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现浇混凝土大直径管桩(简称PCC桩)由于具有较大的内、外壁摩阻力,在竖向荷载作用下表现出与一般实心桩不同的静、动力特性。采用建立的解析公式,对PCC桩、等截面积实心桩和等外直径实心桩3种桩的动力响应进行了对比分析,研究结果表明,当桩端阻力相对较小时,3种模型位移幅值差别不大;当桩端阻力较大时,3种模型幅频曲线和相频曲线存在较大差别;等面积实心桩位移幅值比PCC桩稍大,而等外直径实心桩的位移幅值比PCC桩稍小;位移相频曲线呈现等间距的震荡,实心桩的震荡峰值比PCC桩要高,且震荡峰值对应的频率各不相同,PCC桩出现震荡峰值的频率比实心桩小;3种计算模型动刚度震荡幅值差别较大,等直径实心桩的动刚度最大,等面积实心桩次之,PCC桩最小;等直径实心桩的虚部最大,PCC桩次之,等面积实心桩最小,振动过程中等直径实心桩桩顶阻尼最大;等面积实心桩的速度导纳最大,PCC桩次之,等直径实心桩最小。PCC桩充分发挥了单方混凝土的性能,比等截面实心桩具有更小的动力响应,比等外径实心桩更节省混凝土。 相似文献
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为探讨海上风机在风、浪等水平往复循环荷载下大直径单桩基础的循环弱化特性,设计了稳定输出长期循环荷载的机械加载装置,开展了软黏土中长期水平循环荷载下海上风电大直径单桩基础和传统长桩基础的模型试验对比研究。根据API给出的骨干曲线和Masing二倍准则构建循环荷载下的p-y（荷载-位移）曲线,并借鉴前人工作,采用累积塑性应变描述软黏土的不排水抗剪强度弱化,提出了分析大周数水平循环荷载下单桩基础循环弱化的理论方法。该方法将循环荷载次数、幅值等外界条件与桩周土体的循环弱化特性建立联系,以适应海洋环境复杂多变的水平循环荷载形式。通过模型试验和理论研究认为,大直径单桩基础因刚度较大,在同样的水平力循环荷载条件下,其抵抗循环荷载的能力明显优于传统长桩。在海上风机大直径单桩的设计中采用基于黏土残余强度的循环后稳定水平承载力更为合理。 相似文献
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基于郑州三环快速路工程开展的6个场地19根大直径灌注桩现场足尺试验,通过对比分析后注浆桩与未注浆桩实测结果,研究桩端后注浆对大直径灌注桩承载变形性状、荷载传递规律、桩端承载特性及桩侧摩阻力发挥性状的影响。结果表明,桩端后注浆条件下大直径灌注桩承载变形性能明显提高,且提高幅度受注浆龄期影响较为显著;在黄河中下游以中密～密实粉土、粉细砂及可塑～硬塑粉质黏土为主要冲积地层中桩长40 m左右的大直径灌注桩表现为摩擦型桩,但相比于未注浆桩,桩端后注浆桩传递至桩身下部及桩端的荷载更小;桩端后注浆在桩端下形成水泥沉渣坚硬固结体,有效地处理了桩端沉渣问题,且通过渗透劈裂作用,形成深度可达1 m的网状分布的水泥胶结体,加之对桩端土层的压密效应,显著提高了桩端支承性能与承载刚度;桩端后注浆显著提高大直径灌注桩桩侧极限摩阻力发挥水平,并降低了桩侧极限摩阻力对应的桩土相对位移,使得大直径灌注桩在较小的沉降下表现出较高的承载能力。 相似文献
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Abstract Papadopulos and Cooper's (PC) solution can be used to describe the drawdown resulting from pumping with a constant rate at a large-diameter well. However, this solution is too complicated to be accurately evaluated due to the oscillatory nature of the Bessel functions. The PC approach resulted in tabulated values of dimensionless drawdown at the well with an accuracy of four or fewer digits for selected values of dimensionless storage coefficient versus dimensionless time. Some researchers have fitted the tabulated values with interpolation formulas that are easy to use in engineering applications. Those formulas may be more accurate if the tabulated values are computed with greater accuracy. In this study, we propose an efficient numerical procedure, including a root search scheme, to find the roots of the integrand, Gaussian quadrature for numerical integration, and Shanks transform to accelerate convergence of infinite series. The proposed procedure can evaluate the dimensionless drawdown with greater accuracy and is useful in practice if there is a need for high accuracy for the observation either at the well or in the aquifer at some distance from the pumping well Editor D. Koutsoyiannis Citation Chang, Y.C., Yeh, H.D., and Wang, C.T., 2013. Improvement on the estimation of constant-rate drawdown in large-diameter wells. Hydrological Sciences Journal, 58 (3), 716–727. 相似文献
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大直径钢管桩土塞效应的判断和沉桩过程分析 总被引：5，自引：0，他引：5
港口工程和海洋工程中出现了越来越多的大直径超长钢管桩。由于这种桩直径较大,土塞的形成对桩的可打入性和承载力有较大的影响。鉴于此,根据大直径和超大直径钢管桩土塞性状的特殊性,考虑了桩直径对侧壁摩阻力、端阻力的影响,引入了尺寸效应系数,重新建立了土塞微分体的静力平衡方程,提出了采用改进的静力平衡法进行土塞效应判断,同时采用波动方程法近似模拟土塞与桩管内壁的相互作用,建立了简化的土塞与桩壁相互作用模型,并用该方法进行实际工程的打桩分析,分析结果表明该方法对土塞效应的判断、打桩过程的预测等与工程实测数据吻合较好。 相似文献
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Stability Analysis of Aquatic-Sand Pile Composite Foundation Reinforcing for New Shore-Connecting Structure 总被引：1，自引：0，他引：1
The Yangshan deepwater port is the only container port built in the islands off the mainland of China. Batter piles with a sheet-pile-supported platform bulkhead structure were first used as a new shore-connecting structure to connect the front main wharf structure and the back land. Large-diameter sand columns were also used to reinforce the soft foundation of the shore-connecting structure in the deep water of the open sea. A 3D nonlinear FEM model based on real geological conditions was built to optimize the large-diameter sand columns’ reinforcing scheme and investigate shore-connecting structures’ mechanical properties under different construction conditions. The replacement ratio of 30%, the bottom elevation of the fourth soil layer, and the soft soil just below and directly adjacent to the shore-connecting structure were determined as optimal replacement ratio, reinforcing depths, and reinforcing area of the large-diameter sand columns reinforcement by assessing the force and deformation of the shore-connecting structure. By numerical computing, the maximum displacement of the supported platform was 11.03 cm, which was close to the measured value; and the piles’ maximum stress, displacement and moments were all smaller than the design strength. These indicated that the shore-connecting structure could remain stable by an optimal sand columns reinforcing scheme. 相似文献
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Zhou Xireng Duan Xudong Sang Xuezhu Zhang Rui Dai Jialu Professor Tianjin University Tianjin
Engineer Xiamen Port Office Fujian
Lecturer Tianjin University Tianjin
Senior Engineer Tianjin Port Office Tianjin 《中国海洋工程》1992,(2)
A method of coupled BEM-FEM analysis for the elastic spatial structure system is presented. It can be applied to the calculation of the stress and deformation of the large-diamater cylinder structure system and it is suitable for symmetric or non-symmetric structures under the distributed or concentrated load. Numerical examples show that the proposed method and computer program BEFEM are quite efficient in the analysis of the large-diameter cylinder structure problems in ocean engineering. 相似文献
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大口径页岩气地质调查井（川沐地2井）部署在四川盆地西南缘五指山—天宫堂构造带建全—龙华复向斜的核部,设计井深2500 m,完钻井深2406.00 m。钻探目的是主探须家河组陆相页岩气,兼探雷口坡组常规气。本文介绍了川沐地2井的钻探施工情况,针对侏罗系易垮塌的泥岩和三叠系可钻性差的砂岩,开展了高效提速复合钻进、复杂地层钻井液、下套管固井工艺等应用研究,解决了垮塌段下套管固井难题,提高了钻探效率,建成了一口可供地层含气性测试的合格井,获取了岩心等实物资料,查明了该井区的地层层序,在三叠系须家河组—雷口坡组钻遇37层油气显示,实现了钻探目的及油气发现,为页岩气地质调查评价奠定了基础,对巩固乌蒙山区脱贫攻坚成果具有重要意义。 相似文献
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本文以工程实例，论述了中埋深高承压岩溶水的勘探及大口径井开发的技术问题，与同行共同切磋。 相似文献