新近吹填淤泥地基真空固结理论与强度增长计算方法及加固新技术研究

发布时间：2018-06-28 12:36

本文选题：新近吹填淤泥地基 + 二次处理技术　；参考：《华南理工大学》2015年博士论文

【摘要】：新近吹填淤泥是指原位海积或湖积淤泥经水力重塑和颗粒重新分选后、土颗粒自重沉积尚未完成、颗粒结构极松散、含水率极高(85%-150%、甚至大于150%)、处于悬浮状态或流动状态的吹填淤泥。该类地基目前主要采用“二次处理技术”进行加固—即‘先采用浅表层快速加固技术(属于无砂垫层真空预压技术)对新近吹填淤泥地基浅表层土体进行预处理30天的同时,水力吹填厚度为1.0m左右的中(粉)细砂垫层并机械铺设(吹填)厚度为0.5m左右的中粗砂排水垫层,待真空恒载满45天后卸载,此时的地基便能作为承载排水板施工设备的工作平台,然后采用传统真空预压技术或真空联合堆载预压技术对地基深层土体进行处理”。新近吹填淤泥地基须进行二次处理的主要原因有两方面：(1)新近吹填淤泥地基承载力为零,无法直接承受任何地基处理施工机械设备(如推土机、插板机等)；(2)新近吹填淤泥中黏粒(d≤0.005mm)含量高、白重落淤慢,强亲水矿物含量高、土体所吸附的结合水多。现行规范中塑料排水板的相关性能指标(包括排水性能指标和材料强度指标)与新近吹填淤泥这种固有的工程特性不相适宜。工程实践表明,后一方面的原因直接导致：新近吹填淤泥地基浅表层快速加固过程中,竖向排水井的淤堵问题非常严重,排水效率急剧降低；竖向排水井之间的土体强度很不均匀,土体强度增长十分有限；地基有效加固深度小、承载力低；地基表面形成许多以竖向排水井为中心的“土柱”,不均匀沉降非常明显。因此,经典的砂井地基固结理论和目前已有的砂井地基强度增长计算方法不完全适用于该类地基。本文首先对中国大陆不同区域的新近吹填淤泥的工程特性进行了系统、全面地总结和分析,并依托实际工程开展了不同形式真空预压排水系统现场对比试验研究,探讨了该类地基的负压传递特性及分布模式,建立了相应的真空固结理论；然后,针对该类地基的排水固结特点,推导出其土体强度增长计算公式,并通过实际工程对其合理性进行了验证；最后,针对上述二次处理的两方面真正原因,有针对性地开展了试验研究,研发出了新型大面积砂被垫层工艺技术和新近吹填淤泥地基加固新技术,为新近吹填淤泥地基成功实现一次性排水固结处理的提供了新思路。本文的研究结论概括如下：(1)中国大陆不同区域的新近吹填淤泥是疏浚淤泥处于动水沉积阶段和静水沉积阶段的产物,沉积于出水口附近及远离出水口的区域,由较细颗粒物质和极细颗粒物质组成,其孔隙特征主要以孤立孔隙和粒间孔隙为主,其微观结构特征主要以紊流状和粒状镶嵌结构为主。新近吹填淤泥中的黏粒(d0.005mm)含量和强亲水矿物(伊利石、蒙脱石)含量都偏高；含水量均大于90%,且均大于1.5倍的液限；孔隙比均大于2.0；塑性指数基本大于20；液性指数基本大于2.0。这种极差的工程特性直接致使新近吹填淤泥地基采用传统真空预压技术加固(包括浅表层快速加固技术)时的固结变形特点与一般软基存在较大的差异,宏观上主要表现为竖向排水体出现严重的“弯折”现象以及细土颗粒向竖向排水体周围移动出现严重的“土柱”现象。(2)新近吹填淤泥地基采用传统真空预压技术(包括浅表层快速加固技术)加固过程中,整个排水系统内的负压损失程度较严重,最严重的高达57%；负压从竖井向其周围土体传递过程中的损失程度也非常严重,至少为67%。这是新近吹填淤泥地基真空预压加固后土体强度增长有限的主要原因。而且,新近吹填淤泥地基真空预压加固过程中,排水边界处的负压是非均匀分布的,水平排水垫层中的负压可考虑为随时间变化的线性衰减模式,而竖向排水体中的负压可考虑为随时间变化的非线性衰减模式。基于此建立了负压非均匀分布边界条件下的真空固结理论,并相应地给出了解析解。(3)基于有效应力原理和应力路径法对新近吹填淤泥地基排水固结的强度增长机制进行了定性分析,分析结果表明：地下水位线以上土体的强度增长规律和地下水位线以下的土体的强度增长规律是不尽相同的。并基于有效应力唯一性理论推导出新近吹填淤泥地基排水固结的强度增长计算公式,该计算公式全面考虑了真空荷载及其沿深度方向的衰减程度、外加荷载、地下水位等因素的影响,且依托实际工程对该计算公式进行了验证：按不排水剪强度考虑时,平均误差为8.0%；而按破坏面上的强度考虑时,平均误差为3.2%,因此,计算精度能满足工程要求。(4)新型大面积砂被工作垫层是一种大型的空间立体式结构,为透水性结构,包括扁平结构体、侧向复合式柔性结构体以及柱状结构体(流泥地基中无需设置)。该结构与下卧浮(流)泥地基构成一个整体的、具有较高承载力的承力体系,可以作为深层排水板施工设备的工作平台。该类垫层地基的承载机理主要体现为：似壳体效应(包括应力扩散效应与表层封闭效应)、侧向封闭效应(即侧限作用)、排水固结作用和竖向加筋作用(流泥地基中无该项作用)。该类垫层地基的破坏形式呈冲剪破坏特征。方案7(方案7／)(编织土工布规格为280g/m2)是最佳方案。基于推导出的承载力估算公式进行计算可知,方案7/垫层地基的临塑荷载为Pcr=146.4kPa。该类垫层地基服役过程中,需要做好插板施工过程中的清泥措施和排水措施。(5)现行规范中塑料排水板的相关性能指标(包括排水性能指标和材料强度指标)与高黏粒含量新吹填淤泥固有的工程特性不相适宜、且目前的真空预压设计时采用过快的真空荷载加载速率致使“土柱”现象过早的形成,这两方面共同导致了“新近吹填淤泥地基浅表层快速加固后,土体强度增长有限、有效加固深度小以及承载力仍无法满足建设用地需求。室内试验研究结果表明：新近吹填淤泥地基可采用由中等等效孔径(如O95为0.15mm)的反滤层和抗弯折性强的芯体组成的竖向排水体作为竖向排水系统,以较快的真空荷载加载速率进行分级真空预压加固,从而实现一次性排水固结处理的目的。
[Abstract]:The newly dredged silt is that the self gravity deposition of the soil particles has not been completed, the particle structure is very loose, the water content is very high (85%-150%, even more than 150%), which is in suspended state or flow state. This kind of foundation is currently mainly used in "two treatment techniques". Strengthening - that is, the shallow layer of shallow surface soil is pretreated with shallow surface rapid reinforcement technology (which belongs to vacuum preloading technology without sand cushion) for 30 days, while the hydraulic fill thickness is about 1.0m, the medium (powder) fine sand cushion and the mechanical paving (blow filling) thickness of 0.5m in the medium coarse sand drainage cushion, waiting for vacuum constant load After 45 days of unloading, the foundation can be used as the working platform for the construction equipment of the loading and drainage plate, and then the traditional vacuum preloading technology or vacuum combined loading preloading technology can be used to treat the deep soil soil. The main reasons for the two treatment of the newly dredged silt foundation are two aspects: (1) the newly dredged silt foundation The load is zero, can not directly bear any ground treatment construction machinery equipment (such as bulldozer, slotting machine, etc.); (2) the content of the clay particles (d < 0.005mm) in the newly dredged silt is high, the white heavy and silt is slow, the content of the strong hydrophilic mineral is high and the soil is absorbed by the combined water. The related performance indexes of the plastic drain board in the current regulation (including the drainage performance index) The engineering practice shows that in the process of rapid reinforcement of the shallow surface of the newly dredged silt foundation, the problem of silting in the vertical drain well is very serious, the efficiency of the drainage is dramatically reduced, and the soil strength between the vertical drains. It is very uneven, the soil strength growth is very limited, the effective reinforcement depth of the foundation is small, and the bearing capacity is low; the ground surface forms many "soil columns" centered on the vertical drainage wells, and the uneven settlement is very obvious. Therefore, the classical consolidation theory of sand well foundation and the existing method for calculating the strength of sand Ichi Ki strength are not completely applicable to this In this paper, firstly, the engineering characteristics of the newly dredged silt in different regions of the mainland of China are systematically summarized and analyzed. On the basis of practical engineering, the field contrast test of different forms of vacuum preloading drainage system is carried out. The negative pressure transfer characteristics and distribution patterns of this kind of foundation are discussed, and the corresponding vacuum is established. Then, according to the drainage consolidation characteristics of this kind of foundation, the calculation formula of soil strength growth is derived, and its rationality is verified through practical engineering. Finally, in view of the two real reasons of the above two treatment, the experimental research is carried out pertinent, and a new type of large area sand bed cushion process is developed. The new technology and new technology of dredging silt foundation provide new ideas for the successful implementation of one-time drainage consolidation treatment for newly dredged silt foundation. The conclusions of this paper are as follows: (1) the newly dredged silt in different regions of China is the product of the dredged silt at the stage of dynamic water deposition and hydrostatic deposition. In the vicinity of the outlet and the area far away from the outlet, the fine particles and fine particles are composed mainly of isolated pores and intergranular pores, and the microstructure characteristics are mainly turbulent and granular inlay structure. The content of d0.005mm and the strong hydrophilic mineral (illite, Mongolia) in the newly dredged silt. The content of the destone is high, the water content is greater than 90%, and the liquid limit is greater than 1.5 times, the pore ratio is more than 2, the plastic index is more than 20, and the engineering characteristic of the liquid index is basically greater than 2.0., which directly causes the newly filled silt foundation to be reinforced by the traditional vacuum preloading technology (including the shallow surface rapid reinforcement technology). There is a great difference between the consolidation deformation characteristics and the general soft foundation. On the macroscopic view, the serious "bending" phenomenon appears in the vertical drainage body and the serious "soil column" phenomenon of the movement of the fine soil particles to the vertical drainage body. (2) the traditional vacuum preloading technology (including the rapid reinforcement technique of shallow surface layer) is adopted. In the process of reinforcement, the loss of negative pressure in the whole drainage system is serious, the most serious is up to 57%, and the loss degree of the negative pressure from the shaft to the surrounding soil is very serious, at least 67%., which is the main reason for the limited increase of soil strength after the vacuum preloading of the newly dredged silt foundation. In the process of vacuum preloading of silt foundation, the negative pressure at the drainage boundary is nonuniform, and the negative pressure in the horizontal drainage cushion can be considered as a linear attenuation model with time change, while the negative pressure in the vertical drainage body can be considered as a nonlinear attenuation model with time variation. The theory of vacuum consolidation is given and the analytical solution is given accordingly. (3) based on the effective stress principle and the stress path method, the strength growth mechanism of the newly drained consolidation of the newly dredged silt foundation is qualitatively analyzed. The analysis results show that the strength growth law of the soil above the groundwater level line and the strength of the soil below the groundwater level line are increased. The long law is not the same. Based on the theory of effective stress uniqueness, the formula for calculating the strength growth of the drainage consolidation of new dredged silt foundation is derived. The formula comprehensively considers the vacuum load and its attenuation along the depth direction, the influence of the external load, the groundwater level and other factors, and relies on the actual engineering to calculate the formula. It is verified that the average error is 8% when considering the undrained shear strength, and the average error is 3.2% when the strength is considered on the failure surface. Therefore, the calculation precision can meet the engineering requirements. (4) the new large area sand cover work cushion is a large spatial stereoscopic structure, which is a water permeable structure, including the flat structure and lateral composite. The flexible structure and columnar structure (no need to set up in the mud foundation). The structure is integrated with the bottom floating (flow) mud foundation and has a high bearing capacity system. It can be used as the working platform of the deep drainage plate construction equipment. The bearing mechanism of this kind of cushion Foundation is mainly embodied in the shell like effect (including stress). Diffusion effect and surface closure effect, lateral closure effect (i.e. side limit), drainage consolidation and vertical reinforcement effect (no action in flow mud foundation). The failure form of this kind of cushion subgrade is characterized by punching shear failure. Scheme 7 (scheme 7 /) (woven geotextile specification is 280g/m2) is the best scheme. Based on the derived bearing capacity estimation The formula carries out the calculation, we know that the plastic load of the 7/ cushion foundation is Pcr=146.4kPa. this kind of cushion foundation service process, it is necessary to do well the cleaning measures and drainage measures in the construction process of the plugged plate. (5) the related performance indexes of the plastic drain board in the current standard (including the drainage energy index and the material strength index) and the high clay content new blowing. The inherent engineering characteristics of filling mud are not suitable, and the current vacuum preloading design is too fast to use the vacuum load loading rate to lead to the premature formation of the "soil column" phenomenon. These two aspects jointly lead to "the rapid reinforcement of the shallow surface layer of the newly dredged silt foundation, the strength of the soil is limited, the effective reinforcement depth is small, and the bearing capacity is still retained." It is impossible to meet the demand for construction land. The experimental results show that the vertical drainage body consisting of a medium equivalent pore (such as O95 0.15mm) and a strong bent core can be used as a vertical drainage system, and the vacuum preloading is strengthened with a faster vacuum load loading rate. The purpose of one-off drainage consolidation treatment is now.
【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU447;TU472

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