摘要
在岩土工程理论研究和工程实践中土孔隙度是一个经常遇到和需要明确数值的参数。它的大小由常规土工试验数据换算得出。另外,还可通过压汞试验(包括氦孔隙仪和压汞仪)、薄片观测、扫描电镜图象处理等试验分析得到其数值。这5种不同途径得出的同一套土样孔隙度差别多大?本文以全风化花岗岩为例,通过5种途径对相当数量样品孔隙度进行了试验分析和计算。结果发现,这5种途径得到5种不同孔隙度数值;其差别一方面表现在数值大小上,另一方面显示孔隙度应属不同范畴和物理意义。区别对待这一点对工程计算应用很有意义。物理实验结果换算出的孔隙度为绝对孔隙度,数值结果最大;压汞试验得到的孔隙度是三维空间内孔隙的体积百分比(氦气计测得的为开孔隙度,压汞仪得到的应是有效孔隙度);薄片和扫描电镜图象处理得到的是不同尺度范围上二维平面内孔隙面积百分比,其中以薄片鉴定得到的孔隙度值最小,原因在于在毫米级观察尺度上很多粒内孔隙被忽略掉了。而因为局部结构影响被放大,扫描电镜图象处理得到的孔隙度值变化较大而不很稳定,但微孔隙基本得到了反映。5种孔隙度数值从大到小依次是:绝对孔隙度(物理实验法)>开孔隙度(氦孔隙仪)>SEM孔隙度>有效孔隙度(压汞仪)>薄片孔隙度。总体看它们之间差值较明显。
The porosity is one of the most useful parameters in rock-earth engineering investigation. Usually, its value is calculated from the data obtained from laboratory test. Besides, its values can be gained by means of mercury injection (include helium instrument for porosity test), thin section observation, scanning electronic microscopy (SEM) with digital plates for automatic processing. For the same sample, what is the difference between the results obtained from each method? And what causes these differences? Taking completely decomposed granite (CDG) as an example, this paper tested and analyzed the porosity of the samples through all of these methods.As a result, there exist 5 kinds of results from the 5 approaches. The differences are presented not only in values, but also in their physical meanings. Keeping these distinctive features in mind is significant for computation and application with respect to the porosity. The porosity from physical test is an absolute porosity with the highest value. The porosity from mercury injection test represents the pore ratio in a three dimension (from helium instrument it is the opening porosity, while from the mercury injection is effective porosity). The thin section and SEM observation release pore percentage in a two dimension at different scales. Among them, the porosity from thin section is the smallest since its identification is undergoing in mm scale overlooking some pores within grains or crystals. Local microstructure enlargement makes the porosity from SEM as large as that from helium instrument.From this study, it is found that the porosity values from the 5 approaches is in a sequence from high to low like this: absolute porosity from physical test>opening porosity from helium instrument > the porosity from SEM >effective porosity from mercury injection>the porosity from thin section. Moreover, the differences among these 5 sets of values are obvious.
出处
《地质灾害与环境保护》
2004年第1期75-79,共5页
Journal of Geological Hazards and Environment Preservation
