Deposit characterizations and engineering-geotechical modeling for sustainable urbanisation in the Mila basin (NE...

Rapid urban expansion in Mila (Algeria) has increased exposure to geotechnical hazards related to weak clayey deposits, slope instability, and seismic activity. Its southeastern part (Sanaoua) is particularly affected by settlement, landslides… limiting sustainable urban development. This study presents an integrated geotechnical, geophysical, and hydrogeological investigation to assess subsurface conditions and their implications for foundation performance. The investigation program included Fifteen core drillings (CD), Six pressuremeter (Ps), Twenty-five dynamic penetration tests (P), Ten electrical resistivity tomographiy profiles (ERT), and piezometric monitoring at 10 points (Pz), complemented by laboratory testing. CD results indicate variable colluvial deposits (≈ 0.5-3 m) overlying gray clays containing limestone blocks. These clays exhibit high plasticity (Wl ≈ 61-79%, Ip ≈ 23-49%), near-saturated conditions (Sr ≈ 90%), low to moderate undrained shear strength parameters (c ≈ 0.018-0.043 MPa; φ ≈ 9-16°), and low sulfate content. Ps tests reveal very low stiffness and bearing capacity in the upper 2 m (E_m ≈ 6 MPa; q_ad < 0.15 MPa), with a progressive increase in mechanical competence below 4-6 m and q_ad ≈ 0.45 MPa at depths exceeding 6-8 m. Settlement analyses indicate excessive deformations (60 mm) in shallow layers, decreasing to less than 10 mm at depths greater than 6-8 m. P results highlight strong spatial variability and locally very high resistance values related to limestone blocks, with bedrock depths ranging from 4 to 10 m. ERT profiles confirm thick clay-dominated conductive domains (10-40 Ω.m) locally interrupted by resistive limestone bodies (150 Ω m), explaining the pronounced lateral variability in bearing conditions. Pz monitoring indicates the absence of a permanent groundwater within the explored depth during the monitoring period. Based on these findings, a practical engineering-geological model is proposed within a Mohr-Coulomb framework, demonstrating that shallow foundations are generally unsuitable and that deep or improved foundation systems, together with effective surface-water management, are required to support slope stabilization, erosion control, and seismic-resilient urban development. The main limitations are spatial and depth coverage, temporal monitoring constraints, method-specific uncertainties, and simplifications in modeling. Despite these, the study provides a robust framework for guiding foundation design, slope stabilization, and urban development-but local variations and long-term effects should be addressed with further site-specific investigations.