Assessment of Potential Void Zones along the Adama–Awash Expressway using Integrated Geophysical and Geotechnical Approaches.

Abstract

Potential Void Zones Pose A Serious Geotechnical Threat, Particularly In Regions Underlain By Unconsolidated, Moisture-Sensitive, Or Soluble Materials That Can Lead To Surface Subsidence Or Collapse. This Study Evaluates The Factors Contributing To Potential Void Formation Along A Section Of The Adama?�?Awash Expressway In Ethiopia, Spanning Chainages 25+060 Km To 25+180 Km, Through A Multidisciplinary Approach. A Combination Of Geophysical Methods?�? Electrical Resistivity Tomography (ERT) And Seismic Refraction Tomography (SRT) Was Employed Alongside Geotechnical Investigations, Including Dynamic Cone Penetrometer (DCP) Testing, Atterberg Limits, California Bearing Ratio (CBR), Proctor Compaction, And Permeability Assessments. These Techniques Were Supported By Borehole Logs And Laboratory Analyses, Offering A Comprehensive View Of Subsurface Conditions. ERT Results Identified Several Low-Resistivity Anomalies (<29 ????M), Most Notably Along Survey Lines 3 And 5, Indicative Of Saturated Zones, Dissolution Features, Or Potential Subsurface Voids. Complementary SRT Data Revealed Near-Surface Layers With Seismic Velocities Below 400 M/S, Highlighting The Presence Of Loose, Mechanically Weak Soils. Geotechnical Characterization Classified The Soils Primarily As CL (Low To Medium Plasticity) Under The Unified Soil Classification System, With Liquid Limits Ranging From 38% To 50% And Plasticity Indices Between 17% And 27%, Suggesting Poor Bearing Strength. At Borehole 105, The 1-Meter Layer Exhibited Moderate Compaction (MDD = 1.5 G/Cm??; OMC = 12.4%), Cohesion Of 30 Kpa, And Shear Strength Of 50 Kpa, While The 3-Meter Depth Contained Finer, More Moisture-Retentive Material (OMC = 18.7%) With Higher Cohesion (40 Kpa) And Shear Strength (60 Kpa), But Increased Risk Due To Potential Volume Changes. Similar Patterns Were Observed At Borehole 106. In Contrast, Borehole 107 Revealed Lower Compaction Levels (MDD = 1.3?�?1.4 G/Cm??), Reduced Shear Strength (45?�?48 Kpa), And Cohesion (25?�?28 Kpa), Indicating Lower Mechanical Stability Yet Reduced Susceptibility To Moisture-Induced Deformation. However, Hydrogeological Tests From Borehole 107 Indicated Low Permeability (Hydraulic Conductivity = 8.8 ?? 10?????? Cm/S) And Slightly Alkaline Conditions (Ph = 8.5), Factors That May Promote Carbonate Dissolution And Void Development In Confined Aquifer Conditions. Based On Integrated Analysis, Boreholes 105 And 107 Were Identified As Higher-Risk Areas For Potential Void Formation. Mitigation Recommendations Include Deploying Deep Foundations, Pressure Grouting In Critical Zones, Enhancing Surface Drainage Systems, And Instituting Ongoing Geophysical Monitoring. The Outcomes Of This Research Offer Valuable Insights For Void Risk Management And Long-Term Stability Planning Along The Adama?�?Awash Expressway.