Physical Processes in Earth and Environmental Sciences Phần 6

Ảnh hưởng của áp suất chất lỏng lỗ chân lông trong sự hình thành vết nứt. (a) Với sự khác biệt giữa cao nhấn mạnh gãy xương Coulomb có thể được sản xuất khi các vòng tròn Mohr di chuyển sang bên trái do áp lực chất lỏng lỗ chân lông.
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Physical Processes in Earth and Environmental Sciences Phần 6LEED-Ch-04.qxd 11/28/05 6:56 Page 156 156 Chapter 4 (a) (b) pe lo ve t t en Effective re Applied lu Fai stress stress Applied 2u = 180º 2uf = 120º stress sn s1 Εs3 = T0 Εs1 Εsn s3 s1 Εs1 Εs3 s3 sn sn 2uf = –120º Effective stress Pf Stable field Pf Fig. 4.91 Effect of pore fluid pressure in fracture formation. (a) With high differential stresses Coulomb fractures can be produced when the Mohr circle moves to the left by pore fluid pressure. (b) With low differential stresses, even when the applied stress may be compressive, and fully located in the field of stress stability, fluid pore pressure can reduce the effective stress displacing the circle to the tensile field and producing joints if the condition E 3 T0 is satisfied. to a lower level, while maintaining the differential the field of stress stability, fluid pore pressure can reduce stress(Fig. 4.91). With low differential stresses, even when the effective stress displacing the circle to the tensile field ˜ the applied stress may be compressive, and fully located in and producing joints if the condition E 3 T0 is satisfied. 4.15 Faults Faults are fracture surfaces or zones where several adjacent 4.15.1 Nomenclature and orientation fractures form a narrow band along which a significant shear displacement has taken place (Fig. 4.92a, b). Fault nomenclature is often unclear, coming from widely Although faults are often described as signifying brittle different sources. For example, quite a lot of the terms deformation there is a transition to ductile behavior where used to describe faults comes from old mining usage, even shear zones develop instead. As described in Section 4.14, the term fault itself, and the terms are not always well con- shear zones show intense deformation along a narrow band strained. Fault surfaces can be inclined at different angles where cohesive loss takes place on limited, discontinuous and their orientation is given, as any other geological sur- surfaces (Fig. 4.92c). Faults are commonly regarded as large face, by the strike and dip (Fig. 4.94a). A first division is shear fractures, though the boundary between features made according to the fault dip angle; high-angle faults are properly regarded as shear fractures or joints is not sh ...