Geotechnical challenges of urban expansion in Mila Town (NE Algeria): an integrated Engineering Ground Model (EGM)...

Rapid population growth in the town of Mila, in northeastern Algeria, has made urban expansion essential. However, unfavorable soil conditions pose major challenges to urban development. This study aims to characterize subsurface conditions, assess soil mechanical behavior, and establish a geotechnical zoning framework together with an Engineering Ground Model to support safe urban development. An integrated site investigation program was conducted, including 15 Core Drillings, 49 dynamic penetration tests, laboratory analyses, and hydrogeological monitoring. The subsurface stratigraphy consists of clays and marls containing limestone blocks at depths exceeding 20 m, together with two slip surfaces identified at depths of - 4 m and - 15 m. The results of the dynamic penetration tests divide the study area into two zones: one characterized by low peak resistance (Pr = 4.38 MPa) and shallow bedrock (BR = - 1.6 m), and the other by moderate conditions (BR = - 6 m and Pr = 18.48 MPa). The soils show low chemical aggressiveness (SO₄²⁻ < 5.5 mg/kg), very high clay content (> 75%), high plasticity (21 < P_i < 41.94%), and significant compressibility (Cr = 27.80%, 15.18% < w < 24.54%). X-ray diffraction analysis revealed clay and interstratified minerals dominated by illite (10-30%) and montmorillonite/smectite (≈12.5%). Most of the site is characterized by moderate to low admissible bearing capacity (0.164 < q_ad(max) < 0.842 MPa) for shallow foundations and is susceptible to significant volumetric changes, with settlements exceeding 5cm across large areas. Based on the combined analysis of bearing capacity, settlement potential, groundwater depth, and soil heterogeneity, three geotechnical zones were identified, ranging from highly unfavorable to relatively competent foundation conditions. The spatial distribution of areas with low bearing capacity and high settlement potential closely correlates with the observed patterns of structural damage. The results demonstrate that shallow foundations are largely unsuitable throughout the study area unless ground improvement measures or deep foundation systems are adopted. This study provides a robust Engineering Ground Model and geotechnical zoning framework to guide sustainable urban planning and foundation design in similar clay-dominated, hydro-mechanically sensitive environments.