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玻璃钢螺旋锚锚周土体的破坏面形态与抗拔承载力计算
Failure Surface Morphology and Uplift Bearing Capacity Calculation of Soil Surrounding Glass Fiber-Reinforced Plastic Screw Anchors
玻璃钢(GFRP)螺旋锚作为一种新型支护锚杆,具有施工简单、轻质高强、耐腐经济等优点,但目前关于其抗拔性状及抗拔承载力的计算仍不明确。为分析GFRP螺旋锚在拉拔过程中的破坏形态并确定其抗拔承载力,首先采用有限元数值模拟方法,研究不同锚板埋深对锚固土体破坏面形态的影响及演化规律。在此基础上,提出了GFRP螺旋锚锚固土体的统一破坏面形态,进而分别推导了不同锚板埋深下抗拔承载力的计算公式,公式中的参数均有明确的物理意义,反映了GFRP螺旋锚的埋深比(H/D,H为锚板埋深、D为锚板直径)、土体的密实度、内摩擦角等因素的影响。结果表明: ①随着锚板埋深从浅埋逐渐增大到深埋,破坏面形态经历了从“喇叭口”状转向“高脚杯”状,最终形成封闭“灯泡”状的演化过程,但难以得到锚板“浅埋”与“深埋”的明确界限;②利用数值模拟数据和试验数据,验证了本文所提出的抗拔承载力计算公式的合理性和准确性。
[Objective] As a new type of support anchor, the Glass Fiber-Reinforced Plastic (GFRP) screw anchor is increasingly used in engineering practice due to its simple construction, light weight, high strength, corrosion resistance, and cost-effectiveness. Previous calculation formulas for uplift bearing capacity of screw anchors mostly based on artificially defined boundaries between shallow and deep embedment, resulting in large differences in critical embedment depth ratio H/D (where H is the embedment depth and D is the anchor plate diameter) given by different scholars. This study aims to propose a calculation formula for uplift bearing capacity based on the generalized unified failure surface morphology, providing theoretical support for the design of GFRP screw anchors in engineering practice. [Methods] Using finite element numerical simulation software ABAQUS, numerical simulations of the uplift performance of GFRP screw anchors under different embedment ratios were conducted. The maximum uplift bearing capacity of vertical GFRP screw anchors in soil and the evolution of the failure surface morphology of anchored soil were investigated. [Results and Conclusion] (1) The load-displacement curves of GFRP screw anchor during uplift in anchored soil could be divided into three stages: the elastic stage, the local plastic stage, and the penetration failure stage. In the elastic stage, the load and displacement showed linear relationship, with the slope of the curve representing the equivalent stiffness of the anchor plate-soil system. In the local plastic stage, plastic deformation occurred in the local soil zone, deformation of the anchored soil gradually increased, system stiffness decreased, load-displacement relationship became non-linear (indicated by a gradually decreasing curve slope), and the interaction between the GFRP screw anchor and the anchored soil began to exhibit non-linear characteristics. In the penetration failure stage, the resistance of the anchored soil reached its ultimate value, cracks in the anchored soil became interconnected, the soil failure surface formed, and the curve entered a stable phase where the load no longer changed with displacement increase. The uplift bearing capacity factor Nγ showed a trend of initial increase followed by gradual stabilization with embedment ratio, which matched well with experimental results from other scholars, thereby verifying the simulation’s validity. The turning point occurred near H/D=9, suggesting that an embedment ratio H/D=9 could be considered as the critical embedment ratio distinguishing shallow from deep embedment. (2) Numerical simulation showed that during uplift, the anchored soil could be divided into three zones based on stress state: conical active zone formed by compaction above the GFRP screw anchor, passive zone extending outward along screw anchor edge influenced by extrusion from soil within failure surface, and transition zone between active and passive zones in plastic state. The soil within the failure surface consistently extruded the soil outside failure surface. Except for the outermost region, which might be in a state of at-rest earth pressure, the soil on the failure surface was generally in a state of passive earth pressure. With increasing embedment ratio, the failure surface morphology of the anchored soil underwent a dynamic evolution from “trumpet” shape➝“goblet” shape➝“light bulb” shape. No distinct “critical embedment ratio” between shallow and deep embedment for GFRP screw anchors existed. (3) By integrating the maximum uplift bearing capacities obtained from numerical simulations and the evolution patterns of the failure morphology in the anchored soil, a generalized unified failure surface model that did not require distinguishing between shallow and deep embedment for the soil anchored by GFRP screw anchors was proposed. This model was derived by introducing a cubic term based on the “trumpet” shape (with inclined linear boundaries) failure surface. On this basis, a calculation formula for the uplift bearing capacity under different embedment depths of GFRP screw anchors was derived, and the formula was compared and validated with numerous experimental results from domestic and international studies. The results demonstrated that the proposed calculation formula could effectively predict the maximum uplift bearing capacity under different embedment depth ratios.
玻璃钢(GFRP)螺旋锚 / 破坏面形态 / 有限元法 / 数值模拟 / 埋深比 / 抗拔承载力
glass fiber reinforced plastic (GFRP) screw anchors / failure surface morphology / finite element method / numerical simulation / embedment ratio / uplift bearing capacity
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This paper addresses scaling issues related to small-scale 1-g model tests on plate anchors in sand under drained loading conditions. Previous centrifuge studies from the literature have suggested that the results of conventional 1-g model testing are inaccurate because of scale effects. Other studies have suggested, however, that scaling errors can be reduced in 1-g model tests if the results are presented in dimensionless form and the constitutive response of the model soil is representative of the prototype behavior. There are no experimental studies in the literature that have tested the validity of this approach for plate anchors. A simple 1-g scaling framework was developed for vertically loaded, horizontal plate anchors. Small-scale 1-g model tests were performed on square plate anchors in dry sand, and combined with existing centrifuge and 1-g model test data from the literature to test the scaling approach for both capacity and deformation. The 1-g model tests provided a reasonable representation of the full-scale prototype behavior when the scaling approach was applied.
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Soil anchors are commonly used as foundation systems for structures that require uplift or lateral resistance. These types of structure include transmission towers, sheet pile walls and buried pipelines. Although anchors are typically complex in shape (e.g. drag or helical anchors), many previous analyses idealise the anchor as a continuous strip under plane strain conditions. This assumption provides numerical advantages, and the problem can be solved in two dimensions. In contrast to recent numerical studies, this paper applies three-dimensional numerical limit analysis and axisymmetrical displacement finite element analysis to evaluate the effect of anchor shape on the pullout capacity of horizontal anchors in sand. The anchor is idealised as either square or circular in shape. Results are presented in the familiar form of break-out factors based on various anchor shapes and embedment depths, and are also compared with existing numerical and empirical solutions.
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The pullout capacity of slab anchors in homogeneous sand depends on several factors including the type and density of the sand, and the depth, size, inclination, and shape of the slab. Although numerous publications have reported results of pullout tests on small models and prototypes, the investigations described have generally been limited to a study of the effects of one or two of the above factors, and no attempt has been made to develop an integrated approach to the problem. This paper presents such an approach by reanalyzing the results of published experimental data as well as those of a series of pullout tests performed on prototype slabs placed at various inclinations and depths in a dense sand profile. A simple theoretical expression is found to reasonably predict the pullout capacity of a continuous, horizontal slab as a function of depth-to-width ratio. Factors to account for shape, and inclination, are then established leading to expressions for the estimation of pullout capacity of any slab anchor. Key words: anchors, field tests, model tests, pullout capacity, sand, slabs, plates.
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