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Date: October 11, 1995
Author: Thomas E. Jewett, Vice President Engineering Services
Subject: Allan Block / MANTA RAY® Hybrid Retaining
Wall
Project Site: 7670 Bush Lake Drive; Bloomington, Minnesota (U.S.A.).
Residential retaining wall on "spec" home.
Description of Problem: Local site conditions preclude normal excavation
for installation of geo grid for this type of wall.
Site / Design Conditions:
Wall #1 4.2' - 4.8' tall
Wall #2 6'4" above and 5' - 14' behind wall #1
Access only from driveway in front of walls.
Proposed Solution / Selected Solution: Where excavation is impossible
or impractical, this type of wall could not be installed. This would require an expensive cast-in-place gravity
wall or sheet pile wall. Use of the MANTA RAY® anchors as tie backs allow this hybrid style wall to be installed
quickly and cost effectively
Installation Details:
Anchor / Grid / Wall Attachment Sequence
1. Drive & lock anchors into bank.
2. Stack block up to bottom of anchor grid.
3. Place anchor gird and next course.
4. Drape anchor grid back over front face of wall.
5. Place backfill between back of anchor grid and where anchor rods protrude from cut face.
6. Place anchor grid over anchor rods and keep it taut.
7. Place 2" pipe over anchor rods and grid and tighten with nuts and washers.
8. Stack blocks up to top of anchor grid.
9. Backfill up to top of anchor grid.
10. Place top of anchor grid over blocks and continue to build wall as usual.
Anchors: MANTA RAYÆ MR-2-24G equipped with 3/4 - 10 x 6' galvanized
all-thread rod. Embedment depth after load locking - 9' behind heel of wall #2. Minimum proof load 10,500 lbs.
Installation Equipment: (1) Bobcat 843 Skid Steer
(1) Bobcat #2560 Mounted Breaker
(1) SG-250 Drive Steel Shank
(1) SG-3-96 8' Drive Steel Tip
(1) SG-2-72 6' Drive Steel Extension
(2) SG-4 Drive Steel Couplers
(1) LL-1 Load Locker
(1) ASB-24-20 Adapter Setting Bar
Actual Anchors Installed:
|
#1
|
10,500 ~ 5' Depth Behind Cut Face
|
| #2 |
10,500 ~ 5' Depth behind cut Face |
| #3 |
15,000 |
| #4 |
15,000 |
| #5 |
15,000 |
| #6 |
14,500 |
| #7 |
14,500 |
| #8 |
14,250 |
| #9 |
14,000 |
| #10 |
14,000 |
Installation Notes: "Free Swinging" mounted breaker worked
well. Operator had some initial alignment problems, but improved with practice. Reaching up and over wall #1 worked
well, although the 14' drive steel length provides some unavoidable bowing. See photograph #1.
All anchors (except #1, #2) were driven ti 10' to 11' depth in under 5 minutes. All anchors were driven, locked
between 8:30 a.m. and 1:30 p.m. with a 1 hour lunch break and discussion / training time between anchors.
More care need to be taken during driving to maintain alignment, or excessive drive steel wear will occur.
"Flat bottom" LL-1 FPM equipped with 10" x 10" square plate base would have significantly eased
anchor locking. Use of current LL-1 FPM with LL-1 BP baseplate is very cumbersome. See photograph #2.
Conclusion / Results: Concept works well.
- Allan Block personnel are convinced:
- of the concept;
- this will help their distributors / producers win more jobs.
- Bobcat\2560 mounted breaker works well.
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