真空预压加固新近吹填土新工艺及机理研究

发布时间：2018-05-20 00:06

本文选题：真空预压 + 硬壳层　；参考：《天津大学》2015年博士论文

【摘要】：随着沿海城市建设及对外开放的需要,围海造陆已成为沿海工程建设和海岸开发工程中的重要组成部分。在天津、深圳、广州等沿海软土地区,围海造陆的方式一般是在原地面上吹填一层吹填土,通过真空预压加固,形成可以作为建筑地基使用的陆域。随着围海造陆工程向海域延伸,需要吹填的泥层厚度不断增加,使得传统真空预压工艺已经不能满足工程要求,需要提出新的工艺。同时,真空预压对吹填土的作用效果与对天然沉积的土层的效果有很大差别,用传统固结理论计算的吹填土在真空压力作用下的固结度与吹填土实际的固结度有很大差别,因此有必要建立计算吹填土在真空预压作用下的固结度的新方法。传统的真空预压工艺需要大量的中粗砂,而天津地区的砂源非常匮乏,需要开发不用或少用砂料的真空预压工艺。针对这些问题,本文进行了比较系统的研究,主要研究内容和取得的成果如下:(1)新近吹填的吹填土的承载力很低,在深厚吹填土上面形成打设排水板机械的工作层是制约真空预压工期的主要因素之一。本课题根据室内模型试验和魏西克(Vesic)双层地基承载力计算公式,提出了在吹填土表面吹填一定厚度的粉细砂形成硬壳层的方法,可以快速形成一个硬壳层,其承载力能够满足打设排水板机械的承载力要求,解决了这个工程难题。该工艺和推荐的硬壳层的厚度(0.6-0.8m)已在天津滨海新区围海造陆工程中得到广泛应用,大大节省了施工工期,降低了工程造价,加快了吹填土加固的施工进度。(2)通过模型试验模拟了高含水量吹填土在水土分离、插板期间、真空预压期间的沉降过程,从而可以比较准确地计算出吹填土在水土分离阶段、插板期和真空预压阶段的沉降量,可以为吹填造陆工程提供合理的吹填标高建议,避免由于吹填量过多或过少引起的浪费和工程问题。(3)模型试验和现场实际工程的观测数据表明,采用传统的固结理论计算的吹填土固结度与实测值有很大的差距。本课题首先研究了该问题的机理,即靠近排水板和地表的土体,由于排水路径短,有效应力增加较快而导致渗透性降低,阻碍了较远处土体的排水通路,进而使得土体的整体固结速率下降。在此基础上建立了变固结系数的固结方程,并提出了方程的数值解法。该成果对于正确评估经真空预压处理的吹填土地基的固结程度和不均匀性有重要意义。(4)提出了用砂量较小的二次吹泥自密封真空预压加固吹填土的工艺,该方法不仅可以解决天津地区砂源匮乏的问题,而且使真空预压技术更加经济、环保。泥密封通过直排式真空预压模型试验的研究可以发现,该工艺在加固效果上达到了真空预压加固的目的,加固效果较好,可以进行现场的中试工作,以完善大面积的真空预压施工工艺。本文根据非饱和土力学中收缩膜的概念,从微观角度,分析了在这种工艺加固过程中土体的开裂问题。通过分析收缩膜在基质吸力、水膜张力和周围边界传递的拉力的平衡条件,建立了收缩膜的受力模型;通过水膜与附着物的张力试验类比了土体开裂过程中收缩膜的张拉作用;通过不同尺度和形状的模型槽试验研究了饱和土在干燥和蒸发条件下裂缝发生、发展和终止的过程。研究结果可加深对土体开裂机理的认识水平,并在直排式真空预压工艺中得到应用。(5)本文应用ABAQUS软件对复杂应力路径的吹填土加固过程进行模拟,分析了浅层人工插板、一次真空预压、吹砂铺膜、深层插板、二次真空预压、填土堆载、真空-堆载预压等施工全过程中吹填土的应力变化,通过有限元中均布荷载、超孔压、真空度等加荷方式模拟土体中的应力状态,并计算在外荷载作用下的土体固结沉降,实测结果与计算结果吻合较好。数值计算时不仅考虑土体渗透系数随孔隙比变化的影响,而且真实模拟了真空载荷与堆载随时间的梯度变化,更符合真实情况。最后通过分析不同的工况作业时间对吹填土沉降影响,得出,延长插板时间不能改变土体的总体沉降,但可以减少深层抽真空时间,节约能源。(6)通过吹填土自重固结试验的研究发现,在吹填土自然晾晒初期,土体的蒸发速率与纯水的蒸发速度相当。在无降水情况下,表层20cm厚度土体会在2个月内形成硬层,此时表层土体的含水量降低至50%以下,随后土体的蒸发速率、沉降速率都减慢。应用土力学三相性质关系,得出土体含水量变化与土体沉降间的规律,并通过一维自重固结现场试验,得到不同深度土体含水量的发展趋势,完善了现有一维固结理论中对含水量变化关系的研究。根据现场数据拟合,可以预测未来时刻土体的含水量沿深度变化。研究结果为天津临港工业区围海造陆工程的吹填标高的计算提供理论依据,并能以此来安排施工进度。
[Abstract]:With the construction of coastal cities and the need of opening to the outside world, the land reclamation has become an important part of coastal engineering construction and coastal development project. In Tianjin, Shenzhen, Guangzhou and other coastal soft soil areas, the way of reclamation in the sea is generally to fill a layer of dredger fill in the original ground and be reinforced by vacuum preloading to form a building site. The land area used by the base. As the sea reclamation project extends to the sea area, the thickness of the mud layer needs to be continuously increased, which makes the traditional vacuum preloading process can not meet the requirements of the project and requires a new process. At the same time, the effect of vacuum preloading on the dredger fill is very different from that of the naturally deposited soil, with the traditional consolidation. It is necessary to establish a new method to calculate the degree of consolidation of the dredger soil under vacuum preloading. The traditional vacuum preloading process requires a large amount of coarse sand, while the sand source in Tianjin is very scarce and needs not to be developed. In view of these problems, this paper makes a comparative systematic study on these problems. The main research contents and achievements are as follows: (1) the loading capacity of the newly filled and filled dredger fill is very low, and the formation of the working layer on the deep fill soil is one of the main factors that restrict the vacuum preloading period. Based on the indoor model test and the calculation formula of the bearing capacity of the Vesic double layer foundation, the paper puts forward a method of forming a hard shell layer with a certain thickness of fine sand on the surface of the dredger fill, which can quickly form a hard shell. The bearing capacity of the hard shell can meet the bearing capacity requirements of the drainage plate machinery, and the engineering problem is solved. The thickness (0.6-0.8m) of the hard shell layer (0.6-0.8m) has been widely used in the surround sea reclamation project in Binhai New Area, which has greatly saved the construction period, reduced the cost of the project and accelerated the construction progress of the reinforcement of the dredger. (2) through the model test, the high water content blows are simulated during the soil and water separation, during the plugged plate and during the vacuum preloading period. The settlement process can be used to accurately calculate the settlement of the dredger fill in the stage of soil and water separation, the plugged stage and the vacuum preloading stage. It can provide a reasonable proposal for the blow filling elevation for the land reclamation project, and avoid the waste and engineering questions caused by too much or too little blow filling. (3) the model test and the observation of the actual project in the field. It is shown that there is a big gap between the consolidation degree calculated by traditional consolidation theory and the measured value. This topic first studies the mechanism of this problem, that is, the soil near the drain board and the surface of the earth, because the drainage path is short and the effective stress increases rapidly, which leads to the permeability reduction, which hinders the drainage path of the soil in the far distance, and thus makes it possible. The consolidation rate of the soil is reduced. On this basis, the consolidation equation of the coefficient of consolidation is established, and the numerical solution of the equation is proposed. The results are of great significance for the correct assessment of the degree of consolidation and the inhomogeneity of the fill foundation treated by vacuum preloading. (4) a self sealed vacuum preloading with two sands with less sand is proposed. The technology of reinforcing the dredger fill can not only solve the problem of the shortage of sand source in Tianjin, but also make the vacuum preloading technology more economical and environmentally friendly. Through the study of the model test of the vacuum preloading through the straight row vacuum preloading, it can be found that this process has achieved the purpose of strengthening the vacuum preloading, and the reinforcement effect is better and can be carried out. According to the concept of the shrinkage film in the unsaturated soil mechanics, this paper analyzes the problem of soil cracking in the process of strengthening this process in the light of the concept of shrinkage film in the unsaturated soil mechanics, and establishes the balance condition of the tension of the contraction film in the matrix suction, the water film tension and the surrounding boundary. The stress model of the shrinkable film is made. The tensile test of the shrinkage film in the process of soil cracking is analogized by the tension test of the water film and the attachment. The process of cracking, development and termination of the saturated soil under the conditions of drying and evaporation is studied by the model groove test of different scales and shapes. The results can deepen the recognition of the mechanism of soil cracking. It is applied in the horizontal vacuum preloading process. (5) in this paper, the ABAQUS software is used to simulate the reinforcement process of the complicated stress path. The shallow layer artificial plugged plate, the first vacuum preloading, the sand blowing, the deep sanding, the two vacuum preloading, the fill loading, the vacuum loading preloading and so on are analyzed. The stress state of the soil is simulated by means of uniformly distributed load, super pore pressure and vacuum degree in the finite element method, and the consolidation settlement of soil under the external load is calculated. The measured results are in good agreement with the calculated results. The numerical calculation not only considers the influence of the soil permeability coefficient with the change of the pore ratio, but also the real simulation. The change of vacuum load and load with time gradient is more in line with the real situation. Finally, through the analysis of the effect of different working working hours on the settlement of the dredger fill, it is concluded that the extension of the plate time can not change the overall settlement of the soil, but can reduce the deep vacuum time and save the energy source. (6) through the study of the self consolidation test of the dredger fill, the study found that In the early stage of natural air drying, the evaporation rate of soil is equal to the evaporation rate of pure water. In the case of no precipitation, the surface 20cm thickness of the soil will form a hard layer within 2 months. At this time the water content of the surface soil is reduced to less than 50%, and the evaporation rate and settling rate of the soil are slowed down. The law of body water content change and soil settlement, and through one dimensional self weight consolidation field test, the development trend of soil moisture content in different depths is obtained. The relationship between water content and water content in the existing one-dimensional consolidation theory is perfected. According to the field data fitting, it can be used to predict the water content along the depth of the soil in the non coming time. The results provide a theoretical basis for the calculation of dredger fill elevation in Tianjin Lingang industrial area, and can be used to arrange the construction progress.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU472.33

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