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1.
This study has evaluated the vertical bearing capacity by conducting static load tests for noise-free and vibration-free screw pretensioned spun high-strength concrete (PHC) piles installed using two different methods (end-squirting shoe and pre-boring methods). Vertical bearing capacity differences seem to occur due to the displacement of soils near the external circumference of a pile, depending on the installation method. A method by which to evaluate the bearing capacity of screw concrete piles is suggested by considering the equations that already have been used to calculate the bearing capacity of piles. Based on static load tests and analysis, the pile installed using the end-squirting shoe method was assumed to be a bored pile and it was reasonable to use the equation proposed by the Japanese Geotechnical Society. At the same time, the pile installed using the pre-boring method was deemed a low soil displacement pile and so it was reasonable to apply the equations proposed for calculating the bearing capacity of the driven pile suggested by the Architectural Institute of Japan. 相似文献
2.
A research on super-long piles has been primarily based on cast-in-place bored piles. In this article, field tests associated with selected measuring technologies were conducted on two super-long steel pipe piles in offshore areas to investigate the behaviors and performance of super-long steel pipe piles. The strain along the pile shaft was monitored by adopting the Brillouin optical time domain reflection and fiber Bragg grating techniques. Static load tests were also conducted on two test piles to determine the bearing capacities. In addition, the axial forces, relative displacements between piles and soils and pile shaft resistances were calculated based on the measured strain. According to the results of the static load tests, the ultimate bearing capacities of the two test piles are greater than 15,000 and 15,500 kN. Both of these values meet the design requirements. In addition, the two test piles can be treated as pure friction piles, and the load transfer mechanism and relationships between the pile shafts and relative displacements are also discussed. Finally, recommendations for practical engineering and significant conclusions are presented. 相似文献
3.
Drilled displacement (DD) piles with a screw-shaped shaft (referred to as DD piles) are installed using a continuous full thread hollow rod (without a displacement body) inserted and advanced in the soil by both a vertical force and a torque. As a type of newly developed pile, current understanding of the bearing mechanism of DD piles is unsatisfactory, which restricts their further applications in engineering. The primary aim of this paper is to study the bearing mechanism of this type of pile using a numerical method. First, a numerical model for calculating the bearing capacity of the DD piles was created and validated by a laboratory test. Then, the effects of the parameters of pile–soil interface, soil strength, and pile geometrical parameters on the bearing mechanism of the DD piles were investigated in parametric studies. The results of parametric studies show that the limit shear stress on the pile–soil interface, the friction angle of surrounding sand, screw pitch, and thread width significantly influence the bearing capacity of the DD piles, whereas the friction coefficient at the pile–soil interface and the thread thickness have little effect. Based on the results of the parametric studies, the failure mechanism of the DD piles under vertical load is analyzed. Finally, an equation for predicting the ultimate bearing capacities of helical piles based on cylindrical shear failure was used for estimating the bearing capacity of the DD piles, and the calculated results were verified with the numerical results. 相似文献
4.
In this article, two full-scale pile loading tests were conducted to observe the field performance of the super-long bored piles, and a simplified approach for nonlinear analysis of the load-displacement behavior of a single pile was presented. The field tests on piles indicates that, under the maximum test load, more than 70% of the pile top settlement is caused by the compression of pile shaft. For practical purposes, the pile top settlement can be reduced through improving the pile shaft strength. When the load reaches the maximum test load, the proportion of the load carried by the pile tip is approximately 30%. The super-long pile is functioning as an end-bearing friction pile. The skin friction at shallow depth is fully mobilized and decreases from a peak value with increasing load. However, the skin friction of deeper soil is not fully developed due to less relative displacement. Furthermore, a BoxLucas1 model is used to capture the relationship between unit skin friction and pile-soil relative displacement, whereas a hyperbolic model is used to describe the relationship between toe stress and pile base displacement. Based on the BoxLucas1 model and the hyperbolic model, a load transfer method is used to clarify the response of a single pile, and a computational flow chart is developed. The efficiency and accuracy of the present method is verified using the field tests on piles. The proposed simple analytical approach is economical and efficient, resulting in savings in time and cost. 相似文献
5.
AbstractThis study investigates the impact of pile cap size, soft layer thickness and pile strength on load transfer and settlement behaviors of embankments supported by floating and fixed T-shaped deep cement mixing piles and conventional DCM piles under volume control. Preliminary investigation is performed by a series of small-scale physical model tests. The results reveal that the differential settlement can be substantially reduced with an enlarging pile cap as a result of larger embankment load transferred to the piles. The extended numerical analysis results demonstrate that the pile efficacy is related to the individual pile bearing capacity, which, in turn, depends on the pile cap size. The soft layer thickness has an insignificant effect on differential settlement but a significant effect on average settlement, while the pile strength plays an important role in differential settlement only when the cap size is not very large. Shape factor of at least 3.0 is recommended to ensure the reduction in differential settlement and minimize the effect of the change in pile strength. 相似文献
6.
螺旋桩芯劲性复合桩（helix stiffened cement mixing pile，简称HSCM桩）是一种新型复合桩，其成桩工艺会对桩身及其承载性能有较大影响。为验证HSCM桩在软黏土中同步旋进注浆工艺的可行性，并研究其成桩参数对抗压承载性能的影响，设计了2组缩尺模型试验，包括不同叶片数量与钻进速度的HSCM桩与对比螺旋桩。通过在高岭土制备的软黏土中成桩，并进行抗压承载性能及桩身几何尺寸测试，分析HSCM桩的成桩参数与水泥土桩身间的关系。试验结果表明：同步旋进注浆工艺能够在螺旋桩周围形成倒圆台状的水泥土桩身，水泥土桩身的平均黏结直径约为叶片直径的1.17～1.35倍；适当增加叶片数量能够使水泥与土体充分拌和，提高水泥土桩身的完整性与连续性，以改善HSCM桩的成桩质量；钻进速度大幅提高会导致注浆量不足，减小水泥土桩身的黏结直径与刚度；试验条件下HSCM桩的抗压极限承载力是螺旋桩的3.83～3.93倍，桩径扩大提高了侧摩阻力，注浆工艺加固并提高了土体强度，弥补了叶片在旋进过程中扰动土体造成强度降低的问题。 相似文献
7.
Study of the Bearing Capacity at the Variable Cross-Section of A Riser-Surface Casing Composite Pile
Reducing the cost of offshore platform construction is an urgent issue for marginal oilfield development.The offshore oil well structure includes a riser and a surface casing.The riser,surface casing and oil well cement can be considered special variable cross-section piles.Replacing or partially replacing the steel pipe pile foundation with a variable cross-section pile to provide the required bearing capacity for an offshore oil platform can reduce the cost of foundation construction and improve the economic efficiency of production.In this paper,the finite element analysis method is used to investigate the variable cross-section bearing mode of composite piles composed of a riser and a surface casing in saturated clay under a vertical load.The calculation formula of the bearing capacity at the variable section is derived based on the theory of spherical cavity expansion,the influencing factors of the bearing capacity coefficient Nc are revealed,and the calculation method of Nc is proposed.By comparing the calculation results with the results of the centrifuge test,the accuracy and applicability of the calculation method are verified.The results show that the riser composite pile has a rigid core in the soil under the variable cross-section,which increases the bearing capacity at the variable cross-section. 相似文献
8.
In the field of ocean engineering, pile foundations are extensively used in supporting several structures. In many cases, piles are subjected to significant lateral loads. The environment prevalent in the ocean necessitates the piles to be designed for cyclic wave loading. In this investigation, the behaviour of rigid piles under cyclic lateral loading has been studied through an experimental programme carried out on model piles embedded in a soft marine clay. Static tests were also conducted on piles embedded in a clay bed prepared at different consistencies suitable to field situations. Cyclic load was applied by using a specially designed pneumatic controlled loading system. Tests were conducted on model piles made of mild steel (MS), aluminium and PVC with wide variation in pile soil relative stiffness. For cyclic load levels less than 50% of static lateral capacity, the deflections are observed to increase with number of cycles and cyclic load level and stabilise after a certain number of cycles. For cyclic load levels greater than 50% of static lateral capacity, the deflections are observed to increase enormously with number of cycles. The results of post-cyclic load tests indicate that the behaviour under static load can improve for cyclic load levels less than 40% of the static lateral capacity. The variations in the load capacity due to cyclic loading are explained in terms of the changes in strength behaviour of soil. 相似文献
9.
Most field tests are carried out using working piles for verification purposes in China, and loading tests are terminated before achieving true pile capacity. In this work, two full-scale destructive loading tests on tension piles instrumented with strain gauges were conducted to capture true pile capacity. The load-displacement response, load transfer, and threshold of the pile-soil relative displacement for fully mobilizing skin resistance in the uplift case were discussed. It was found that the shaft resistance degradation is observed to be along the pile depth with a reduction factor of 0.905 to 0.931, and the thresholds of pile-soil relative displacement for fully mobilizing skin resistance of the tension pile in different soils are found to be in the range 0.67% to 1.34% of the pile diameter. Based on the field test results, a simple softening model was proposed to describe the degradation behavior of skin friction along the pile-soil interface. Further study was conducted to assess the influence of the threshold of pile-soil relative displacement for fully mobilizing skin friction and the reduction factor on the skin friction. As to the analysis of the response of single pile subjected to tension load, a highly effective iterative computer program was developed using the proposed skin friction softening model. Comparisons of the load-settlement response for the well-instrumented tests were given to demonstrate the effectiveness and accuracy of the proposed simple method. 相似文献
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11.
Large-scale field tests were conducted to study set-up effect in open-ended prestressed high-strength concrete pipe piles jacked into stratified soil. Four open-ended prestressed high-strength concrete pipe piles with 13 and 18 m in embedment depth were fully instrumented with fiber Bragg grating sensors and installed. Several restrike dynamic tests were performed on each test pile, with the time interval from 21.5 to 284 hours after installation. Static loading tests (SLTs) were later performed on each test pile at 408 hours after installation to substantiate the dynamic tests. Changes with time in pile bearing capacity and in the shaft and toe resistances were studied based on the results of the pile tests. The development of shaft resistance set-up in different layers was studied in particular. It was found that set-up effect in the shaft resistance is significant and the toe resistance increment was minor. The overall set-up factor of total bearing capacity was found to range from 0.09 to 0.53, and the set-up effect of friction pile is much larger than the end bearing pile. More significant set-up in shaft resistance was observed in fill and alluvium layer. The dimensionless set-up factor A for shaft resistance in marine deposits ranges from 0.5 to 1.43, and it contributes the most to the shaft resistance as the shaft resistance in marine deposits is higher. 相似文献
12.
For the static pressure pile, the most important is to determine the standard value of ultimate bearing capacity of single pile. At present, the bearing capacity of pile foundation is usually determined by the cone penetration test (CPT) test. The empirical formula was used in practice, but the effect of excess pore water pressure generated in the penetration on the measured cone-tip resistance and side friction is neglected. In this study, based on the field test results at Fengyu playground at Yancheng Institute of Technology by CPT and CPTU methods, the bearing capacity of pile was predicted by the standardized methods, the LCPC (France method) and CPTU direct prediction methods. The prediction was also compared with the results by the static load test method. The prediction accuracy of the CPTU method was then discussed as well. The results reveal that the accuracy of the CPTU method was the highest, which was consistent with the results obtained by the static load test method. It is the best method and worthy of being applied for predicting bearing capacity of piles in engineering applications. 相似文献
13.
AbstractIn onshore and offshore fields of ocean engineering, piles are used as foundation systems for various structures. Piles are classified into different types depending on their materials, geometries, and particularly, installation methods, which have advantages or limitations. Companies and engineers have developed a new group of piles, because of necessity to improve their performance in terms of increasing the bearing capacity, reducing impacts of traditional installation procedures, implementing by low- torque power equipment, and utilizing them in widely different ground conditions, including in a marine environment. In the present study, three different models of a new pile with an expander body are introduced to increase the shaft and pile-toe diameters and its self-expansion in the embedment depth under the titles of the Bubble pile (BP), Self-Expanded pile (SEP) and Wing pile (WP). The main subject of this research is to achieve increased bearing capacity, reduced installation effects, and decreased required installation torque. The frustum-confining vessel of Amirkabir University of Technology (FCV-AUT) was employed for this purpose. Up to 14 axial compressive and tensile load tests were carried out on different model piles on sand collected from Anzali shore located on the northern coast of Caspian Sea in Iran, with relative densities of 45% to 50% within FCV-AUT. Comparing the performance of introduced pile with traditional pile corresponding to the same characteristics, the results indicated a significant increase in the axial bearing capacity and reduced disturbance effect of the pile. Also, a lower installation torque of the SE pile was required compared to the helical pile. The test results also demonstrated that the new pile could resist considerable compressive and uplift loads, and could be a possible alternative to traditional piles in the onshore sector. 相似文献
14.
Yogendra Tandel Mohsin Jamal Chandresh Solanki Atul Desai Jignesh Patel 《Marine Georesources & Geotechnology》2017,35(4):504-511
Granular piles are frequently used as a method of improving soft grounds as they provide increased bearing capacity and reduce foundation settlements. However, in very soft clayey soils, they may not derive their load-carrying capacity by low confining pressure provided by the surrounding soil. In such circumstances, granular piles may be reinforced with suitable geosynthetic to increase its load-carrying capacity and to reduce excessive bulging. In this study, the performance of small group of geosynthetic-reinforced granular piles (GRGPs) is examined in terms of load-carrying capacity, settlement, and modulus by laboratory model tests. The parameters investigated include modulus of reinforcement material, area replacement ratio (ARR) based on the column diameter and reinforcement length. The results indicated that increasing the modulus of the reinforcement and the ARR based on the column diameter enhances the overall performance of the GRGP group. It was also observed that reinforcement on top portion of the granular pile is sufficient to substantially increase the load-carrying capacity of granular pile group. 相似文献
15.
《中国海洋工程》2021,(3)
The low side friction of piles in coral sand results in the low bearing capacity of foundations. In this paper, expansive concrete pile is utilized to improve the bearing capacity of pile foundations in coral sand. Both model tests and numerical simulation are performed to reveal the bearing mechanism of expansive concrete pile in coral sand.Results showed that the lateral earth pressure near pile increases obviously and the side friction of piles is improved,after adding expansion agent to the concrete. The horizontal linear expansion is 1.11% and the bearing capacity increased 41% for the pile, when 25% expansion agent is added. Results in finite element numerical simulation also show that ultimate bearing capacity increases with the increase of the linear expansion ratio. Besides, the area for obvious increase in side friction is below the surface of soil about three times the pile diameter, and the expansion leads to a high side friction sharing of the pile. Therefore, the cast-in-place expansive concrete pile is effective in improving the bearing capacity of piles in coral sand. 相似文献
16.
A fundamental study of pile–soil systems subjected to lateral loads in offshore deposit was conducted using experimental tests and numerical analysis. The emphasis was on the soil–pile rigidity of a laterally loaded pile in marine clay. Rigid- and flexible-pile analyses were conducted for comparison. A framework for determining the lateral load transfer curve (p–y curves) is proposed based on both field and laboratory model tests. A numerical analysis that takes into account the proposed p–y curves was performed for the pile flexibility parameters such as pile diameter, pile length, pile-bending stiffness, and the modulus of subgrade reaction. Based on the analysis, it is shown that the differences in bending moment and lateral displacement are more significant for flexible piles rather than rigid piles. It was found that the p–y curves influence the behavior of flexible piles more than rigid piles, thus the magnitude and distribution of the p–y curves are significantly important in flexible pile design. 相似文献
17.
AbstractAn experimental study of the performance of concrete pipe piles during installation under different penetration speeds and static load tests on the piles in sand is presented. The applied jacking force, the amount of pile penetration, length of soil plug formed and ultimate bearing capacity were measured during the model tests. The results showed that the concrete pipe piles were partially plugged and the behavior of the soil plug was significantly affected by the penetration speed. The lower the penetration speed, the larger the soil plug formed which in turn leads to a greater ultimate bearing capacity. The size of soil plug can be evaluated by the m value defined as the ratio of the volume of the soil plug to that of the penetrated pile wall. The relationship between the m value and the penetration speeds can be used to estimate the amount of soil plug and the depth of penetration for an open-ended concrete pipe pile jacked into sand. 相似文献
18.
针对海相软土地区螺旋钢管桩承载力低与腐蚀问题,提出一种新型压力注浆螺旋钢管桩,并设计5根足尺试验桩,进行现场抗拔承载性能试验,研究螺旋叶片直径与排布方式对成桩直径与桩基抗拔承载性能的影响.结果表明,成桩直径与螺旋叶片直径呈正相关,在每节延长段钢管末端设置螺旋叶片利于提高水泥土柱完整性,使成桩直径更为饱满,提高桩基的抗拔承载性能.将试验结果和现行规范抗拔极限承载力计算结果进行对比,计算结果约为实测平均值的94％,在此基础上提出压力注浆螺旋钢管桩抗拔承载力计算参数修正建议,为后续的设计提供参考. 相似文献
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20.
桩基础是我国海上风电工程中应用最为广泛的基础形式,其中嵌岩桩因其施工难度大,承载力高备受关注。与其他类型的桩基础不同,嵌岩桩的水平承载力不仅受到围岩强度的影响,更与其成桩质量与灌浆材料的强度相关。采用有限元方法分析了嵌岩深度、桩基直径与壁厚、桩身倾斜度等多种因素对嵌岩桩水平承载力的影响,提出了确定嵌岩桩水平极限抗力的标准。研究表明：桩与围岩间的灌浆环会先于桩身发生破坏,因此可将灌浆环受拉破坏作为判断嵌岩桩达到水平极限承载力的标准;桩身倾斜度对嵌岩桩的水平极限承载力影响较大,直径和壁厚的增加,均能提高桩基的水平承载力。 相似文献