Case History – Dinosaur National Monument headquarters and maintenance facility
The Dinosaur National Monument is located in both northwest Colorado and northeast Utah. The headquarters is located in Colorado on Highway 40, 1½ miles east of the town of Dinosaur. Both of the administrative and maintenance buildings are located within the water gap of the Frontier Sandstone hogback along Dripping Rock Creek. The administrative building is located on the alluvial fan where the creek exits the hogbacks. The maintenance building is inside the hogback (Figure 1).
Figure 1. View west of Dinosaur NationalMonument headquarters along the strike of the Frontiers Sandstone member of the Mancos Shale. This hogback marks the beginning of the Uinta uplift to the north. The administrative building is on the left. The maintenance building is on the right, nestled between the Frontier and Dakota Sandstone hogbacks. Note close proximity of the eastern end of the maintenance building to the exposed ridge of bedrock. Photo by Jon White.
The administrative building has had moderate problems with settlement, but the distress at the maintenance facility has been severe. The long rectangular structure spans collapse-prone soil that is relatively shallow (3.5 feet deep) at the eastern end near where the tilted bedrock becomes exposed. On the west end, near Dripping Rock Creek, the collapsible soil is much thicker, over 41 feet deep, and several inches of settlement occurred. The difference in thickness of the collapsible soil column caused huge differential rates of settlement and basically caused the structure to unhinge from the northeast corner where bedrock is shallow and settlement was negligible (Figure 2a, 2b, and 2c).
Figure 2 (a, b, c). Differential settlement damage to the maintenance building by 1998. Photos by Jon White, CGS.
Case History – The Terraces in Glenwood Springs
The town of Glenwood Springs lies within the valley confluence of the Roaring Fork and Colorado Rivers. Almost the entire town lies on coalesced alluvial fan and colluvial soils that were derived from sediments that were shed from the steep valley sides. These soil deposits are highly susceptible to hydrocompaction. The Terrace development included 13 two-story structures with basement-level garage drive-outs. Thick collapsible soils were previously mapped and identified at the site (Figure 1).
Figure 1. Oblique aerial photo of the Terraces development under construction on the west valley side of the Roaring Fork River. Area enclosed in red dashed line contains a mantle of coalesced alluvial fan and colluvial soil deposits, burying the river terrace gravel. These soils thicken upwards, to just below the slope break where the valley wall begins and bedrock becomes exposed. The wall constructed behind the development was built for rockfall and debris flow mitigation. Photos by Jon White, CGS.
Significant errors were made in design, construction, and grading and landscaping. The back of the units did not have proper drainage and rain gutters were omitted from the roof line (Figure 2). These units were built from 2001 to 2003 and within 6 months of the first units completed and sold, collapse of the soil was causing settlement of the back concrete retaining-wall foundations, which caused deflection of interior beams (Figure 3), a host of interior cracks and structural offsets, and distortion of windows and doors (Figure 4). The homeowners association settled a lawsuit against the developer, the engineering consultants, and builder for $12 million in 2005. Compaction grouting was used to structurally lift the settled areas of the buildings.
Figure 2. View of the back of the Terrace units. Note the poor drainage of the nearly flat, rock-in area that is adjacent to the heavy concrete basement retaining wall needed for garages. Most significantly, note the lack of rain gutters at the roof.
Figure 3. View down concrete retaining wall at basement/garage level. Note deflection of ceiling beam due to settlement of the wall.
Figure 4. Settlement of the back of unit has “tweaked” the entire structure, which can be easily seen in door jambs. In this picture downward deflection on the right side at the back of the unit has pulled the right door jamb down to the point that the door cannot close properly.
Case History – Carbondale rancher’s pond
A Carbondale, Colorado, rancher’s stock watering pond excavated in a pasture collapsed because of hydrocompaction. A bowl-shaped depression 60 feet across and 8 feet deep resulted when he attempted to pond water in his field. The soils were so permeable that the pond would not hold water, and the wetted soils under the pond collapsed. Many roads and other improvements in the vicinity have been destroyed or damaged by soaking of collapsible, low density soils.
Case History – CDOT and I-70
The Colorado Highway Department, recognizing that severe hydrocompaction along a highway alignment could totally destroy a road, investigated the potential for hydrocompaction along the alignment of I-70 from Rifle to Debeque. Water was impounded in a small pond and a road fill was placed beside the pond as a model of probable future conditions. The result of the test was that the ground surface sank three feet in one month. The test provided design information to prevent the possible future total failure of a portion of the highway. The engineering geologic investigation may have saved taxpayers millions of dollars.