Friction properties of rock are closely connected with the anisotropy. The anisotropy of rock friction can provide a valuable assessment for geotechnical and geological engineering. In this study, the rotary friction tests were conducted to analyze the water effect on the friction property and the friction anisotropy of the four types of rock. The drilling response model (DD-model) was employed to characterize the rotary friction behavior of the rocks. The parameters of this model include the three types of friction parameters: 1/ς, μ, and f, where 1/ς and μ are constant, and f is a variable. A quantitative method is proposed for assessing the anisotropy of rock friction. The results of the rotary friction tests indicate that the relation between torque force and thrust force conforms to the DD-model. The changes of two friction constants 1/ς and μ from dry state to water-saturated state suggest that the water effect on the friction strength of the rocks exhibits significant anisotropy. The friction strength determined by the friction variable f increases first, then decreases, and finally stabilizes with the increasing of depth. AI_f is an anisotropy index calculated by the proposed method. The percentage difference of the average value of AI_f between water-saturated and dry states shows the degree of the water effect on the friction anisotropy of the rocks, mudstone (MU) > granite (GR) > fine sandstone (FS) > argillaceous siltstone (AS). The quantitative model is hopefully constructed for characterizing the relation between the anisotropic friction strength of rock and the moisture state in future.

岩石的摩擦特性与各向异性密切相关。岩石摩擦的各向异性可以为岩土工程和地质工程提供有价值的评估。本研究通过旋转摩擦试验来分析水对四种岩石摩擦特性和摩擦各向异性的影响。钻井响应模型（DD模型）用于表征岩石的旋转摩擦行为。该模型的参数包括三类摩擦参数：1/ς、μ、f，其中1/ς、μ为常数，f为变量。提出了一种评估岩石摩擦各向异性的定量方法。旋转摩擦试验结果表明，扭矩力和推力之间的关系符合DD模型。两个摩擦常数1/ς和μ从干燥状态到水饱和状态的变化表明水对岩石摩擦强度的影响表现出显着的各向异性。由摩擦变量f决定的摩擦强度随着深度的增加先增大，然后减小，最后趋于稳定。 AI _f 是通过所提出的方法计算的各向异性指数。饱和水态与干燥状态下AI _f 平均值的百分比差值表示水对岩石摩擦各向异性影响的程度，泥岩(MU)>花岗岩(GR)>细砂岩(FS) > 泥质粉砂岩 (AS)。未来有望构建定量模型来表征岩石各向异性摩擦强度与含水状态之间的关系。