The cutting roadbed, especially when deep excavation, creates new slopes, accompanied by a change in the inherent stress state, and gradually establishes a new equilibrium. Weak rocks in Vietnam are usually mechanical sediments or shales, layered structure and with high to moderate weathering. When cutting hillsides and mountains to construct highways at locations where this type of layered soft rock exists, a new form of slope instability often occurs, which is plane failure in the weak zone or layered surface of the rock mass. In many cases, when surveying and designing, it is not possible to determine the strike, dip and characteristics of the weak rock layers that are often encountered in construction practice in our country. This, possibly the main reason, makes the analysis of slope slope stability analysis under design inefficient and unreliable. As a result, during the cutting slope process, plane failures occur easily.
In a typical case, there is a excavated roadbed that is not too deep (<12 m) but the plane failure occurs very complicatedly, even when the roadbed is cut from the bottom of the slope at the central route of Cao Bang city. It not only endangers people, adversely affects existing works, but also generates construction costs. In this study, using geotechnical data from survey, actual construction, current state of rockslide at the typical study site, conducting an assessment of characteristics, mechanisms and numerical model analysis, making the basis for determining rock slope stablize solutions by combining types of mechanically stabilized earth, reinforced concrete retaining wall, soil nail and ground anchor.