There are many factors influencing subgrade settlement, among these factors, natural ones are the leading cause.
1. Geographical condition.
Terrain, landscape and altitude can not only influence plan and design of road route, but also influence design of subgrade. The different terrain can also cause different hydrological condition of subgrade. In plain area, terrain is flat, but it is difficult for water drainage. Underground water level is quite high, so subgrade needs the smallest depth of fill. In hilly area, terrain is steep, if drainage design is improper, it may occur slope slide, collapse and other phenomenon of destruction.
2. Geological conditions.
Rocks’ variety, weathering degree, layer’s strike, inclination, stratification, thickness and degree of joint development, all have influence on stability of subgrade.
3. Climate conditions.
Air temperature, humidity, sunlight, rainfall, frozen depth, annual evaporation capacity and wind power, direction, etc. all affect water temperature of subgrade. In a year, with seasonal variation of climate, water temperature condition of subgrade will change accordingly. Also, climate is affected by terrain, such as the peak and foot, south and north slope of mountain, they all have a strong impact on stability of subgrade.
4. Hydrological and hydrogeological condition.
Hydrological condition mainly refers to surface runoff, flood stage, normal water level, hydrops and length of hydrops. Hydrogeological condition refers to underground water level, movement of underground water, interlayer water and spring water, etc. All these conditions will influence stability of subgrade in varying degrees.
Rock bolts in subgrade support can much decrease and control deformation, ensure stability and prevent settlement of subgrade.