Experimental Study on the Soil Conditioning Materials for EPB Shield Tunneling in Silty Sand

Table 2

Test levels and foaming parameters.

Level	Concentration of foam solution (A) (%)	Air pressure (B) (MPa)	Air flow (C) (L/min)	Liquid pressure (D) (MPa)	Liquid flow (E) (mL/min)
1	2.0	0.2	1.0	0.2	50
2	3.0	0.3	2.0	0.3	100
3	4.0	0.4	3.0	0.4	150
4	5.0	0.5	4.0	0.5	200