Maintenance Items Hwy 43 was twinned through the site by TRANS in - PDF document

ALBERTA TRANSPORTATION GEOHAZARD ASSESSMENT PROGRAM PEACE REGION – GRANDE PRAIRIE DISTRICT 2017 CALL OUT Site Number Location Name Hwy km GP045 Hwy 43/Smoky River East Hwy 43 Smoky River East Valley 43:04 35 Legal Description UTM Co-ordinates SW¼ 16-072-02 W6M 11U E 420292 N 6121228 Date PF CF Total Previous Inspection: Current Inspection: 12-June-2017 15 4 60 Road AADT: 7360 Year: 2016 Rocky Wang, TRANS Shawn Russell, Thurber Ed Szmata, TRANS Nicole Wilder, Thurber Inspected By: Ted Prue, TRANS Dwayne Lowen, TRANS Photographs Report Attachments: Plans Maintenance Items Hwy 43 was twinned through the site by TRANS in 1999/2000 under Contract No. 6335/01 with the construction of a new SBL/EBL, while the original highway became the new NBL/WBL. A landslide and a sinkhole have developed in the median backslope above the SBL/EBL of Hwy 43:04 at km 35. The site is situated along the east valley slope of the Smoky River valley and is about 0.8 km southeast of the Smoky River bridge (Photos 4 and 14). Primary Site Issue: The landslide and sinkhole was first noticed by the local MCI and the highway maintenance contractor in 2015 and activated in the fall of 2016. The sinkhole appeared in the spring of 2017 and the local MCI also indicated that here was bubbling observed within the sinkhole in early April of 2017. Some erosion of the toe of the EBL west sideslope is occurring above the outlet of a 900 mm dimeter SWSP (Photos 18 and 20). The ACP surface of the WBL at km 36 has degraded with several cracks and ruts present (Photos 22 to 25). The landslide is estimated to be about 75 m wide and extends 55 m from the EBL east side ditch up the median backslope. The height of the drop along the backscarp varies from 1 m to 2.3 m and open with apertures measuring up to 0.5m with several small grabens developing near the crest of the backscarp (Photos 4 to 12). Dimensions: The sinkhole 18 meters wide and extends from the toe to 18 meters up the median backslope. Drops along the top edge of the sinkhole vary in height from 1.8 m to 2.3 m. The estimated depth of the water accumulated in the sinkhole, as measured using a flexible tape measure from the crest, is about 1m (Photos 13 to 17). Client: Alberta Transportation Date: June 12, 2017 File No.: 13353 Page 1 of 3 E File: \\H\13353\2017 GP45 Call Out Report

The erosion in the west sideslope of the SBL/EBL above the 900 mm diameter SWSP extends 40 m across the toe of the slope above the outlet (Photos 18 to 20). No maintenance has been performed recently at the site. Maintenance: Observations: Description Worsened? There is rutting and cracking in the ACP of the NBL/WBL of Hwy 43:04 above the inlet to Pavement Distress a 1,200 mm diameter CSP at km 36 (Photos 22 to 25). The landslide in the median backslope is showing signs of recent retrogression with Slope Movement openings and grabens developing along the backscarp. The toe roll has encroached into the east side ditch of the SBL/EBL (Photos 3 to 12). Erosion is occurring along the toe of the west sideslope of the SBL/EBL ditch above eh outlet to a 900 mm diameter SWSP (Photos 18 and 20). Erosion of the slide debris accumulated in the SBL/EBL ditch from the toe roll of the landslide in Erosion the median backslope is occurring with the effluent sediment accumulating downstream of the slide and flattening the profile of the ditch bottom (Photo 5). The ditch water appears to be overtopping the ditch during higher flow events as noted by the presence of salt and oxides further up the median backslope (Photos 1 and 2). Although not directly observed, seepage from breakages in either abandoned /grouted centerline culverts, or current centerline culverts is suspected to be the underlying cause of the sinkhole feature that is occurring in the median backslope above the SBL/EBL (Photos 13 to 17). Seepage Seepage from water accumulating the inlet of a 1200 mm diameter CSP centerline culvert at km 36 of the NBL/WBL is likely causing a progressive softening of the subgrade material of the highway embankment and the resulting distress observed to the ACP surface of the roadway at the same location (Photos 22 to 26). A 900 mm diameter SWSP is frozen at the outlet on the west sideslope of the SBL/EBL at km 35+76 (Photo 21). Bridge/Culvert Distress Water is accumulating at the inlet to a 1200 mm diameter CSP on the east sideslope of the NBL/WBL at km 35.8 (Photo 26). Slumped material at the toe of the landslide is at the margin of the SBl/EBL east ditch. To maintain ditch flow, slumped material that accumulates at Other the toe of the slides and overflows into ditch will need to be periodically removed. Client: Alberta Transportation Date: June 12, 2017 File No.: 13353 Page 2 of 3 E File: \\H\13353\2017 GP45 Call Out Report

A sinkhole is forming at the median backslope above the SBL/WBL east side ditch at km 35.76 (Photo 13 to 17). Instrumentation: (There are currently no instruments at the site) Assessment: A detailed review of the information on file for contract for the twinning (6335/01) should be performed prior to proceeding with any assessment of the landslide/sinkhole activity at the site. It is likely that the sinkhole is developing at either a disconnected section of an existing centerline culvert or due at the end of a former centerline culvert that has been grouted. Based on the as- constructed drawing No. RD-10276-C (Attached), there appears to be some discrepancy as to the actual location and size of some of the culverts. Once the underlying cause of the sinkhole has been determined, the failed area should be rebuilt by carefully excavating and removing the soft/failed material and rebuilding the cavity with properly conditioned cohesive soils. The landslide in the backslope is occurring at location that sits at a stepper overall slope angle (20 degrees from the horizontal) than the reminder of the slopes located with the median. The landslide might also be located at the outlet of a 1200 mm diameter CSP centerline culvert from the NBL/WBL. Repairs required to remediate the backslope will likely involve the excavation/removal of the failed material and the rebuilding on the failed area with properly conditioned cohesive soils of granular fill placed in horizonal lifts progressing from the base upwards to progressively buttress the toe of the median backslope. Subdrains should also be installed at the based of the repair prior to backfilling and daylighted into dissipation areas constructed into the east side ditch of the SBL/EBL or manholes that are connected to downpipes that daylight at the toe of the west slope. Consideration should also be given to flattening the slope angle in the area of the landslide to an overall angle of 14 degrees from the horizontal (4H:1V) or flatter. Recommendations: Cost Short Term Thurber is to perform a desk top file review of as-constructed information available Desk Top with Alberta Transportation. Study The MCI and the maintenance contractor should regularly monitor the site and Maintenance notify Thurber of any signs of further deterioration and the development of cracks within the roadway right-of-way. The inlet to the 1200 mm diameter culvert on the east side of the NBL/WBL at km 36 should also be cleared once the status of the culvert has been determined (abandoned or active). Medium Term to Long term The grouting of abandoned culverts, repairs to existing dislocated centerline Investigation culverts, the excavation and rebuild of the landslide and the sinkholes areas should be performed within the next 2 to 3 years to avoid causing further distress to the roadway embankment. Thurber should perform preliminary engineering assessment prior to preparing detailed tender drawings and documents for the work. Client: Alberta Transportation Date: June 12, 2017 File No.: 13353 Page 3 of 3 E File: \\H\13353\2017 GP45 Call Out Report