Table 2. The calculated Lagrange multipliers under different confining pressures.

Rock classification	Confining pressures /MPa	Lagrange multipliers
		λ 0	λ 1	λ 2	λ 3
Sandstone	0	4.45679	0.02667	-2.053725×10−4	3.95647×10−7
	5	4.26732	0.02475	-2.40024×10−4	6.24729×10−7
	10	5.45264	0.02547	-2.84668×10−5	-5.45348×10−8
	20	4.57542	0.01621	-5.45348×10−8	-1.98512×10−8
Marble	3.5	3.90680	0.07510	-1.4×10−3	5.58639×10−7
	7	3.97580	0.04340	-2.0×10−4	-4.15684×10−7
	14	4.17670	0.04660	-5.0×10−4	-1.27865×10−8