【作者】 冯涛；

【导师】 吴光；

【作者基本信息】 西南交通大学 ， 岩土工程， 2007， 博士

【摘要】 球状风化是花岗岩层中十分常见的一种现象,关于球状风化的研究,一般都是在工程实践中,结合某一个或几个特定的工点,提取少数钻孔岩芯样品进行室内试验,研究其对工程产生的危害性、对施工造成的复杂性以及相应的工程处治措施,而没有对球状风化的工程特性进行系统研究,尤其缺乏从显微组构特征方面对球状风化花岗岩力学性能的分析成果。针对花岗岩地段普遍发育的球状风化现象,本学位论文结合科研项目“武广客运专线韶关至花都段球状风化花岗岩工程特性与综合勘探成套技术研究”,对武广客运专线韶关至花都段沿线的球状风化花岗岩,采用岩矿微观分析试验、地质调绘、原位测试、室内试验等多种手段,对风化花岗岩的显微组构变化特征及其对花岗岩力学性能的影响以及风化花岗岩的宏观物理力学性能变化特征进行了分析,并从微观和宏观两个角度,对球状风化体的形成机理、分布规律及工程特性进行了分析,建立了球状风化花岗岩的综合勘察技术,并提出相应的工程处理措施。主要的结论和研究成果如下:(1)花岗岩的不同风化层具有不同的显微组构特征,无论是在细观组构特征(包括结构、微裂隙发育程度、矿物晶形自形程度、矿物表面模糊程度、矿物成分及相对含量、风化产物成分及相对含量)还是微观组构特征(包括整体微结构、矿物粒间联结方式、微裂隙发育程度以及矿物中元素相对含量)上,都有着明显的区别。显微组构特征的不同也导致了不同风化层具有不同的力学性能,这也从对风化花岗岩宏观物理力学性能变化特征的分析上得以印证。根据上述从微观和宏观两个不同角度的分析,可对风化花岗岩的物理力学性能有一个比较全面的认识。(2)风化球体具有与同等风化程度的风化层岩样相似的显微组构特征和宏观物理力学性能。无论是在细观组构特征、微观组构特征还是宏观物理力学性能上,弱风化球体都具有和弱风化岩样相似的特征,强风化球体都具有和强风化岩样相似的特征,这也意味着风化球体将具有明显区别于赋存环境周围岩土体的物理力学性能。(3)球状风化花岗岩的形成机理:在花岗岩中,三组原生节理将岩体分割为许多呈长方体或正方体形态的岩块,在风化过程中,原生节理相交的部位表面积最大,风化作用最集中,风化速度最快,从而更容易被风化掉,岩块体的棱角逐步被圆化,岩块逐步变小。有些部位的岩块,由于具有有利于岩块力学性能提高的显微组构特征,当风化作用进行到这些部位的时侯,风化速度减小,此时周围的岩土体的风化速度高于这些部位,随着时间的推移,这些部位的风化程度会明显的低于周围岩土体的风化程度而呈现出“孤石”的状态。由于棱角的不断圆化,这些部位的呈“孤石”状态的岩块的表面棱角很少,而常常表现出似椭圆体的形态。(4)花岗岩球状风化分布规律:在地表,风化球体成单个零星分布、线状分布或群体分布,地表风化球体发育往往意味着地下赋存有风化球体;在地下,风化球体的分布规律具有以下特征:风化球主要分布在全风化带中;风化球体的表现形式主要为全风化带(W4)中含强风化(W3)球体或弱风化(W2)球体;风化球体大小主要集中在0～5m,风化球体所在高程主要集中在0～60m之间,其中20～30m之间的最多;风化球体的埋深主要集中在0～40m,其中0～20m最为集中。由上往下,从全风化带向强风化带,风化球体表现出“上小下大、上多下少”的总体变化趋势。(5)球状风化花岗岩综合勘察技术:首先,应对花岗岩地段,进行详细的花岗岩风化球的地表调绘,并按照发育和不发育两种类型对花岗岩地段进行分区;其次,针对地表风化球发育的地段,展开钻探工作,揭示局部的风化球体的发育情况、赋存特征、地质特征,从而为工程设计和施工提供参数和处理意见;而对于地表风化球不发育的地段,可只选择部分地段进行钻探。(6)球状风化花岗岩的工程特性:风化球体的存在,破坏了所在风化层力学性能的宏观均匀性,二者所形成的“整体岩体”的变形破坏机制也不同于无风化球体存在的风化层岩体,它的力学强度高于不含风化球体的风化层,低于与风化球体具有相同风化程度的风化层,变形破坏也相对于不含风化球体的风化层更难,而相对于具有相同风化程度的风化层更易。风化球体往往具有“近椭圆形”的外观,且其长轴平面并不都是水平面,而往往是倾斜面,容易引起风化球体的不均匀沉降变形和转动。因此,含风化球体的风化层既不能视为具有与风化球体相同风化程度的风化层“基岩”,也不应完全不考虑风化球体。(7)球状风化花岗岩的工程处理措施:加强对球状风化的地质勘察,在勘察阶段已发现风化球发育的情况下,桩基设计应尽量避免风化球发育带;如果无法避开,则在地表风化球体发育的地段,钻探深度要适当加深,尽量避免误将弱风化球体视作基岩。在路基工程中,对于埋深较浅而块径较小的风化球体可以人工挖除,并填土压实,对于块径较大的可以考虑爆破清除,或者在上布置砂垫层以扩大受力面积,减少风化球体的影响。在桥基工程中,也可采用人工挖除、爆破清除和布置砂垫层的方法,不可将风化球体作为受力层而在上面布置端承桩和摩擦桩等桩基础。更多还原

【Abstract】 Spheroidal weathering is a very common appearance in granite or bassalt or sandstone,which is similar to different weathering.But,the different weathering usually occurs in the different rocks,while the spheroidal weathering in the same rocks.About the spheroidal weathering,we usually get some drilling samples in certain or some bores during engineering geological prospecting for experiment analysis,which can help us to realize its damage and adverse effect and operation characteristic to construction.At the same time,the research on its mechanism and occurrence and engineering properties are ignored.And now the problem is expected to be solved .In this article, on the basis of geologic drilling on the granite area along the Shaoguan-Huadu section of the Wuhan-Guangzhou high-speed railway, the author analyzed the weathering microproperties of the drilling samples by the optical microscope and scanning electron microscope and X-ray diffractometer to get the microscopic mechanism.On the other hand,by percussion boring and in situ tests and laboratory tests,the macroscopic physical and mechanical properties of weathered-granite layers were analyzed.Then based on the results of micro analysis and macroscopic analysis,the mechanism and occurrence and engineering properties of spherodial weathering of granite were analyzed,and the comprehensive survey method was built,and the corresponding engineering safety measures were suggested.The research work involves several aspects as follows:1.By the optical microscope and scanning electron microscope and X-ray diffractometer experiments,the author found the difference of micro-structure in the diffent weathered layers of granite,which concluded the texture, the development degree of micro crack,the main mineral constituent,the weathering products constituent ,the visibility of the minerals’ optical surfaces, the visibility of the crystalline form,and the jointing modes of particles,and so on.The difference of micro-structure would result in the difference of mechanical properties of rock,and this guess had been confirmed by the macroscopic analysis.2.The micro-structure properties and the physical and mechanical properties in the spheres which weathering degree were weak were similar to the weakly weathered samples,and the micro-structure properties and the physical and mechanical properties in the spheres which weathering degree were strong were similar to the strong weathered samples.3.The mechanism of spheroidal weathering of granite could be described as following:in the weathering process,the sections in which the joints intersected had maximal surface areas,and were more easily weathered,and their edges would be rounded.Some rocks in the granite rock mass had the micro-sturcture which was more advantageous to mechanical properties would be weathered more slowly,and their weathered degree would be more weak than the rocks all round and be isolated.So the isolated spheres would apperanced.4. By statistically analysis about the characteristics of the weathered-granite spheres,the occurrence of above-ground spheres could be showed as follows:the conclusion of the surface geological survey was accordant to the conclusion drawn by analyzing the drilling samples,that is,when large spheres were found baring above ground,the subsurface spheres could be expected,otherwise,founding the subsurface spheres would be unlikely.Further more, the occurrence of subsurface weathered-granite spheres could be showed as follows: (1)the weathered-granite spheres were mainly located at the complete-weathering zone,and almost of the spheres were strongly weathered while the other were weakly weathered;(2)the appearance of the weathered-granite spheres was mainly complete weathering-strong weathering-complete weathering or complete weathering-weak weathering-complete weathering,secondly strong weathering-weak weathering-strong weathering;(3)the vertical diameter of the weathered-granite spheres ranged from 0 to 5 m,and almost of them were located at the complete-weathering zone;(4) the weathered-granite spheres were mainly located at the depth of 0 to 40 m below the ground surface,even 0 to 20 m;(5)the height of the weathered-granite spheres ranged from 0 to 60 m,even 20to 30 m;(6)generally speaking,the occurrence could be generalized as "upper small and many ,while lower big and few".5.The comprehensive investigation method of spheroidal weathering of granite was showed as follows:firstly,the surface geological survey should be done;and then in the places where large spheres were found baring above ground,the geological exploration should be done. 6.The engineering properties of spherodial weathering of granite could be described as following:the spheres altered the homogeneity of original weathered layers,and the "whole rocks" were anisotropic.The mechanical strength of the "whole rocks"was higher than the original weathered layers but lower than the spheres,and its modification and breakup was more hard than the original weathered layers but more easy than the spheres.On the other hand,differential settlement usually occurred in the spheres.7.The corresponding engineering safety measures of spheroidal weathered granite were suggested as following:the comprehensive investigation of spheroidal weathering was necessary in the first stage of engineering,which could help us to find the occurrence of spheroidal weathering.And the drilling depth would be more big in the section where the spheres were found.And by manual excavation and explosive excavation we could clear the spheres.更多还原