砂井地基沉降的二维有限元分析(一)--三维问题转换为二维平面应变问题

砂井地基严格地说是一个三维问题，需要用三维有限元来分析。本文作者考虑了砂井地基的井阻和涂抹区效应，建立了轴对称砂井和平面砂墙之间渗透系数以及几何尺寸的等效关系式，使三维问题的砂井地基转化为二维问题来处理，以减少三维问题很大的计算工作量。     

海堤工程砂井排水固结变形分析

对采用砂井地基处理的深厚软基上泉港峰尾海堤工程试验段施工过程进行了监测。应用Biot固结理论的平面有限元方法,将砂井地基的三维问题转化为平面二维问题,对该工程砂井地基固结沉降、孔隙水压力进行分析与预估。计算结果与实际监测数据进行对比,有较高的吻合度。该方法能较好地反应地基的沉降过程和固结特性,评价软基处理方法的效果,并...     

堆载预压下砂井地基固结有限元分析

采用砂井地基平面应变等效方法,结合ABAQUS软件对堆载预压下地基的侧向位移、沉降及孔压分布进行有限元模拟,并分析计算值与实测值之间的差异;计算结果能很好地预测砂井地基位移与孔压的变化,可为地基处理的设计提供参考。     

天然地基大型油罐沉降有限元数值分析

依托广西石化1 000万吨/年炼油项目为代表的三项工程实践,建立天然地基大型油罐沉降的二维有限元模型,分析了油罐沉降。此外,根据实际监测结果,调整二维平面模型,通过反演给出合适的岩土层参数。三项工程计算结果表明:二维数值方法适用于天然地基大型油罐沉降分析,其计算结果稍大于实际监测结果,可保证设计安全;油罐沉降是一个长期的过程,需加强后期监测与控制。     

塑料排水板等效排水直径有限元计算

利用ABAQUS有限元软件对砂井地基的固结进行了模拟分析,并与谢康和砂井地基固结解析解进行了对比,在此基础上建立了塑料排水板地基固结三维有限元模型,通过有限元模型计算得到的平均固结度—时间关系曲线反算排水板等效排水直径,结果表明计算所得等效排水直径与Hansbo（1979年）公式计算结果比较接近。     

真空排水预压法加固软土地基的沉降计算

分析了单向分层层和法用于计算砂井真空排水预压地基沉降存在的问题，并提出了相应的修正方法。     

有限元方法在基础沉降计算中的应用及实例

用有限元方法和理论模型,研究高层及多层建筑的天然地基沉降计算值与分层总和法及实际沉降值的差别。《建筑地基基础规范》(GB50007—2002)推荐使用分层总和法计算地基沉降,并用沉降计算经验系数加以修正,取得较好的结果。用有限元方法计算的地基沉降值与分层总和法的结果比较,能够取得同样良好的结果。有限元方法更适合计算机使用,能得到复杂条件下地基沉降计算值以及地基土的实际应力分布。     

真空预压法有限元计算比较

 按照固结度等效的原则,提出将单井涂抹效应对涂抹区内土体渗透性的弱化作用转化为减小单井影响区内土体水平向渗透系数的方法,并讨论单元尺寸对固结度的影响。该计算方法既可减少前处理工作量,又可考虑涂抹效应。结合广州南沙港一真空预压工程,建立三维模型进行有限元计算分析,并通过实测资料和目前常用的平面应变简化方法对计算值进行比较和讨论。研究结果表明,J. C. Chai方法将砂井地基转换为均质地基,所得结果偏保守,而“砂墙”等效方法通过砂井间距来调整渗透系数,会使计算结果偏大,三维有限元法比平面应变方法更能反映砂井地基的固结变形。     

爆炸挤淤置换法筑堤沉降的有限元分析

利用室内试验获得的模型参数结合有限元计算,对深厚淤泥质软基处理建成后的海堤短期和长期沉降问题开展了计算分析。对抛石填料和地基土分别采用莫尔-库伦模型和修正剑桥模型,在地应力平衡的基础上,实施抛石堆载,堆载完成后,开展了工后10年的沉降分析。分析表明,抛石体堆载后,地基土地应力急剧增加,海堤两侧土体向上隆起,下部土体沉降;海堤建成后的621.2天累计沉降达1.2m,孔隙水压仍未消散;建成10年后,海堤累计沉降达1.55m;表明海堤建成后的短期和长期沉降均较大,对重大海堤工程,工后的沉降研究与控制显得必要。     

基于理正岩土软件和Plaxis在某工程实例沉降计算的对比

目前地基处理经常涉及沉降计算问题。地基沉降计算理论分析方法分为理论公式法和数值分析法,理正岩土可以得到二维解析解,而Plaxis软件可以得到二维有限元数值解。应用理正岩土和Plaxis软件对一项地基处理后实例工程的沉降计算结果进行对比,相互验证。     

真空-堆载联合预压加固软基简化计算方法

在深入了解真空预压机理和砂井地基固结理论的基础上 ,根据固结度等效的原则 ,推导了与单井固结理论等效的成层均质地基等效渗透系数 ,从而将复杂砂井地基转化为无砂井成层地基 ,以达到简化计算的目的 ,并结合真空-堆载联合预压的加固特点 ,提出一种简化的真空-堆载联合预压法的有限元计算方法 ,并结合工程实例对简化方法的可靠性进行了研究 ,通过与实测资料和常规砂井地基有限元计算值对比 ,表明该简化方法具有较高的准确性 ,可方便地应用于工程设计和实践。     

Nonlinear consolidation analysis of soft soil with vertical drains considering well resistance and smear effect under cyclic loadings

In this paper, the nonlinear consolidation behavior of soft soil with vertical drains considering well resistance and smear effect under cyclic loadings was investigated. Using the variables separation method, a series of analytical solutions were derived to calculate the excess pore water pressure and the average degree of consolidation of the soil subjected to various cyclic loadings including trapezoidal cyclic loading, rectangular cyclic loading, triangular cyclic loading and haversine cyclic loading. The correctness of the proposed solutions was verified through degenerating into the existing solutions. Finally, the effects of different parameters on the nonlinear consolidation behavior of soil with vertical drains under cyclic loadings were analyzed.     

真空和堆载作用了砂井地基固结的边界元分析

边界元法是70年代发展起来的一种新的数值计算方法。本文把边界元法应用于求解真空压力和堆载压力作用下的软粘土砂井地基固结变形的平面应变问题。笔者在文中推导了线性比奥固结理论的边界积分方程,并结合天津新港软土地基的真空预压袋装砂井加固工程就真空预压和堆载预压两种情况进行了计算对比分析;对于砂井地基和无砂井地基的预压效果问题也进行了相应的计算;在文中还把边界元、有限元及差分的计算结果与实测值做了对比。     

均质未贯穿竖井地基粘弹性固结分析

针对均质深厚软土地基竖井未打穿情况,采用Merchant流变模型,将现有未贯穿竖井地基线弹性固结理论进行了推广,推导了竖井未打穿均质地基的粘弹性固结解析解。该解考虑了涂抹和井阻作用以及竖井打设区和下卧层的相互影响。将解答编制成应用程序,用该程序分析了一竖井未打穿均质地基。分析表明,土体粘滞性对前期固结几乎没有影响,但后期固结度明显降低。土体粘滞性对下卧层的影响程度大于对竖井打设区的影响程度。     

Numerical Analyses on Consolidation of Clayey Ground Improved by Vertical Drain System Based on 3-D Elasto-Viscous Model

This paper addresses a proposal on the three-dimensional elasto-viscous consolidation theory and discusses on its applicability. In order to predict the three-dimensional consolidation behavior of clayey ground improved by vertical drain system, one-dimensional consolidation theory based on an elasto-viscous liquid model proposed by Yoshikuni et al. (1994), which can express secondary consolidation without considering any distinction between normally consolidated and overconsolidated regions, is extended to three-dimensional condition. This theory is applied to the consolidation of a hollow cylindrical body that models a clayey ground improved by a vertical drain system. Then, a rigorous solution of elastic consolidation theory, a FEM solution based on elasto-plastic theory and a FDM solution using three-dimensional elasto-viscous theory are compared with the test results obtained using the three-dimensional consolidation test apparatus developed by the authors (Baek and Moriwaki, 2004). Based on the results of analyses, it is evident that the three-dimensional consolidation theory proposed by authors could simulate the consolidation behavior of clayey ground improved by vertical drains, such as the secondary consolidation and the radial displacement during the three-dimensional consolidation process.     

公路软基蠕变—固结耦合有限元分析

软土的蠕变特性常常导致路堤出现沉降过大、甚至失稳等现象。本文采用同时考虑蠕变和固结效应的修正的广义Kelvin蠕变—固结模型,对公路软基的时效性变形进行了有限元分析。在某软基上路堤填筑工程的变形分析中,该方法的计算结果和监测数据基本吻合,由此验证了该模型的有效性。本文针对该工程进行了一系列的参数分析,讨论了软土的蠕变效应、塑料排水板布置方式和堆载速率等因素对该路堤变形发展和路堤稳定性的影响。     

塑料排水板处理软土地基的离心模型试验研究

采用大型土工离心机对某海上机场工程近海软土地基上堤坝施工期及运行期进行了模拟。原型中采用塑料排水板固结法处理软土地基,模型中则根据固结过程相似的原理,换算成等效圆截面排水体,在模型制作中采用等效透水滤芯来模拟。试验中采用停机加载法模拟分级施工加载过程。根据激光位移传感器试验数据可以计算得出相应原型软土地基的沉降特性。利用试验得到的沉降曲线,采用"经验双曲线法"推算出了地基最终沉降,然后得出按沉降推算的分层地基平均固结度随时间的变化。对比沉降推算的运行5 a时软土地基固结度和理论计算结果,二者基本接近,表明文中塑料排水板的模拟方法用于离心模型试验是可行的。通过与理论计算结果比较,表明试验采用的塑料排水板模拟方法是可行的。     

An observational method for consolidation analysis of the PVD-improved subsoil

Surcharge preloading together with prefabricated vertical drains (PVDs) have been widely used to improve properties of thick clay deposits. To assess the performance of soil improvement works, the average degree of consolidation needs to be estimated. A curve fitting formula is proposed in this paper to simulate the degree of consolidation versus a non-dimensional time factor relationship. The proposed formula fits the theoretical consolidation solutions well with a regression coefficient R² larger than 0.9996 and an error of less than 1.2%. Based on the formula, a modified Asaoka's observational method is proposed to predict the ultimate settlement and calculate the coefficient of consolidation using field settlement monitoring data. The effectiveness of the proposed observational method has been verified using some well-documented case histories. Comparisons between the proposed method and the Asaoka's method indicate that the proposed method will give a less than 1.0% higher ultimate settlement than that by the Asaoka's method and the proposed method is able to predict the c_h value with the consideration of both vertical and horizontal flow through the ratio of time factor in horizontal and vertical direction ν_hv.     

Prefabricated and electrical vertical drains for consolidation of soft clay

The use of prefabricated vertical drains to consolidate soft clay is a common ground improvement method. In large projects laboratory testing of PVDs for selection and quality assurance is considered important. This paper presents a review of PVD laboratory testing. The need to provide simulated site conditions in the test is emphasized. In addition instrumented PVDs show that installation stresses in deep soft clay deposits could cause filter rupture under tensile failure. It is also shown that the maximum required discharge capacity of a PVD is obtained by equating the flow rate of the PVD under the installation and consolidation states to the maximum rate of volume reduction of the influential clay cylinder of the PVD. Consolidation can be enhanced much faster in clay soils if vertical drains manufactured with conducting polymer are used. Some laboratory tests, field tests and field applications of such electric vertical drains (EVD) are presented. A minimum current density at appropriate applied voltage is required to benefit from the electric osmosis (EO) application. EVD in dewatering clay soils, extracting heavy metals in clay soils and few other geotechnical applications are also presented.