福州江滨地区超高层建筑灌注桩成孔工艺分析          下载免费PDF全文

张志刚 《探矿工程》2017,44(6):84-87

以福州江滨地区2个有代表性的超高层建筑桩基础工程实例为依据,通过无卡式冲击 正循环,旋挖 气举反循环,回转 泵吸反循环3种成孔工艺之间的比对,提出了在福州市江滨地区超大粒径厚层卵石与花岗岩地层灌注桩施工成孔工艺方面的一些见解,认为回转 泵吸反循环是较为可靠的工艺。  相似文献   

Behavior of drag anchor in clay with linearly increasing shear strength under unidirectional and combined loading     

《Applied Ocean Research》2017

Drag anchor is a widely used economical anchor option for offshore floating structures. The anchor behavior under unidirectional loading and combined loading is important for anchor selection. The anchor behavior under combined loading, characterized by the yield envelope, can also be used for the prediction of anchor installation, which is still an issue in anchor design. However, most existing studies on anchor capacity are for plate anchors which focused only on the anchor pullout capacity in soil with uniform shear strength. The behavior of drag anchor under unidirectional and combined loading in soil with linearly increasing shear strength profile is seldom investigated. The current 2D finite element studies investigate the anchor behavior for a horizontal anchor fluke in clay with linearly increasing shear strength under unidirectional vertical, horizontal and rotational loadings first. Then based on the results of anchor unidirectional loading behavior, the yield envelopes for anchor under combined loading for both shallow and deep embedded flukes are studied. The effect of anchor embedment depth, soil non- homogeneity, soil overburden pressure and the soil/anchor interface breakaway conditions are studied to provide insight for drag anchor design.  相似文献   

Toward a quick evaluation of the performance of gravity installed anchors in clay: Penetration and keying     

《Applied Ocean Research》2017

Gravity installed anchors (GIAs) are the most recent generation of anchoring solutions to moor floating facilities for deepwater oil and gas developments. Challenges associated with GIAs include predicting the initial embedment depth and evaluating the keying performance of the anchor. The former involves high soil strain rate due to large anchor penetration velocity, while the later influences the subsequent behavior and pullout capacity of the anchor. With the coupled Eulerian–Lagrangian method, three-dimensional large deformation finite element models are established to investigate the penetration and keying of GIAs in non-homogeneous clay. In the penetration model, a modified Tresca soil model is adopted to allow the effects of soil strain rate and strain softening, and user-defined hydrodynamic drag force and frictional resistance are introduced via concentrated forces. In the keying model, the anchor line effects are incorporated through a chain equation, and the keying, diving and pulling out behaviors of the anchor can all be replicated. Parametric studies are undertaken at first to quantify the effects of various factors on the performance of GIAs, especially on the penetration and keying behaviors. Based on the results of parametric studies, fitted formulae are proposed to give a quick evaluation of the anchor embedment depth after the installation, and the shackle horizontal displacement, shackle embedment loss and anchor inclination at the end of the keying. Comparative studies are also performed to verify the effectiveness of the fitted formulae.  相似文献   

Model tests on installation and extraction of suction caissons in dense sand     

Yukun Zhang  Yufeng Gao 《Marine Georesources & Geotechnology》2017,35(7):921-929

A series of model tests were performed on steel- and Perspex-made suction caissons in saturated dense marine sand to explore installation and extraction behaviors. The extractions of the caisson were conducted by applying monotonic loading or by pumping water into the caisson. Responses of suction caissons to pullout rates, aspect ratios, and extraction manners were examined. Test results show that a cone-shaped subsidence region occurs around the suction caisson during the suction-assisted installation. The pullout bearing capacity of the suction caisson in sand is dominated by the loading rate and the loading manner. For the suction caisson subjected to monotonic loading, the maximum bearing capacity is reached at the pullout rate of about 20.0?mm/s. The mobilized vertical displacement corresponding to the pullout capacity increases with increasing the pullout rate. The passive suction beneath the suction caisson lid reaches the maximum value when the pullout bearing capacity is mobilized. In addition, during the suction caisson extracted by pumping water into the caisson, the maximum pore water pressure in the caisson is obtained under the displacement of approximately 0.04 times the caisson diameter. The absolute values of the maximum pore water pressures for the suction caissons approximately equal those of the maximum vertical resistances at the monotonic pullout rate of 5 mm/s. When the vertical displacements of the suction caissons with the aspect ratio of 1.0 and 2.0 reach 0.92 and 1.77 times the caisson diameter, respectively, the seepage failure occurs around the caissons. Using a scaling method, the test results can be used to predict the time length required for the prototype suction caisson to be extracted from the seabed.  相似文献   

Evaluation of pullout load capacity of suction caissons in sand using a three-dimensional displacement approach     

Hiroyoshi Hirai 《Marine Georesources & Geotechnology》2017,35(8):1121-1134

An investigation was conducted to obtain analytical solutions for the pullout behavior of a suction caisson undergoing inclined loads in sand. The inclined load is transformed into an equivalent load system in which the vertical, horizontal, and moment loads are applied on the center of the lid of the suction caisson. The vertical and lateral stiffness coefficients along the skirt of the suction caisson in sands are presented using the new three-dimensional elastic solutions taking into account the nonhomogeneous and nonlinear properties of the sand. The vertical, lateral, and rocking stiffness coefficients on the base of the suction caisson are presented considering the solutions of a hollow rigid cylindrical punch acting on the surface of a soil. The yield, pullout, and failure for sands with the nonhomogeneous and nonlinear characteristics are taken into consideration. The effects of the load inclination, the loading depth, and the aspect ratio on the pullout load capacity of the suction caisson are presented. Behaviour of the suction caisson in sand prior to failure is clarified from the relationship between tensile load, displacement, and rotation and that between depth, vertical pressure, and lateral pressure.  相似文献   

基于有限差分原理的预应力锚索抗滑桩改进计算方法     

吴润泽  周海清  胡源  钟一洋  李鹏举  杨玖宏 《岩土力学》2015,36(6):1791-1800

针对现有预应力锚索抗滑桩计算模型及其相应计算理论存在的问题,基于有限差分法的原理,提出了改进的锚索桩计算模型并进行了详细的理论推导。根据实际的施工和受力过程,该模型包括预应力施加和滑坡推力作用两个阶段,通过滑坡推力分布形式的改进和桩锚协调变形方程的修正来真实反映预应力锚索抗滑桩的主动式受力特点。同时利用Matlab编制成相应的计算程序进行算例验证,并同目前普遍采用的计算理论进行对比分析。结果表明,该改进计算方法及其相应的计算程序充分考虑了预应力施加这一锚索桩特有的过程所带来的影响,且在计算中不必将锚索拉力等效为在桩顶处施加的剪力和弯矩。另外还可对桩前滑面以上存在任意厚度滑体和任意复杂地基条件的情况进行合理地设计计算,相对于目前已有的计算理论,该改进方法更加合理、可靠。  相似文献   

预应力锚杆对岩体板裂化的控制机制研究     

周辉  徐荣超  张传庆  卢景景  孟凡震  沈峥 《岩土力学》2015,36(8):2129-2136

为探究预应力锚杆对岩体板裂化破坏的控制机制,首先进行了岩体板裂化破坏的室内物理模型试验,并运用FLAC数值模拟技术,模拟了平面应变状态下板裂化破坏的形成过程;在此基础上,通过3种不同的预应力锚杆施加方案,进行预应力锚杆对岩体板裂化破坏控制机制的数值试验。研究结果表明：预应力锚杆的作用削弱了裂隙尖端应力集中现象,有效地抑制了岩体内裂隙的扩展与贯通、板裂化破坏的形成;作用在板裂区边界的预应力锚杆,不仅能够抑制板裂化破坏的形成,而且能在一定程度上控制板裂化破坏的范围;作用在板裂破坏区内的预应力锚杆,可有效限制板裂岩体向临空面的位移,体现出提高板裂岩体整体变形刚度的作用。研究结果对认识深埋隧洞围岩板裂化破坏的形成机制、板裂化破坏的合理支护控制以及岩爆防治具有重要指导价值。  相似文献   

让压锚索在边坡支护中的应用试验研究及摩阻力问题的探讨     

汪波  徐建强  吴正恺  朱安龙  王勇 《岩土力学》2014,35(12):3370-3376

为研究让压锚索在边坡支护中的自身让压特性,获取让压实测资料,以江西洪屏电站高边坡为工程背景,结合图强工程材料有限公司研发的新型让压锚索,针对不同锚索长度、自由段长度等各种工况进行了现场试验,试验表明：在让压锚索张拉过程中,部分锚索出现了让压滑移现象,让压效果显著;但让压时,长锚索孔口张拉力与设计基础让压力相差很大,说明锚索孔口张拉力并未如理想状态那样全部传递给锚孔内部的锚索,而是很大一部分孔口拉力将用来克服锚索与锚孔之间的摩阻力,且量值上已达到不容忽视的程度。试验同时揭示了锚索长度、锚固长度、锚束及锚孔施工质量对摩阻力的大小起到关键性影响,锚索长度、自由段长度越长、锚束越多、锚孔质量越差,则摩阻力越大。并据此提出了未来边坡防护锚索设计中重点关注及有待于进一步研究的内容。  相似文献   

非连续变形岩石断裂分析中的一种全长剪切锚杆     

陈云娟  李术才  朱维申  王文  王旌 《岩土力学》2014,35(1):293-297

锚杆从锚固方式上可划分两种：端部锚固方式和全长锚固方式。全长锚固锚杆作为工程支护中的一种重要锚杆类型,具有广泛的应用前景。非连续变形分析（DDA）以及在此基础上发展的非连续变形的岩石断裂分析（DDARF）方法中锚杆为端锚形式,且只考虑了锚杆的轴向作用,而忽略了锚杆作用力对锚固岩体的侧向限制。为了更好地理解锚杆的支护机制,考虑锚杆的剪切作用,提出了DDARF中一种新的锚固形式--全长剪切锚杆支护形式。用改进的全长剪切锚杆支护方法对一公路隧道稳定性进行了分析,并与端锚支护形式进行了对比,结果表明,提出的全长剪切锚杆支护方法是有效的,锚固效果比端锚支护更好。  相似文献   

考虑吸力变化的非饱和高液限黏土-土工织物界面剪切特性研究     

刘毓氚  陈志福 《岩土力学》2014,35(6):1585-1592

以高液限土为填料的加筋挡墙广泛在南方地区应用,加筋挡墙土体吸力经常随气候变化而发生变化,直接影响筋土界面强度特性,考虑吸力变化的非饱和高液限黏土-土工织物界面强度特性亟待深入研究。利用ZFY-1A型非饱和土应变控制式直剪仪对非饱和高液限黏土-土工织物界面进行控制吸力的剪切试验,探讨吸力循环变化（干湿循环）对筋-土界面剪切特性的影响。研究表明,高液限黏土-土工织物界面的抗剪强度随着净法向应力的增加而增大;随着循环次数的增加,界面强度呈现先升高而后衰减的变化规律。经历3次干湿循环的界面强度低于未经历干湿循环的强度。随着循环次数的增加,界面强度总体上呈降低趋势。吸力增加的速率 随吸力循环次数的增加先增大后减小,有效界面摩擦角 、界面有效黏聚力 、界面综合摩擦系数 、综合摩擦系数比K与此类似。 含水率变化量的最大值随着净法向应力、循环次数的增加而增大。最大剪胀量 随循环次数的增加先增大后减小,随净法向应力的增大而减小。最后通过对数拟合,得出经历若干次基质吸力循环后的界面强度计算公式。  相似文献