乾/濕 砂岩力學行為差別初探

Abstract

In the western Taiwan is almost sedimentary rock of tertiary period. However, these sandstones are often cemented and compacted not well, and sometimes full of unfavorable geological conditions, such as joints, faults and broken mass. Due to a special geological background, it may be caused the following characteristics of sandstone: shear dilation, wetting deterioration and squeezing. Several unsuccessful cases concerned with underground excavation through special geological zone , had been often occurred. In this research, it focuses on the mechanical behavior of dry and wet sandstones with Mushan sandstone which were collected from Beitou area. The experiments included immediately and time-dependent, and types of samples included dry and wet sandstones. Notably, we proceeded a series of pure shear stress tests in order to isolate the influence of volumetric stress and shear stress to the volumetric behavior. According to the experimental results, when samples were wet, which strengths decreased about 45-55% in uniaxial compressive tests, and decreased about 12-15% in triaxial compressive test. In creep tests, the dry samples were broken when shear strength reached to 95% of shear failure strength, and wet samples happened when shear strength reached to 90% of shear failure strength. When volumetric stress raised, both dry and wet samples, the amount of volumetric strain increment which brought about volumetric stress had been smaller and smaller. However, the deformation of wet samples was larger than dry samples. The volumetric strain which brought about shear stress, both dry and wet samples transformed compressibility into dilatability when shear stress had risen. Furthermore, The shear strain which brought about shear stress, both dry and wet samples were linear increment at first, and the shear strain developed fast when shear stress closed to shear distend threshold. The Samples would yield to failure when shear stress closed to failure strength. However, the deformation of wet samples was larger than dry samples. Both dry and wet samples, we had observed the deformation of plasticity and visco-plasticity, they had similar developments.