Characteristics of Unloading Creep of Tuffaceous Sandstone in East Tianshan Tunnel under Freeze-Thaw Cycles

Table 4

The variation of volume creep.

Stepwise unloading	T0 specimen		T20 specimen		T40 specimen		T60 specimen
	Differential stress (MPa)	(10^−3)	Differential stress (MPa)	(10^−3)	Differential stress (MPa)	(10^−3)	Differential stress (MPa)	(10^−3)
Initial state (20 MPa)	158	1.49	134	1.31	114	1.27	100	1.16
First step (17 MPa)	161	0.72	137	0.42	117	0.24	103	0.02
Second step (14 MPa)	164	−0.34	140	−0.65	120	−0.94	106	−1.62
Third step (11 MPa)	167	−1.52	143	−2.05	123	−2.42	109	−3.39
Fourth step (8 MPa)	170	−3.46	146	−4.51	126	−5.12	112	−5.67