Yeager failed slope

What could have gone wrong in Yeager Airport Expansion slide?

Yeager airport landslide
Yeager airport landslide

Recent news and photographs present the spectacular slide that occurred in the Yeager Airport Expansion Runway 5. The slide occurred in the South slope which was among the highest if not the highest (~74m) reinforced earth slope in the US. The project had received the award of Excellence – TenCate Geosynthetics in 2007 International Achievement Awards. According to FHWA Manual the Yeager Airport in Charleston WV had been constructed as a massive earthwork in 1940’s. The mountainous conditions around the airport produced steeply dipping slopes to the Elk and Kanawha Rivers. In order to meet FAA Safety Standards runway 5 required a 150m extension in order to create an emergency stopping apron. The most cost effective solution was a 74m high 1H:1V reinforced steepened slope (RSS). The chosen solution is presented in Figure 1 taken from Lostumbo 2010.

2010 STGEC - Yeager Airport - Tallest Reinforced Slope in N America
Figure 1: Reinforced 1:1 earth slope extension of runway 5

As can be seen from Figure 1, most of the reinforced earth area is above the original ground and only a small part in the slope base is excavated in order to found the reinforced earth structure. Based on Lostumbo, 2010 over 100 borings were performed, with extensive laboratory testing and the final outcome was that the site consisted of primarily fill, colluvial and shallow rock. The material parameters used for the bearing soil zone were unit weight γ=22kN/m3, φ’=40ο and c’=0kPa. I would like to provide some speculations regarding this incident based on the available data found on line and photographs from the news and Google earth. I must point out that these are only speculations since no official data are available to me, nor the exact design or construction plans. These speculations are made just by observations and engineering imagination!   I am sure that significant investigation will take place in the coming months and years which will produce the actual conditions and reasons for this spectacular failure. A picture from Google earth taken on 9/2005 presents the initiation of excavation for the construction of the reinforced earth slope.

Yeager SW slope copy
Figure 2: Google earth image of excavation at Southwest slope of runway 5

A newer picture taken on 4/2006 presents the progress of works in which a part of the reinforced earth slope has been constructed.

Yeager airport partially constructed slope
Figure 3: Google earth image with partially constructed slope

It is very interesting to note that the excavation and foundation of the earth structure did not go all the way to the base of the hill. It is possible that good foundation material (assuming rock) was found in some elevation and was considered appropriate for founding the structure. After all the large earth structure is placed on sound rock (mostly sandstone) with a compressive strength between 30-95MPa! Weathered sandstone from the borrow area had a friction angle between 38.9-39.6o. The placement of the reinforced earth structure on top of bedrock can be observed in figure 4. The bedrock is clearly visible in the back and some moisture can be observed a bit higher in the slope.

Is the “competent” foundation bedrock to blame?, is the design of the reinforced slope to blame? Is the construction practice? Is the intense rainfall? Usually many factors contribute to such a large failure, but at this point with very limited information I would like to focus on the bedrock conditions and the fill material placed on the bedrock.

Yeager airport reinforcement placement
Figure 4: Site photograph shown the placement of reinforcement near the base of the slope, rock formation is clearly visible in the back (Lostumbo 2010).

Is a sound bedrock always appropriate for placing such a large structure? Based on the unconfined compressive strength I would say yes, but are other conditions at play here? Based on Huang et al, 2014the on-site geomorphology consisted of weathered sandstone underlain by sandstone and some shale.” and “The compressive strength of the rock foundation varied from 30MPa to 95MPa. The high bearing capacity of the underlying sandstone foundation and the high friction angle of the onsite weathered sandstone soil meant that the extent of the reinforced slope could be kept to a minimum, and maximum use could be made of the onsite soil.”

Notice the phrase “sandstone and some shale”. Could this simple phrase be the key for what happened? It is well known that even small intercalations of shale can produce enormous geotechnical problems as was the case of Landslide on No.3 Freeway in Taiwan (Duncan, 2013). The first reason is that shale materials have much lower compressive strength but more importantly considerably lower friction angle. Furthermore if not fractured, they present a very low permeability barrier. Usually water is seeping in the sandstone – shale interface, asymmetrically weathers the shale and also produces increased pore pressures in that interface. Could such an interface (or failure surface) had been formed in this case? The answer is, it may be possible and can be seen in the following very simple model in figure 5. (will not go into much detail about the model it is just an example of the possible formation of such a failure surface).

Yeager airport slide model copy
Figure 5: Very simple model evaluating the possibility of failure due to weathered shale intercalation

Now let’s go back to actual observations, figure 6 is a Google earth image taken on 3/2012. Please observe the stones between the slope and the road in the red circle. Then let’s go to Google street view in the same location and what we see is shown in figure 7. The layering of the bedrock is clearly visible, furthermore some form of fissure can be observed even with some horizontal movement one can argue based on this image. Could such a feature or a similar one in different elevation be the weakest link of this structure? Could it have been in marginal stability and all it took was some heavy rainfall that increased the pore pressures in this interface and initiated the slide? Food for thought until the actual investigation comes out and the real conditions that lead to instability, which I really hope are much more complex, can be addressed.

Yeager airport google earth 1
Figure 6: Google earth image before the failure, note the rocks between slope and road
Yeager airport toe slope possible failure surface
Figure 7: Google street view in the road just where the rocks are seen. Observe a possible shear surface.


Duncan J. M. (2013). “Impact of time on the performance of reinforced slopes” Geo-Congress 2013.

Huang Z., Al-Saad Q., Nasrazadani S., Wu Felix H. (2014). “Understanding and optimizing the geosynthetic-reinforced steep slopes“, EJGE Vol. 19, 2014

About Chrys Steiakakis

Chrys Steiakakis is a practicing geotechnical engineer with more than fifteen years of experience in the field of geotechnical engineering. He earned his bachelor and master in mining engineering from the Technical University of Crete, Greece and a second master’s degree in Civil Engineering from Virginia Polytechnic Institute and State University, USA. He has been the technical director of engineering department of General Consulting ISTRIA for four years and now he is a partner and also provides his own consultancy services via Geosysta ltd. He has been involved in numerous highway, railway and mining projects. Chrys with his long term collaboration with the Technical University of Crete has participated in numerous research projects in the field of geotechnical engineering and rock mechanics and has provided self sustained seminars of geotechnical engineering in related areas for the Industry. His main field of experience covers all aspects of tunnel design, earthworks design and monitoring (slope stability, embankment in difficult ground, reinforced embankments and retaining walls), landslide investigation and mitigation, foundations for bridges and structures, risk assessment in geotechnical projects and value engineering in large projects.

3 thoughts on “What could have gone wrong in Yeager Airport Expansion slide?

  1. The long shots (pics) of the failure prompted me to ask following simple queries to understand the problem – (I) what was the run-off drainage arrangement at the top of the “this failure” crown area and (ii) any reports of seepages at the base of the slope in vicinity to the settlements that are visible in the pics?

  2. interesting point of view , i happen to have a weird translational slide in a very gentle slope composed of a non compressible clay over a weathered shale , both of them are saturated

  3. Chrys

    Very astute observations. I have some firsthand information about Yeager Airport and landslides. I battled a landslide here of similar elevations difference to the northeast of the south end of Taxiway C back in 1984. The airport was built in the late 1940’s to 1950 and was deep valley fills between hilltops using 4′ to 6′ boulder size fill particles. The geology of the hills are Mississippian and Pennsylvanian age rock with the Freeport coal as the divide between the two. Generally the sandstone is massively bedded at the higher elevations but is interbedded with shale and indurated clays with occasional trace seams of coal at the lower elevations. The indurated clays in this area were once mined for bricks. While the sandstones and sandy shales have a high compressive strength when extracted from a rock core, the shale and indurated clay experience accelerated weathering when exposed or disturbed. Many Interstate embankments were built on 1.5H:1V fill slopes because laboratory triaxal testing on the crushed shale used as fill indicated high internal friction. However, after years of weathering, some of these shales had friction angles as low as 20 resulting in a lot of roadside landslides. It is very likely that there is a shale or indurated clay layer below the reinforced soil mass with a high density but a low friction angle. Water seepage is also very probable and was a major factor in the landslide correction that I designed. The sandstone drains fairly well, but the shale is nearly impervious and causes seeps to occur along down gradient sides of slopes. I doubt very seriously that this was a bearing capacity failure. It was more likely a friction issue aggravated by water.

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