【作者】 吕国仁；

【导师】 唐春安；

【作者基本信息】 山东大学 ， 工程力学， 2008， 博士

【摘要】 随着我国国民经济的快速发展,高速公路的交通量迅速增长,相当一部分建成使用的高速公路和等级路已不能适应交通量迅速增长和经济社会发展的要求,需要改建和扩建。对旧路拓宽进行升级改造,既节省费用,缩短工期,又可以少占用土地,并有利于环境保护。但高速公路拓宽改建工程会遇到三个关键的问题:(1)新旧地基路基间的差异沉降及其引发的路面纵向开裂问题;(2)新旧路基压实度不均匀问题;(3)新旧路基结合的整体性和强度的一致性问题。本文针对以上高速公路扩建工程中相关的关键技术问题,采用数值模拟和理论分析、现场试验等相结合的方法,对新旧路基的相互作用特性以及强夯技术进行了专门的研究,主要研究内容及成果如下:1)在调研国内外大量高速公路拓宽工程的基础上,对路基拓宽存在的问题进行了综合分析,对路基拓宽差异沉降和开裂机理的研究进行了综述,对目前高速公路拓宽改建工程中采取的消除差异沉降的各种技术措施进行了评价。2)运用有限差分方法模拟高速公路改造中旧路基直接利用的施工过程,对路基不均匀沉降进行流固耦合分析,从而研究旧路基直接利用引起的地基和路基不均匀沉降规律。着重研究了加宽方式、新旧路基高度等多个因素对地基、路基及其差异沉降的影响规律。对地基初始固结进行了计算,并按施工进度进行了模拟;对不同新旧路堤条件下的路堤速度矢量和沉降盆进行了分析;对由于偏心度不同而导致的地基路基最大沉降点的位置进行了探讨。研究发现,高速公路旧路基利用中,若不作处理,在新旧路基的拼接处产生的差异沉降最大。3)基于离心加载方法,利用材料破裂过程分析数值计算方法RFPA,模拟了高速公路扩建工程中引起的路基路堤沉降、基层和面层纵向开裂过程,对单侧、双侧不同拓宽方式及不同填筑高度情况下,路基纵向开裂机理进行了研究,发现路基纵向开裂易发生在新旧路基拼接处。新填筑路堤越高,其稳定性越差,产生的不均匀沉降越严重,随着新路基沉降滑移的不断增加,路基路面产生的附加弯拉应力和附加剪切应力越大,附加应力过大的直接后果就会导致基层产生纵向开裂,基层的裂缝进而反射到沥青面层引起面层纵向开裂。4)对旧路利用中地基路基强夯工艺关键参数进行研究。通过现场动态水压力、超静孔隙水压力和动土压力试验与分析,对地基强夯最优夯击能,两遍夯实之间的时间间隔等关键参数进行了研究,分析了路堤强夯相对于一般地基强夯的不同之处。用动态有限差分法对夯锤与路堤的相互作用过程进行了动态模拟,分析了土体在夯锤作用下的动态响应。运用量纲分析和数值分析等方法,对路堤强夯最优单击夯击能、最优夯击次数、有效深度加固系数的确定进行了研究。给出了考虑地质条件和各种强夯参数的有效深度加固系数的计算公式。通过路面弯沉计算,论证了强夯在旧路利用中的有效性,以及80cm均匀路床区起到的支撑层和缓冲层的作用。5)对威乳高速公路路堤加宽试验段实施了两种方案的强夯试验:第一种为松铺填筑新路堤与旧路,齐平后一起强夯:第二种为分层碾压填筑新路堤,新旧路堤齐平后,对拼接处进行强夯。研究了旧路堤利用中的强夯工艺。提出了强夯质量采用压实度与贯入度控制和相应的检测方法,给出了与以往用固定的贯入度作为止夯标准不同的路堤止夯标准计算公式。夯后进行了压实度测试、回弹、弯沉试验及沉降观测,结果证明两种强夯方案都能满足道路设计要求,但从成本和工期这两个方面来看,方案一优于方案二。通过现场试验的经验和教训,给出了强夯施工工艺要点。6)针对强夯施工振动对周围环境的影响引起纠纷和延误工期等问题,对强夯振动对建筑物的危害和对人员的影响进行了研究,通过现场试验,用快速傅立叶变换对振动数据进行了频谱分析,发现强夯振动主频,与大多数建筑物的主频非常接近,而且竖向振动主频也在人的敏感频率带内。参照国际通用振动界限,通过试验场地及振动测试,得出了建筑物的振动安全距离、人体舒适性降低极限距离、工效降低极限距离以及暴露极限距离。通过对强夯振动产生的应力波传播方式进行理论分析,提出了路堤强夯振动的缩小效应现象。用工程类比的方法,归纳出反映路堤高程的质点振速近似公式。更多还原

【Abstract】 With the rapid economic development of our country, the traffic volumes of expressway are rapidly increasing. A considerable number of expressways in service can not meet the demand of increasing traffic volumes and economic development. Thus they need to be reconstructed and extended. The widening extension of the existing expressway not only saves the costs, shortens the construction period, but also occupies less land and is favorable for environmental protection. But, there are three critical problems widening project of expressway. The first one is the differential settlement between the new and the former roadbed. The second one is the non-uniform compaction between the new and the former roadbed. The last one is the consistency of integrity and strength for combination of two roadbeds. Aiming at the critical technical problems in reconstructed project of expressway, numerical simulation, theoretical analysis and in situ experiments were adopted to study the interaction of new and existing roadbed and dynamic compaction. The main points and achievements were as follows.(1) On the basis of surveying of substantive expressway widening projects home and abroad, the existing problems of widening roadbed were systematically investigated and the techniques were evaluated. The mechanism and the main influencing factors were analyzed for differential settlement of new and existing roadbed.(2) The construction process of direct use of existing roadbed was simulated by the finite difference method. The fluid-solid coupled analysis was performed for the differential settlement of roadbed. The influence law on foundation, roadbed and differential settlement, caused by widening mode and height of roadbed, was studied mainly. The initial consolidation of the foundation was calculated, and the simulation was performed according to the construction progress; the velocity vector and sedimentation basin of the embankment were analyzed under different new and old embankment; the largest settlement points’ position of the roadbed foundation caused by the different eccentricity was probed. The result showed that there would be great differential settlement in junction of roadbed if the existing roadbed was utilized directly without treatment. The value of differential settlement can not meet the demand of specification.(3) On the basis of the centrifugal loading method, the settlement process of roadbed and road embankment, also the longitudinal-cracking process of base course and surface were simulated by using RFPA with the numerical calculation method of material cracking process analysis. The study on the cracking mechanism of roadbed was carried out, under the condition of unilateral and bilateral widening and different fill depth. It was found that the cracking often happened in the junction of new and existing roadbed. The higher embankment was, the worse stability was, the more serious differential settlement was. With the increase of settlement slip of widening roadbed, the value of additional bending tensile stress and shear stress became higher and higher, and it directly resulted to the longitudinal cracking of the base course. Furthermore, longitudinal cracking of asphalt surface happened, infected by cracks of base course.(4) The key parameters of dynamic compaction in using of existing roadbed were studied. From the results of the tests and analysis of the site dynamic water pressure, the excess pore water pressure and the dynamic soil pressure, the key parameters were drawn such as the optional energy of dynamic compaction and the interval distance of two consolidates. The interaction between rammer and embankment were simulated by FLAC3D, and the dynamic response of the soil under the action of rammers was analyzed. Utilizing dimensional analysis method, the determinations of the optional click tamping energy, the optional number and the reinforcement coefficient of effective height were studied. The formula of reinforcement coefficient of effective height was derived considering geological condition and dynamic compaction parameters. The effectiveness of the use of the dynamic compaction in the existing roads was demonstrated through calculation of road face deflection, and it found that 80cm uniform roadbed played a role as support layer and buffer layer.(5) Two options of trial dynamic vibration were conducted in the embankment test section of the Wei-Ru expressway. The first trial was that fill the new road embankment until it was flush with the existing one and perform dynamic compaction for both two embankments. The second trial was that perform stratified rolling compaction for the new road embankment until it was flush with the existing one and carry out dynamic compaction on the junction. It was presented that the quality of dynamic compaction should be controlled by degree of compaction and length of penetration. And the corresponding testing method was proposed. The formula of cease-compaction standard for road embankment was derived, which was different to the former one. According to the compaction degree tests, rebound and deflection test, and settlement observation, both two options can satisfy the design requirements. But the first one was better than the second one if cost and time were considered. The key points of dynamic compaction were obtained on the basis of practical experience.(6) With regard to disputes and delays caused by construction of dynamic compaction to surrounding environment, the author conducted a research about the hazards to the building and the personnel influence caused by the construction of dynamic vibration. The filed tests were performed and the spectral analysis was done for vibration data using Fast Fourier Transform method. It was found that the main frequency caused by dynamic vibration was close to the frequency of majority of buildings. Moreover, the vertical vibration frequency was also located in the people’s sensitive frequency band. According to international general vibration limits and the site and vibration tests, the safe distance of the buildings, the human comfortable limit distance, the work efficiency limit distance, and exposure limit distance were gained through the in situ test and vibration tests. The contraction effect of road embankment was found under the vibration of dynamic compaction and was theoretically analyzed through the transmission way of the stress wave. An approximate formula was introduced through engineering analogy method, which is to show the particle velocity at the height of the embankment.更多还原