Research On Engineering Properties Of Spheroidal Weathering Granite In Shaoguan-Huadu Section Of The Wuhan-Guangzhou High-Speed Railway

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.