Maintenance Items Landslide affecting the Hwy 2 off ramp. Active - - PDF document

Client: Alberta Transportation Date: September 10, 2014 File No.: 15-16-305 Page 1 of 4 E File: \\H|15\16-305 2014 PH9 Shop Inspection Report

GEOHAZARD ASSESSMENT PROGRAM PEACE REGION – PEACE-HIGH LEVEL CALL-OUT INSPECTION (AUGUST 12, 2014)

Site Number Location Name Hwy km

PH9 Peace River Shop Slide 684:02 31.43

Legal Description UTM Co-ordinates

SW¼ 31-083-21 W5M 11V E 480339 N 6232158

Date PF CF Total Previous Inspection:

9-Jun-2014 14 8 112

Current Inspection:

12-Aug-2014 15 8 120

Road AADT:

3750

Year:

2013

Inspected By:

Ed Szmata Don Proudfoot Shawn Russell

Report Attachments:

Photographs Plans Maintenance Items

Primary Site Issue:

Landslide affecting the Hwy 2 off ramp. Active landslide movement is most pronounced at NW end of slide, near junction with 99 Avenue.

Dimensions:

Active landslide affects approximately 200 m length of off-ramp, while dormant slide extends over approximately 300 m length of road. Slide extends upslope (SW) 90 m and downslope (NE) 80 m (plan distances) of the off-ramp. Crest of dormant slide is at

• EL. 409 m and toe of active slide is at EL. 370 m.

Maintenance:

In Fall of 2010, the Town of Peace River replaced pipe rack supports for water and sewer line pipes, re-graded the site around the pipes and covered the disturbed areas with coconut matting. The Town also re-graded area of about 30 m in width by about 50 to 60 m in length, to the south of the pipe racks, after a surface slide

• ccurred on May 13-14, 2011.

In 2013, the Town offloaded more material and placed geomembrane sheets below the off-ramp embankment to channel the seepage from the springs and the ditches.

Observations: Description Worsened?

Pavement Distress

Slight change in cracking / dip at north end of

• slide. Cracks across regional pathway have

grown (Photo 1). The backscarp of the slide feature above the piperacks has retrogressed further past the guardrails into the roadway shoulder (Photos 5, 6, 13 and 15). Cracks, with drops up to 50 mm in ACP patching along guardrail, along the island and in the SW road shoulder at the southern end of the island (Photos 14, 15 and 17). A distinct dip is apparent at the flank crack across road at southern end of active sliding. (Photo 23).

Client: Alberta Transportation Date: September 10, 2014 File No.: 15-16-305 Page 2 of 4 E File: \\H|15\16-305 2014 PH9 Shop Inspection Report

Slope Movement

Pavement distress and fresh cracking on the slope indicate further movement of the lower (active) slide area. The slump in the sideslope just south of the pipe rack has grown and retrogressed beyond the guardrail posts (Photos 13 and 15). The flow slide in the bush to the north of the pipe rack has grown with a 3m drop off at the end of the geomembrane sheets and enlargement in the north-south direction. (Photo 4). The landslide scarp noted above the rail line at the southern end of the site has grown and the slide block has a vertical offset of about 3 m (Photo 24) and a backscarp height of 1.7 m.

Erosion

There is on-going erosion in the flow slide mass. The inlet and outlet of the culvert at the 99 avenue intersection were severely eroded during the August 2, 2014 heavy precipitation event (Photos 10 and 12). An erosion gully has formed below the highway near the lower slide backscarp (Photos 19 and 20).

Seepage

Seepage emanating from several gravel seams within the Hwy 2 off-ramp embankment is shedding water over the re-graded area to the north of the pipe racks (Photo 2 and 3). Water is also percolating through the asphalt pavement at the 99 avenue intersection. (Photo 11.

Bridge/Culvert Distress Other

The overall downslope movement of the slides in the immediate area of the piperacks is causing the pipes to bend and dislodge from the piperacks (Photos 7, 8 and 9).

Instrumentation: (From the May 2014 Readings)

SI05-1 Low rate of movement (7 mm/yr) – no significant movement at depth. SI05-2 & 3 Sheared at 10.7 m (SI05-2) to 17.5 m (SI05-3) depth. Significant movement at 10-12 m depth in SI05-2 and 16 -18 m in SI05-3. SI05-4 Has sheared off at a depth of 6.7 m since the spring 2011 readings and had exhibited roughly 55 mm total cumulative movement at 6.5 m depth. SI09-1and 2 Located near the water and sewer pipelines at the NW end of the site. About 150 mm of movement to 2.2 m depth observed in SI09-1 in June 2011, with about 4 mm and 11 mm at 8 m and 12 m depths, respectively. SI09-1 was assessed to have been sheared at 1.8 m on September 22, 2011. Near surface movement of roughly 150 mm (upper 2 m) since Fall 2010 in SI09-2. Instrument was destroyed during the sewer line pipe rack repair in Fall of 2011. SI09-3 Small creep movements observed in SI09-3 since 2010 (toe of slope between rail line and Shaftsbury Trail). SP05-1 to SP05-5 Variations in water level of between -0.76 m to +0.08 m since the fall 2013 readings. VW09-1 to 4 SP09-5 to 7, and SP09-10 and 11 Variations in water level of between -1.56 m to +0.27 m since the fall 2013 readings, with higher increases in groundwater levels noted in piezometers situated in the vicinity of the active lower slide scarp (0.05 m to 0.07 m), the pipe rack (0.27 m) and below the seepage zones (0.15m). SP09-8 and 9 Have remained dry since installation in 2009.

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Assessment:

On August 12, 2014, Don Proudfoot, P. Eng. and Shawn Russell P. Eng. visited the site with Ed Szmata

• f Alberta Transportation following a request for a call-out from the Town of Peace River. On

August 2, 2014, the west side of the Town of Peace River region received in excess of 25 mm of precipitation during a brief 0.5 hour period. Evidence of the high water flow from that day was observed by the scouring/wash-out of the 99 Avenue culvert inlet and outlet, the extensive ditch erosion along the SBL ditch of the off-ramp (Old Hwy 2) and the presence of a gully along the NBL downslope. The dip features in the NBL of the Hwy off-ramp have become more pronounced and the backscarp along the NBL shoulder has retrogressed to 0.6 m into the roadway shoulder beyond the guardrail. As indicated in Thurber’s most recent annual Geohazard Inspection Report dated June 9, 2014, this site is characterized by a complex, deep-seated slide movement affecting the hillside above and below the

• road. The slide bowl above the road appears to be currently dormant. While the lower slide is active, the

highest rates of movement appear to be at the NW corner of the lower slide bowl, where the Town of Peace River had to re-grade the slope to protect a sewer and water supply line in 2008/2013 and replaced the pipe rack supports for both the water and sewer lines in 2010. The lower slide scarp remains active as noted by the dip in the Hwy 2 off ramp pavement patch, bow in guardrail and increased cracking. The increase in downslope movement was likely triggered by the recent heavy rains and resulting higher ground water levels. As a result, the landslide backscarp is now into the roadway shoulder past the

• guardrail. The landslide material is moving and placing additional mass against some of the pipe rack
• supports. The pipes are showing some signs of distress and are beginning to lift off of the roller supports
• n the pipe racks. It must be assumed that if the above ground section of the pipes are in compression

that a portion of the utility pipes that are situated below ground, further upslope, must be in tension due to the landslide activity. Movement has continued in the area unloaded by the Town at the north end of the slide, as the slope inclinometers have sheared in the area. Cracking and retrogression of slide movement continues upslope

• f the unloaded area – the area of the road affected by slide movement is expected to expand to the

north in the near future. Water continues to pour onto the slope from gravel seams within the roadway

• embankment. Although the Town has placed geomembrane sheets to line a channel to contain the water,

this only extends about partway down the slope and the scour below the end of the membrane continues to grow below, with the flow slide encroaching into CNR’s right of way and the resulting debris fan regularly obstructing the west railway line ditch. CNR has been removing the slumped soil from the west ditch and placing it on the east side of the railway trunk.

Recommendations: Cost

FLOW SLIDE: Install subdrains feeding into a larger downslope collector drain pipe, located below, a gabion mattress lined channel, extending down the valley through the slide area. Re-grade the sides of the flow slide area (outside the gabion lined channel) to a consistent slope to mitigate enlargement at this slide area. Due to the increased concentrated water flow that would be generated at the base of the slope, a centerline culvert should be installed beneath the CNR track by auger boring at the same location to provide an outlet for the flow. UTILITY LINES: Implement a controlled shutdown of the utility pipes in order to excavate into the slope at each end of the pipes to de-stress the pipes. The pipes should then be inspected for buckling and stretching and compromised sections should be cut-out and replaced. The pipe racks should then be re-adjusted as necessary (on-going requirement) to fully support the pipes. Alternatively, re-align the utility pipe crossing by directional drilling below the landslide features, or relocating the pipelines along a more stable alignment should be considered if the highway slide repairs are not carried out in the near future. Maintenance / Town HIGH PRIORITY

Client: Alberta Transportation Date: September 10, 2014 File No.: 15-16-305 Page 4 of 4 E File: \\H|15\16-305 2014 PH9 Shop Inspection Report

PATH: Re-align pathway outside of slope backscarp and possibly fence off the landslide area. HIGHWAY: Carry out the long term remedial measures which constitute the refined Option E as described in our engineering report dated November 6, 2009. These consist

• f removing the climbing lane and flattening the sideslope at an inclination varying

from 3.5 to 4.5H: 1V, constructing an earth-fill toe berm retained by a 3.5 to 5 m high MSE wall to avoid encroachment into the CNR ROW, installing a pile wall under the MSE wall to satisfy local stability issues related to the wall and installing a series of sub-horizontal drains extending from 100 m to 120 m into the hillside to lower the groundwater table. $5,000,000