试论市政公路工程软土路基施工技术

介绍了市政道路软土路基的特性,分析了软土路基施工中的不足之处,并从排水固结技术、砂垫层法、添加剂法、真空预压技术四方面,阐述了软土路基常用的施工方式,有利于提高市政道路软土路基的施工水平。     

用真空加固软土地基的机制与计算方法

本文结合用真空加固软土地基的实际工程问题,通过固结模型分析了真空对软基的作用机制,明确了土体在负压作用下发生的排水-变形过程与在正压荷载作用下的固结过程是相似的,都是通过孔隙水应力的变化将外荷载传递给土骨架的过程;二者的区别在于孔隙水应力的初始条件与边界条件不同,因此也可以用固结理论进行设计计算。在三轴仪中进行的上样在负压作用下的固结试验验证了这一结论。在计算方法上,本文给出负压作用下一维固结方程的理论解以及二维问题的有限单元分析方法,并与试验或工程实测数据进行了比较。     

高真空击密法加固机理研究及应用

强夯法处理饱和软土地基的关键是孔隙水的排出和超孔隙水压力的快速消散。该工法既是针对这一关键问题进行研究和提出解决办法的。本文第一遍高真空排水固结通过特制与安设的高真空排水设备的排水,可迅速在所需处理的土体范围内生产高真空,促使孔隙水和孔隙气体快速排出而导致土体固结。随之而插入的高真空管作用下产生孔隙水压力差而加速孔隙水排出与超孔隙水压力消散,进一步导致土体的排水固结。高真空排水对饱和软土的固结作用。     

超载真空预压动力排水固结联合法运用实例

结合汕头市东部城市经济带市政基础设施建设项目试验段某区软基处理工程实例,介绍了超载真空预压动力排水固结联合法,通过检测结果表明,采用超载真空预压动力排水固结联合法能够有效加速软土固结,减少软土工后沉降。     

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。     

真空降水动力固结法设计施工需注意的问题

对真空动力固结法加固饱和软土的工艺进行探讨,提出了设计施工应注意的问题,确保真空降水动力固结法地基处理的效果.     

真空预压和堆载预压模型试验研究

采用室内模型槽试验,研究了真空预压法和堆载预压法加固软土的固结机理和特性,得出两种加载情况下土样的含水率都随深度的增加而增加,十字板剪切强度随深度的增加而减小的结论。在相同压力作用下,真空作用下土样的含水率比堆载作用下的土样偏小。而且真空作用下土体前期固结沉降的速率远大于堆载作用下土体固结沉降速率。     

排水板真空度损耗的排水固结解析解

无砂真空预压吹填软土在国内造地工程中广泛应用,但实践表明传统固结解析解已不足以预测其加固性状和加固效果。从固结方程出发,在原有的等应变假设基础上,在定解条件中增加了吹填土特有的高度欠固结特性和无砂真空预压特别明显的真空度损耗,重新推导得到径向和竖向完全协调的新的等应变解析解——JJJ解答,以解决无砂真空预压吹填软土的排水固结设计理论问题。JJJ法作为固结方程的原生解答,兼容以往所有该类解析解的同时,增加了针对高度欠固结土类和排水板真空度损耗严重的排水固结问题的解决能力。经现场和试验验证,JJJ解析解可相当精确预测无砂真空预压吹填软土的复杂固结过程和加固土体超孔压分布和孔压消散分布,该解答同时也适用于堆载和真空预压的工况。     

真空动力固结法处理软基效果的试验研究

首先总结了强夯法在处理饱和吹填软土地基时所遇到的问题,然后介绍了一种能有效解决这些问题的地基处理方法-真空动力固结法.结合某工程饱和吹填软土地基所采取的真空动力固结试验,从地面变形规律、承载力、有效加固深度、振动效应等方面评价了真空动力固结方法处理饱和吹填软土地基的效果,得到了一些有价值的结论,可供类似工程应用时参考.     

软土地基真空预压加固的有限元分析

以平面应变比对固结理论为基础,通过比较前人研究成果,选择考虑竖向排水体涂抹效应的砂井地基等效计算方法,根据真空预压加固软土地基的机理,运用有限元分析,提出一种真空预压计算方法。由于真空预压过程中地下水头将降低,因此在计算中采取降低地下水头的方式等效模拟地基表面施加的的真空度。结合工程实例给出算例,对该方法的可靠性进行研究。通过将计算结果同实测资料进行对比,验证了该方法的准确性。     

砂井地基固结分析半解析方法的改进

本文改进了真空预压砂井地基固结分析半解析方法,使它也适用于堆载预压和成层地基情况。其计算简便,对加固面积和砂井根数无限制,可考虑土的粘弹性、固结三向性、砂井群共同作用、井阻和涂抹的影响。改进后侧向位移计算结果的精度比原方法有很大提高。     

Centrifuge modeling of a geogrid-reinforced embankment with lime-stabilized soil as backfill on soft soil

A centrifugal model test was performed to investigate the behavior of a geogrid-reinforced embankment on a 20 m thick soft silty clay subsoil. The lime-stabilized soil embankment was 4 m high, 26 m wide with slopes of 1:1.5 and included sand wick drains. Displacements, earth pressures and pore water pressures were measured during the test. Test results showed settlement on the front face of the foundation was approximately 90% of that measured by displacement sensors; the elastic displacement was approximately 11% of the total displacement; and the reinforced embankment remained serviceable despite a 300 mm wide crack on the embankment surface and up to 1.73 m settlement at the centerline of the embankment.     

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。     

Performance of marine clay stabilised with vacuum pressure: Based on Queensland experience

Stabilising soft marine clay and estuarine soils via vacuum preloading has become very popular in Australasia over the past decades because it is a cost-effective and time-efficient approach. In recent times, new land on areas outside but adjacent to existing port amenities, the Fisherman Islands at the Port of Brisbane(POB), was reclaimed to cater for an increase in trade activities. A vacuum preloading method combined with surcharge to stabilise the deep layers of soil was used to enhance the application of prefabricated vertical drains(PVDs). This paper describes the performance of this combined surcharge fill and vacuum system under the embankment and also compares it with a surcharge loading system to demonstrate the benefits of vacuum pressure over conventional fill. The performance of this embankment is also presented in terms of field monitoring data, and the relative performance of the vacuum together with non-vacuum systems is evaluated. An analytical solution to radial consolidation with time-dependent surcharge loading and vacuum pressure is also presented in order to predict the settlement and associated excess pore water pressure(EPWP) of deposits of thick soft clay.     

Consolidation of System of Clay and Thin Sand Layers

Formulations are developed to compute the consolidation behaviour of a clay soil containing multiple thin sand layers. One-dimensional loading and two-dimensional flow are considered. The formulations are based on the transfer matrix approach, which is found to be very convenient and efficient for analysing the consolidation of a multi-layered soil system. Special attention is given to accommodating thin sand layers in a computationally efficient way. The formulations developed are verified by using available field observation records and a formulation that is based on a different approach. Coupling of the consolidation of clay soil and the discharge flow in sand layers is found to be primarily governed by the parameter λ, defined herein. Based on this finding, a design criterion is proposed for designing multiple thin sand layers to accelerate the consolidation of a constructed clay ground. An example is provided to use the above design criterion.     

Long-term performance predictions in ground improvements with vacuum assisted Prefabricated Vertical Drains

Investigation into time dependent long-term performance of Prefabricated Vertical Drains (PVDs) combined with vacuum consolidation in thick deposits of clay has been extremely limited. Predicting both settlements and excess pore pressures in such cases has become increasingly challenging when time duration is long-term, e.g. several years. In discussing such matter, finding a suitable model to predict the long-term performance is inevitable. Elasto-plastic analysis models such as Cam-Clay cannot predict long-term time-dependent deformational behaviour in soft soils. In this technical note, a Biot type fully-coupled creep-based elastic viscoplastic (EVP) finite element (FE) numerical model has been extended for application in vacuum consolidation. The vacuum consolidation section of the embankment constructed in Ballina, New South Wales, Australia (hereafter referred as Ballina embankment), is analysed using the model through a unit cell analysis and the numerical predictions are compared with field performance monitoring data up to 1200 days (>3 years). The proposed analysis method for PVD combined with vacuum consolidation involving an EVP model is found to be capable of predicting both short-term and long-term deformational behaviours. Predictions are improved when an exponential function is used for the secondary compression index in the EVP model. Comparison has also been carried out at another location in the embankment where the foundation clay thickness was different to check the precision of the methodology and for better understanding of ground settlement behaviour. Details of the analysis methodology and its validation against field performance data are presented in this note.     

双真空面处理吹填土地基的计算和模拟

真空预压在软基工程中的应用越来越广泛。基于太沙基一维和轴对称固结理论,建立双面真空预压的固结解答,推导砂井地基向均质地基转化时渗透系数的等效公式,进一步建立单面负压和双面负压下土体固结度与时间的关系。利用有限元软件ABAQUS分别针对常规单面真空预压和双面真空预压的工况进行模拟,比较了地基总沉降、分层沉降在2种工况下的差异。最后对应采用双面真空预压法时使吹填土和原地基土同时达到固结稳定的工程需求,通过计算分析吹填土厚度和砂井间距的优化选择。研究结果表明,双面真空预压在吹填土和原地基土的固结效率上都有相当的优势,优势的大小与土体厚度﹑土体渗透性及砂井参数有关。