Since Mollema and Antonellini observed compaction bands in the field in 1996,different patterns of compaction bands have been found in laboratory experiments.There are some discrepancies between the laboratory experiments and the field observations:compared to the field observation,the stress levels required to induce compaction bands in laboratory experiments are usually higher than the inferred in the field,and the grain crushing are more intense in the laboratory experiments.In this paper,compaction bands were observed at the maximal principal stresses below 8 MPa,which is lower than the stress level inferred in the field,and there was no severe comminution inside the compaction bands.Experimental results indicate that the porosity and confining pressure have great impacts on the types of localization bands.Lower porosity and confining pressure can promote the growth of shear bands and high-angle shear bands.Higher porosity and confining pressure can promote the growth of discrete compaction bands.Intermediate porosity and confining pressure are favorable for the growth of hybrid modes involving two of the three,i.e.,discrete compaction band,diffuse compaction band and high-angle shear band.The formation of discrete compaction bands is more unstable compared to diffuse compaction bands.The two types of compaction bands can appear in the same type rocks,and diffuse compaction bands are formed under lower confining pressure compared to discrete compaction bands.The reduction of permeability was within 2 orders of magnitude in this study,and it is 2 3 orders of magnitude lower than those obtained by other researchers.
