The principle of nonlinear equation proposed by E. Hoek is elaborated, then based on that, new algorithm of obtaining shear strength of rock mass is brought forward by considering the overall or average level when rock mass is broken. Through the new algorithm, the magnitudes of shear stress can be calculated at different given normal stress, generating a series of shear stress and normal stress, and the values of cohesion and friction were determined via linear regression analysis. Then take the research on shear strength of rock mass from China-Myanmar Oil and Gas Pipelines (Domestic Section) Lancang River across domain engineering as an example. It is shown that the values of cohesion and friction according to the new algorithm are consistent with these gained through the Hoek-Brown criterion fitting algorithm. Further comparison study also presents the new algorithm's rationality. The results will provide an important guide for engineering design and construction.
How to obtain reliable shear strength of rock mechanics parameters, it has been an important subject of geotechnical engineering scholars[1]. In many methods to obtain the mechanical parameters of rock mass, large-scale in-situ test is the most direct method and the most accurate, but this test needs long cycle, high cost, and there are still some technical problems that needs to be solved. Therefore, to obtain strength shear strength parameters of rock mass is still relatively difficult, and its development is restricted.
Seeking for methods accepted widely for many engineering practice is becoming a focus of attention for another goal and trend in recent years[2]. It has been found that regard indoor rock mechanics test as a benchmark, considering comprehensive the influence of joint fissure, groundwater and size effect, the rock mechanics parameters are revised and converted into shear strength mechanical parameters of rock mass, which can meet the needs of the engineering. Therefore, this kind of method has obtained the rapid development, mainly including[3–4]: M. Georgi method, Singer method, Chinese academy of sciences institute of geological method, Hoek-Brown criterion fitting algorithm. While Hoek-Brown criterion fitting algorithm is the most widely used and the best effect among these methods[5–7], which can reflect the characteristics of the rock mass structure on the influence of the rock mass strength. But the fitting algorithm is aimed at the maximum and minimum effective stresses, for some applications, this process cannot be gained the shear strength of rock mass under the condition of normal stresses. So the shear strength of rock mass of nonlinear equation proposed by E. Hoek is elaborated, then algorithm of obtaining shear strength of rock mass is brought forward in accordance with the nonlinear equation. The algorithm[8–9] take nonlinear mohr strength envelope line intercept as rock mass failure of cohesive force value, the value is the minimum of any normal stress, Which Can not preferably reflect the overall or average level when rock mass is broken, and the results is the smaller; While in the calculation of the overall or average angle of internal friction, due to introduction of smaller cohesive force and led to the angle of internal friction calculation results is slightly larger.
