Uplift Resistance Research Articles

사질토 지반에 설치된 판앵커의 인발속도에 따른 저항력 분석

Anchors are primarily designed and constructed to resist outwardly directed loads imposed on the foundation of a structure. These outwardly directed loads are transmitted to the soil at a greater depth by the anchors. Buried anchors have been used for thousands of years to stabilize structures. Nowadays, various types of earth anchors are used for the uplift resistance of transmission towers, utility poles, submerged pipelines, and tunnels. Anchors are also used for the tieback resistance of earth-retaining structures, waterfront structures, at bends in pressure pipelines, and when it is necessary to control thermal stress. In this research we analyzed the uplift behavior of plate anchors in sand using a laboratory experiment to estimate the uplift behavior of plate anchors under various conditions. To achieve the research purpose, the uplift resistance and displacement characteristics of plate anchors caused by the embedment ratio, plate diameter, and loading rate were studied, compared, and analyzed in various cases.

Failure model of soil around enlarged base of deep uplift piles

This paper presents an investigation into the failure behaviours of low-cohesive (c ≤ 10 kPa) or non-cohesive (c = 0) soils around the enlarged bases of deep uplift piles. An axisymmetric elasto-plastic finite-element method is used for analysing displacements and plastic strains in the soil–pile system induced by uplifting. Numerical results are examined in detail to reveal the relationships of the accumulated equivalent plastic strain contours in soils and the uplift displacements of piles with the diameters of enlarged bases. The investigation finds that for the pile to reach ultimate uplift failure, the pile has to experience a large upward displacement. A serviceability failure limit of pile upward displacement equal to 10% of pile shaft diameter is adopted for determining pile uplift resistance capacity. At serviceability failure limit, examination of the accumulated equivalent plastic strain contours in the soils leads to the establishment of two logarithmic spiral functions for the estimation of the plastic zone envelope and the slip surface around the enlarged base. The plastic zone envelopes and slip surfaces are axisymmetrical, peach-shaped, closed and curved surfaces, completely beneath the ground surface. The models and functions have been used to formulate analytical solutions for estimating uplift resistance capacity for deep piles with enlarged bases.

Vertical uplift resistance of two horizontal strip anchors with common vertical axis

With an application of the upper bound finite element limit analysis, the vertical pullout capacity of a group of two horizontal strip plate anchors, with the common vertical axis and placed in a cohesive-frictional soil, has been computed. The variation of the uplift factors <i>F_c, F_q</i> and <i>F_y</i>, due to the contributions of soil cohesion, surcharge pressure and unit weight, respectively, has been evaluated for different combinations of <i>S/B</i> and <i>H/B.</i> As compared to single isolated anchor, the group of two anchors generates significantly greater magnitude of <i>F_c</i> for Φ ≤ 20° especially with greater values of <i>H/B</i> and under fully bonded anchor-soil interface condition. The factor <i>F_c</i> attains almost the maximum value when the upper anchor plate is placed midway between ground surface and the lower anchor plate. The factors <i>F_q</i> and <i>F_y</i>, on the other hand, for a group of two anchors are found to remain almost equal to that of a single isolated anchor as long as the levels of the lower plate in the group and the single isolated anchor are kept the same.

Model Test Studies on Soil Restraint to Pipeline Buriedin Bohai Soft Clay

Under high thermal stress, buckling of submarine pipelines may occur to release the stresses accumulated in the walls of the pipelines. The likelihood that buckling occurs is largely determined by the capability of the soil to resist pipeline movements. Therefore, it is very important to determine the soil resistance in upheaval buckling when designing submarine pipelines. A series of large-scale model tests were carried out with soft clay chosen as the supporting medium in view of Bohai Sea geotechnical conditions. Pipe segments with diameters of 30, 50, and 80 mm were used. The pipes were buried in different depth-to-diameter ratios between 1 and 9. The uplift, lateral, and axial resistances were recorded during the tests. The test results have shown that the soil resistance depends on the pipe’s diameter and cover depth. According to the uplift test results, the load-displacement relationships with smaller depth of cover differ greatly from those with larger depth of cover. The results of the lateral sliding and axial pull-out tests have shown that the soil resistance initially increases before a peak value is reached. However, once the peak value is reached, the soil resistance will remain at approximately the same level. For the same cover depth, the lateral soil resistance is more than twice as much as that of the uplift. The observed data were compared with existing formulae, among which the best fit is selected. Meanwhile, the coefficients for the chosen formula were determined. These formulae and coefficients can be used in calculating the soil resistance in the Bohai Gulf.

Investigation of the vertical uplift capacity of deep water mudmats in clay

Subsea mudmats are used in deep water oil and gas fields to support seabed structures, such as pipelines, manifolds, and well heads. On soft soil, removing mudmats during maintenance or decommissioning may be difficult and costly due to the significant suction that develops at the mudmat–soil interface, considerably increasing the uplift resistance beyond the submerged self-weight of the mudmat. This paper describes a series of centrifuge tests performed to investigate the uplift resistance of plain mudmats resting on lightly overconsolidated clay. The model mudmat invert was instrumented with pore pressure transducers to monitor the suction developing at the mudmat invert at various uplift velocities, uplift eccentricities, and mudmat skirt lengths. The results show an increase in uplift resistance with pull-out velocity and the dominant role played by the uplift eccentricity in reducing suction at the mat invert. Simple predictive methods based on bearing capacity theory and combined loading interaction diagrams are provided.

인발력을 받는 팩마이크로파일의 주면마찰력

일반마이크로파일의 저항성능을 개선시키기 위해 최근에 토목섬유을 활용한 팩마이크로파일이 개발되었다. 팩마이크로파일은 일반마이크로파일의 강봉이나 강관을 토목섬유팩으로 감싸고 주입재와 주입압을 토목섬유팩 내부에 가하여 제작한다. 이 주입압에 의하여 천공 직경이 크게 확대된다. 동일한 한 지반 속에 설치된 세 개의 마이크로파일을 대상으로 일련의 말뚝인발시험을 실시하였다. 세 말뚝 중 두 개는 팩마이크로파일였고 나머지 하나는 강봉을 사용한 일반마이크로파일이였다. 토목섬유팩에 적용된 주입압에 의하여 팩마이크로파일의 경우 천공직경이 152mm에서 220mm으로 확대되었다. 마이크로파일의 주면에서 발달하는 단위주면마찰력은 말뚝두부의 인발변위량의 증가와 함께 서서히 증가하여 한계상태에 도달한 한계변위량에서 수렴치에 도달한다. 팩마이크로파일의 인발저항력은 일반마이크로파일의 인발저항력보다 크게 나타난다. 이와 같은 팩마이크로파일의 인발저항력을 증대시킬 수 있는 원인으로는 크게 두 가지를 생각할 수 있다; 첫째는 마이크로파일에 설치한 토목섬유팩내 주입압으로 마이크로파일의 단면적을 증대시키므로 말뚝주면의 마찰저항면적을 증대시킬 수 있기 때문이고, 둘째는 마이크로파일의 단면이 확대될 때 확대되는 부분의 체적만큼의 토사가 주변지반을 압축시켜 말뚝과 지반 사이의 마찰저항력을 증대시킬 수 있기 때문이다. 이 압축효과는 지표면 부근 보다 깊은 지층에서 크게 나타났다. 말뚝 주면에서 발휘되는 단위주면마찰력은 말뚝의 직경이 작은 경우가 더 크게 발휘된다. 즉 마이크로파일의 주면에서 발달되는 단위주면마찰력은 대구경 현장타설말뚝의 주면에서 발달되는 단위주면마찰력보다 크게 나타난다. Pack micropiles were recently developed to improve pile capacity of general micropiles. Pack micropiles were made by warping thread bar or steel pipe of general micropile by geotexlile pack and grouting inside the pack with pressure. According to the pressure, the boring hole could be enlarged. A series of pile uplift tests were performed on three micropiles. Two out of the three piles were the pack micropiles and the other was the general micropile, in which a thread bar was used in the boring hole. According to the pressure applied to the pack micropiles, the diameter of boring hole was enlarged from 152 mm to 220 mm. Unit skin friction mobilized on side surfaces of micropiles increased with displacement of pile head and reached on a constant value, which represents that the relative displacement between piles (or thread bar) and soils was reached on critical state. And the uplift resistance of pack micropile was higher than that of general micropile. Two reasons can be considered: One is that the frictional surface increases due to enlarging diameter of boring holes and the other is that the unit skin friction could increase due to compressing effect of surrounding soils by soil displacement as much as the enlarging volume of boring hole. The compression effect appeared at deeper layer rather than surface layer. The unit skin friction mobilized on micropiles with small diameter was higher than the ones on large bored piles.

Erosion of a tectonically uplifting coastal landscape, NE Sicily, Italy

We investigate the relative importance of tectonic uplift, climate, and bedrock resistance as controls upon channel morphology in the active orogen of NE Sicily. The study area displays spatial variations in uplift rate, precipitation, and bedrock resistance. The significance of each of these gradients was tested using established morphometric relationships. Twenty catchments were investigated using the 28-m Aster digital elevation model (DEM) for longitudinal profile analysis, Google EarthTM to determine channel widths, and Schmidt Hammer readings to quantify bedrock strength. Based on channel morphologies and hillslope gradients, the basins exhibit three distinct reaches: upper, middle, and lower. The upper reaches of the bedrock channels display concave longitudinal profiles, positive correlation between uplift rate and steepness, and exponents in the width–area relationship of 0.4–0.5, indicating that uplift is the major control on the morphology of this reach. The middle reaches, however, display sublinear longitudinal profiles, weak correlation between uplift rate and channel steepness, and no systematic width–area relationship. We interpret this to be caused by the presence of a shear zone, which, through fracturing, has tectonically increased the bedrock erodibility, irrespective of its lithology. In the lower reaches, the channels are alluvial. Neither channel concavity nor steepness seems to be affected by the spatial variation in precipitation in any of the reaches, indicating that climate does not noticeably affect channel morphology. These observations suggest a strong tectonic influence on channel evolution in this active mountainous region. Our study illustrates how reach-scale morphometric analysis can aid understanding of how fluvial systems vary with potential controlling parameters.

Centrifuge study of capacity of a skirted foundation under eccentric transient and sustained uplift

Environmental and buoyancy forces impart overturning moments and potentially direct uplift to offshore foundation systems. Shallow skirted foundations are an attractive design solution, as negative excess pore pressures developed within the soil plug provide temporary uplift resistance. This paper presents the results of beam centrifuge tests on a shallow skirted foundation in a lightly overconsolidated clay under eccentric transient and sustained uplift. When compared with the response under concentric uplift, the experimental results show a reduction in capacity and an increase in the rate of degradation of capacity under sustained loading.

Uplift Behavior of Vertical Piles Embedded in Oil-Contaminated Sand

AbstractThere are several problems when dealing with oil-contaminated soil that affect environmental quality and alter the geotechnical properties of the soil. The influence of oil contamination on the uplift performance of model concrete piles embedded in sand at various densities is investigated. In this study, the model parameters are varied, namely, the thickness and diameter of the contaminated layer, type of oil contamination, pile surface roughness, and pile installation method. Contaminated-sand layers were prepared by mixing the sand with an oil content of 0–3% with respect to dry soil to match the field conditions. The results were then analyzed to study the effect of each parameter. To evaluate the scale effects, two sizes of model piles were tested, and the results were compared. This paper also discussed the effect of oil contamination on the relative ground movement around the pile surface. The results indicated that the uplift resistance was drastically reduced by oil contamination. The max...

Centrifuge Test to Evaluate the Geotechnical Performance of Anchored Buried Pipelines in Sand

AbstractThe aim of this study was to evaluate the uplift capacity of buried pipes to propose a new anchoring system using geogrids as an alternative and to improve the uplift resistance and inhibit the upward movement of pipes, which can compromise pipeline operation. The simulation was performed in a general scale model of 1/10 using the geotechnical centrifuge of the State University of Norte Fluminense (UENF) at 10 times earth gravity acceleration to keep the similitude between the prototype and the model. The tests were carried out for two different sand densities, two geogrid widths, and three burial depths. The geogrid was manufactured in a laboratory to mimic the behavior of a real-scale geogrid when subjected to upward displacements. Therefore, an amount of 24 pullout tests were conducted in small-scale models at 10 g. A pipe of outer diameter D was anchored to a geogrid with a width of 2D in six tests and to a geogrid with a width of 3D in six other tests. No anchoring system was used in 12 tests...

Vertical uplift capacity of a group of two coaxial anchors in a general c–ϕ soil

The vertical uplift resistance of a group of two horizontal coaxial strip anchors, embedded in a general c–[Formula: see text] soil (where c is the unit cohesion and [Formula: see text] is the soil friction angle), has been determined by using the lower bound finite element limit analysis. The variation of uplift factors Fc and Fγ, due to the components of soil cohesion and unit weight, respectively, with changes in depth (H) / width (B) has been established for different values of vertical spacing (S) /B. As compared to a single isolated anchor, the group of two anchors provides a significantly greater magnitude of Fc for [Formula: see text] ≤ 20° and with H/B ≥ 3. The magnitude of Fc becomes almost maximum when S/B is kept closer to 0.5H/B. On the other hand, with the same H/B, as compared to a single anchor, hardly any increase in Fγ occurs for a group of two anchors.

Ultimate Uplift Capacity of Transmission Tower Foundation in Undisturbed Excavated Soil

Excavated transmission tower foundation in stiff soil is intensively recommended because it can basically keep soil undisturbed and thus adequately exert the strength of soil to resist the tension from transmission tower line. However, Chinese current code for design of this type of foundation exist certain problems. Therefore, this paper employed finite element method to simulate foundation uplift behavior in undisturbed soil and explained the difference among the results of two methods in code and FE analysis. Moreover, the effects of embedment depth, soil property, extended angle of foundation base on failure mode and ultimate uplift capacity are investigated by means of parametric analysis. It is concluded that shallow mode and deep mode occur for different embedment depth. Friction angle has significant effects on sliding surface, and cohesion slightly affects the shape of sliding surface. Base extended angle of 45°corresponds to the largest sliding surface and ultimate uplift resistance by contrast with other angles.

Mobilization Distance for Upheaval Buckling of Shallowly Buried Pipelines

Buried pipelines may be subject to upheaval buckling because of thermally induced compressive stresses. As the buckling load of a strut decreases with increasing out of straightness, not only the maximum available resistance from the soil cover, but also the movement of the pipeline required to mobilize this are important factors in design. This paper will describe the results of 15 full-scale laboratory tests that have been carried out on pipeline uplift in both sandy and rocky backfills. The cover to diameter ratio ranged from 0.1 to 6. The results show that mobilization distance exhibits a linear relationship with H/D ratio and that the postpeak uplift force-displacement response can be accurately modeled using existing models. A tentative design approach is suggested; the maximum available uplift resistance may be reliably predicted from the postpeak response, and the mobilization distance may be predicted using the relationships described in this paper.

Investigating Particle-Size Effect on Uplift Mechanism of Pipes Buried in Sand Using Distinct Element Method

Uplift of pipeline due to buckling deformation and the resultant soil resistance are key concerns in its design. This paper investigates the particle-size effect on uplift resistance of a pipe buried in sand and the ground deformation mechanism using the distinct element method (DEM). Two granular grounds, one for coarse-sand ground and the other for fine-sand ground, were examined in this simulation. The results show that both cases exhibit similar deformation mechanism of four featured stages: mobilization of peak uplift resistance, infilling of soils beneath pipe, formation of shear bands, and flow of soils around pipe. The uplift resistances in both cases gradually increase to a peak and then drop to a constant value with the upward displacement of the pipe. However, higher peak resistance and shear bands with gentler slope are observed in the coarse case.

Generalized load cycles for dynamic wind uplift evaluation of rigid membrane roofing systems

Roof is an integral part of building envelope. It protects occupants from environmental forces such as wind, rain, snow and others. Among those environmental forces, wind is a major factor that can cause structural roof damages. Roof due to wind actions can exhibit either flexible or rigid system responses. At present, a dynamic test procedure available is CSA A123.21-04 for the wind uplift resistance evaluation of flexible membrane-roofing systems and there is no dynamic test procedure available in North America for wind uplift resistance evaluation of rigid membrane-roofing system. In order to incorporate rigid membrane-roofing systems into the CSA A123.21-04 testing procedure, this paper presents the development of a load cycle. For this process, the present study compared the wind performance of rigid systems with the flexible systems. Analysis of the pressure time histories data using probability distribution function and power spectral density verified that these two roofs types exhibit different system responses under wind forces. Rain flow counting method was applied on the wind tunnel time histories data. Calculated wind load cycles were compared with the existing load cycle of CSA A123.21-04. With the input from the roof manufacturers and roofing associations, the developed load cycles had been generalized and extended to evaluate the ultimate wind uplift resistance capacity of rigid roofs. This new knowledge is integrated into the new edition of CSA A123.21-10 so that the standard can be used to evaluate wind uplift resistance capacity of membrane roofing systems.

Model test based soil spring model and application in pipeline thermal buckling analysis

The buckling of submarine pipelines may occur due to the action of axial soil frictional force caused by relative movement of soil and pipeline, which is induced by the thermal and internal pressure. The likelihood of occurrence of this buckling phenomenon is largely determined by soil resistance. A series of large-scale model tests were carried out to facilitate the establishment of substantial data base for a variety of burial pipeline relationships. Based on the test data, nonlinear soil spring can be adopted to simulate the soil behavior during the pipeline movement. For uplift resistance, an ideal elasticity plasticity model is recommended in the case of H/D (depth-to-diameter ratio)>5 and an elasticity softened model is recommended in the case of H/D≤5. The soil resistance along the pipeline axial direction can be simulated by an ideal elasticity plasticity model. The numerical analyzing results show that the capacity of pipeline against thermal buckling decreases with its initial imperfection enlargement and increases with the burial depth enhancement.

Vertical Uplift Resistance of a Group of Two Coaxial Anchors in Clay

The vertical uplift resistance for a group of two horizontal coaxial rigid strip anchors embedded in clay under undrained condition has been determined by using the upper bound theorem of limit analysis in combination with finite elements. An increase of undrained shear strength of soil mass with depth has been incorporated. The uplift factor Fcγ has been computed. As compared to a single isolated anchor, a group of two anchors provides greater magnitude of the uplift resistance. For a given embedment ratio, the group of two anchors generates almost the maximum uplift resistance when the upper anchor is located midway between ground surface and the lower anchor. For a given embedment ratio, Fcγ increases linearly with an increase in the normalized unit weight of soil mass up to a certain value before attaining a certain maximum magnitude; the maximum value of Fcγ increases with an increase in embedment ratio.

Uplift Capacity of Belled and Multi-Belled Piles in Dense Sand

This paper evaluates the uplift capacity of belled and multi-belled piles in dense sand. A two-dimensional distinct element (DE) analysis was applied in pullout tests on single piles to investigate the uplift resistance of the piles, the soil behavior around the piles, and the interaction between the soil and the pile surface. It was observed from the DE analysis that the soil mass adjacent to the projections of the belled and multi-belled piles moved vertically, and that the soil movements leaned slightly with the occurrence of relative displacement between the soil and the pile surface. A theoretical solution for predicting the uplift capacity of belled and multi-belled piles was derived from an upper bound limit analysis based on the soil movements in the DE analysis. The solution was able to reproduce the ultimate uplift resistance in the DE analysis using the friction angles in the aggregates and on the pile surface that were evaluated from a simulation of direct and simple shear tests. In addition, a continuity equation that satisfied the relationship between the displacement vector of the soil mass adjacent to the projections and the change in volume around the soil mass was proposed for predicting the uplift capacity of actual piles under axisymmetric conditions. The theoretical solution obtained with the continuity equation was in good agreement with the pullout resistance of the belled and multi-belled piles in centrifuge model tests and full-scale tests conducted in situ.

Wind Uplift Performance of Composite Metal Roof Assemblies

A common factor in roof failures is wind forces, which inflict considerable damage every year, even to new roof structures. Metal roofs are a popular low-sloped roof assembly. On the basis of their layout, metal roofs can be categorized as either composite or noncomposite assemblies. In North American practice, five main test procedures—ASTM E1592, ANSI/FM 4474, UL 580, UL 1817, and CSA A123.21-04—are used to determine the wind uplift performance of metal roofs. The fundamental differences between these test protocols lie in the way they represent wind effects on the performance of metal roofing systems. Of the five, CSA A 123.21-04 is the only one that assesses the wind uplift resistance under dynamic wind load conditions. To evaluate the wind uplift performance of noncomposite and composite metal roofing assemblies, eight assemblies with two different types of panels—SNAP-IT and MR-24—were tested by using the CSA A123.21-04 dynamic test protocol. By relating air intrusion characteristics of the subsurface components to panel behavior, this paper shows how composite assemblies resist wind uplift pressures better than noncomposite assemblies. This paper reveals that increased air intrusion resistance of the sub surface components in composite assemblies results in increased suction resistance, decreased panel deflection, decreased stress on the panels, and increased wind uplift resistance.

A Test Protocol to Quantify the Uplift Resistance of Adhesive Applied Roofing Specimens Subjected to Tensile Loading

Abstract Adhesive applied roofing systems (AARS), a new generation of built-up roofs, are gaining popularity in North American low slope application. AARS uses no fasteners and all components (e.g., deck, vapour barrier, insulation board, and membrane) are integrated by the use of adhesives. As there are no metal fasteners, AARS can offer an advantage of reduction in condensation and thermal bridges for the roof assemblies. Even though, AARS have been in use, there have been no standard that exists to quantify its wind uplift performances. An industries-university-Canadian government collaborative research project, “Development of Wind Uplift Standard for Adhesive Applied Low Slope Roofing System,” has been initiated with three major tasks: Experimental investigation, formulation of a numerical model and development of wind design guide and standards. This paper documents a standardized small scale laboratory test method for the quantification of uplift resistance subject to tensile loading. As part of Task 1 of the project, this systematic investigation focuses on three key parameters: Loading rate, specimen size and end condition. The investigations were completed by constructing over 400 specimens. Both the maximum uplift resistance and the consistence in the failure plane are equally considered during the test method standardization. The data from this small scale testing can facilitate roofing industries to optimize the material combinations such that the uplift resistance data can be used as an indicator before performing a full-scale wind uplift testing.