties of the subject and confining formations. In hydraulic fracturing design, Young's modulus is one criterion used to define the most appropriate fracturing fluid and other design considerations. Young's modulus provides an indication of how much fracture conductivity, kfw, can be expected due to width and embedment considerations. Without adequate fracture conductivity, production from the hydraulic fracture will be minimized if not completely eliminated. This paper discusses conditions where Young’s modulus is shown to decrease

Diverse Embedment Model for Steel Fiber-Reinforced Concrete in Tension: Model Development

Abstract: In this paper an analysis model is presented for calculating the response of steel fiber-reinforced concrete (SFRC) members subjected to tension. To predict the tensile stress of fibers across a crack, the pullout behavior of a single fiber with both sides embedded in cracked concrete is analytically investigated, considering both frictional bond behavior and mechanical anchorage effects. Thus, the proposed Diverse Embedment Model (DEM) can be applied to end-hooked and straight fibers. The model is derived with consideration given to all possible fiber orientations and embedment lengths and as influenced by the member’s finite dimensions. The details of the experimental verification for the proposed analysis model, including the proposed fiber orientation factors, are presented and discussed in an accompanying paper.

Keying of rectangular plate anchors in normally consolidated clays

Abstract: The loss in anchor embedment during keying, as it rotates to become normal to the cable load, reduces the uplift capacity of anchors in normally consolidated clay. The keying behavior of plate anchors has been studied previously by using centrifuge and field model tests. In this paper, a large deformation finite-element approach incorporating frequent mesh regeneration and allowing for evolution of the anchor-chain profile, was developed to simulate the keying process of rectangular and strip plate anchors. A parametric study was undertaken to quantify the loss in anchor embedment during keying in terms of the anchor geometry, soil properties, loading eccentricity, and inclination. The embedment loss decreased dramatically with increasing loading eccentricity and decreasing chain angle at the mudline to the horizontal. The loss in anchor embedment during keying increased as the local soil strength increased relative to the weight of the anchor, up to a limit determined by the eccentricity of loading. In c...

Numerical study on plate anchor stability in clay

Abstract: Although the pullout capacity of plate anchors in clay has been studied extensively, the results considering the coupling effects of anchor inclination, clay non-homogeneity and self-weight are relatively rare. In the present paper, finite-element analyses are carried out to investigate the coupling effects of these factors on the pullout capacity of strip plate anchors in clay. The numerical solutions are presented in the familiar form of pullout capacity factors based on various anchor embedment depth, clay strength profile and clay self weight, and are also compared with existing numerical and empirical solutions. A design procedure based on the data-fitting equations of the present finite-element solutions is also presented for the convenience of design engineers.

Diverse Embedment Model for Steel Fiber-Reinforced Concrete in Tension: Model Verification

Abstract: Results obtained from the Diverse Embedment Model (DEM) for analysis of steel fiber-reinforced concrete, described in an accompanying paper, are compared with experimental results produced by several independent researchers. Variation of the fiber orientation factor, which accounts for the effects of finite member dimensions on fiber orientation and embedment, is also theoretically investigated and compared with experimental data. Verification studies show that the proposed model provides accurate predictions of the tensile stress and crack width relationship of uniaxial tension specimens containing straight or end-hooked steel fibers. In addition, the proposed model provides accurate calculations of the distribution of tensile stress provided by fibers. The proposed model is also shown to be useful in modeling aspects of the tensile behavior, such as crack spacing and tension stiffening, of fiber-reinforced concrete (FRC) members reinforced with ordinary steel reinforcing bars.

Three-dimensional numerical modelling of discrete piles used to stabilize landslides

Abstract: Three-dimensional finite difference analyses have been carried out to investigate the behaviour of a single pile used to stabilize a slipping mass of soil by embedment into a stable stratum. Analys...

Dynamic Response of a Sheet Pile of Fiber-Reinforced Polymer for Waterfront Barriers

Abstract: This paper presents the results from a combined experimental and advanced computational study to understand the dynamic response of a pultruded fiber-reinforced polymer (FRP) sheet pile of 9 m length that is installed into the ground near Venice, Italy The peak embedment force of 10 kN is applied at the top as a sinusoidal compression force having a maximum frequency of circa 760 Hz Physical measurements from accelerometers are reported for the lateral deformation response of a single sheet pile and of a unit restrained by an installed waterfront barrier A finite-element modeling methodology for the two test configurations is developed by using the Strand7 code, so that advanced computational results can be compared against the field application measurements Closed-form equations for the fundamental frequency are developed, with one accounting for the presence of rotary inertia and shear deformation Dynamic responses at different embedment lengths (1–7 m) are examined, and a very good correlation is found between theory and practice Numerically, the performance of the FRP sheet pile is compared with the response of a fictitious sheet pile of steel and with two new FRP geometries that increase stiffness to minimize flexure about the minor axis of bending By increasing the mass by 10%, the maximum lateral displacement can be the same as the steel unit and 1/20 of the tested FRP unit Findings of the research demonstrate that the FRP unit can be installed by using the same pile driving rig and procedure for steel sheet piling

Consolidation around partially embedded seabed pipelines

Abstract: When a pipeline is laid on a soft clay seabed, excess pore pressure is generated. During the subsequent dissipation process, the effective stress at the pipe-soil interface and the available axial pipe-soil resistance rise. This 'set-up' of axial resistance is an important consideration in various aspects of pipeline design, including the mitigation of thermal and pressure-induced expansion, the stability of the pipeline on sloping ground and the assessment of pipe-soil forces during installation. A set of finite-element analyses has been conducted to assess the pore pressure dissipation and consolidation beneath partially embedded seabed pipelines, extending existing solutions for strip footings. It is shown that the curved shape of a pipeline increases the normalised rate of consolidation compared with a strip footing. Dissipation curves for various levels of embedment are presented and the calculated response is shown to compare well with data from a field test conducted on a soft clay. The dissipation curves have been used to derive the development of effective contact force between the pipe and the seabed as consolidation progresses. These results highlight the significant enhancement of this force - and therefore the available axial resistance - that arises from a 'wedging effect' related to the curvature of the pipe-soil contact surface. This wedging effect leads to a beneficial enhancement of the axial resistance.

Effect of anchor width on pullout capacity of strip anchors in sand

Abstract: By incorporating the variation of peak soil friction angle (ϕ) with mean principal stress (σm), the effect of anchor width (B) on vertical uplift resistance of a strip anchor plate has been examined. The anchor was embedded horizontally in a granular medium. The analysis was performed using lower bound finite element limit analysis and linear programming. An iterative procedure, proposed recently by the authors, was implemented to incorporate the variation of ϕ with σm. It is noted that for a given embedment ratio, with a decrease in anchor width (B), (i) the uplift factor (Fγ) increases continuously and (ii) the average ultimate uplift pressure (qu) decreases quite significantly. The scale effect becomes more pronounced at greater embedment ratios.

A centrifuge study on the effect of embedment on the drained response of shallow foundations under combined loading

Abstract: Drum centrifuge tests with surface and buried circular footings on medium dense silica sand subjected to planar combined loading are reported. The experimental work specifically addresses the effect of the footing embedment within a work-hardening plasticity approach, which to date has been used predominantly for interpretation of the behaviour of small-scale models of surface foundations. Vertical loading and swipe tests were carried out, and results are compared with existing data from similar studies on small-scale 1g foundation models. The overall trend of the centrifuge results confirms the general framework, suggesting that a work-hardening plasticity approach in terms of force-resultant modelling for the soil–footing system (the so-called ‘macro-element') applies under properly scaled stress conditions. The data also indicate that the traditional assumption of a yield surface, isotropically expanding with increasing vertical penetration is not suitable for an embedded foundation. An enhancement of ...

Modelling the dynamic embedment of seabed pipelines

Abstract: The as-laid embedment of a seabed pipeline is an important design parameter. As a pipe is laid on the seabed it oscillates, owing to vessel motion and hydrodynamic loading of the hanging pipe. This movement significantly increases the pipe embedment beyond the theoretical value related to the static pipe weight, even when corrected for any stress concentration caused by the hanging catenary. Dynamic lay effects are either ignored in practice, or are accounted for by scaling up the static embedment by an empirical factor, leading to significant uncertainty in this important design parameter. A series of centrifuge model tests has been conducted using two clays – kaolin and a high-plasticity natural clay – to simulate the dynamic embedment process. The results indicate that only a few cycles of small-amplitude oscillation (±0·05D) are required to double or triple the pipe embedment, owing to the combined effect of lateral ploughing and soil softening. In these experiments the pipe embedment increased to up ...

Electronic watermark embedding method, device, and program, and electronic watermark detecting method, device, and program

Abstract: An electronic watermark embedding device for embedding embedment information as an electronic watermark in an input signal having N or more dimensions (N is 2 or more an integer) and an electronic watermark detecting device are disclosed. The electronic watermark embedding device creates an embedment sequence according to embedment information, creates an (N-1)-dimensional pattern according to the embedment sequence, modulates a periodical signal according to the value on the (N-1)-dimensional pattern, thus creates an N-dimensional embedment pattern, superimposes the embedment pattern on the input signal, and outputs the resultant signal. The electronic watermark detecting device measures the component of a predetermined periodic signal in one dimensional direction of the input signal, obtains an (N-1)-dimensional pattern, obtains a detection sequence from the values of the (N-1)-dimensional pattern, and detects the embedded electronic watermark according to the magnitude of the value of the correlation between the detection sequence and the embedded sequence.

Penetration Resistance and Stiffness Factors for Hemispherical and Toroidal Penetrometers in Uniform Clay

Abstract: This paper reports numerical analyses of shallowly embedded hemispherical and toroidal penetrometers under torsional and vertical load. These novel penetrometers are a new design suited to the assessment of near-surface soil strength and are aimed at the analysis of pipeline embedment and axial pipe-soil interaction. The geometry of the penetrometers avoids the complication of end effects that arise if a short pipe segment is used, as is the current practice. The operation of these devices involves vertical penetration typically of up to half a diameter, followed by rotation about the vertical axis, whereas the corresponding loads are recorded. The FE analyses explore the undrained bearing capacity and stiffness factors required for the measured loads to be converted to soil strength and stiffness for application in design. On the basis of these analyses, the geometry of the toroidal penetrometer has been optimized to minimize the size of the instrument and limiting interference across the toroid, which would hamper comparisons between the penetrometer response and a pipeline. It is shown that a relatively compact toroid can be used.

3D FE Analyses of Buried Pipeline with Elbows Subjected to Lateral Loading

Abstract: This study investigates the interaction between soil and pipeline in sand subjected to lateral ground displacements with emphasis on the peak force exerted to a bended elbow-pipe. A series of three-dimensional (3D) finite-element (FE) analyses were performed in both opening and closing modes of the elbow section for different initial pipe bending angles. To model the mechanical behavior of sands, two soil models were adopted: Mohr-Coulomb and Nor-Sand soil model. Investigations also included the effects of pipe embedment depth and soil density. Results show that the opening mode exhibits higher ultimate forces and greater localized deformations than the closing mode. Nondimensional charts that account for pipeline location, bending angle, and soil density are developed. Soil-spring pipeline analyses of an elbow-pipe were performed using modified F-δ soil-spring models based on the 3D FE results and were compared to the findings of conventional spring model analyses using the standard two-dimensional soil-...

Bolted and Dowelled Connections in Radiata Pine and Laminated Veneer Lumber Using the European Yield Model

Abstract: Connections with mechanical fasteners are important for all cases of timber structures. The failure of these connections may occur in either ductile or brittle manner. For the calculation of the ductile failure strength or the load carrying capacity, the European yield model (EYM) is used in many standards and accepted as a very accurate model. In the current New Zealand timber standard NZS 3603:1993 (Standards New Zealand, 1993) and the Australian one AS1720.1-1997 (Standards Australia, 1997), the design concept for bolted or dowelled connections is not based on the EYM, and depends only on the diameter, the timber thickness and the species group. The most important parameters for the EYM are the fastener yield moment and the timber embedment strength, but embedment strength values are not available for New Zealand Radiata pine or laminated veneer lumber (LVL). To obtain the missing information and to implement the EYM into the New Zealand and Australian standards, embedment tests parallel, perpendicular and under various load-to-grain angles with different dowel diameters in Radiata pine lumber and LVL were conducted and compiled to build a database of embedment strength values. This paper includes the latest results of the investigations with dowel diameters extended up to 30 mm. Furthermore, different international testing standards are compared and their evaluation methods are used. The test results are also compared with the corresponding results using the Eurocode 5 formulas, and show that adjusted formulas of the Eurocode 5 can be used to predict the load carrying capacity of bolted and dowelled connections in Radiata pine lumber and LVL. Design examples comparing the current methods from the New Zealand/Australian design standards and the proposed method adopted from the EYM of the European design standard are given as well.

Passive earth pressure on embedded vertical plate anchors in sand

Abstract: Passive earth pressure on embedded anchor plates constitutes a viable resisting force for the design of underground structures. In the current practice, these forces are empirically calculated, ignoring the effects of the depth of embedment and the level of consolidation of the surrounding soil, which takes place during plate installation on the in situ stress levels. Accordingly, wide discrepancies between predicted and measured pullout capacities of these plates were reported in the literature. Numerical model was developed using finite-element technique and the constitutive law of Mohr–Coulomb to simulate the case of a retaining wall partially supported by an embedded anchor plate in sand. The results produced in this investigation showed that the passive earth pressure acting on anchor plates increases due to the increase of angle of shearing resistance and the overconsolidation ratio of sand, and it decreases due to an increase of the embedment depth of anchor. Design theories were developed for the case of embedded anchor plate in overconsolidated sand. The theories developed will satisfy the design needed in terms of allowable pullout load and/or displacement.

Location of Failure Plane and Design Considerations for Narrow Geosynthetic Reinforced Soil Wall Systems

Abstract: The design of a Geosynthetic Reinforced Soil (GRS) wall for internal stability against pullout failure requires computing the reinforcement embedment length. Therefore, the location of failure plane is an important input for this design. The current FHWA MSE wall design guidelines assume the location of failure plane based on Rankine theory. While this assumption holds true for conventional walls it is unconservative for GRS walls under constrained spaces, also known as “narrow GRS walls”. This paper presents a limit equilibrium study to accurately locate failure planes within narrow GRS walls. The critical failure planes within narrow GRS walls are searched using Spencer’s method with a function of noncircular failure plane. The predicted results from limit equilibrium analyses are verified by the experimental data from centrifuge tests conducted on narrow GRS walls. The results indicate that the critical failure plane is bilinear: The failure surface being formed partially through the reinforced soil and partially along the interface between the GRS and the stable wall face. The results show the inclination angles of the failure planes for narrow GRS walls being 10~ 20 less than those calculated by Rankine theory. The effect of wall aspect ratio on the inclination angle of the critical failure plane is investigated for the cases studied in this paper. Design considerations against pullout failure for narrow GRS walls are also discussed at end of this paper.

Experimental Testing of Pile-to-Cap Connections for Embedded Pipe Piles

Abstract: For bridges supported by piles, acceptable system performance under seismic loading depends on effective pile-to-cap connections. A fixed pile-to-cap connection is often desirable to help control deflections during lateral loading when soft soils are present. While reinforcement bar cages that extend from the pile into the cap are effective in providing a fixed pile-to-cap connection, it is more economical to rely on pile embedment to provide fixity and moment resistance. This study investigated embedded pile-to-cap connections for concrete-filled pipe piles. Four full-scale specimens, each consisting of a cap with two piles, were investigated in the field under cyclic loading. The specimens had minimal reinforcement and varying amounts of pile embedment. Results show that the moment resistance of pile-to-cap connections can be significantly greater than what is typically calculated based on the flexural reinforcement and embedment bearing. Excess moment capacity may be explained by friction between the p...

Bearing Capacity of Embedded Strip Footings in Two-Layered Clay Soils

Abstract: This paper studied the effect of embedment on the ultimate bearing capacity of rigid strip footings embedded in two-layered clay soils with relatively different shear strengths. The ultimate collapse loads were calculated using the finite element method. A parametric study was performed for a relative depth of embedment D/B varying from 0 to 1 (where D and B are the footing embedment and width respectively), relative thickness of the top clay layer H/B from 0.125 to 4, and strength ratio of the two clay layers cu1/cu2 from 0.5 to 7, where cu1 and cu2 are the undrained shear strengths of the upper and lower clay layers respectively. The finite element results were presented in terms of a modified bearing capacity factor that accounts for the footing embedment and the relative shear strength and thickness of the two clay layers. The finite element results for surface strip footings and embedded footings in homogeneous clay were within the narrow ranges defined by the rigorous lower and upper bound solutions available in the literature. The finite element results for embedded footings were compared with those obtained using approximated bearing capacity equations for two-layered clay soils. The paper also described the changes in the type of the collapse mechanism as the footing relative depth of embedment (D/B) and relative layer thickness (H/B) vary as functions of the strength ratio (cu1/cu2) of the two clay layers.

Uplift Capacity of Horizontal Strip Anchors in Cohesionless Soil

Abstract: This paper presents the details of the theoretical analysis of net uplift capacity of horizontal strip anchor in cohesionless soil using Kotter’s equation. A plane failure surface inclined at a characteristic angle with the ground surface is assumed. Results obtained using the proposed method are compared with the available experimental results of 30 cases for dense to loose cohesionless soil, with the maximum embedment ratio of 8. It is observed that the proposed method leads to the predictions of net uplift capacity of horizontal strip anchor that are very close to the experimental results in 93% cases. The comparison of results with available theoretical solutions shows that, proposed method makes better predictions for anchor embedment ratio less than 8 in dense cohesionless soils.

Intermediate transfer belt, method for producing the same, and image forming apparatus

Abstract: An intermediate transfer belt including a resin layer, which is a surface layer of the intermediate transfer belt, wherein the resin layer has a concavo-convex pattern formed by spherical resin particles which are independently embedded in the resin layer so that the embedment rate of the spherical resin particles in the thickness direction of the resin layer is higher than 50% but lower than 100%.