다짐된 흙의 균열특성

Abstract

For quantitive measurement of the cracking behavior of soil, determining the tensile strength is one of simplest approaches. However, in geotechnical and geoenvironmental engineering practice, tensile strength of soil is assumed to be insignificant because it is a relatively small value compared with compression strength and the lack of a satisfactory measure. Thus, theoretical and experimental study of the unconfined penetration test (UP) method used to determine the tensile strength was conducted, and then the UP device and experimental procedure were modified to reduce the measurement errors and named as the Improved Unconfined Penetration (IUP) test. Using the IUP test, experiments were carried out to examine the variation in tensile strength as a function of disk diameter, loading rate and pH level. Results of the experiments provided the following important findings. The tensile strength increases with increase in the disk diameter. The disk diameter with 25.4mm is suitable for the IUP tests, because the specimen's failure pattern for this selected disk diameter satisfy the theory of perfect plasticity adopted in this study. The tensile strength is not sensitive to the loading rate in the range of 0.1%/min ∼ 1.0%/min. The ASTM recommendation for the axial strain for the unconfined compression test is recommended. The tensile strength of specimen compacted with pH 9 of water is smaller than that of specimen compacted with for pH 3 and 6 of water. That is, with a low pH value, the higher the tensile strength, because a lower pH solution increases soil particle bonding stresses. The polluted pore fluid as reflected on pH solution affects the particle size and particle distribution trends. Especially, there are significant variations of the value of D10 causing pollution as reflected by pH solution. The tensile strengths obtained from the IUP test show a little lower values than those the split tensile test, but generally good agreement between two values is observed. Therefore, the IUP test is enough reliable for determination of the tensile strength of the compacted sand-bentonite mixtures. In addition, the results of this study can be usefully used for understanding the cracking behavior of compacted soils and also for design, construction, and maintenance of the geotechnical structures.