Dahoua L. Improvement of the method for calculating the stability of the escarpments of the road subgrade and slopes (on the example of Algeria)

As a result of the Thesis, a theoretical generalization and a new solution of the scientific-applied issue, which is to improve the Bishop's method for calculating the stability of the road subgrade escarpments and slopes for the conditions of Algeria was carried out. The relevance of the topic is confirmed by the preconditions (shifts, landslides, consequences of earthquakes) that occur on the road network of Algeria. As in all Mediterranean countries, Algeria is severely affected by unforeseen shifts. In recent years, these shifts have tended to increase, leading to large losses in many sectors of the economy and, in particular, in road infrastructure. The relevance is also confirmed by the fact that in Algeria there is no simple engineering method for calculating the stability of escarpments and slopes of excavations or embankments, taking into account the forces of earthquakes, groundwater and restraining forces of reinforcement. The essence of improving the method is to enter the values of variables (c ') and (φ') in the Coulomb-Mohr failure criterion to take into account soil fatigue, parameter (Fs) to take into account the impact of seismic forces, force (r) to take into account part of the leaked water, and the forces (Geo) occur from the inclusion of geosynthetic layers in the polygon of Bishop’s forces, which must be in equilibrium. The action of groundwater on the state of the shifting slope is manifested in different ways, causing a change in the stress state of the array and the physical and mechanical properties of soils, as well as causing the development of filtration deformations. Its influence is taken into account by the calculation of pore pressure and the corresponding coefficient of pore pressure, which was once proposed by Bishop and Morgenstern. The impact of earthquakes was taken into account by the introduction of additional forces acting in the horizontal and vertical directions. In our method the assumption that the filtration and seismic forces are shear forces is accepted, ie directed parallel to the base of the compartment. As a result, we obtained a new engineering method for calculating the stability of escarpments and slopes; On the basis of the developed method in the dissertation work the technique of calculation of the geotextile-reinforced slopes of road subgrade which allows making engineering calculations of stability of escarpments of the road subgrade and slopes is developed; Mathematical and numerical modeling of the stability of escarpments and slopes and verification of the adequacy of the developed method were also performed in the work. Four variants of retaining structures for the slope of PC 240 + 847 of the motorway A1 were investigated. Numerical calculation with the use of the finite element method shows that the strengthening of slopes by geosynthetic layers gives better stability compared to other proposals. Another task of the research was to develop a method of using geographic information systems (GIS) to evaluate the stability of slopes in the mountainous areas of Algeria. The main purpose of this part of the study was to evaluate the predisposition of soils in the Hanifa area to landslides in order to suggest an alternative road route that is less prone to such phenomena based on geographic information systems and the developed improved Bishop’s method. A method of GIS data analysis has been developed, on the basis of which a map of landslides in Algeria on the highway A1 in the Buirae district has been constructed. This method allows making more accurate design decisions when designing highways in the mountainous conditions of Algeria. In particular, the calculated new trajectory of the route significantly reduces the risks (up to 30%) and losses of the road industry when changing the trajectory of only 21% when bypassing the areas with the highest risks of landslides.