Loess is a wind deposited, fine grained soil whose particles fall mainly in the silt range — finer than sand, coarser than clay. It formed during the cold stages of the ice ages, when strong winds picked up dust from bare plains and dropped it elsewhere. Thick loess blankets occur across central Europe, in the American Midwest and in northern China; in the Netherlands it is found almost exclusively in South Limburg.
Properties
- Particle size — predominantly silt, the fraction between clay and sand. Between your fingers loess feels like flour: not gritty like sand, not sticky like clay
- Lime content — fresh loess is calcareous; near the surface the lime is often leached out by rainwater, leaving a loam
- Open structure — dry loess is surprisingly stable and can stand in near vertical faces, as in old sunken lanes
- Erodible — that same loose structure means bare loess washes away quickly in heavy rain. Mudflows in loess landscapes have their origin here
What it means for building
- Moisture sensitive behaviour. Dry loess carries load well, but on saturation the open particle structure can collapse. That makes a leaking drain or badly discharged rainwater beside a foundation a real risk
- Ground investigation is not optional. The thickness of the loess and the depth of competent ground beneath it determine the foundation. Have a borehole or cone penetration test carried out before designing an extension or basement
- Excavation. A face cut in loess looks stable in dry weather but can collapse without warning after rain. Batter the sides or use shoring, and keep the excavation drained
- Building material. Loess and loam have long been the raw material for mudbrick, earth plaster and infill panels in timber framing — a tradition still visible in South Limburg and the neighbouring German regions
Related terms
- Soil type
- Loam
- Soil mechanics
- Ground investigation
- Erosion
- Settlement
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