Jan. 13 project update: The latest on mining and barging
Posted on Jan 13 2016 2:59 PM
Seattle Tunnel Partners resumed mining Tuesday evening, using trucks to remove excavated material while they continued working to resolve an issue with a soil-removal barge. STP crews resumed excavation at 7 p.m. Tuesday.
Approximately two hours later, a sinkhole developed within STP’s work zone near South Main Street, about 35 feet north of the access pit. It is located more than 100 feet south of the cutterhead's current location, in ground that crews mined through last week. STP filled the sinkhole overnight with 250 cubic yards of concrete.
This section of the tunnel drive is protected by an underground wall built by STP before tunneling. The wall was designed to isolate ground movement and protect the nearby Alaskan Way Viaduct. A manual survey of the viaduct conducted after the sinkhole developed found no movement. WSDOT and STP will continue surveying and monitoring the ground, viaduct, utilities and other structures.
The cause of the sinkhole is still under investigation. STP is analyzing the portion of the tunnel that crews have excavated since mining resumed. There is no indication that any other locations have experienced ground loss.
STP is reviewing their daily operations as a result of this incident. Immediately they will enhance monitoring protocols by requiring crews to manually verify the amount of soil removed during excavation of each ring.
The protocols STP outlined to enhance monitoring were used in the first 1,000 feet of tunneling and WSDOT is disappointed they were not used when STP restarted tunneling in December 2015. STP has several hundred feet of mining before they reach the next planned maintenance stop. Before leaving the maintenance stop, STP’s operational protocols will undergo an additional review by an expert to assure public safety.
STP has temporarily stopped mining to prepare the muck storage pit to receive excavated material. They plan to resume tunneling this week using trucks to remove excavated material.
STP’s inspection of piles at Terminal 46 is ongoing. The terminal is structurally sound, but crews noted damage to some piles. STP is preparing to install fenders along the pier that will allow them to continue safely barging from this location.
Work to move material from the damaged barge to a second barge is expected to be completed later today or tomorrow, according to STP. Once complete, STP will be able to determine the amount of clean material that spilled into Elliott Bay. Repairs will be needed before the damaged barge can be used again in the tunneling operation.
Continued focus on safety
Safety remains our top priority as we work to replace the seismically vulnerable Alaskan Way Viaduct. We expect STP to further investigate this incident and take the appropriate corrective action as they continue to build this important project.
This map shows the approximate location of the sinkhole that developed on Jan. 12.
For earlier program updates, please visit our archive page.