碎屑流地质灾害常常会引起惨重的人员伤亡和巨大的经济损失，因此广被研究。但是以往研究对于坡度和基底滑动面类型对碎屑流的影响不够系统详尽。因此研究中设计了直剪试验以测定试验材料及其与界面间的力学性质，在此基础上开展了不同坡度和不同基底滑动面使得干碎屑流模型试验，以研究碎屑流的运动特征、堆积形貌、运动能力。研究中利用直剪试验为碎屑流模型试验的理论计算提供基础参数（摩擦系数），通过3D扫描仪和高速相机记录模型碎屑流的运动过程。试验中主要得到：

（1）较小坡度时，光滑滑动面上碎屑流的运动过程和动力参数与粗糙滑动面上的明显不同；但在较大坡度时，碎屑流运动过程受滑动面类型差异影响较小。粗糙滑动面的粗糙程度对碎屑流的运动过程和动力参数影响不显著。碎屑流运动时受力状态是极不稳定的，尤其是前缘颗粒，会受到后续颗粒的碰撞力作用，从而具有较大的加速度。在大坡度时，其加速度数值接近甚至超过了重力加速度。粗糙滑动面相比于光滑滑动面能够很大程度上约束碎屑流的影响范围，这种约束在较小坡度时更加显著。但粗糙滑动面的粗糙程度对碎屑流影响范围产生的影响较小。

（2）结合砂箱试验发现：横向脊是碎屑流颗粒在缓慢挤压堆叠中形成的；双峰形态是后期碎屑流体对前期已抵达底板的碎屑流体进行冲击造成的；共轭槽是碎屑流体在前阻后推侧约束的力学条件下沿平整光滑基底面整体向前运移的过程中形成的。横向脊和双峰形态的形成主要依赖于坡度条件，基底滑动面光滑与否会改变这些表面形态产生的坡度范围，并不是这些表面形态产生与否的先决条件。共轭槽的形成同时依赖于坡度条件和滑动面条件，只有当基底滑动面较为平整光滑，且在中等坡度下才会产生。实际中乱石包岩崩同时满足共轭槽形成时所需的这两种条件。

（3）随着坡度的增大，试验碎屑流的视摩擦系数呈指数形式增大，对于以往研究也是如此。试验碎屑流的运动距离随着坡度的增大呈线性减小的趋势，在平整光滑滑动面上时的减小速率更快，而在粗糙滑动面上时减小速率较慢。

（4）基于物体因与固定面发生碰撞而产生的能量损耗率与该物体运动方向和固定面法线方向间锐夹角呈指数关系的条件，研究中推导出的视摩擦系数随坡度的理论方程能非常好的与文中试验数据和先前学者的数据相吻合，并且能较好的反映实际岩崩碎屑流随坡度的发展趋势，因此能较好的用于试验和野外碎屑流视摩擦系数的预测。

Debris flowslides are intensively studied due to their extreme effects to human life and economy. Nevertheless, it is not systematical and detailed to the research of debris flowslides under the influences of slope angles and the types of basal surface. Hence, we employed the direct shear tests to obtain the mechanical properties of experimental materials and the shear interfaces, which served for the theoretical deduction of experimental debris flowslides. In addition, we conducted sandbox experiments at different slope angles and different basal surfaces to probe the debris flowslides’ motion process, deposit morphology, and mobility. These experimental debris flowslides were monitored with an advanced 3D scanner and two High-speed cameras. The main conclusions are as follows:

(1) At relatively low slope angles, the motion process and the kinetical parameters of the experimental debris flowslides on the smooth basal surface are significantly different with those on coarse basal surfaces, which attributes to the basal friction that affects their motion behavior mainly. However, it is converse at relatively large slope angles because the gravity force during free falling of the particles affects their motion behavior mainly. Their motion processes and dynamical parameters are less depending on the coarse degree of the coarse basal surfaces. Their dynamic states are extremely unstable, especially to front particles. They will subject to the collision force from rear particles, and therefore gain a large acceleration that will be close to and even exceed the gravity acceleration. The coarse basal surfaces can constrain the influence area at a large extent compared with the smooth basal surface. The lower the slope angles are, the more obvious the constraining effect will be. However, the influence area of the debris flowslides is less influenced by the coarse degree of the coarse basal surfaces.

(2) From the sandbox experiments, we found that the transverse ridges were formed during the process of slow compression and stacking; the double upheaval was formed due to the impact effect of the later sliding mass to the sliding mass already reached to the horizontal plate; the conjugate troughs were formed in the process that the debris flowslides moved forward along the smooth basal surface under a condition of resisting at front, pushing at back, and confining at flanks. The slope angles determine whether there are transverse ridges and double upheaval, while the basal surfaces are not a basic condition for the formation of these two surface structures. However, what the basal surfaces are smooth or not will change the slope range for the formation of these two surface structures. The conjugate troughs rely on both slope angles and basal surfaces. They could form only at a smooth basal surface and moderate slope angles. In fact, these two conditions are confronted for the Luanshibao rock avalanche.

(3) The apparent friction coefficient increased exponentially with the slope angles, and the same is true of others studies. The runout of the experimental debris flowslides decreased linearly with the increase of slope angles. The decreasing rate of runout is fast at smooth basal surface, but slow at coarse basal surfaces.

(4) A theoretical function between the apparent friction coefficient and the slope angles is proposed, based on a hypothesis the ratio of energy dissipation occurring when an object collides with a plane is exponentially related to the sharp angle between the object’s direction and the plane’s normal direction. The theoretical function can reflect well the field data and the data of the experiments and of others studies. Therefore, it can be used to predict the runout of experimental and field data if we know their slope angles.

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