预应力管桩联合塑料排水板加固软土地基技术探讨

在沿海地区修建高速公路时,软土地基的处理一直是一个难以解决的问题。在分析前人相关软基处理方法的基础上,结合实际工程,提出预应力管桩联合塑料排水板加固软土地基的加固方法。该处理方法中塑料排水板在复合地基中起到排水通道的作用,两种软基处理方法的结合,使得处理效果更好。同时,还对该方法的加固机制进行初步探讨,且通过现场的工程实例分析,对预应力管桩联合塑料排水板方法加固软土地基的处理效果进行验证和分析,证明该方法适用于工期紧、软基埋深大的软土地基。     

斗轮机地基处理与监测分析

采用塑料排水板、堆载预压以及强夯等施工综合措施对斗轮机地基进行了处理,根据现场监测数据,分析了软土地基在塑料排水板堆载预压作用下的表层沉降变化规律,孔隙水压力和分层沉降变化规律。现场监测结果表明,通过塑料排水板堆载预压处理斗轮机地基具有良好的效果。     

塑料排水板堆载预压法在软土地基处理中的应用

根据工程实例,结合实际问题,对塑料排水板堆载预压法处理软土地基进行了介绍,并提出一些在设计过程中和在实际施工过程中的可操作的优化、改进方法,以便指导设计和施工,进而提高塑料排水板堆载预压法处理软土地基的可靠性和使用效果。     

沿海高速公路软土地基变形规律及处理效果

以河北沿海高速公路软土地基试验工程的测试结果为基础,分析了塑料排水板及水泥搅拌桩超载预压两种处理方法下从路堤填筑到超载卸载以及路面结构层施工阶段软土地基的变形规律,并分析了地基处理的效果,从而为同类工程的设计和施工控制积累经验。     

塑料排水板与碎石桩处理公路软土地基的数值模拟与分析

简要介绍了塑料排水板与碎石桩处理软土地基的工作原理,并依托四川某高速公路K26+283标段,利用有限差分软件FLAC3D建立模型分别进行模拟塑料排水板与碎石桩处理软土地基的情况,并比较了这两种处治方法的处治效果。结果表明,针对该段软土地基,路堤填高为5m时,塑料排水板处理后的地基和未处理的地基总沉降量为40cm,预压180d后工后沉降量分别为5.1cm和23.8cm;碎石桩处理后的地基总沉降为14.2cm,预压180d后工后沉降量为1.0cm。塑料排水板可以加速土体固结,减小工后沉降量,但不能降低总沉降量;碎石桩处理软土地基既可以降低总沉降量,又可以加速地基固结,减小工后沉降量。     

南岗河堤真空预压处理软土地基施工技术

本文介绍了南岗河整治工程中大型石堤基础采用真空预压法,并配合塑料排水板进行软土地基处理的施工过程、技术应用及效果。     

真空预压法处理软土地基

阐述了南岗河整治工程中大型石堤基础采用真空预压法，配合塑料排水板进行软土地基处理的施工过程、技术应用及效果。     

塑料排水板在软基加固中的应用分析

软土具有含水量高,强度低,压缩性高等特性,导致在该地基上的建筑物存在着较大地安全隐患。塑料排水板技术作为软土地基处理的一种常用技术,既可以起到良好的加固效果,同时也能有效地提高地基承载力,减少地基沉降。文章在国内外学者研究的基础上,对塑料排水板在软基处理中的加固机理、加固效果、影响因素、沉降变化规律等方面进行探讨,指出地基处理中存在的问题,以期为建筑工程软土地基施工提供一定参考。     

浅议滨海滩涂地区塑料排水板软基处理施工质量控制

近年来,采用塑料排水板固结软基成为一种新兴的方法,因其具有排水速度快、耐久性强、施工方便、成本低廉等特点,已成为目前处理软土地基,特别是滨海地区深厚层滩涂软土地基处理的首选施工方法。本文结合工程实践,介绍了塑料排水板在滩涂软基础处理中的施工工艺、质量控制,供同行参考。     

塑料排水板预压法处理深厚软基的试验研究

采用塑料排水板排水固结预压法处理深厚软土地基,从分层沉降、孔隙水压力、深层水平位移、静力触探及室内土工试验等方面对其加固处理效果进行分析,结果表明:塑料排水板排水固结预压法处理该深厚软土地基是可行的,完全能满足设计要求.     

提高软基深层加固效果的措施

经过现场对广东某高速公路监测断面的观测及试验资料分析发现,排水通道形式对深层软基加固有很大影响。研究表明,不同竖向排水通道中真空度的传递规律是不同的,对地基的真空预压加固效果的影响也不同。最后提出了能够有效减少真空压力沿程损失和消除地基深层沉降的新型竖向排水通道形式。     

Effects of pressurizing timing on air booster vacuum consolidation of dredged slurry

Air booster vacuum preloading is a newly improved method applied in land reclamation projects. Highly pressurized air can provide an additional pressure difference between the prefabricated vertical drain (PVD) and injection point, thereby increasing the hydraulic gradient and generating small fractures that can improve the soil permeability and the transmission efficiency of the vacuum pressure. However, with a premature activation time, the pressurized air can create air channels connected to the PVD, which may drastically decrease the vacuum pressure. With a delayed activation time, the strength of the dredged clay may be too high to permit fractures, thus limiting the permeability improvement. In this study, soils with degrees of consolidation (DOCs) of 0%, 40%, 60%, and 80% were selected for testing the efficacy of initial booster activation times in four tests. The results show that the pressurizing groups were more effective in improving the consolidation of soils, and the best effect of the use of air booster is obtained when soil has been consolidated to a DOC of 60%. The lower soils of the pressurized groups showed greater increase rates than those demonstrated by conventional vacuum preloading.     

广东沿海软基堤坝破坏机制及工程对策

广东沿海堤坝较多位于软基上,其破坏特征与软土变形有关。据此,系统分析软基上海堤失稳原因和破坏机制;同时,阐述在软基上修筑堤坝并提高其防御能力可从提高地基承载力、消减波浪能量、优化断面型式及采用轻质堤坝等多方面考虑。基于优化设计理论和堤基堤身整体分析模型,通过一个简单算例计算上下游坡比、填筑材料自重和地基加固区域等对软基上海堤稳定性的影响。优化分析结果表明,采用下游较上游缓的坡比对堤坝的整体稳定有利,且采用轻质材料填筑堤坝能有效克服软基的诸多不利因素;另外,软基加固更应针对堤下浅层地基。     

真空覆水预压处理房建软基效果评价

针对深厚软基的房建项目在后期使用过程中因仅对主体建筑进行地基处理而引起的差异沉降、甚至主体结构开裂倾斜等病害;采用真空联合覆水预压法对某房建项目之深厚软基进行前期处理,并从理论计算、现场施工、施工监测、工后检测等方面对该工法进行分析,认为真空覆水预压法处理房建项目深厚软基可以消除后期项目运行过程中的差异沉降等问题。该工法处理房建项目深厚软基可满足设计要求、施工方便、工期较短、且可消除以往直接采用桩基处理等方法产生的病害、切实可行、值得推广应用。     

沿海滩涂软土路基堆载预压沉降变形特征与卸载时机研究

沉降变形与卸载标准是铁路路基堆载预压的主要问题。针对处于沿海滩涂软土路基之上的铁路专用线,采用插塑板与堆载预压相结合的方案进行地基处理,开展了大量的表层沉降、孔隙水压力、分层沉降等观测项目。据实测资料,总结分析了路基表面的沉降规律,并考虑了路基分层沉降与孔隙水压力的变化规律,全面地揭示了整个路基地层的沉降变化特征,运用双曲线合理地预测了工后沉降,且推算出路基整体的固结度,采用工后沉降与地基固结度建立卸载时机判别标准。为堆载预压的卸载时机判别标准研究提供了一种新的思路。     

深圳机场停机坪桩网结构软基处理沉降监测分析

深圳机场普遍分布有深厚的海积淤泥层,该土层具有承载力低,压缩性大等特点,机场扩建停机坪软基处理成功运用了桩网复合地基处理技术。本文详细介绍了桩网复合地基的施工和沉降监测情况,并根据观测成果分析这一方法的可行性,为同类工程积累经验。     

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.     

Instability of a geogrid reinforced soil wall on thick soft Shanghai clay with prefabricated vertical drains: A case study

A 7.6 m high geogrid reinforced soil retaining wall (RSW) was constructed at the end of an embankment on very thick, soft Shanghai clay with 12 m deep prefabricated vertical drains (PVDs). The settlement of the ground, the wall movement and pore water pressure were monitored during the construction. From day 118, halfway through the construction, unexpected pore water pressure increment was recorded from the pore water pressure meters installed in the PVD drained zone indicating a possible malfunction of the PVDs due to large deformation in the ground. After the last loading stage, on day 190, a sudden horizontal movement at the toe was observed, followed by an arc shaped crack on the embankment surface at the end of the reinforced backfill zones. The wall was analyzed with a coupled mechanical and hydraulic finite element (FE) model. The analysis considered two scenarios: one with PVDs fully functional, and the second one with PVD failure after day 118 by manually deactivating the PVDs in the FE model. The comparison between the measured and simulated ground settlement, toe movement, and pore water pressure supported the assumption on the malfunction of the PVDs. It is believed that the general sliding failure in the wall was caused by the increase of pore water pressure in the foundation soil and soils in front of the toe. It is suggested that possible failure of PVDs should be considered in the design of such structures, and the discharge rate of the PVDs and the pore water pressure should be closely monitored during the construction of high soil walls on soft soils to update the stability of the structures, especially for grounds where large deformations are expected which may cause the failure of the PVDs.     

Innovative thermal technique for enhancing the performance of prefabricated vertical drain during the preloading process

This paper examines the effect of raising the temperature of soft Bangkok clay, up to 90 °C, on the performance of the prefabricated vertical drain (PVD) during the preloading process. The effect of temperature on the engineering behavior of soft Bangkok clay was first investigated using a modified triaxial test apparatus and flexible wall permeameter which can handle temperatures up to 100 °C. The results of the triaxial tests on clay specimens demonstrate that raising the soil temperature increases its shear strength, under drained heating condition, as well as its hydraulic conductivity. In addition, large oedometer tests were performed to investigate the performance of PVD at elevated temperatures. The response of the soil sample with PVD for the thermal consolidation path which involved increasing the soil temperature at constant vertical effective stress condition and the thermo-mechanical path which involved increasing simultaneously both the soil temperature and the vertical effective stress were investigated. The consequent results indicated that the thermo-mechanical path shows promising results regarding the consolidation rate. For both reconstituted and undisturbed specimens, higher consolidation rate was observed for the soil specimen with PVD loaded under elevated temperature. This behavior can be attributed to the increase in the soil hydraulic conductivity as the soil temperature increases. Therefore, raising the soil temperature during the preloading period can enhance the performance of the PVD, particularly, by reducing the drainage retardation effects due to the smear zone around PVD.     

Measured and predicted performance of prefabricated vertical drains (PVDs) with and without vacuum preloading

This paper presents the effectiveness of vacuum preloading in accelerating the consolidation of PVD improved soft Bangkok clay by comparing with the corresponding results without vacuum preloading. Laboratory tests were conducted using a large scale consolidometer having diameter of 300 mm and height of 500 mm with reconstituted specimens installed with prefabricated vertical drains (PVD) with and without vacuum preloading. In addition, field data were collected from Second Bangkok International Airport (SBIA) site improved by PVD with and without vacuum pressures. Analyses were carried out to compare the compressibility parameters (C_h and k_h/k_s) by back-calculation of laboratory and field settlements using Hansbo (1979) method. From the laboratory tests, the horizontal coefficient of consolidation (C_h) values from reconstituted specimens were 1.08 and 1.87 m²/yr for PVD without and with vacuum pressure, respectively and the k_h/k_s values were 2.7 for PVD only and 2.5 for vacuum-PVD. After the improvement, the water contents of the soft clay were reduced, thereby, increasing its undrained shear strengths. Similarly, the field data analysis based on the back-calculated results showed that the k_h/k_s were 7.2 and 6.6 for PVD without and with vacuum, respectively. The C_h values increased slightly from 2.17 m²/yr for PVD only to 3.51 m²/yr for vacuum-PVD. The time to reach 90% degree of consolidation for soils with vacuum-PVD was one-third shorter than that for soils with PVD only because of higher C_h values. Thus, the addition of vacuum pressure leads to increase horizontal coefficient of consolidation which shortened the time of preloading. The PVDCON software was found to be useful to predict the settlements of the PVD improved ground with and without vacuum preloading.