Maintenance Items On the evening of July 9, 2016, Alberta - - PDF document

Client: Alberta Transportation Date: June 5, 2017 File No.: 13351 Page 1 of 3 E File: \\H\13351 2017 PH009A Inspection Report

ALBERTA TRANSPORTATION GEOHAZARD ASSESSMENT PROGRAM PEACE REGION – PEACE-HIGH LEVEL 2017 INSPECTION

Site Number Location Name Hwy km PH009A-1 Shaftsbury Bricks Hill Slide 684:02 9.240 Legal Description UTM Co-ordinates SE¼ 21-082-23 W5M 11U E 467287 N 6219688 Date PF CF Total Previous Inspection: 14-July-2016 15 4 60 Current Inspection: 5-June-2017 15 4 60 Road AADT: 280 Year: 2016 Inspected By: Rocky Wang, TRANS Don Proudfoot, Thurber Shawn Russell, Thurber Report Attachments:

Photographs Plans Maintenance Items

Primary Site Issue: On the evening of July 9, 2016, Alberta Transportation was alerted by the maintenance contractor that the EB paved shoulder of Hwy 684:02 had been affected by a slide which extended

• downslope. This site lies adjacent to the west side of the previously

monitored Bricks Hill wash-out feature which was repaired in 2004. Dimensions: A landslide with approximate dimensions of 85 m in length by 40 m in width extends up into the edge of the SBL, affecting approximately 15 m of shoulder pavement. Maintenance: A 36-m long patch the full width of the EB driving lane and shoulder was placed in September 2015. In the fall of 2016, pending a decision on a repair, Alberta Transportation built a ACP paved single lane detour along the north side of the NBL and closed the SBL. In addition to the detour, Alberta Transportation regraded the NBL ditch and armored it with rip rap. Concrete jersey barriers were placed along the edge of the backscarp. Observations: Description Worsened?

Pavement Distress

Eastbound shoulder over a length of 13 m has

• dropped. Cracks are developing between the

backscarp and the concrete jersey barriers in the closed SBL.

Slope Movement

The EB shoulder and highway embankment dropped up to 4.3 m vertically, and slide debris extended 85 m from the highway.

Erosion

Some scouring/settlement was

• bserved
• ccurring in the bottom of the NBL ditch in the

summer of 2015.

Seepage Bridge/Culvert Distress Other

Client: Alberta Transportation Date: June 5, 2017 File No.: 13351 Page 2 of 3 E File: \\H\13351 2017 PH009A Inspection Report

Instrumentation: The slope inclinometer (SI-SB1) previously installed along the shoulder off the SBL to the east of the toe berm repair has since been destroyed and is no longer visible at ground surface. In June of 2017, Thurber installed one SI, two pneumatic piezometers and four standpipe piezometers as part of a preliminary geotechnical investigation. The instruments were read at the completion of their installation and read twice following their initialization on June 28 and on September 28, 2017. SI17-1 Installed in the center of the upper portion of the landslide bowl about 10 m downslope of the highway. Prior to being measured as sheared off on September 28, 2017 at a depth of 2.74 m below the existing ground surface (Elevation 430.287 m), on June 28, 2017 (three weeks following its installation), SI17-1 had indicated 67 mm of total movement from 0.9 m to 4 m depths with a movement rate of 1.3 m/year. PN17-1-1 and PN17-1-2 Installed with SI17-1, at depths of 9.14 m and 19.35 m below the existing ground surface respectively. On September 28, 2017, PN17-1-1 indicated that there was 0.37 m of water above the tip and PN17-1-2 indicated 0.7 m of water above the tip. SP17-2 Installed to a depth of 14.84 m below ground surface in NBL ditch below the new detour at about 8 m northwest of the original edge of the highway. The standpipe was dry each time that it was read. SP17-6 Installed to a depth of 14.84 m below ground surface in the backslope about 30 m northwest of the highway. The standpipe was dry each time that it was read. SP17-7 and SP17-8 Installed about 30 m north and south of the center of the landslide along the shoulder of the SBL to depth of 11.4 m and 8.9 m below the top of pavement

• respectively. SP17-7 was dry each time that it was read while SP17-8 indicated a

groundwater level of 7.8 m below the top of pavement. SP17-9 Installed about 30 downslopes of the highway in the center of the landslide bowl at a depth of 9.p m below the existing ground surface. SP17-9 was dry each time that it was read. Background/Assessment: A previous landslide adjacent to the east edge of this site was repaired towards the end of 2004. Thurber continued to visit the site until 2006 after which it was removed from the annual Geohazard inspection tour due to favourable overall performance of the toe berm repair and drainage measures. A callout was performed by Thurber in September, 2015 after a crack and some subsidence was

• bserved in the eastbound lane. This landslide cracking in the road had occurred adjacent to the west

edge of the previous toe berm repair from 2004. This landslide movement warranted that the affected eastbound lane asphalt be patched in order to maintain a smooth enough surface for traffic at the current posted highway speed of 80 km/hr. A geotechnical investigation consisting of test holes and slope inclinometer installations to define the depth/rate of slide movements was recommended. This site was then put back on the annual Geohazard tour in 2016, with the last inspection performed in June, 2016. At that time, a 300 mm slide scarp was observed just off the edge of the highway, with more visible cracking extending over a 13 m length into the paved shoulder. On the evening of July 9, 2016, the maintenance contractor notified Alberta Transportation that a slide

• ccurred, after about 40 mm of rain had fallen earlier in the day. The slide scarp was 4.3 m high,

affecting a 15 m length of the EBL of the highway, extending as far back as the edge of the driving

• lane. At the time of this callout inspection, the only visible signs of water were on/adjacent to the

remnant of the dismantled upslope (west) highway ditch erosion protection where some small ponding was observed, the remainder of the slide scarp/debris area appeared dry.

Client: Alberta Transportation Date: June 5, 2017 File No.: 13351 Page 3 of 3 E File: \\H\13351 2017 PH009A Inspection Report

It is anticipated that the heavy rain/runoff got into the previously visible and open slide cracks, creating a saturated basal sliding surface, possibly along the boundary of native/previous placed highway embankment fill. Based on the length of the slide debris which extended 85 m downslope of the highway, and the fence/ditch erosion protection which had moved in the order of 6 m downslope and was still partially intact, the slide was anticipated to have occurred very rapidly and to be fairly deep-seated. Some scouring/settlement about 0.3 m deep by 0.5 m wide x 3 m long was also observed in the upslope (north) ditch bottom directly across from the slide scarp. The 8.5 m wide roadway was measured to consist of a pavement structure of 290 mm ACP (which included the 65 mm thick patch placed in 2015) over 250 mm of GBC. This differs from the pavement management strategy records which indicates a 325 mm thick ACB (Asphalt Concrete Base Course) structure. In the fall of 2016, pending a decision on a repair, Alberta Transportation built a ACP paved single lane detour along the north side of the NBL and closed the SBL. In addition to the detour, Alberta Transportation re-graded the NBL ditch and armored it with rip rap. Concrete jersey barriers were placed along the edge of the backscarp. Preliminary Engineering Assessment Thurber was requested by Alberta Transportation to perform a preliminary geotechnical assessment to determine possible repair options for the landslide repair in the spring of 2017. A geotechnical investigation was performed by Thurber in June 2017 to assess the mechanism of failure and to design repair measures for this slide. On August 21, 2017, Thurber presented Alberta Transportation with preliminary concept drawings and “A” estimate prices for four remedial options to repair the landslide. Option 1 consisted of building a 90-m long cast-in-place concrete pile wall in the SBL ditch. This option would allow for the reconstruction of the highway embankment along its previous alignment. Option 2, consisted building a 70-m long cast-in-place concrete pile wall along the edge of the backscarp of the landslide in the former SBL combined with a minor correction realignment of the highway. Option 3 consisted of about 600 m of realignment of the highway about 30 m into the backslope to circumvent landslide. Option 4 consisted of rebuilding the highway embankment at its current location using granular fill. Recommendations: Cost Thurber was requested by Alberta Transportation to proceed with the preparation

• f a tender document and design drawings for the implementation of repair Option
• No. 1 combined with a partial realignment of the highway onto the recently paved
• detour. This work is currently in progress and it is anticipated that the tender will

be submitted for approval by the end of 2017. ~$2,5 Million to $3 Million