Deformation Characteristics and Influence Factors of a Shallow Tunnel Excavated in Soft Clay with High Plasticity

Table 1

Characteristics of deformation evolution of the Qinggangshan tunnel exit section and suggestions for construction.

Deformation type		Deformation characteristics		Suggestions for construction
Type	Form	Initial rate	Development trend
Stable development type	“a” line	Slower	The rate decreases and stabilizes rapidly	Increase the construction footage or weaken the strength of support
	“b” line	Slow	The rate increases slowly and then decreases quickly and tends to be stable	Maintain the support strength and construction method in the current state and ensure that support is carried out in time
Rapid development type	“c” line	Faster	The rate decreases slowly or unchanged, develops rapidly, and breaks through critical value in 1-2 days	Unable to do monitoring and early warning, stop construction, and use high strength temporary support
Sustained development type	“d(e)” line	Fast	The rate is relatively stable and lasts for a long time (about 2 weeks); the deformation value increases continually	Strengthen the monitoring and early warning, close the support structure in time, or take some strengthening measures