LD_11_Questions-Answers.pdf

L&D 11 Questions

Questions Submitted on FBO Prior to Industry Day

1) Spec 31 23 19 paragraph 3.3 states in part, “at all times while the lock chamber is dewatered, maintain the ability to fill the lock chamber to the tail water elevation in less than 60 minutes.” Is this refilling process to be executed with the contractors pumping systems or is there a system within the lock chamber that allows water to flow back into the chamber without pumping?

There is no lock system for rapid flow back into the chamber. There has never been an emergency that has required a rapid refill in the past, so there is no preferred Government method. When dewaterings are performed by MVR, the emergency rewatering plan calls for using a crane to pull out the dewatering bulkheads until they are overtopped. Any feasible alternatives would be acceptable.

Update 5/1/2017: The Government will be performing all work related to the lock chamber unwatering except what is reflected in the revised 31 23 19. Emergency rewatering will be perfomed by Government personnel if needed.

2) Spec 31 23 19 paragraph 3.3 states in part, “Maintain a minimum 5 foot water level in the lock chamber during the dewatering process during non-daylight hours.” Is this 5’ of water required every night during non-daylight hours when working on the chamber floor?

No. The 5 ft requirement is only for the dewatering process itself. The intent of this requirement is that it would be preferable for the last several feet of dewatering, when the risk of problems with the floor occurring is highest, to occur during daylight when there would be the most personnel available to address problems. Once the chamber has been fully dewatered, the intent is to keep the chamber fully dewatered, unless some sort of emergency required otherwise. If the contractor would like to dewater during nighttime hours it must be included in an approved dewatering plan.

Update 5/1/2017: The Government will be performing all work related to the lock chamber unwatering except what is reflected in the revised 31 23 19. Dewatering will be performed by Government personnel.

Unanswered Questions from Industry Day

3) Does USACE have the ability to leave the bulkheads on USACE barge instead of placing on land?

The Government will be solely responsible for delivery, placement, and removal of the bulkheads.

Questions Submitted to Contract Specialist Following Industry Day

4) Sheet S-201 calls for drilling a finished 16” hole with 8” well screen and gravel pack filter of 4” all around. This will require an initial hole of approximately 18” diameter to allow the temporary steel casing pipe called out in 33 26 00 para 3.1.3. Driller is asking if a 12” x 8” (12” bore hole w 8” gravel packed screen) would be considered. This smaller bore hole would allow for a drilling method that would eliminate circulation of drilling fluid (including mud), the need for potential temporary casing during well construction, and the risk of formation displacement while drilling, yet still ensure precise placement of the well components (screen, filter pack, etc.) and proper alignment. This would allow less than 4” gravel pack all around.

See required dimensions on S-201. A minimum 4” gravel pack all around the 8” diameter well screen is a USACE design requirement. Any method of drilling which does not provide a minimum 4” gravel pack around the perimeter of the well screen would not be acceptable.

5) Spec 33 26 00 para 3.1 states that wells may be drilled by the reverse rotary circulation method or other method approved. Will sonic drilling method be allowed? Advantages to using the sonic drill method include: using clean water to drill and maintain head pressure to hold the hole open; can more easily advance the casing to the bottom of the hole; can maintain hole plumbness easier; gravel pack around the screens will be settled better due to vibrations during retraction of the casing; eliminates larger quantities of drilling waste and mud; a single well should be drilled and placed in one day.

Sonic drilling would be allowed under this requirement provided the Contractor addressed Government concerns with densification of soils immediately below the lock floor, voids related to densification, and issues with flowing sands during tooling extraction. These concerns and the submittals required to address them are discussed in Specification Section 33 26 00, Paragraphs 1.2 (Relief Well Installation Plan and Drilling Program Plan) and 3.1.

6) Plan sheet S-201 detail A1 shows a horizontal check valve at the top of the riser pipe. The accompanying note states that the horizontal check valve is to be installed on the riser pipe prior to riser pipe installation in the well. Due to limited space inside the well casing, can the horizontal check valve be installed after dewatering the lock chamber? This may require a temporary vertical valve on top of the riser.

See revised plan sheet S-201 detail A1.

7) Plan sheet S-101 location tables indicate many of the relief wells to be located 1.5 feet from the guide wall. Industry day meeting notes requested feedback regarding drilling room and concrete block placement and pinch points. The 1.5’ location makes for very tight conditions and if required to be maintained will add significant costs to both tooling and installation.

What is the maximum permitted distance from the guide wall? Since several of the relief wells noted on the location table have offsets from the wall from 4.5’ to 6.5’ due to underwater sills, why not move the others that same distance to allow drill rig access? 4.5’ to 6.5’ would allow plenty of room for drill rig to operate over the side of the barge.

Lock operation requires protection blocks to be as close to the lock wall as possible. See S-101 for dimensions.

8) If sonic drilling method is not approved can we use a vibro hammer to install 18” casing pipe after core hole is cut thru the chamber concrete floor and/or grout if encountered?

The use of a vibro hammer would be allowed under this requirement provided the Contractor addressed Government concerns with densification of soils immediately below the lock floor, voids related to densification, and issues with flowing sands during tooling extraction. These concerns and the submittals required to address them are discussed in Specification Section 33 26 00, Paragraphs

1.2 (Relief Well Installation Plan and Drilling Program Plan) and 3.1.

9) Plan sheet S-101 general note 5 states in part: contractor shall provide NAD83 coordinates of the drilled location of each well. Must these specific locations be recorded by a licensed surveyor or can the contractor record them with our own survey equipment?

See Section 00 73 05 para 1.28.

10) Plan sheet S-101 shows eight each relief wells at rows 24, 25, 37, and 38. After upstream bulkheads are set in place, can the miter gates be opened before the lock chamber is dewatered to allow barge access to drill wells? After the lock chamber is dewatered can the miter gates be opened to allow equipment access to complete the concrete cap placement or must the miter gates remain closed?

Government personnel can open the miter gates both prior to and after the chamber has been dewatered to allow barge and equipment access.

11) Are the relief wells intended to be pumped during the dewatering phase?

The relief wells are to allow for passive, not pumped, dewatering. The check valve temporarily installed as shown on S-201 detail A1 will allow the relief wells to function for the dewatering during construction

12) If the wells are not intended to be pumped, what will be the process for lowering the water level in the lock to conduct work at the lock floor?

The Government will perform the dewatering of the lock using portable pumps and the sumps located on the intermediate wall. See S-101 for locations. Anticipated water depth of the dewatered chamber is approximately 1 foot.

13) Will initial testing of the wells and associated discharge be used to evaluate the effectiveness of the installed wells?

See CLIN 0005 and Section 33 26 00 para 3.7 for relief well testing requirements.

14) Divers are to locate each proposed well with respect to the closest weep hole. What is the minimum distance required from the edge of any existing weephole?

There is no minimum distance requirement for this project. The relief well locations are such that there should be no overlap between weepholes and relief wells.

15) The well riser is intended to be SCH 80 PVC , correct?

See Section 33 26 00 para 2.2.

16) Is the PVC riser intended to extend to a point at or above the water surface inside of the lock chamber after well completion?

See revised S-201 detail A1.

17) Does all drilling spoil need to be tested by certified lab prior to removal off site?

See Section 33 26 00 para 3.9.

18) Can all well drilling spoils be deposited inside the lock chamber and removed later when the lock is emptied?

See Section 31 23 19 para 2.1.1.

19) Section 31 23 19- Observation well and monolith joint monitoring -

• Where are the existing monitoring wells located?

The observation wells at Lock 11 are installed adjacent to the Tainter valve bulkhead slots. Requirements for the Contractor to monitor the observation wells have been deleted from this requirement.

• What is the criteria for the maximum allowable difference between the observation well readings and lock water level readings?

The dewatering of the lock will be performed by the Government. Observation well readings and their interpretation have been removed from this requirement.

20) Section A-1 on Sheet S-201 shows the relief well discharge turned horizontally and through a check valve, is there a determined elevation that the relief well discharge is to be turned horizontally at? And where is the discharge supposed to terminate?

See revised S-201 detail A1.

21) The relief well protection block section drawing A-3 on Sheet S-103 appears to indicate two (2) check valves and flapper valve heading in opposite direction. Are these valves supposed to be cast in place in the protection block?

See Section 03 40 00 para 2.3.3.

22) Flapper valve is indicated to be 304 stainless, is the inline check valve to be stainless as well?

See Horizontal Check Valve in Section 05 50 13 Part 2.

23) Will there be a gasket between the protection block and cover plate?

There is no gasket between the protection block and cover plate. See S-301 details C1 and C3.

24) Will the precast protection blocks be reinforced?

See revised S-501 details A3 and A4.

25) Will the installation of the relief wells and protection blocks constitute the complete contract?

There will not be other major maintenance that takes place inside the lock after the relief wells are completed?

For L&D 11, there is no other maintenance to take place inside the lock chamber. If Option A is awarded there is work to be done on the land wall concurrently with the relief well and protection block installation.

26) Is the use of a vibrated steel casing to the proposed well depth an acceptable installation method?

Vibrated steel casing would be allowed under this requirement provided the Contractor addressed Government concerns with densification of soils immediately below the lock floor, voids related to densification, and issues with flowing sands during tooling extraction. These concerns and the submittals required to address them are discussed in Specification Section 33 26 00, Paragraphs 1.2 (Relief Well Installation Plan and Drilling Program Plan) and 3.1.