a me PART 8: JULY 2000 SITE VISIT LANDSLIDE RISK ASSESSMENT PEACE - - PDF document

PART 8: JULY 2000 SITE VISIT LANDSLIDE RISK ASSESSMENT

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PEACE REGION (PEACE RIVER VALLEY/HIGH LEVEL) LEGAL LOCATION: Location along Highway: AI FILE: Date of Site Visit:: Shop Slide Significant Observations SITE PH9: SHAFTSBURY TRAIL 31-83-21-WSM, 22-82-23-WSM Shop Slide, along the old Hwy. 2, near ATU warehouse, west side

• f the Peace River

Shaftsbury Trail Overpass at CNR crossing of Hwy. 2, west side of the Peace River Brick Hill Slide 20 km south of Peace River towards Grimshaw SH684 July 17, 2000

• The Shop Slide is located along the old Hwy. 2, above the railway tracks. At the Shop

Slide, the highway is in cut and fill. A crack and settlement in the road surface define the northern end of the slide, they extend onto the slope, where a very clearly defined scarp has developed.

• The slope appears to have been regraded in the past.
• The slope appears relatively dry, seepage was not observed.
• A slope inclinometer is present just above the railway tracks.
• Slope failures have developed in the cut slope uphill of the highway. It is not clear

whether the failures uphill of the road are connected with the failure of the road surface.

• In the past gabion mattresses have been placed in the roadside ditch.

Changes from Previous Visits There is very little information regarding this slide in the file, and the latest dates back to 1986. It would appear that the cracks and settlement in the road have developed after 1986. Discussion The slide appears to be a relatively shallow failure of the .fill slope. It is not clear whether the rupture surface is in fill or native material. The rate of movement appears to be low. The road appears to have been patched since 1985, but it does appear that more extensive measures have not been implemented.

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Assessment Shop Slide: PF(9) * CF(2) = 18, unchanged from file review. Recommendations It is recommended that three boreholes be drilled and slope inclinometers be installed in the Shop Slide to determine the depth and nature of the movement. The cost of the boreholes and the installation is estimated at$ 15,000. Shaftsbury Trail Overpass Significant Observations

• At the Shaftsbury Trail Overpass, movement of the fill structure appears to have
• ccurred in the past. The initial overpass was constructed in 1982, and two spans were

added at the western abutment in 1986, to unload the embankment. Construction required a very thick fill. The abutments are founded on piles.

• At the eastern abutment, the bolts that hold the bridge deck in place indicate movement
• f the bridge deck towards the northeast relative to the abutment. At the western

abutment, the bridge deck appears to move towards the west. This suggests that the western abutment is moving towards the east, pushing the bridge deck in the same direction.

• Concrete slabs at both abutments have moved downward relative to the abutment piers,

causing buckling around the piers. Changes from Previous Visits There is no data in the file past 1986. It appears that the bridge deck has experienced movement since the spans were added in 1986. Discussion After removal of fill and addition of two spans, the western abutment still appears unstable. It appears that the slope has not been monitored for a number of years, such that the rate of movement is not known. However, judging from the damage to the abutment seats, it appears significant movement is occurring. Assessment The slide could impact two roadways: Shaftsbury Trail and Hwy. 2. Continued movement of the slide would probably not affect Shaftsbury Trail, because it is well removed from the bridge abutment where movement appears to be occurring. The main risk is to the bridge across

• Hwy. 2.

Risk Assessment PF(9) * CF(4) = 36. The site appears active and the abutments appears to be affected. However, a failure would depend on the response of the structure, which is not addressed by this risk assessment.

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Recommendations A bridge engineer should provide an indication of the risk associated with this site. Brick Hill Slide The Brick Hill Slide is located a few hundred metres downhill of the Shaftesbury Trail Slide, described in the file review in Part A. Significant Observations

• The road is in cut and fill. The slope below the road is approximately 30 m high in this

area. The lower part of the slope is gentle, but it is steep just below the road (approximately 2H:1 V).

• The settlement and cracks in the road surface were observed where the road crosses a

small drainage course. No cracks were observed in the soil.

• A culvert is not present at the ravine, instead, the water is channeled into the roadside
• ditch. A drainage ditch is located parallel to and downhill of the road and discharges into

a buried culvert that carries the water down the hill. The culvert also receives water from the upstream ditch.

• There were a number of shallow slumps in the cut slope uphill of the road, which were

being regraded. Previously, they may have impeded the flow of water down the ditch.

• Remedial work was being undertaken, but it appeared to address the failures in the cut

slope only.

• Slope inclinometer readings from J.R. Paine indicated a distinct shear zone at 8 m

depth, with movement of 45 mm between December 1999 and August 2000. During the summer, movement was faster than during the winter. The slide has been investigated by J.R. Paine (for the MD) who have installed two slope inclinometers. Changes from Previous Visits There was no report of previous site visits in the file. Discussion It appears that the setting of the slide is similar to the Shaftsbury Trail Slide. That slide was relatively deep-seated and the surface of rupture of that slide was interpreted to be in shale

• bedrock. To date we have not received the borehole information from J.R. Paine.

Assessment Risk Assessment: PF(9) * CF(4) = 36, the slide is active with moderate but increasing rate of movement. This is a relatively small fill, but in case of a failure, it may require closure of the road.

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Recommendations It is recommended that the report and monitoring by J.R. Paine be made available to AMEC. Since the rate of movement is relatively high, it is recommended that maintenance personnel monitor the road more intensely than usual. It should be noted that failure of the Shaftsbury Trail Slide occurred rapidly and that this could occur here also.