Engineers are narrowing down options for a solution to repair the collapsed safety overrun area at Charleston's Yeager Airport.
A plan to fix the collapsed safety overrun area by anchoring a 60-foot concrete retaining wall to the hillside a short distance above Keystone Drive near the base of the slide, building a second 70-foot wall just below runway grade, and distributing 600,000 cubic yards of fill between the two structures was identified as the best of eight re-build options by representatives of the firm hired to design the massive repair job during a meeting of the Charleston Airport's construction committee on Thursday.
The preferred alternative, along with six other options, is expected to cost in the vicinity of $20 million to build, according to Allen Cadden, director of strategic development for Schnabel Engineering. An eighth option - rebuilding the slope at a 2:1 slope grade using 1.5 million cubic yards of fill, requiring the relocation of both Keystone Drive and Elk Two-Mile Creek - would cost substantially more.
The two-wall alternative was deemed by Schnabel to be the best of the eight options because it requires substantially less fill, all of which could be obtained from airport property, than most of the other options, and does not involve additional property purchases from airport neighbors. It also keeps Keystone Drive in its current alignment and requires no further re-channeling of Elk Two-Mile creek, unlike several other options.
"None of the options will be easy," Cadden told construction committee members. "But the risks and challenges of a project like this are mitigated best with the two-wall system."
The re-build options will be outlined and discussed during a meeting of the airport's governing board later this month, and are expected to be put to a vote at a later date.
Other options identified and considered by Schnabel included building a 90-foot high bridge to extend the safety overrun area toward Keystone Drive; using seven tiers of gabions - baskets of stone enclosed by steel mesh - to secure the slope; building a 125-foot-high concrete wall at the base of the slope; using three tie-back walls at the base, middle and top of the slope; building a single 75-foot-high retaining wall just below runway grade, and using reinforced fill to create a 1:1.25 slope grade.
All of the options call for restoring Yeager's safety overrun area to its pre-landslide length, and rebuilding its Engineered Materials Arresting System (EMAS) area, a bed of concrete blocks designed to crumble under the weight of an aircraft aborting a takeoff or overshooting a landing and bring it to a safe stop.
"The goal is to get it back to the condition it was, or even better," prior to the March 12 slide, Cadden said.
So far, S & E Clearing and Hydroseeding, the contractor stabilizing the slide zone, has removed 90,000 cubic yards of material, established a bench at 35 feet below runway grade, and removed an additional 10-foot layer below the bench.
"Every day it gets a little safer," Cadden said.
Work on the stabilization project is expected to be complete by the end of October.
Precisely when rebuilding work will begin on the safety overrun area remains unknown, according to Yeager Airport Director Terry Sayre, pending settlement of insurance claims and the disposition of lawsuits stemming from the slide.
Meanwhile, the Federal Emergency Management Agency has approved a grant to clear earth and rocks from the slide off Keystone Drive, according to Sayre. That work, to be done by the state Division of Highways, is expected to take place in October, in conjunction with the final phase of S & E's stabilization work.
Reach Rick Steelhammer at rsteelhammer@wvgazette.com, 304-348-5169 or follow @rsteelhammer on Twitter.