How can you determine the appropriate slope angle to prevent soil creep?

1 Identify the soil type

Different types of soil have different properties and behaviors when subjected to shear stress and strain. You need to know the soil type, texture, structure, moisture content, and density of the slope material, as well as the underlying bedrock or foundation. You can use soil maps, field tests, laboratory tests, or geotechnical software to identify and classify the soil type.

2 Analyze the slope geometry

The slope geometry refers to the shape, size, orientation, and gradient of the slope. You need to measure or estimate these parameters using surveying methods, aerial photos, or digital elevation models. The slope geometry affects the distribution and magnitude of the forces acting on the slope, such as gravity, water pressure, and friction.

3 Calculate the factor of safety

The factor of safety (FOS) is a ratio that compares the shear strength of the soil to the shear stress induced by the slope geometry and external loads. The shear strength is the maximum resistance of the soil to sliding or failure, while the shear stress is the force per unit area that tends to deform or displace the soil. You can use formulas, charts, or software to calculate the FOS for different slope angles and conditions. A FOS greater than 1 means that the slope is stable, while a FOS less than 1 means that the slope is unstable and prone to creep or failure.

4 Consider the environmental factors

The environmental factors include the climate, vegetation, drainage, and human activities that can influence the soil creep rate and direction. You need to assess how these factors affect the soil properties, such as moisture, temperature, erosion, and compaction. For example, heavy rainfall can increase the water content and pore pressure of the soil, reducing its shear strength and increasing its weight. Vegetation can provide root reinforcement and surface protection, increasing the soil cohesion and reducing the soil erosion.

5 Choose the optimal slope angle

The optimal slope angle is the angle that minimizes the soil creep potential and maximizes the slope stability and safety. You need to compare the FOS values for different slope angles and select the one that is closest to or above 1. You also need to consider the environmental factors and their variations over time and space. You may need to adjust the slope angle according to the seasonal or spatial changes in the soil conditions and external loads.