J. A. Bland writes: A similar approach to the least-squares fitting of the linear Mohr envelope has been presented by Bland (1980, 1981).
Here the theoretical tangent is τ = a¡ + c and for each Mohr circule m=½(¡3 + ¡1), r =½(¡3 -¡1).
Now the above equations (1) and (2) yield equations identical to equations (2) of Lisle & Strom. Furthermore, equations (1) and (2) of Bland (1981) [the iteration in Bland (1980) is not necessary] together with equation (12) of Bland (1980) yield equations (3) of Lisle & Strom.
Another least-squares fitting of the linear Mohr envelope is given by Craig (1974) where the problem is considered in (m, r) space (cf. Fig. 2). Here γ= a¡+c becomes r=a′m+c′ and standard linear regression is used to determine a′ and c′. The shear strength parameters ϕ and c are then determined from