فهرست نشریات علمی دسترسی آزاد ایران

Urban underground construction has expanded rapidly in response to surface land scarcity and growing metropolitan transport demands. Executing tunnels, metro lines, and subsurface utilities in densely built environments introduces compounding geotechnical challenges: liquefiable loose sands, high groundwater tables, and the differential settlement sensitivity of overlying heritage and contemporary structures. Soil improvement, encompassing techniques that enhance the in-situ mechanical and hydraulic properties of problematic soils, has evolved from an optional precaution into a primary risk management instrument. This paper presents a systematic analytical review of five principal improvement methods: Tube-a-Manchette (TAM) cement grouting, vibro stone columns, deep soil mixing (DSM), biologically induced calcite precipitation (MICP), and vertical drainage. Drawing on field instrumentation datasets from three landmark projects, namely Rome Metro Line C, Mashhad Metro Line 2, and the Karbala deep excavation, the study benchmarks each method against two standardised performance indicators: Settlement Reduction Ratio (SRR) and Strength Improvement Factor (SIF). Key findings demonstrate that real-time compensation grouting reduced surface settlement by up to 75%, constraining maximum displacement to 8 mm against a 15 mm heritage-structure threshold. Deep soil mixing achieved unconfined compressive strength (UCS) exceeding 5.5 MPa and permeability of 10 to the power of negative eight m/s. MICP-based biogeotechnical methods offer a carbon footprint up to 20 times lower than cementitious alternatives but remain constrained by treatment depth and the fingering effect in heterogeneous strata. A multi-criteria sensitivity framework and research agenda for next-generation sustainable soil improvements are proposed.