**5. Road slope stability**

### **5.1 Identification of the geotechnical problem and modeling results**

In the second case, the geotechnical problem is represented by a slope instability, apparently unjustified even in the case of poor geotechnical properties of the materials but occasionally worsened by groundwater from a nearby stream [12, 13].


#### **Table 2.**

*Geotechnical properties of the materials.* 

#### **Figure 21.**

*Case 2: flowchart of iterative analysis modeling—Sensitivity calculations.* 

**Figure 22.**  *Numerical model of the slope.* 

**Figure 23.**  *Cohesion of the different materials.* 

*Application of Seismic Tomography and Geotechnical Modeling for the Solution of Two Complex… DOI: http://dx.doi.org/10.5772/intechopen.81876* 

**Figure 24.**  *Displacement vectors of the slope instability.* 

In accordance with the results of exploration drilling and geophysical survey (see geotechnical properties in **Table 2** and flowchart of **Figure 21**), a geotechnical model was reconstructed whose solution was obtained with numerical methods and the application of the 2D FLAC software [2] (see **Figures 22**–**24**).

The numerical model was corrected according to an iterative procedure to reconstruct the instability mechanism observed in situ. The next step was to highlight the effects of a growing groundwater. The datum to which the simulation referred was the presence or not of the groundwater level (GL or not GL in the **Figure 25**).

The results obtained are highlighted in the diagrams of **Figure 25**, which show the trend of the SF versus the cohesion of the altered marls, for two cohesion conditions (15 and 10 kPa) of intact marls. The diagrams show that to verify instability (SF ≤ 1), two conditions are necessary: (i) the presence of a water table under the

**Figure 25.** 

*SF versus altered marlstone's cohesion (kPa) for two conditions of intact marls (C = 10 and 15 kPa) and groundwater level presence (GL) and absent (NO GL).* 

roadway and (ii) the circulation of water that causes the reduction of cohesion in the altered marls below the value of 5 kPa.
