REPAIR OF AN 80-YEAR- OLD DRY STACK WALL. Ryan Eaves, E.I.T. Bridge Division Geotechnical Branch

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1 REPAIR OF AN 80-YEAR- OLD DRY STACK WALL Ryan Eaves, E.I.T. Bridge Division Geotechnical Branch October 2015

2 Project Location Located on Texas miles southwest of San Angelo Remote area 10 miles west of Sheffield 2

3 Dry Stack Wall Construction Initial construction in 1930s From 10 feet to 25 feet in height and 400 feet in length Repair of an 80-Year-Old Dry Stack Wall October

4 Existing wall cross section Gravity wall relies entirely on self weight of stacked rock to resist lateral load Battered wall face common to dry stack walls Sensitive to erosion weathering of rock can result in instability 4

5 Project Background San Angelo District contacted Bridge Division in spring 2014 Found two severely voided zones spanning 55LF and 33LF along the wall Barrier undermined and void extends to roadway surface Rock on surface shows signs of significant deterioration 5

6 Project Background 6

7 Project Background Smaller of the two severely weathered areas 7

8 Project Background Resulted in pavement and barrier distress on the surface above the wall 8

9 Project Background As a result, traffic control measures were put in place Two way traffic was condensed into one lane Signalized system managed traffic Project was let as a Routine Maintenance Contract 9

10 Design Considerations Preserving historic value both barrier and retaining wall 10

11 Design Considerations Weathering/deterioration present throughout wall Decided to treat the entire wall with soil nails Made most economic sense to cover entire wall with permanent shotcrete and sculpt to match original 11

12 Design Considerations Remove barrier original materials and set aside After retaining wall repair is completed, a masonry expert can reassemble the barrier using the original materials Concrete cap on top would then be recast 12

13 Design Considerations Soil nails minimally invasive to existing structure Provided option to use hollow core self drilling soil nail anchors to help with hole stability 13

14 Design Considerations Installed anchors on existing face of the voided zones Coupled on to the nails to lengthen to proposed wall face Build up section with welded wire wall 14

15 Pre-Construction Contractor recommended 2-inch flash coat of shotcrete Shotcrete to be fiber reinforced Fiber reinforcement allowed for decrease in face thickness 15

16 Pre-Construction Site equipment access issues were a concern Decided to build a temporary berm at the bottom of the wall to allow small equipment access Two methods used to install nails 16

17 Wall Construction Drill by reaching over the top of the wall with an excavator Used for the top couple of rows of nails Could not reach the bottom few rows 17

18 Wall Construction Wagon Drill Frame that orients and holds drill Able to scale and attach to wall Used for the lower portion of the wall 18

19 Construction Soil nail testing verification testing to verify soil strength assumptions and evaluate drilling methods done before construction began did not reach rock material shown in the boring logs 19

20 Wall Construction Initially the test holes took 20 times the theoretical volume of grout to fill grout seeped into voids in the stacked rock volumes Decided to ensure at least 5-foot minimum tag into rock layer grout added 20% 30% more than theoretical 5 volume Contractor verified that corrosion due to the unbonded portion would not affect the 75-year design life of the wall 20

21 Sculpted Face Small shotcrete layer added on top of flash coat to create smooth surface Application of final shotcrete layer and sculpting completed in increments 21

22 Sculpted Face Man-lift from roadway above used to reach the top portions of wall Shotcrete face was then stained to reflect original rock color after shotcrete cured 22

23 Project Completed Wall repair finished in eight weeks Only delay was acquiring water for the grout mixture Approximate total project cost: 23

24 Finished Barrier Barrier reconstructed and new concrete cap cast Pavement damage repaired 24

25 Cost Summary RW(temp) $ 166, RT(soil nailed) gunite $ 398, Soil Nail Anchors $ 268, Additional gunite $ 29, Horizontal Drains $ 60, Stone Wall $ 7, Wall Base Benching $ 7, Pavement Repair (Removed) $ (25,400.00) Retaining Wall Total $ 913, Mobilization $ 92, Barricades $ 32, Mobilization Total $ 124, Project Total $ 1,038,

26 Final Thoughts Contractor and TxDOT able to: work together to swiftly handle challenges as they arise in construction come up with solutions to unique problems complete the project quickly with minimal effect on the travelling public 26

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