Groundwater rise and problematic soils as controlling factors of seismic ground hazard: A multi-site synthesis of engineering-geological investigations in Uzbekistan

Abstract

Seismic ground hazard in the loess-covered territories of Uzbekistan is governed by two water-controlled mechanisms: collapse of unsaturated loessial soils and liquefaction of the same soils once saturated. This paper synthesises engineering-geological investigation reports completed in 2023–2025 for six construction sites in five regions of Uzbekistan (seismicity 7–9 points), comparing seismic intensity, soil profile, collapsibility parameters, penetration resistance and two groundwater positions — observed and forecast maximum. Three regularities emerge: type-I collapsible loess is reported at all unsaturated sites, with initial collapse pressures down to 0.09 MPa; wherever groundwater was encountered, its forecast maximum lies 0.4–1.5 m above the observed level; and where the water table has entered the loess thickness, penetration resistance drops to N = 2–9 and the hazard changes its nature from collapse to liquefaction, with the liquefaction potential index growing from 32 to 46 under the forecast rise at a nine-point Tashkent site. Collapse and liquefaction are argued to be two states of a single water-controlled hazard, and a paired-scenario assessment for two groundwater positions is proposed as a normative requirement for loess sites in zones of seven points and above.