Moose_Creek_Dam_Mod_Industry_Day_Questions.docx

Moose Creek Dam Safety Modification Industry Day Questions Chena River Lakes Flood Control Project The Moose Creek Dam Safety Modification project is for construction of a mix-in-place barrier wall in the embankment of Moose Creek Dam at the Chena River Lakes Flood Control Project. This will consist of constructing 4.5 miles of barrier wall 56 to 66.5 feet below the crest of the dam embankment with Portland Cement and Bentonite. The barrier wall is expected to be between 18 and 30 inches wide and have an unconfined compressive strength of 200 psi at 28 days and approach 500 psi in the long term. Sheet pile will be driven around the low point drain and control works to have a continuous wall through penetrations in the embankment. The intent of the barrier wall is to sever a continuous fine grained sand / silty sand that is highly erodible under the embankment material. Mix in place methods shall be utilized to mix the embankment and foundation materials with Bentonite and Portland Cement in order to construct a Barrier Wall through Moose Creek Dam. Any methods that utilize a bentonite slurry trench to support the embankment while excavation of the barrier wall takes place will NOT be utilized at Moose creek Dam. The potential loss of slurry could result in failure of the embankment into the excavation during construction due to highly pervious foundation materials.

Questions for Sources Sought Technical

1. Experience on USACE/far north projects?

2. Wall width min/max?

3. Wall depths min/man?

4. What method of Wall construction would you propose?

5. Starting and Stopping?

5.1. Does the machine need to be removed from the ground?

6. What method is used to tie into existing structures?

6.1. Is the structure damaged?

6.2. How close is the tie in to the structure?

6.3. How would you propose creating a positive/complete wall at the control works where it is at a 5V:1H slope at 20 feet below the crest?

7. How easy is it to change depths?

8. Work platform requirements?

8.1. Degrade crest?

8.2. Other site prep?

8.3. Does work Platform need to have access around wall equipment? (Passing room for trucks)

9. Concerns with permafrost?

10. Concerns with foundation materials?

11. Does high water table effect placement?

12. Segregation concerns?

13. Does a certain type of mix work better with your machine than another? (Cement, Bentonite, etc.)

14. Ambient operating temperature?

15. What sort of QC has been performed for placement?

15.1. Data collection capability? (logging machine location, speed of advance, RPM, verticality, material take/flow rate, etc. for post-construction quality verification)

16. Typical working platform required?

17. Mix design?

17.1. How would you conduct a mix design?

17.1.1. What method would you follow?

17.2. Do you agree with the results of the Golder Mix Design?

17.2.1. Does it accurately portray findings of mixes and quantities of materials?

17.3. Do you have a Laboratory that you would use for Mix Designs?

17.3.1. Why do you use this lab to perform the mix design?

17.4. What kind of mix factors do you look at for your mix design?

17.4.1. How is bentonite and cement factored in your mix design?

17.5. What have you seen for strength gain over time for a mix in place wall?

17.6. Thoughts on dry mixing and its application at Moose Creek Dam?

17.7. How do you expect the cold ground water temperature (below 40 degree F) to affect curing of the mix-in-place wall?

18. The existing drain must remain intact. What means and methods would you recommend to limit the potential loss of cementitious materials into the adjacent rock drain at the base of the embankment during installation of the barrier wall?

18.1. Do you have any additional thoughts or concerns?

19. Permafrost is expected to be encountered. What limitations might this known site condition impose on the ability to achieve a uniform mix, with the required mix performance for the various types of M.I.P. equipment?

20. The purpose of the barrier wall is specifically to prevent internal erosion of the foundation soils through horizontal flaws above a certain depth. What QC/QA procedures would you employ during construction to ensure the finished barrier wall will have adequate properties to achieve this "no-erosion" goal?

21. What kind of depth transitions can your equipment perform?

21.1. Is it easy to change depths?

21.2. How often would you recommend depth changes and at what interval?

22. How do you account for mass volume calculations when determining quantities for a mix-in-place wall?

23. How do you handle water content below water table and above water table?

24. What is the lowest psi you would recommend for construction of this wall?

24.1. What would you expect the final psi to be for that recommendation?

25. Cobbles in the foundation were encountered during recent drilling operations. How would this affect your production and construction of the wall?

26. If placement of the wall was rejected what means and methods would you use to repair deficiency/replace?

27. Would you recommend any other construction technology for placement of the barrier wall? Note: A slurry that could seep into the gravel drain or highly permeable foundation material would not be permitted since loss of slurry would result in embankment not being supported.

Wastage

28. At MCD, we'll be going from finer grained (embankment) into coarser materials (foundation) so waste generation will vary with depth. Would it be possible to adjust slurry addition (and waste) by depth by varying rotation and insertion rates?

29. What waste factor would you typically expect?

30. Re-use of waste material?

31. Based on concern for waste generation and considering the embankment and foundation at MCD, what M-I-P method would you use and why?

32. How much migration (laterally) into the formation is expected with your construction technology based on soils?

33. How much waste comes to the surface?

34. What waste factor would you use for different construction technology from your experience? (Muli-auger, CSM, TRD, others)

Crew Data

35. Typical crew composition? (equipment/labor loadouts)

36. Production rates? (SF wall/HR)

37. Typical Hours of Operation/Work Schedule?

38. Seasonal weather concerns? (extreme cold, precip, etc.)

39. Mob/demob to Fairbanks, AK, concerns?

40. Specialty crews required?

41. How long would the job take? (generally in working days)

41.1. Would you consider multiple concurrent crews/equipment?

41.2. Construction window/seasons?

41.3. Wintering over ideas?

41.4. Mothball/multi-mob/demobs?

41.5. Equipment availability/ competing projects?

Are there any other items for consideration?