PEACE REGION (PEACE RIVER- HIGH LEVEL AREA) GEOHAZARD ASSESSMENT CALL-OUT PH56: EMBANKMENT FAILURE ON HWY 35:08 SOUTHWEST OF MEIKLE RIVER CROSSING

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5 - THURBER ENGINEERING LTC. GEOTECHNICAL ENVIRONMENTAL MATERIALS September 30, 2008 File: Alberta Transportation Room 301, Provincial Building Avenue Peace River, Alberta T8S 1T4 Attention: Mr. Ed Szmata PEACE REGION (PEACE RIVER- HIGH LEVEL AREA) GEOHAZARD ASSESSMENT CALL-OUT PH56: EMBANKMENT FAILURE ON HWY 35:08 SOUTHWEST OF MEIKLE RIVER CROSSING Dear Sir: This report presents the results of a call-out for a slope instability area located on the northwest sideslope of Highway 35:08, south of the Meikle River Bridge. The inspection was undertaken by Thurber Engineering Ltd. (Thurber) in partial fulfillment of our Geotechnical Services for Geohazard Assessment, Instrumentation Monitoring and Related Work contract (CE1 05/2008) with Alberta Transportation (TRANS). The inspection was undertaken on August 5, 2008 by Mr. Don Proudfoot, P. Eng., and Mr. Gustavo Padros, P. Eng., of Thurber, along with Mr. Ed Szmata and Peter Van de Ligt of TRANS. The latter made the call-out request. 1. BACKGROUND Highway 35:08 has been subjected to a history of instability problems along the Meikle River valley crossing section dating back to Slope failures and continued downslope creep movements have been observed in the west sideslope of the highway, north of the Meikle River crossing at three geohazard sites (PH-5, 44 and 45). At Site PH5, located about 115 m north of the bridge, the highway was constructed on a sidehill fill that has experienced creep movements producing distress on the pavement. At Site PH44, located about 500 m north of the bridge, three slope failures up to 30 m wide by 100 m long have occurred on the west sideslope of the embankment. At Site PH45, located about 900 m north Su1te 200, Avenue, EDMONTON, AB, Canada T6E 6A5 T F www thurber.ca EDMONTON CALGARY FORT McMURRAY VANCOUVER VICTORIA TORONTO KAMLOOPS SQUAMISH

6 .. THURBER ENGINEERING LTC of the bridge, a pile wall about 110 m long was constructed in 1997 as a result of a slope failure that occurred in In late June 2008, a new slide was noted south of the Meikle River Bridge, in the northwest sideslope of the highway, cutting into the highway shoulder, prompting a call-out request. 2. OBSERVATONS The slope failure occurred in the northwest sideslope of Highway 35:08, approximately 70 m south of the Meikle River Bridge. At this location, the highway embankment is about 10 m high, measured from the pavement surface to the toe and has an inclination of about 17 degrees. The site is shown on Figure PH56-1 and 2. From aerial photo interpretation it appears that the northwest sideslope of the road is located on the lower reach of the valley slope that descended towards a previous location of the Meikle River which has since meandered and moved its location. The slump is about 18m wide and 33 m long. Wet, high plastic clay was noted in the backscarp, which is about 2.4 m in height and reaches the highway shoulder. The toe roll of the slump is located at the base of the embankment. The guardrail has lost support and is currently hanging. No cracking was noted on the pavement surface but an erosion gulley has developed inside the backscarp of the slump, caused by highway runoff draining into the slide. Two fiber optic telephone cables installed parallel to the highway were found crossing the surface of the slump. Outside the slump limits, the surface of the slope is well covered with grass and no erosion features were observed. A slightly depressed area was noted on the highway sideslope, about 30 m north of the slump and is shown on Figure PH56-1. This area might possibly be an old slump, which is currently covered with grass. Further downslope, past the slump, an old slide scarp was noted inside a gently sloping treed area and tilted trees were observed. This point of the slope appears to gradually flatten onto an old terrace of the river. An old spoil pile was noted beyond the toe of the embankment further north towards the river. A 150 mm void was also noted under the angle iron of the Meikle River Bridge south approach slab. Client: Alberta Transportation Fi le: e-file: 08\15\ et PH56 Date: September 30, 2008 Page 2 of 4

7 - THURBER ENGINEERING LTD ASSESSMENT The slump appears to behave as a shallow rotational slope failure. High plastic clay appears to have been used to construct the embankment. Weathering over time may have reduced the cohesion in the clay fill. The slope failure could have been triggered by heavy rainfall and runoff from the highway, filling up desiccation cracks in the clay which exerted lateral pressures causing an additional destabilizing moment. Also, precipitation infiltrating into the soil may have added weight to the slope during periods of heavy rain, increasing the destabilizing moment. The old slide noted downslope from the slump was likely initiated long ago when the river alignment was closer to the valley toe. It appears to be still subject to slow creep movement. There is a risk that the slide could retrogress further into the highway pavement so repairs should be implemented as soon as possible. Repair works will have to take into account the proximity of the Telus fiber optic lines, which are currently located about 10 meters northwest of the highway shoulder. 4. RISK LEVEL Based on TRANS' risk level rating system, the risk level for this site has been assessed as follows: Risk (52) = PF (13) x CF (4) [Eq. 1] This risk level was based on a Probability Factor (PF) of 13 (active with high rate of movement and increasing) and a Consequence Factor (CF) of 4 (high fill where partial closure of the highway could be a direct result of a further slide retrogression). 5. RECOMMENDATIONS In the immediate term, water runoff from the highway should be prevented from draining into the sideslope. A shallow asphalt curb or sock tube filled with gravel could be placed along the outside edge of the shoulder to divert surface water to a controlled discharge point away from the slide. Traffic warning signs and barricades should also be placed for traffic safety. Client: Alberta Transportation Fil e: e-file: 08\15\ et PH 56 Date: September 30, 2008 Page 3 of 4

8 - THURBER ENGINEERING LTC. --Also in the immediate term, the damaged joint at the Meikle River Bridge south approach slab should be repaired. Details for the repair should be obtained from a qualified bridge engineer. A possible long term remedial option consists of excavating the slide mass and reconstructing the slope with granular fill. The excavation and granular fill will likely need to extend back to at least half way into the south bound lane and to a few meters below the toe elevation of the embankment slope. The ball park cost for this option is $500,000. Another remedial option is to install a cantilever pile wall to retain the shoulder of the highway and to regrade the embankment slope at the flatter slope below the wall. This option would also cost in the order of $500,000. The costs for the above options do not include engineering. A large toe berm is not recommended due to the presence of the old slide area beyond the toe of the recent slide. Prior to completing the design, a geotechnical investigation consisting of a test hole in the roadway and a test pit at the toe of the slide should be carried out. A topographic survey of the site will also be required. 6. CLOSURE We trust that the above information is sufficient for your present requirements. However, if you have any questions or require any additional input please do not hesitate to call us. Yours truly, Thurber Engineering Ltd. Don Proudfoot, P. Eng. Review Principal Project Engineer /dw Attachments Photos 1 to 7 Client: Alberta Transportati on File: e-file: 08\15\ let PH 56 Date: September 30, 2008 Page 4 of 4

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13 PHOTO 1 - Backscarp reaching shoulder and hanging guardrail, looking south. PHOTO 2 - Backscarp reaching shoulder and hanging guardrail, looking northeast PH56

14 PHOTO 3 - View from the bottom of the slump looking east. PHOTO 4 - View from the bottom of the slump looking east. 08\15\ PH56

15 PHOTO 5- View of the slump from the highway, looking west. PHOTO 6- View of the slump from the highway, looking northwest. 08\15\ PH56

16 PHOTO 7 - Damaged joint in bridge south approach \ PH 56

17 cr> 0 0 N Lri 0 c --, "' ~ "' :;: 1: 01:, " cd 0.0 I a.. I C') N cd.;, c;:; N J,.;, it) N TO MANNING t ~ TO MEIKLE RIVER BRIDGE Q._ 32.4m TELEPHONE ~ TELEPHONE CABLES AT GROUND SURFACE BROKEN PHONE CABLE BOX SLIGHTLY DEPRESSED ~ AREA, POSSIBLE OLD SLIDE GRASSED OVER \\. A' ---~ LEGEND ~ SLIDE BACKSCARP (j)----7 PHOTO AND DIRECTION SITE MAP NOT TO SCALE OLD SPOIL PILE (!) z ~s E Z -- ~ "~', l lil:g'3 N I I- I --~ I , ~. I I ~I \ I ~~ -SLID E I I :X: I 1 1 _!i i I w CXl ~ 0 Gl m SITE PLAN NOT TO SCALE SITE SKETCH PLAN FIGURE PH56-1 PH56 : HWY 35:08 - SOUTHWEST OF MEIKLE RIVER CROSSING -... PEACE REGION (PEACE RIVER I HIGH LEVEL) GEOHAZARD ASSESSMENTS DATE: AUGUST 2008 THURBER PROJECT# THURBER ENGINEERING LTC. GEOTECHNICAL ENVIRO NMENT AL MArERIALS

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