Interaction between Vetiver Grass Roots and Completely Decomposed Volcanic Tuff under Rainfall Infiltration Conditions

Table 7

Results of large-scale direct shear test.

Sample number	Designed normal stress/kPa	Peak state			Residual state		Root area ratio
		Displacement/mm	Normal stress/kPa	Shear; stress/kPa	Normal stress/kPa	Shear stress/kPa
Rooted_1	20	16	22.4	32.2	24.5	19.8	1.98%
Rooted_2	40	18	51.3	39.5	42.9	25.4	0.88%
Rooted_3	60	32	71.5	46.6	67.5	41	1.60%
Rooted_4	80	22	82.9	54.4	84.6	41.4	2.45%
Rooted_5	120	16	124.2	76.1	128.4	62.2	2.11%
Nonrooted_1	10	15	10.7	14	9.6	10.4	- - -
Nonrooted_2	80	29	80	45.5	79	34	- - -
Nonrooted_3	120	36	120	63	120.3	54	- - -