It is difficult to accurately measure and quantitatively classify mountainous highway earth-rock mixed waste slag caused by their complexity and man-made accumulation characteristics. Standard and threshold values for quantitative classification are presented by big data for engineering. Subdivision of waste slag is conducive to scientific design and safe protection. Depending on measured particle composition and angle of repose of the multi-phase

multi-position waste slag at several key slag sites in mountainous highway areas

the big data base of earth-rock mixed waste slag is formed. Subgroup features of mountainous highway waste slag composition and angle of repose are statistically analyzed by these engineering data. Main conclusions are drawn as follows: 1) The big data for engineering prove that mountainous highway waste slag has obvious subgrouping characteristics. Using coarse-fine ratio k

the waste slag is divided into three types such as earth-type waste slag

whose k is less than 0.3

earth-rock mixed one

whose k is larger than 0.3 and less than 1.4

and rock-type one

whose k is larger than 1.4. 2) Fine particle proportion of mountainous highway waste slag is less and the coarse particles are the dominant. Probability distribution of waste slag’s coarse-to-fine ratio is N(0.85

0.338 9)

and that of waste slag’s natural angle of repose is N(37.64

3.057 8). The angle of repose of earth-type waste slag is less than 32.6º

that of earth-rock mixed one is larger than 32.6º and less than 42.7º

that of rock-type one is larger than 42.7º. The classification solves problems of sampling and test results’ representativeness. 3) The controlled slope ratios for different types of waste slag are obtained using the formula of safety factor for cohesionless slope

classification and safety factor for different grade slag sites. The controlled slope ratio of earth-type waste slag is less than or equal to 1:2

that of earth-rock mixed one is less than or equal to 1:1.75

and that of rock-type one is less than or equal to 1:1.5. It is found that medium and long stability of the slope can be ensured under these slope ratios suggested. The above conclusions can present basic parameters for dynamic design of mountainous highway waste slag engineering

has remarkable engineering analogy value

and is conducive to forming regional experiences.