| Granite Residual Soil(GRS),is distributed widely in south of China.There are a large amount of pre-existing fracture inside the soil and is prone to the development of secondary crack if surroundings changing for its special genetic.The properties of GRS are inhomogeneous and are prone to softening and disintegrating when encountering water. Therefore,engineering accidents is always initiated by GRS.Taking the urban railway traffic engineering in Guangzhou as the case,there are several accidents during construction for the reason of unclear understanding of the engineering characteristics of GRS.It is a vital subject that recognizing its engineering characteristics,especially disintegration characteristics.The research contents of this paper are discussed as follows.The reconnaissance reports collected in Guangzhou have been investigated thoroughly and statistical analysis has been carried out in order to understand the engineering properties of GRS.Besides,field sampling and supplementary tests(including rock mineral identification, mineral and chemical ingredient,SEM tests and normal physical & mechanical tests) have also been accomplished.Based on all the outcomes,classification system of GRS in Guangzhou currently was questioned,and a new advice was also discussed as the evidence for geological engineering plotting to classify the GRS and division of fundamental geological elements.Based on the understanding of engineering geological characteristics of GRS in Guangzhou, disturbed soil from sampling spot Tianhe has been chosed and samples of different control factors has also been confected to used to take indoor disintegrating test using self-regulating disintegrating testing device.52 sets of sample has been totaled tested observing the disintegrating process,mensurating the disintegrating amount at various time,and plotting disintegrating curve.So that quantificational estimates can be gained.Conclusions can be drawn as follows.The average speed of stability stage,which is also considered as the slope of linear stage,has been used as the main factor to estimate the disintegration properties of soil.1.The process of disintegration is not homogenously.In actually fact,it is a process that from incursion of water to run-through of fracture and at last breakage,which is also a slaking process from surface to inside.The modality of chipping result from disintegration is always dusty and granular,and sometimes appears as nubbly.There are large quantities of blebs coming during the course of tests,and the water quality become feculent gradually.2.The results of samples with different disturbed state(but the same previous water content with 17.7%,the degree of compaction 100%) can be shown as follows.It costs the least time in samples after losding water treatment in the process of disintegration,lies between 10.9～12.02min.The diachronic of samples after maintencance treatment is longer,lies between 32.6～36.35min,while samples after water absorption and maintencance treatment costs the longest time,56.8min.3.The results indicated that previous water content and the degree of compaction during confecting samples are the immediate factors controlling the disintegrating velocity if the surrounding and composition are the same.The disintegrating velocity of GRS samples decreased with increasing previous water content and the degree of compaction.4.The previous water content and the degree of compaction during confecting samples determine the effective void ratio,namely the ratio of the volume of gas inside the soil sample to the volume of soil particle.Linear regression analysis has been carried out between various effective void ratio and the disintegrating velocity of GRS samples.The results indicated that the correlation coefficient is up to 0.9,which is also reveal that effective void ratio can be another dominate factor impacting the disintegrating property of soil.5.According to the general view,the velocity of disintegrating increases if the temperature becomes higher.The influence of temperature(from 15℃to 35℃) to the disintegrating velocity is not so obvious,namely the velocity in case of higher temperature is not lower than the case of lower temperature.The factor of temperature is also considered synthetically with other control factor,from which the conclusion is the same.6.Grey correlation model has been also used to analyze the influence of previous water content,compaction degree during confecting samples,surrounding temperature and effective void ratio(porosity).The ordering of grey correlation degree can be illustrated as follows:effective void ratio＞effective void porosity＞compaction degree＞previous water content＞surrounding water temperature.7.Soil is a kind of porous media.So there can be a difference of reading data(denoted by x) between the initial reading data(denoted by R0 ) and the reading data that gas inside the sample released(denoted by R1).The tested results indicated that x is positively,correlated with the effective void ratio(porosity) of sample.If x is considered during calculating disintegrating amount,and assumed the process of gas releasing is homogeneous,the calculated amount is lager than the case that not considering it.The above conclusion can be applied to correcting the indoor test results.Based on all above research and other thorey,the mechanism of GRS's disintegration has also been discussed.It is considered that disintegration of soil needs the following 3 sufficient conditions:①There are enough routes for water infiltrating into the soil;②Cementation between granule of soil has been destroyed by the phenomenon of intenal stress concentration, which is not reversible;③Soil water stability of dolomite cement is not strong enough and is prone to dissolution once contact with water.Besides,exsitence of freeing surface can be considered as the necessary condition of disintegration of soil.In metro construction of Guangzhou,the main geotechinical problem exists in excavation of underground chambers and tunnels(especially during mine method construction) as well as deep foundation trech excavation.There can be a certain significance of the conlusions of this paper to metro construction of Guangzhou.The innovative points of this paper lie on the following 2 points.1.Based on the equation presented by literature[51],systematic error because of emitting of gas inside the soil sample has been discussed from the disintegrating test,so that can be applied to modify the disintegration amount calculated from measured index.2.The surrounding water temperature is considered as the influence factor of the disintegrating characteristic.Disintegrating tests have been carried out at different temperature (from 15℃to 35℃),so that the disintegrating correlative quantitative index can be gained. Based on all these index,temperature has been considered as an major factor applied to analysis separately and coupled with other factors.
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