Distribution characteristics and controlling factors of vertical joint spacing in sand-mud interbedded strata

• DOI: 10.1016/j.jsg.2019.103886
• Publication Date: 2019-09-03T12:47:23Z
• Authors: Han Bao; Yong Zhai; Hengxing Lan; Keke Zhang; Qun Qi; Changgen Yan
• Keywords: Outcrop; Saturation (graph theory); Log-normal distribution

Abstract Nearly 3,600 vertical joints were measured in sand-mud interbedded rock masses from 30 outcrops in the Yan'an area, China. Information such as joint spacing, joint aperture and the thickness of sandstone formations was obtained. Results show that the vertical joints are well developed in the study areas, and the fracture spacing tolayer thickness ratio (S/T) can reach 0.79. The joint spacing has a strong positive linear relationship with the thickness of the sandstone layer and presents a lognormal distribution in each sandstone layer. However, the morphology of the lognormal distribution is related to the degree of joint development; the higher the degree of joint development, the smaller skewness of the joint spacing distribution. In addition, although the value of S/T for saturate joint is generally 0.8–1.2, the vertical joints may reach saturation at greater S/T by penetrating multiple layers of sandstone when the intervening soft layer is thin.