共查询到18条相似文献，搜索用时 133 毫秒
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开发了一种新型平台桩靴,可通过活动板转动实现自升式平台不同阶段桩靴受力面积的灵活变化。基于大变形有限元方法,模拟新型桩靴基础在“砂-黏”地层中的贯入过程,分析了活动板转角、砂层厚度比、摩擦角和黏土层不排水抗剪强度对新型桩靴贯入阻力的影响,并与普通桩靴的贯入响应比较。数值分析中,上覆砂土和下层黏土分别采用摩尔库伦模型和修正Tresca模型进行模拟。结果表明：新型桩靴穿刺时,土层参数对峰值阻力的影响规律与普通桩靴相同,但其峰值阻力随活动板转角的变化而变化,无法直接使用具有等效面积普通桩靴的穿刺预测方法。考虑各项关键影响因素,结合穿刺破坏时的地基破坏模式,基于数值模拟结果提出了适用于新型桩靴的贯入阻力预测公式。 相似文献
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《中国海洋大学学报(自然科学版)》2015,(7)
在分析桩靴式钻井平台插桩过程中地基土的破坏形式的基础上,将桩靴下土体破坏面假定为锥形面,根据极限平衡理论,推导出了均匀、双层地基土中基于被动土压力的插桩阻力计算公式。通过插桩实例对所推导的公式进行了验证,分析比较了极限承载力与插桩阻力的异同,讨论了插桩阻力计算公式推导过程中土体假设为锥形破坏面的合理性,认为本文推导的插桩阻力计算公式作为桩靴式钻井平台插桩深度预测方法更接近实际插桩结果。 相似文献
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自升式钻井平台插桩是地基土在桩靴荷载作用下发生连续的塑性破坏的动态过程,当地基极限承载力等于桩靴荷载时插桩完成。经典土力学极限承载力理论对土体潜在滑动面做了假设,无法有效分析土体内部的破坏过程。本研究应用有限元法（FEM ）对插桩过程进行了模拟,得到地基土的破坏机制以及中间荷载下土体的应力、应变情况,通过和各理论公式计算的极限承载力进行对比分析,分析影响地基极限承载力的因素。研究表明,基础宽度与硬土层厚度的比值 B/H越大,下卧软土层越容易发生塑性破坏,极限承载力明显下降,当B/H＜0．286时,可以忽略下卧软土层对地基承载力的影响。 相似文献
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海上自升式钻井平台以其造价低廉、便于移动和安装的优势被广泛应用于海洋地质勘察、风电安装和油气开采等领域,其基础类型多为桩靴基础。为了保证平台能在恶劣的海洋环境中安全作业,桩靴基础需要贯入海床以下一定深度以获得足够的承载力。然而,当桩靴基础在上硬下软土层中贯入时可能发生穿刺破坏导致平台损坏甚至倾覆。已有的桩靴穿刺破坏分析方法基于预设的地层参数预测穿刺荷载,由于无法考虑海床中地层及土性的不确定性,其准确性有待提高。将桩靴基础贯入过程中的监测数据与穿刺破坏机理相结合,通过66组离心机模型试验结果表征土体不确定性的影响,发展贝叶斯预测模型,实现了峰值阻力和穿刺深度的实时预测。基于规范推荐的荷载扩展分析法和冲剪系数分析法,建立了适用于规范法的概率模型,采用该模型对上砂下黏土层中桩靴基础的穿刺行为进行了预测,结果表明所提方法的预测精度随着监测数据的增加而提高,预测得到的峰值阻力误差在10%以内。 相似文献
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本文基于刚塑性极限分析理论,按照Hill塑性破坏模式,构建了砂性海床土体运动许可速度场。对饱和不排水砂性海床上浅埋圆形管道的极限承载能力以及管道的入泥深度进行了理论推导,给出了浅埋圆形管道承载能力与入泥深度的上限解答。同时,为了验证本文给出的承载能力和入泥深度上限解答的合理性,将计算结果与国内外规范中常用的Terzaghi等计算公式进行了对比分析。对比结果证实了本文上限解答与失稳模式较为合理。 相似文献
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基于现有规范与文献研究提出的减小桩靴踩脚印附加响应的相关措施,首先基于耦合欧拉—拉格朗日(CEL)定量分析了传统纺锤形桩靴与新型桩靴在不同工况条件下插桩时桩靴地基土体相互作用机制,明确了最不利桩靴踩脚印工况时的插桩偏心距与桩坑深度。基于该最不利工况条件,对比分析了新型六孔莲蓬形桩靴、试踩法与地基钻孔法3种桩靴踩脚印应对措施的适用性与有效性。结果表明,相较于传统纺锤形桩靴,采用六孔莲蓬形桩靴使桩靴倾斜角与桩腿偏移距分别降低了33.13%和48.26%,说明结构在位稳定性更高。此外,通过对比分析得出,采用最佳设置方式进行试踩与钻孔处理后再进行桩靴贯入时,桩靴受到的水平滑动力峰值与桩腿RP1处弯矩峰值相较于未处理时分别降低了29.47%、29.17%、34.7%、37.7%。可见,3种应对措施均能有效降低桩靴踩脚印后产生的不利影响,提高桩靴结构的在位稳定性。以最终减小不利附加响应程度作为评定标准：地基钻孔法>新型六孔莲蓬形桩靴>试踩法,由于地基钻孔法与试踩法均需增设额外机械设备及施工工序,大幅提高了工程造价,因此,在实际工程中,需要根据实际情况恰当选择应对措施。研究成果可为实际工程中应对桩靴踩脚印工况响应提供一定参考与借鉴。 相似文献
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自升式平台作业前需对桩靴基础进行预压安装,使桩靴具备抵抗竖向-水平-弯矩复合荷载的能力。安装过程中,桩靴上部将形成一定深度的孔洞。弱超固结黏土地基中,土体强度较高,桩靴最终贯入深度较浅,而形成的上部孔洞较深,因此孔洞将对桩靴就位后的承载力产生影响。通过有限元分析,研究弱超固结黏土中桩靴上部孔洞对承载力的影响,结果表明:1)与无孔洞的情况相比,孔洞的存在对桩靴的单向和复合承载力有削弱作用; 2)当桩靴与孔洞底部距离大于桩靴直径时,承载力不再受上部孔洞的影响; 3)当桩靴埋深小于等于0.75倍桩靴直径时,无论桩靴上部有无孔洞,现有预测公式都不能较为合理地预测弱超固结黏土地基的复合承载力,为此提出了考虑孔洞影响的桩靴复合承载力包络面预测公式。 相似文献
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复杂土层中自升式平台桩靴安装穿刺预测 总被引：1，自引：1，他引：0
由于复杂海洋工程地质条件的普遍性,自升式平台在安装过程中穿刺事故频发,近年来涌现出大量针对自升式平台桩靴基础在复杂土层中穿刺预测方法的研究。为了方便工程设计人员的理解和使用,首先简单介绍这些研究中所采用的技术手段,总结现行规范ISO 19905-1建议的桩靴在复杂土层中贯入阻力的预测方法以及最新文献中提出的新的设计方法,并对规范方法和新方法的优缺点进行了评价。所总结的设计方法针对国内外常见的含穿刺风险的海洋地基形式,包括双层"砂—黏"、三层"硬—软—硬"黏性土、三层"软—硬—软"黏性土、三层"黏—砂—黏"地层以及四层"黏—砂—黏—硬层土"地层。通过对离心机模型试验的预测,对规范方法和新方法的预测精度进行了比较,对比结果显示新方法对桩靴穿刺破坏的预测更为合理精确。 相似文献
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Jack-up platforms of the Ocean engineering structures always withstand the vertical gravity loads which are applied to the seabed by spudcan, so it is important to determine the bearing capacity and the penetration depth of the spudcan for its geometry. In fact, it is up to the deformation law and the failure modes of soil surrounding the spudcan which can calculate the ultimate bearing capacity of the spudcan foundation on the soil seabed. By using the finite element analysis software Abaqus, the deformation law of soil around the spudcan is analyzed in detail, and the failure modes of soil surrounding the spudcan foundation are achieved. At the same time, based on the limit equilibrium theory, by use of static permissible slip-line field, the ultimate bearing capacity of the spudcan foundation is analyzed and the lower limit solution is derived theoretically, and the effect of the spudcan angle on the ultimate bearing capacity is investigated. The numerical results are compared with those obtained by the theoretical formulas deduced in this paper. On the basis of the lower limit solutions in this paper, the effect of the spudcan angle on the ultimate bearing capacity is revealed, and a practical bearing capacity formula is given to take the effect of the spudcan angle into consideration. 相似文献
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This paper conducts laboratory tests to investigate detailedly the soil deformation law around the pipeline and its penetration depth under self-gravity. The seabed model is prepared by consolidating saturated soil using vacuum pressure technology, and the pipeline models are specifically designed to possess different radii. Based on the experimental results and digital images, the soil deformation process is analyzed and summarized, a kinematic admissible velocity field is given and an upper bound solution of pipeline penetration depth and soil reaction force is derived and proposed in this paper. In order to verify the accuracy of the upper bound solution deduced in this paper,a comparison is made among some published results and the solution suggested in this paper, the comparison results confirm that the upper bound solution and the soil failure mode are reasonable. Finally two empirical formulas are given in this paper to estimate the soil reaction force of seabed and the penetration depth of pipeline. The empirical formulas are in agreement with the upper bound solution derived in this paper, and the conclusion of this paper could provide some theoretical reference for the further study of the interaction between the pipeline and the soil. 相似文献
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The mechanisms of soil structure interaction have drawn much attention in the past years in the installation and operation of jack-up platform. A bionic spudcan produced by biomimetic of egg and snail shell is proposed, and the performance of the penetration and extraction are analyzed by numerical method. The geometric contour of egg and snail shell is measured, and its mathematical model is established respectively. According to the structure of existing spudcan of jack-up platform, three kinds of typical biomimetic spudcan are designed. Furthermore, numerical analysis models of biomimetic spudcan are established respectively to study the soil structure interaction mechanism in the process of penetration and extraction, and contrastive analysis of resistance characteristics are carried out. To conclude, the results show that the biomimetic spudcan facilitates the platform installation, and it is also beneficial to the improvement of the bearing capacity of spudcan. 相似文献
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Undrained bearing capacity of spudcan under combined loading 总被引：1，自引：0，他引：1
The bearing capacities of spudcan foundation under pure vertical (V),horizontal (H),moment (M) loading and the combined loading are studied based on a series of three-dimensional finite element analysis.The effects of embedment ratio and soil non-homogeneity on the bearing capacity are investigated in detail.The capacities of spudcan under different pure loading are expressed in non-dimensional bearing capacity factors,which are compared with published results.Ultimate limit states under combined loading are presented by failure envelopes,which are expressed in terms of dimensionless and normalized form in three-dimensional load space.The comparison between the presented failure envelopes and available published numerical results reveals that the size and shape of failure envelopes are dependent on the embedment ratio and the non-homogeneity of the soil. 相似文献
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在海洋工程中,移动钻井平台在作业结束后需要转场时,经常会遇到拔桩困难的问题,桩靴底部的吸附力是上拔力的重要组成部分,明确其产生机理及发展规律对于上拔力计算与缓解上拔困难问题有重要意义。通过室内模型试验研究了黏土中桩靴底部真空度对桩靴吸附力产生机理的影响,试验结果表明,桩靴底部真空度的变化对上拔力的影响显著,而桩靴贯入深度和上拔速率会对真空度产生影响。当真空度达到峰值时,桩靴底部吸附力与上拔力几乎同时达到峰值,因此可以通过减小桩靴底部真空度的措施来减小上拔力。根据试验结果,提出了运用真空吸盘理论来计算桩靴底部吸附力的计算公式。所述吸附力计算方法与试验结果进行对比,其误差较小,对工程实践具有一定的参考意义。 相似文献
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This paper presents a finite element approach to calculate the full resistance profile of a spudcan deeply penetrating in dense sand overlying clay, in which a potential for an installing spudcan to experience a sudden uncontrolled punch-through failure exists. A modified Mohr-Coulomb model characterized by incorporating a four-phase variation of the mobilized strength and dilation parameters with an equivalent accumulated plastic strain is developed and tested for the overlying dense silica sand. An extended Tresca model is used for the strain softening of the underlying clay. A series of large deformation finite-element (LDFE) analyses are carried out, varying the strength and dilation parameters as well as the spudcan geometries. A fairly good performance of the present approach is verified by validating against groups of centrifuge tests data, allowing the numerical study to be extended parametrically. The four-phase variation of the mobilized strength and dilation parameters involved in the progressive failure of the upper dense sand is parametrically studied and extended to cover the range of sand relative densities that are of practical interest. Additionally, comparisons with the typical existing LDFE analyses using both simple and sophisticated constitutive models are carried out. It shows that the present approach performs fairly well to calculate the full resistance profile of a spudcan deeply penetration in both thin and thick dense sand overlying clay, especially the peak and post-peak resistance, within around 5% of the corresponding centrifuge tests results. 相似文献
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采用CEL大变形非线性有限元方法并结合非线性地基梁模型对海洋石油941钻井船在番禺10-2平台钻井插桩时对邻近导管架平台群桩的影响进行了分析,并得到以下结论:1)钻井船插桩过程中,桩身最大位移及出现的位置随钻井船插桩深度增加而下移且钻井船插桩位置与群桩距离越近,对桩的影响越大;2)在插桩过程中,桩身最大弯矩出现的位置与桩身最大位移出现的位置一致,而桩身最大剪力出现的位置较桩身最大弯矩出现的位置偏下;3)与没有插桩影响的群桩相比,桩身最大弯矩与桩身最大剪力明显增加。 相似文献
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Study on Failure Mechanism and Bearing Capacity of Three-Dimensional Rectangular Footing Subjected to Combined Loading 总被引：2，自引：0，他引：2
This paper presents two kinematic failure mechanisms of threc-dimensional rectangular footing resting on homogeneous undrained clay foundation under uniaxial vertical loading and uniaxial moment loading. The failure mechanism under vertical loading comprises a plane strain Prandti-type mechanism over the central part of the longer side, and the size of the mechanism gradually reduces at the ends of the longer side and over the shorter side as the corner of rectangular footing is being approached where the direction of soil motion remains normal to each corresponding side respectively. The failure mechanism under moment loading comprises a plane strain scoop sliding mechanism over the central part of the longer side, and the radius of scoop sliding mechanism increases linearly at the ends of the longer side. On the basis of the kinematic failure mechanisms mentioned above, the vertical ultimate bearing capacity and the ultimate bearing capacity against moment or moment ultimate bearing capacity are obtained by use of upper bound limit analysis theory. At the same time, numerical analysis results, Skempton＇ s results and Salgado et al. ＇s results are compared with this upper bound solution. It shows that the presented failure mechanisms and plastic limit analysis predictions are validated. In order to investigate the behaviors of undrained clay foundation beneath the rectangular footing subjected to the combined loadings, numerical analysis is adopted by virtue of the general-purpose FEM software ABAQUS, where the clay is assumed to obey the Mohr-Coulomb yielding criterion. The failure envelope and the ultimate bearing capacity are achieved by the numerical analysis results with the varying aspect ratios from length L to breadth B of the rectangular footing. The failure mechanisms of rectangular footing which are subjected to the combined vertical loading V and horizontal loading H （Vertical loading V and moment loading M, and horizontal loading H and moment loading M respectively are observed in the finite e 相似文献