Land subsidence due to induced water pressure changes in aquifers and confining layers
A. Dassargues [email protected] Hydrogeology & Environmental Geology
IAGA Workshop 26‐27/05/2021 ‘Quantum gravimetry in space and ground’ Land subsidence due to induced water pressure changes in aquifers and confining layers
Outline ► Introduction ► Definitions of aquifers and confining layers ► Piezometric heads and water pressure ► Terzaghi principle ► Consolidation processes ► Land subsidence in unconfined aquifers ► Land subsidence in confined aquifers ► Other causes of land subsidence ► Non linear effects on the hydrogeological properties ► A few example of sinking areas/cities: the crucial truth ► References Introduction
(Poland 1984) 3 Definitions of aquifers and confining layers Aquifer = geological medium where groundwater can be exploited/produced
h piezometric head = top free water level of the aquifer
Unconfined aquifer
h piezometric head
Top of the geological layer corresponding to the aquifer
Confined aquifer
4 Hydrogeological definitions of aquifers and confining layers
(Dassargues 2018, 2020)
5 Piezometric heads and water pressure in the geological layers 𝑝 𝜌𝑔 ℎ 𝑧 ℎ 𝑧 𝑝⁄ 𝜌𝑔 𝜕𝑝 𝜕ℎ 𝜌𝑔 𝜕𝑡 𝜕𝑡
Depth to groundwater table
Pressure head Piezometric head p p hp h z .g .g
Elevation head P Considered point h z g Reference datum (Bear & Cheng 2010)
6 6 Groundwater flow and properties
𝒌𝜌𝑔 𝒌 𝒒 𝑲·𝛻ℎ ·𝛻ℎ · 𝛻𝑝 𝜌𝑔𝛻𝑧 𝜇 𝜇
𝐾 𝐾 𝐾 Hydraulic conductivity 𝑲 𝐾 𝐾 𝐾 𝐾 𝐾 𝐾
In most cases: 𝐾 𝐾 𝐾 and 𝐾 𝐾
𝜕𝑞 𝜕𝑞 𝜕𝑞 𝑑𝑖𝑣 𝒒 𝛻·𝒒 𝜕𝑥 𝜕𝑦 𝜕𝑧