【作者】 艾英钵；

【导师】 施建勇； 陈贵；

【作者基本信息】 河海大学 ， 建筑与土木工程， 2006， 硕士

【摘要】 本文结合广州港南沙港区真空预压加固吹填陆域软土地基工程开展抽真空对周围环境影响的现场试验研究及有限元分析研究,现场试验研究重点围绕三个有代表性的试验区开展,观测了抽真空过程中周围土体沉降及水平位移随抽真空时间的变化,结合三个试验区的现场试验,采用基于比奥固结理论编制的有限元程序,通过计算结果与现场实测资料的对比,验证计算方法的合理性,在此基础上,研究反映土体特性的本构模型参数的变化对真空预压加固区周围土体的沉降及水平位移的影响,并对采用格栅状水泥搅拌桩及水泥旋喷桩的防护效果进行了分析。结果表明,抽真空对加固区周围土体的影响距离及深度与加固区外土体的土质条件有关,周围土体的土质条件越好,影响距离及深度越小;土质条件越差,影响距离及深度越大。试验区的土质条件下,最大影响距离超过50m,影响深度在15m以上,而对于加固区外已加固的试验区,由于土质条件好,影响距离约15m。抽真空对周围环境的影响随抽真空时间的增长逐渐减弱,开始抽真空后的30天内影响最大,该段时间内的沉降及水平位移占抽真空完成时的80%以上。随土体特性的参数K、e₀、κ的增大,加固区周围土体的沉降和水平位移相应增大且随距离的增加逐渐衰减。土体抗剪强度c、φ提高,拉裂区范围明显减小,而表层土体抗剪强度较低时,离加固区边界60m处都有可能出现拉裂破坏。打设旋喷桩或者水泥搅拌桩墙,对周围土体的沉降及水平位移起很好的调节作用,使土体变形主要集中在隔离墙内侧,大大减小加固区外侧周围土体的变形,并减小抽真空对建筑物的张拉应力,相比之下,打设格栅状水泥搅拌桩的效果稍好于旋喷桩,因此,采用隔离防护时,应尽量选择宽度大的格栅状挡墙。更多还原

【Abstract】 Field studies and finite element analyses of the impact of vacuum preloading on surrounding soils were carried out for a soft ground improvement project of Nansha hydraulic filling area of Guangzhou harbor. The emphasis of the field studies were placed on the observation of settlement and subsurface lateral displacement during vacuum preloading of three representative pilot test sites. A finite element program was coded based on the Biot consolidation theory, and the rationality of the program was verified by comparing the calculated results with the field test results. With the program, the influence of soil constitutive model parameters on the settlement and the lateral displacement of the soils surrounding the ground improvement area was studied. The protection effect of grid-shape cement-mixing piles and spiral spray piles were also analyzed. It has been shown that the extent and the depth of the influencing area of the vacuum preloading are related to the soil conditions outside the preloading area. The better the soil conditions, the lesser the influence extent and depth will be, and vice versa. Under the soil conditions of the pilot test sites, the maximum influence distance is over 50 m, the influence depth is over 15 m. For the ground-improved test site outside the improving site, the influence distance is approximately 15 m due to its relatively well soil conditions. The influence of vacuum preloading on the surrounding soils weakens gradually with the duration of vacuum pumping, and the significant influence occurred in the first thirty days. During this period, over 80% of total settlement and lateral displacement was completed. With increasing soil parameters K、 e0、k, the settlement and lateral displacement increase, but reduce gradually with increasing distance away from the preloading boundaries. With increasing soil strength parameters c and φ the extent of tension fracture area reduces obviously. However, when the shear strength of upper soil layer is lower, the tension fracture may appear within a distance of 60 m away from the preloading boundaries.Jet grouting pile wall and grid-shape soil-cement deep mixing pile wall play an important role in adjusting the settlement and lateral displacement of surrounding soils. With these piles, soil deformations concentrated mostly inside the walls. The soil deformations outside the wall and the tensile stress on buildings induced by the vacuum pumping were reduced greatly. Comparatively, the influencing effect of the grid-shape cement-mixing piles is better than that of the spiral spray piles. Therefore, relative wide grid-shape cement-mixing pile wall should be adopted at the first priority to isolate the influence of vacuum preloading on the surrounding soils.更多还原