【作者】 张皓；

【导师】 蔡袁强； 孙宏磊；

【作者基本信息】 浙江大学 ， 岩土工程， 2024， 博士

【摘要】 疏浚淤泥及工程废浆的有效处理是岩土工程领域的焦点问题之一,是达成“无废城市”建设和“双碳”目标的重要基石。城市化进程飞速推进下,疏浚及工程废弃泥浆年产量超百亿方,造成了严重的环境污染和土地资源占用,泥浆不断增长与受纳处理能力有限的矛盾日益激化。现有泥浆处理工艺主要有自然脱水法、机械压缩法、真空预压法以及土工管袋法,但上述方法存在处理效率低、周期长、成本高、占地面积大等单个或多重问题。因而,兼顾真空预压法的高效便捷优势及土工管袋法的灵活低廉特性,一种新型的土工管袋联合水平排水板(Prefabricated Horizontal Drains,PHD)真空预压脱水处理淤泥浆技术应运而生,具有以下优势:排水板不易弯折;拥有内板及表面织物多重排水路径;无需机械插板;无需预处理表层;疏浚、运输、充填和脱水可同步进行。然而,由于是新兴技术,其理论方面的研究几乎空白,对基本脱水机理的认知匮乏阻碍了其推广应用。本文通过建立理论模型并进行试验验证的方法,针对土工管袋水平排水板真空预压处理淤泥浆的关键科学问题,进行了系统的深入探索。主要研究工作及创新成果归纳如下:(1)基于土工管袋水平排水板系统垂直剖面的对称性,提出了具有混合边界的分析计算单元,准确考虑排水板宽度与间距,建立了二维渗流平面应变固结模型;利用拉普拉斯变换、傅立叶余弦变换和傅立叶余弦逆变换等方法求得了模型半解析解,并通过一维模型初步验证;进行了四组室内模型试验探究管袋系统脱水效率,并验证提出的二维模型;分析了PHD间距、管袋填充高度、土体各向异性和真空堆载预压比对模型固结效率的影响,揭示了管袋系统的效率最优点,提供了常用固结度下的管袋系统简化设计方法。(2)基于透水土工管袋的快速自重脱水特性和不透水膜袋的真空预压维持能力,研发了复合式土工管袋-膜袋淤泥浆真空预压处理技术,实现了泥浆的高效、深度脱水处理;建立了复式二维固结模型,描述复合袋内泥浆脱水固结的阶段性连续过程,基于等效率原则提出了复合袋的理论模式转换点;进行了室内模型试验,验证了复式固结模型;分析了主要设计参数对该理论转换点的影响,发现PHD间距的减小和管袋填充高度的增大使得理论转换点提前。(3)基于Gibson一维大应变理论,考虑物质点及模型边界的持续移动,考虑土体压缩渗透性的持续变化,建立了同时考虑土体几何非线性和力学非线性的大应变二维固结模型;采用交替方向隐式(ADI)差分方法获得了精确数值解,首先将一维退化解与一维大应变基准模型解对比,再进行大尺寸土工管袋真空预压泥浆脱水现场试验,验证了模型有效性;与小应变模型相比,大应变模型描述的土体最终有效应力平均值更低,分布形式偏离同心圆状。(4)针对真空诱发的颗粒快速迁移重组问题,将真空预压影响范围划分为持续变化的三个区域:细颗粒补充区、细颗粒损失区和正常区,考虑颗粒级配变化与压缩、渗透指数的非单调关系,建立了考虑土体本构关系时空演化的真空预压大应变淤堵固结模型,揭示了真空预压处理淤泥浆的真空沿程显著衰减及不均匀固结机理;通过成层土一维大应变固结模型和管袋室内模型试验验证了模型数值解;研究发现,细颗粒补充区和渗透指数对整体固结效率起着主导作用。(5)基于真空预压固结中气液界面最终超孔压不为零的事实,提出了由临界进气值(CAEV)控制透水边界条件的大应变固结模型,并通过室内及现场模型试验加以验证;通过分析e-σ’、e-ψ(吸力)和e-AEV曲线的相对位置关系,阐明了CAEV的确定方法;根据真空预压与CAEV的相对大小,脱水过程可分为固结并去饱和与仅固结两种情况;基于有效应力原理,定量土体吸力与有效应力差值,分析了上部或下部气液面被气体突破后的内层土体响应模式。(6)为模拟高含水量泥浆真空预压脱水的耦合过滤-固结过程,提出了基于压缩屈服应力P_y(φ)和阻碍沉降系数r(φ)的二维压缩流变模型,解决了传统固结模型在描述零和低有效应力状态下的流固及固固相互作用的局限;研发了交替式真空抽滤装置,用于测定统一的P_y-r-φ关系;通过与现有一维压缩流变模型和管袋现场模型试验对比验证了模型解的有效性;进行了参数分析,评估了管袋主要设计参数和压缩流变本构参数对淤泥浆脱水效率及效果的影响。更多还原

【Abstract】 The effective treatment of dredged sludge and engineering waste slurry is one of the key issues in the field of geotechnical engineering and is an important cornerstone for achieving the goals of“waste-free cities”and“carbon peaking and carbon neutrality”.With the rapid advancement of urbanization,the annual production of dredging and engineering waste mud exceeds 10 billion cubic meters,causing severe environmental pollution and land occupation.The contradiction between the continuous growth of slurry and the limited capacity for processing it is increasingly intensifying.The existing slurry treatment methods mainly include natural evaporation,mechanical compression,vacuum preloading,and geotextile tubes.However,these methods have single or multiple problems,such as low efficiency,long duration,high cost,and large land occupation.Therefore,taking into account the efficient and convenient advantages of the vacuum preloading method and the flexible and low-cost characteristics of the geotextile tube method,a new technique of slurry dewatering using geotextile tubes combined with vacuum-assisted prefabricated horizontal drains(PHD)has emerged,possessing the following advantages:drain boards do not bend;inner borads and surface fabrics provide multiple drainage paths;mechanical insertion of boards is not required;pre-treatment of the surface soil layer is not necessary;and slurry dredging,transportation,filling,and dewatering can be carried out simultaneously.However,as an emerging technology,theoretical research on this tube system is almost blank,and a lack of understanding of its basic mechanisms hinders its application and promotion.This thesis conducted a systematic and in-depth exploration of the fundamental scientific issues of vacuum preloading treatment of slurry using combined geotextile tubes and prefabricated horizontal drains by establishing theoretical models and conducting experimental verifications.The main research work and innovative achievements are summarized as follows:(1)Based on the symmetry of the vertical profile of the tube-PHD system,an analyzing unit with hybrid boundaries was proposed,and a two-dimensional plane-strain consolidation model was established,considering the width and spacing of the drainage boards.The semi-analytical solution of the model was obtained using methods such as Laplace transform,Fourier cosine transform,and inverse Fourier cosine transform and was preliminarily verified through a one-dimensional model.Four sets of indoor model tests were conducted to explore the dewatering efficiency of the tube-PHD system,and the proposed consolidation model was validated by the test results.The influence of PHD spacing,tube filling height,soil anisotropy,and vacuum-surcharge preloading ratio on the consolidation efficiency of the model is analyzed,and the optimal efficiency of the tube system is confirmed.A simplified design method for the tube system under commonly used consolidation degrees is provided.(2)Based on the rapid self-weight dewatering characteristics of the permeable geotextile tubes and the excellent vacuum maintenance ability of the impermeable geomembrane tubes,a combined geotextile-geomembrane tube system used for slurry dewatering was developed,achieving efficient and deep treatment of slurry.A two-dimensional consolidation model was established to describe the staged dewatering and consolidation of slurry inside the composite geo-tube.A theoretical switching point corresponding to the iso-efficiency state of the geotextile tube and geomembrane tube was determined for the tube conversion.A laboratory model test was carried out to verify the consolidation model.Parametric analyses were conducted to explore the influence of the primary parameters on the theoretical switching point,and it suggests that the decrease in PHD spacing and the increase in tube filing height advanced the theoretical switching point.(3)Based on Gibson’s one-dimensional large strain theory,a two-dimensional large-strain consolidation model incoparating both the geometrical and mechanical nonlineariteis of soil was established,considering the continuous movement of material points and model boundaries as well as the varying soil compressibility and permeability.Numerical solutions were obtained using the alternating direction implicit(ADI)difference method.The one-dimensional degradation solution was compared with the one-dimensional large strain benchmark model,and a large-scale geotextile tube on-site test was conducted to verify the effectiveness of the proposed model.Compared with the small-strain model,the large-strain model indicates a smaller average final effective stress of the soil,and its distribution deviates from the concentric circle shape.(4)In response to the rapid migration and reconstitution of soil particles induced by vacuum,the effective influencing area of vacuum preloading is divided into three constantly changing zones:the fine particle filling zone,the fine particle loss zone,and the normal zone.Given the non-monotonic relationship between particle size distribution changes and compression and permeability indices,a large strain clogging-consolidation model considering the spatiotemporal evolution of the soil constitutive relationship is established,revealing the significant vacuum attenuation and uneven consolidation mechanisms of the vacuum-preloaded clayey slurries.The numerical solution was verified through a one-dimensional large-strain consolidation model for layered soil and indoor model tests of geo-tubes.Research has found that the filling zone and permeability index play a dominant role in the overall consolidation efficiency.(5)Based on the fact that the final excess pore-water pressure at the air-liquid interface of soil under vacuum preloading is not zero,a large strain consolidation model with permeable boundaries controlled by the critical air entry value(CAEV)is proposed and verified through indoor and on-site model tests.By analyzing the relative positional relationship among e-σ’,e-ψ(suction),and e-AEV curves,the method for determining CAEV is elucidated;According to the relative size of vacuum and CAEV,the dewatering process can be distinguished into two situations:consolidation and desaturation,and only consolidation.Based on the principle of effective stress,the difference between pore suction and effective stress was quantified,and the response mode of the inner soil layers after air breakthrough on the upper or lower air-liquid surface was analyzed.(6)To simulate the coupled filtration-consolidation process of vacuum-preloaded dewatering of high water content slurry,a proound model constituted by the compressive yield stress P_y(φ)and hindered setting factor r(φ)is proposed.The compressional rheology model solves the limitations of traditional consolidation models in describing fluid-solid and solid-solid interactions of soil at zero and low effective stress states.An alternating vacuum filtration device is developed for measuring a consistent P_y-r-φrelationship.The effectiveness of the model solution was verified through comparison with existing one-dimensional compressional rheology models and field test results.Parametric analysis was conducted to evaluate the impact of the main design parameters of the geotextile tube and the main constitutive parameters of the compressional rheology theory on the dewatering efficiency and dewatering effect of the slurries.更多还原