Loess is a soil that can exhibit large deformations upon wetting. Cases of wetting induced collapse in loess have been documented for natural deposits and man-made fills. These issues are of concern to the Indiana DOT due to the growth of the state’s infrastructure in regions with significant loess deposits.

The research reviewed the existing literature on loess, focusing on index properties, structure, mineralogy, criteria used for quantifying collapsibility, methods for measuring collapse potential, and, in particular, the collapsibility of compacted loess. Additionally, available documentation on loess deposits in Indiana was reviewed and summarized.

This research also included experimental work conducted on two loess samples, obtained in one in Daviess (Soil A) and in Tippecanoe (Soil B) county. The soils have similar characteristics, with close to 70% silt content and plasticity characteristics that classify both of them as CL (USCS) and A-2-6 (AASHTO).

Experiments performed on the two soils included index tests, standard Proctor compaction tests, and an extensive program of double odeometer tests to measure the wetting induced strains as a function of stress level. Specimens of soils A and B were compacted over a wide range of values of relative compaction (from 75% to close to optimum) and of water contents (from 5-6% points dry of optimum to optimum). The collapse potential of each specimen was quantified using the ASTM D5333 criterion. All specimens but one (compacted at close to optimum conditions) showed some wetting induced collapse. The collapse strains increased with decreasing relative compaction and decreasing compaction water content, in some cases exceeding 10%. In some tests significant wetting induced strains were measured under relatively small stresses (50-100 kPa), indicating that this problem may require consideration even for small fill heights.

The results of the experiments were compared to literature data for other soils, and overall found to be consistent with previously reported behavioral trends.

Based on the results of the testing, recommendations are made for field compaction specifications.

Report Number



Compacted loess, collapsibility, double oedometer, collapse potential, wetting, SPR-3109

SPR Number


Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, Indiana

Date of this Version


3109_TechnicalSummary.pdf (200 kB)
Technical Summary