Reference work entry
A joint is a small fracture that lacks any measurable displacement. Based on the time of formation, joints can be categorised as primary joints that formed during rock formation and secondary joints that formed after the rock had formed. Based on the causes of formation, they can be categorised as structural joints and nonstructural joints. According to their mechanical properties, joints can be divided into tensional joints and shear joints. Based on the bedding attitude, joints can be divided into strike joints, dip joints, diagonal joints and bedding joints. Based on the form of the joints and the shape of the rock blocks after being cut by joints, they can be categorised as rhombic joints, columnar joints, plate joints, radial joints, brush joints and torch joints. Joints are the result of tensile stresses, and the distribution of joints is closely related to folding, which is indicative of the mode of the tensile stresses (Fig. 10).
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