Collapsible Soils in Colorado
On-line map viewer of statewide and regional maps of collapsible-soil susceptibily in Colorado. For more information, click HERE
Another type of ground subsidence that commonly occurs in Colorado is the settlement and ground collapse that occurs in certain types of geologically recent, unconsolidated sediments - usually referred to as soils by engineers and contractors. This group of soils that can rapidly settle or collapse the ground is known as collapsible soils. Ground settlement can damage man-made structures such as foundations, pavements, concrete slabs, utilities, and irrigation works.
Hydrocompactive soil is the most common type of collapsible soil. The term hydro – implies the introduction or presence of water, and compaction – the resultant compaction of the soils once they become wet.
Hydrocompactive soil forms in semi-arid to arid climates in the western US and large parts of Colorado in specific depositional environments. It is characterized by low density and low moisture contents. The soil grains in this dry soil are not packed tightly together. Instead, the grains are precariously stacked, like a house of cards. This loose soil skeletal fabric is preserved because the grains are “tack-welded” to each other by clay and silt buttresses, soil suction pressures, and other sensitive binding agents that all have one thing in common; they are water sensitive. While strong in a dry state (commonly referred to as meta-stable state), the introduction of water into these dry soils causes the “tack-welding” binding agents to quickly break, soften, disperse, or dissolve. The larger soil grains then shift and shear against each other to re-orient into a denser configuration. This relatively rapid densification of the soil causes a net volume loss of the soil deposit, which is manifested at the ground surface as subsidence or settlement.
Ground settlements from the adverse saturation of thick collapse-prone soils have been documented at over 6 feet. The location shown in the photo at right is on an alluvial fan in the town of Meeker where regional settlements have exceeded 4 feet.
This hazard was recognized in western Colorado in the 1890s when raw land was first irrigated. It remains one of the primary geologic hazards that damages home foundations in the region.
For more information on collapsible soils, see Collapsible Soils in Colorado, the 2009 winner of the John C. Frye Award in Environmental Geology, awarded by the Geological Society of America and the Association of American State Geologists.
There are other, less common, types of collapsible soils in Colorado. Click this link to learn more.
11/7/2012 12:53 PM
Please enjoy this video produced by the Colorado Geological Survey:
Hazardous Soils in Colorado
Warped sidewalk due to collapsing soils near Meeker, Colorado. More information can be found in Collapsible Soils in Colorado (Publication EG 14).
This photo illustrates over 4 feet of displacement of a residential roadway after a water main broke beneath it. Note the settlement and downward deflection of the sidewalk and use of a boulder as an additionals tep. Photo by Jon White.