Remediation of Progressive Slope Failure

Bryan Erickson, MBA (Corresponding Author) Fenton Rigging & Contracting

2150 Langdon Farm Rd. Cincinnati, OH 45237

berickson@fenton1898.com (513)-758-1278

Nate Landsperger, PE

Wood 3800 Ezell Rd, Suite 100,

Nashville, TN 37211 nate.landsperger@woodplc.com

(615)-207-8689

Scott Schmidt, EIT Nicholson Construction

4124 Douglas Ave., Kalamazoo, MI 49008 scott.schmidt@nicholsonconstruction.com

(269) 567-0820

NUMBER OF WORDS: 7,500 ABSTRACT On Norfolk Southern Railway’s CNO & TP Lake Division near Crescent Springs, Kentucky, there was a progressive slope failure that accelerated with spring rains and thawing to the point where there was concern for the stability of the rail line. Fenton was contracted to perform emergency remediation work to stabilize the slope for 500 linear ft. Fenton installed 70 drilled shafts as soldier piles then drove sheet piles behind the piles for lagging. Nicholson then installed 26, 88-kip tieback anchors bonded in rock. The 70-foot-long anchors were installed using duplex drilling techniques with an excavator mounted TEI drill mast. The excavator was able to drill from the top of the slope reaching over to install the anchors. Anchors were drilled through ballast, clay, and into weathered shale and limestone. After the anchors were installed, Fenton installed walers to connect the anchors to the solider piles. This provided the stabilization required to stop the progressive slope failure. INTRODUCTION On account of prolonged heavy rainfall and saturated conditions during the winter/spring months of 2018, a large failure mass began to move underneath a 350-foot long stretch of double mainline track situated on a 60-foot high embankment side-hill fill. This movement resulted in track defects prompting reduction in track speed from 25 mph to 10 mph and frequent track geometry surfacing efforts. Due to the excessive effort required to maintain the rail surface, Norfolk Southern tasked Wood (formerly Amec Foster Wheeler) with developing a fast-track design. To accomplish this, Wood performed onsite borings, a topographic survey and relayed this information real-time back to the design group in Nashville to perform a slope stability analysis and determine the resisting forces necessary to stop the movement. Based on the overall geometry and the visible signs of slope movement, Wood made the assumption that the site was

experiencing a deep-seated rotational failure that originated on the upslope side of both tracks and terminated near the bottom of the down slope. SITE LOCATION AND GEOLOGIC SETTING The regional geology underlying the site consists of the Kope Formation. The Kope Formation is a widespread geologic unit covering much of the greater Cincinnati area and extending into Kentucky. The Kope formation generally consists of interbedded limestone and shale bedrock layers. Most notable are the shale layers within the Kope, as these layers weather to a highly plastic, moisture sensitive clay with low strength properties, when exposed to air or water. In areas where Kope Shales outcrop, the natural slopes tend to be relatively flat, typically around a 3H:1V or flatter. The Kope Shales are well-known by DOTs and Railroads in this region, as they are often the root cause of much landslide activity, making the Greater Cincinnati/Northern KY area one of the most landslide prone regions in the county. Landslides are often related to wet weather as groundwater fluctuations tend to over-saturate soil overburden, causing it to become heavier, and at the same time weaken the underlying weathered shale creating potential failure/slide surfaces. Based on the borings performed, Wood confirmed that the site is underlain by a weak shale layer, part of the Kope Formation, and thereby the likely contributor to the slope failure. DESIGN & CONSTRUCTION At the start of the design, Wood worked closely with Fenton to determine steel piling sizes available to provide a stabilization design that could be implemented promptly, without delays due to procurement. Ultimately the analysis showed that an anchored soldier pile wall, consisting of rock socketed HP14x89 at 5-foot spacing with 88-kip capacity anchors drilled into bedrock would be required to satisfy and arrest global stability concerns. As the progression of the design overlapped with emergency response construction, Wood also worked closely with Nicholson to field adjust anchor locations to avoid obstructions during drilling and still maintain the design intent.

Figure 1. Typical cross section of progressive slope failure and design solution.

Soldier Pile Installation Due to the narrow site and the difficult means to access it, the work had to progress in an essentially a start to finish relationship with very few over-lapping activities. It was determined that the installation of the soldier piles would start on the far north end of the site – the point furthest away from the access road, and progress to the south back towards the entrance of the site. As holes were drilled into rock, the drill rig was backed out past the access road to accommodate the installation of the HP14x89 soldier piles as well as the required concrete. When piles were being set and concrete being cast, no other work could take place. Soldier pile installation began in late April of 2018 and lasted until mid-June of 2018. Equipment used for installation of the caissons and rock sockets was a Soilmec 219 drill rig with various casing sizes and bit sizes. Depth of soldier piles varied based on the location of which they were installed but generally, suitable bedrock was at its deepest point on the far north end of the site, progressing upward the further south the piles were installed. Deepest pile installation was near 50 feet in depth from existing groundline and at its most shallow point depth was near 15 to 20 feet. As drilling began it was found that the sub surface conditions had very unstable fill and very caustic materials which meant that not only could a hole not be left open for more than 24 hours, but also that drilling the next location in sequence from one that was previously drilled could cause cave-ins and other issues hindering production. After starting at pile location 1 it was determined to progress with a staggered drilling sequence as opposed to a sequential install (1, 3, 5, 2, 4, 6, 8, 10, 12, 7, 9, 11 as opposed to 1, 2, 3, 4, 5...).

Figure 2. Installation of caissons and rock sockets to facilitate the installation of HP14x89 piling.

Installation of HP14x89 piling followed closely behind the installation of the caissons and rock sockets to satisfy the project requirements of not leaving a hole open for more than 24 hours, but also to

prevent any further cave-ins. Due to the narrow site access, a 38-ton boom truck was utilized to assist in installation of the piling along with on-site excavators with vibratory hammer attachments. As soon as the piling was installed, concrete was released to the project site. Prior to placing concrete, the piles were adequately braced in both the X and Y axis’ and made sure they were plum and at the required 5’ intervals to not conflict with sheet pile spacing for installation of the lagging.

Figure 3. Installation of Soldier piles. Notice the gap between the first two piles showing the staggered drilling sequence.

Sheet Pile Installation As mentioned earlier, Wood worked closely with Fenton to determine which materials would be acceptable based on availability of materials to expedite the project completion to avoid further slope failure. Since the sheet piling was determined not to be structural as it relates to preventing further slope movement, but more so to simply hold back the backfill, a cold rolled section of sheet piling was deemed acceptable. Equipment utilized for installation of the SKZ-16 sheet piling was a CAT 320 track excavator with a Hercules manufactured Sonic Side Grip SP60 Vibratory Hammer. Once soldier pile installation reached pile location number 40, then it was determined that with the site limitations, sheet piling could be stocked on the north end of the site and could continue uninterrupted and not impeded with installation of the soldier piles. Depth of sheeting was only to be 10’ to simply hold back the fill. Sheeting was installed to top of concrete at each

of the soldier pile locations. Once all sheeting was installed the backfill progressed as needed to facilitate the installation of the tiebacks at a later date.

Figure 4. Installation of SKZ-16 sheet piling.

Figure 5. All sheeting installed and backfilled, ready for waler and tieback installation.

Tieback Installation Twenty-five 88-kip and two 100-kip tieback strand anchors were installed by Nicholson ranging in length from 70–94 ft. Duplex drilling was used which involved drilling into the slope at a 45° angle from horizontal through the sheet piles using a TEI drill mast mounted on an excavator with a down-the-hole hammer and 5.5 in. outer diameter steel casing while flushing out the drill cuttings with compressed air. The 3-strand anchor tendons were then inserted into the drill hole and neat cement grout was pumped into the drill hole. The casing was then withdrawn while replacing the volume of each casing length with grout. This procedure allowed the drilling to be done from the top of the wall, while reaching over the sheet piles on the slope where machines could not traverse. This also allowed train traffic to continue unimpeded. Most anchors were drilled perpendicular to the wall, however, due to a culvert that crossed beneath the site, 4 anchors had to be skewed 30° to the east so that they ran parallel with this culvert (Figure 5). The culvert was then “bridged” over with a larger waler (Figure 6).

Figure 6. Plan view of both main lines and culvert traversing beneath the site. Tiebacks are shown as arrows.

Figure 7. Drilling for tieback installation by Nicholson.

Figure 8. Larger waler can be seen in this photo “bridging” over the culvert traversing beneath the site as

well as the skewed anchors in the foreground.

After drilling and grouting the anchors in place, wedge plates were welded to the front of each soldier pile and walers were then welded to the wedge plates for the anchor to bear on. A steel tube referred to as a trumpet was then inserted over the exposed anchor strands between the sheet piles and the waler and filled with grout for corrosion protection of the tieback strands. Once all of the anchors were drilled and grouted and the grout reached a compressive strength of 4,000 psi, each anchor was stressed with a calibrated hydraulic jack to 133% of the design load. After passing this test, each anchor was locked off at the design load and capped for permanent corrosion protection. CONCLUSIONS & LESSONS LEARNED Site access and the physical limitations of this project was everything. It played a major role in all decision making. Had this site allowed for a wider access road and staging area then the work could have been completed in a much more expeditious manner. As a result, coordination between Norfolk Southern, Wood, Fenton, and Nicholson was key to ensure that work progressed in the most efficient way possible and did not hinder one task from getting completed. As such, no one task took a priority over the others because each work task was started and completed with very little lag or overlap from the next work task. One challenge that arose was that the bedrock surface sloped down unexpectedly such that the tiebacks were “chasing” the slope of this rock in order to bond in it. This meant that upon drilling the tieback holes, it was found that the strand lengths that were ordered for several of the tiebacks were too short (even after

having been ordered longer than required) to meet the designed bond length in rock. Therefore, longer tieback strands had to be ordered. This is part of the risk of not having a complete picture of what is truly going on in the ground and another boring on the other side of the track to provide the rock surface slope in this direction would have possibly eliminated this $26,500 surprise. Due to the sense of urgency surrounding this project, the collaboration of the design teams with the installation teams was key to its success. Norfolk Southern and Wood worked closely with Fenton to determine the best most available materials for installation and they followed progress very closely to make sure that if any changes were needed during installation that they were handled and delivered back to the install team with very little downtime. This helped to ensure that not only the desired result was achieved but that all work was installed according to AREMA standards and specifications. Furthermore, Norfolk Southern and Wood worked very closely with Nicholson to facilitate a very expeditious install of the tieback anchors and as such difficult drilling conditions were encountered, the problems and fixes were remedied very quickly because of the quasi design-build nature of this project. Collaboration between all parties proved to be vital and a major key to the project's success. ACKNOWLEDGEMENTS The authors would like to thank David Becker, PE – Norfolk Southern Will Graham – Norfolk Southern Jeff Brewsaugh Sr. - Superior Steel Service of Cincinnati, OH (Handrail and Waler Materials) Alex Granger – Skyline Steel of Cincinnati, OH (H-Piling and Sheet Piling) LIST OF FIGURES

Figure 1. Typical cross section of progressive slope failure and design solution. ........................................ 2 Figure 2. Installation of caissons and rock sockets to facilitate the installation of HP14x89 piling. .............. 3 Figure 3. Installation of Soldier piles. Notice the gap between the first two piles showing the staggered drilling sequence. .......................................................................................................................................... 4 Figure 4. Installation of SKZ-16 sheet piling. ................................................................................................ 5 Figure 5. All sheeting installed and backfilled, ready for waler and tieback installation. .............................. 6 Figure 6. Plan view of both main lines and culvert traversing beneath the site. Tiebacks are shown as arrows. ........................................................................................................................................................... 7 Figure 7. Drilling for tieback installation by Nicholson. ................................................................................. 7 Figure 8. Larger waler can be seen in this photo “bridging” over the culvert traversing beneath the site as well as the skewed anchors in the foreground. ............................................................................................. 8

REMEDIATION OF PROGRESSIVE SLOPE FAILURE

BRIAN ERICKSON, MBA – FENTON RIGGINGSCOTT SCHMIDT, EIT – NICHOLSONNATE LANDSPERGER, PE – WOOD E&IS

NORFOLK SOUTHERN MILEPOST 5.7CNO&TP

CRESCENT SPRINGS, KY

RAIL LINE BACKGROUND• CNO&TP (NORTH END) ORIGINALLY CONSTRUCTED

1870s• CINCINNATI TO LEXINGTON (NORTH END) TO

CHATTANOOGA (I-75)• OWNED BY CITY OF CINCINNATI

SITE LOCATION

GEOLOGIC CONDITIONS

±1,200’

KOPE FORMATION

Image from Kentucky Geological Survey Website

REGIONAL LANDSLIDE ACTIVITY

±1,200’

• Shale rock degrades to clay when exposed • Clay becomes saturated • Failure surface develops along rock interface

Example of typical landslide from USGS Publication

SITE DETAILSDouble mainline, steep grade

Surveyed Topography

SUBSURFACE DATA• Clay fill(brown) to gray clay • Weathered rock/shale layer• Core consistent with Kope

FAILURE ANALYSIS

Conclude movement probable along rock surface

Built-up side-hill fill

PROJECT BACKGROUND

• Due to prolonged heavy rainfall in the spring of 2018, large 350’ long failure occurred

• Wood was contacted to develop a fast track design along with Fenton for construction

• It was determined that 70 drilled shafts with soldier piling, sheet pile lagging, and tieback anchors was the best remediation method

SOLDIER PILE INSTALLATION

• Soldier piles installed with a Soilmec 219 drill rig, drilled to rock at varying depths between 15 and 50’

• Staggered drilling sequence due to tight site conditions as well as spacing of soldier piles (1, 3, 5, 2, 4, 6, 8, 10, 12, 7, 9, 11)

SOLDIER PILE INSTALLATION

SHEET PILE INSTALLATION

• SKZ-16 provided from Skyline Steel (cold rolled section) was selected due to its availability

• Installed with a CAT320 Excavator and a Hercules Sonic Side Grip SP60 Vibratory Hammer

• Spacing between soldier piles was 5’, so one pair of SKZ-16 sheet piles would fit between each pile and connect behind the front face flanges of the HP14x89

SHEET PILE INSTALLATION

• Depth of sheeting was only 10’ or where the concrete was poured to in each of the soldier pile locations.

• Wood determined the sheeting was non-structural to the failure itself, but only as a means to hold back the backfill

SHEET PILE INSTALLATION

SHEET PILE INSTALLATION

TIEBACK INSTALLATION• Excavator mounted drill

• 5.5” casing – 3 strand anchors

• No track obstruction

Williams Form

TIEBACK INSTALLATION

LESSONS LEARNED• Uncertainty of rock surface

• Had to order longer strand• $26,500 added cost

• Possible fixes• Additional boring• Geophysical survey possibly

LESSONS LEARNED

• Site Access was key. Due to the limited size of the site, coordination had to be planned for sequencing of construction every step of the way.

• Collaboration between all parties proved vital. Due to the sense of urgency and the emergency status of the project collaboration helped lead to the overall success.

ACKNOWLEDGEMENTS

• The authors would like to thank• David Becker, PE – Norfolk Southern• Will Graham – Norfolk Southern• Superior Steel Service of Cincinnati, OH – Handrail and

Waler Materials• Alex Granger – Skyline Steel Cincinnati, OH – H-Piling and

Sheet Piling

QUESTIONS