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July 8, 2015 Set 4 TO: All Potential Respondents
RFB 1414 River Tower Shoreline Restoration and Water Quality Improvement Project
FROM: Anita Hoover, Procurement Specialist 3 SUBJECT: Response to Questions QUESTION 1: On plan sheets 3, 4 and 5 in the notes on all three plan sheets it states,
“Deltalok material to be installed as designed by Natural Capital Solutions or approved equal”. I have looked and I have had vendors look and we cannot find any information on Natural Capital Solutions or a supplier for the Deltalok bags.
In the Response to Questions, Set 2. The response to question 11 is: “Envirolock is not an approved equivalent at this time”.
Can the supplier of the Deltalok bags be provided or can the name of an approved equal product be provided?
ANSWER: DeltaLok is now Terra-Gen in the United States. Erosion Management
Systems (EMS) is the regional representative and all questions related to DeltaLok and the Terra-Gen System are to be directed to Thomas Goebel, Natural Capital Solutions, LLC at 4608 N. Hale Avenue, Tampa, FL 33614, 727-458-4524, fax 813-443-5632.
The Terra-Gen System produced by EMS is an approved equivalent to
DeltaLok. Attached is the Engineer’s Manual for Terra-Gen.
Terra-Gen Engineer’s Manual
Engineers Design Manual
Engineer’s Design Manual - 3
Introduction
The Terra-Gen Erosion Control and Restoration System is a unique patented system that can construct
permanent structures with a vegetated face without using concrete rebar or other armored materials. The Terra-
Gen System is also the only earth retention system that does not use concrete or steel.
Terra-Gen amplifies the power of interconnecting sand/soil bags by leveraging upon existing industry practices
and standards. For example, the Terra-Gen System works with MSE (Mechanically Stabilized Earth) principles
that have been used in earth stabilization projects throughout the world for over 25 years. Another example of
how the Terra-Gen System works with existing industry know-how is illustrated through the Terra-Gen GTX line of
sand/soil bags. This line of bags is made from non-woven geotextile, a common material known for its soil
filtration, water permeability, root friendliness and strength.
Before construction begins, standard design guidelines and engineering requirements must be reviewed. Will
the retaining wall be a ‘critical’ structure requiring engineering documentation or will it be a ‘non-critical’ structure
falling within basic design and construction methods? The following conditions will require a full engineering
study:
The wall height, including terraces, exceeds 3’-6’ (depending on jurisdictions)
The wall will be built on unstable soils, such as clays or organic materials
The wall will encounter hydrostatic loading or erosion from wave action, drainage or site runoff
The wall will encounter loading conditions resulting from slopes or structures behind or above the wall
The wall will use geo-grid soil reinforcement or other mechanical stabilization devices
Product Name
Terra-Gen Erosion Control and Restoration System
Manufacturer
Erosion Management Solutions, LLC.
147 Keating Drive Belle Chasse, LA 70037
Tel: (504) 433-8142 Fax: (504) 433-3103 Email: jabentz@emsgreen.com
Engineer’s Design Manual - 4
Height: 1.6 in (50.800 mm)
Length: 12 in (304.80 mm)
Width: 3.5 in (88.900 mm)
# Spikes: 4 with capacity for 4 more
Weight: 0.13 lbs (59 grams)
Product Description The Terra-Gen System is a patented system used to create attractive vegetated earth slopes and walls for a
variety of purposes including environmental walls, erosion control, vegetated retained slopes, stream bank
stabilization and retaining walls.
Terra-Gen standard connector units are made from high strength polypropylene. The standard units are used to
interlock Terra-Gen GTX bags, thereby increasing the shear strength of the structure, enabling the creation of tall,
steep, and eco-friendly earth walls. The units are resistant to damage before, during, and after construction in all
climates. They are recyclable and reusable.
Spikes (for bag interconnection and for geogrid connection) are molded into the Terra-Gen connector units. As
sand/soil bag wall courses are installed, Terra-Gen standard units are positioned such that their spikes interlock
the Terra-Gen GTX bags. At all levels where geogrid is required, Terra-Gen standard units are used to also
connect the geogrid to the wall face.
Specifications
Terra-Gen Standard Connector Unit
Raw material: 100% polypropylene
100% recyclable
Provides a positive connection between the sand/soil bags, effectively interconnecting each and every sand/soil
bag into one solid unit. Terra-Gen GTX Bags
Terra-Gen GTX bags provide the ideal planter block for permanent vegetation.
These bags are water permeable, provide filtration and are root friendly.
Product Name Size Approx. Facing
Area/Bag (sq ft)* Approx. Facing
Area/Bag(sq m)*
Terra-Gen GTX-W 15 in x 35 in 1 sq ft. 0.10
* Facing area per bag will vary depending upon quantity of bag fill
The Terra-Gen GTX-W are manufactured from non-woven geotextile. These bags have the following characteristics:
Physical Hydraulic
Raw Material 100% Polypropylene Raw Material 100% Polypropylene
Grab Tensile Strength 90 lb (0.40 kN) Apparent Opening Size 70 U.S. Sieve (0.212
mm)
Trapezoidal Tear 40 lb (0.178 kN) Permittivity 2.2 1/sec
Mullen Burst 190 psi (1309 kPa) Flow Rate 150 gpm/sf
(6095 1/min/sq m)
UV Resistance 70% @ 500hrs
Engineer’s Design Manual - 5
Terra-Gen GTX bags can be manufactured using alternate geotextile characteristics based on site specific needs.
Minimal project quantities apply.
To maximize wall uniformity and efficiency care should be taken to fill the bags completely and consistently. A
variety of bag filling machines are available for this purpose. Please note that the amount of wall facing covered
by the Terra-Gen GTX bags varies from job to job because of different fill materials, different quantities, and different closing techniques.
Geogrid
Geogrid is a commonly used component for engineered walls and will be specified by the project engineer.
The Terra-Gen System has been designed to work with all brands of geogrid.
When installing geogrid, ensure that it is flat when it is placed onto the backfill. This can be achieved by rolling out
the geogrid, and then pinning it into position (straight back, with flat surface) at the back of the backfill zone. By
placing backfill from the back of the backfill zone to the front of the backfill zone, the weight of the backfill will help
keep the geogrid straight and flat.
Wall Installation
The following topics cover the specific installation instructions for installing a Terra-Gen system.
Tools Required
Safety protection
Shovels
Tape Measures
Compactor
Broom
Site levels
Wheelbarrow
String line
Handheld stitching machine (Optional)
Bag filling machine (Optional).
Excavate Site
The project site may need to be excavated, and should be done so to the lines and grades shown on the con-
struction drawings. During excavation, care should be taken not to disturb additional foundation material.
The foundation must be adequately compacted to minimize wall settlement. The excavated area must be large
enough to accommodate the sand/soil bag embedment, and the required geogrid lengths.
Construct an embedment trench as specified in the engineering documentation, as required.
Take care to place the excavated materials in a convenient location if site materials will be used to fill the bags.
Reasonably Level Base
No footings are required. Only a reasonably level and compacted base is required. Note that a drainage zone
behind the wall face is not required because the wall face is water permeable. The permeability of the wall face
reduces hydrostatic pressure and helps maintain vibrant vegetation by providing hydration to the root zone.
Fill and Close Bag
We recommend filling the bags right at the job site, to minimize transportation and handling costs. Depending on
the job size, a variety of bag filling methods are available, which will work well with the Terra-Gen GTX bags.
To achieve optimum coverage ensure bags are completely filled.
Engineer’s Design Manual - 6
Depending upon the application, suitable bag fill materials include:
Site soils
Top soils
Crushed stone
Blend of above materials
There are also a variety of techniques to close the bags, including:
Zip tie/Cable tie (Zap Strap)
Fold over technique
Industrial handheld sewing machine
Initial Base Course
Once the surface has been reasonably leveled, place filled bags to create the base course. Level the bags front to
rear and side-to-side.
After the base course units have been properly positioned, place and compact soil backfill behind and in front of
the bags to prevent shifting. Install the entire length of the base course before starting succeeding courses, if pos-
sible.
Interlock Base Course & Succeeding Courses
Place Terra-Gen standard units on top of the bags toward the edges so that each standard unit spans two bags
(see diagram on next page). Stagger succeeding courses of bags so that each standard unit pierces the middle
underside of the Terra-Gen GTX bag above it.
Engage interlocking feature by walking along each course of Terra-Gen GTX bags. This practice is recommended
to ensure good contact between the units and the bags.
Place Succeeding Courses
Succeeding courses will be set upon previous courses so that each top sand/soil bag will be placed over two bot-
tom sand/soil bags with one Terra-Gen standard unit sandwiched between the upper and lower courses. This will
create a running bond face pattern. Continue placing sand/soil bags, drainage aggregate and reinforced backfill.
The weight from the top courses will drive the standard units into the sand/soil bags, forming a positive connection
between the sand/soil. 1 Place base course of Terra-Gen GTX
Bags
2 Place a Terra-Gen standard unit such that
it spans the two Terra-Gen GTX bags
3 Place the second course of the Terra-Gen GTX bags
4 Repeat for the entire wall with same pattern
Engineer’s Design Manual - 7
Walking along the courses of Terra-Gen GTX bags, or tamping the tops of the Terra-Gen GTX bags will help
ensure that the Terra-Gen GTX bags are securely interlocked.
Compacting the Backfill for Engineered Walls
Proper compaction of backfill is critical to the stability of engineered or mechanically stabilized earth walls. Poorly
compacted soil puts extra pressure on the wall, especially when loose backfill gets wet. Geogrid reinforcement
does not work if the soil around it is not properly compacted. The backfill soils should be compacted to a minimum
95% Standard Proctor. Both the type of material and the compaction equipment need to be considered when ad-
dressing this issue.
Consult an engineer for specific recommendations and use the following basic guidelines as illustrated on the fol-
lowing page for engineered walls.
a. Backfill material must have the proper moisture content for optimum performance when compacting.
b. Organic or heavy clay material should not be used. These materials hold excessive moisture and will not
compact properly.
c. Walk behind mechanical compaction equipment may be used to compact soils.
d. Ride-on mechanical compaction equipment should be operated no closer than within 3 feet (1 meter) of
the wall face.
e. Avoid over-compacting soils next to the wall face in an uncontrolled manner.
f. Qualified personnel should perform all soil testing. Soil tests should be taken no closer than three feet
from the back surface of the Terra-Gen GTX bags.
The proper thickness of material placed in a single lift is dependent on the type of soils and compaction equip-
ment being used. Most inorganic site soils, which are easily influenced by moisture levels, must be placed in
smaller lifts and will require greater compaction effort.
For your reference Terra-Gen has available standard engineering drawings for engineered walls depicting typical
installations to assist design professionals in specific applications. Install Geogrid for Engineered Walls
Geogrid is used to reinforce retained soil fill. Site, soil, wall loading, and seismic conditions all influence the design
of geogrid reinforcement.
Geogrid reinforcement is placed at wall elevations as shown on the construction drawings. At courses where the
construction drawings indicate that geogrid is required, use Terra-Gen engineered units. The Terra-Gen
engineered units not only interconnect the bags, but also provide a mechanical connection for the geogrid. To
connect the geogrid to the Terra-Gen engineered units, simply fit the geogrid over the hooks and pull taut.
Once the geogrid is anchored, lay the required length horizontally and ensure the highest strength direction is
perpendicular to the wall face.
When installing geogrid, ensure that it is flat when it is placed onto the backfill. This can be achieved by rolling out
the geogrid, and then pinning it into position (straight back, with flat surface) at the back of the backfill zone. By
placing backfill from the back of the backfill zone to the front of the backfill zone, the weight of the backfill will help
keep the geog rid straight and flat.
Build the next wall course to further drive the Terra-Gen engineered units into the bags and help anchor the
geogrid to the wall, then place and compact backfill on top of the geogrid.
Geogrids are usually stronger in one direction than the other, so it is very important to place them in the correct
direction. The strongest direction of the grid must be perpendicular to the wall face. Follow the geogrid manu-
facturer’s directions to ensure the geogrid is properly oriented. Also note, the geogrid type, length, and spacing
varies from different manufacturers and different specifications. Reference to installation guidelines for geogrid
product is recommended.
Engineer’s Design Manual - 8
Repeat
Repeat steps 5-8 until all courses have been placed.
Capping/ Top of Wall
For the final row of taller walls, rotate the bags 90 degrees such that they extend further into the backfill to provide
an effective capping solution if required. Another capping method is to build a self-standing wall at the top as per
the Design Drawings.
Facing Options
Terra-Gen GTX bags are designed to accommodate any desired vegetation; roots can penetrate the Terra-Gen GTX bags without damage. Once established the roots help to increase the strength of the wall.
Vegetation Choice
1. Grasses/Turf
2. Bushes
3. Willow, Alder, Dogwood cuttings
4. Riparian Plants/Native Species
5. Wild Flowers
6. Vines, etc.
Methods of Achieving Vegetated Wall Face
1. Hydroseeding
2. Live Staking
3. Brush Layering
4. Seed Scattering
5. Plugs
Vegetation Selection
When selecting appropriate vegetation species, consider the following points:
1. Maintenance free cover crops can eliminate the need for trimming
2. Drought tolerant species may be recommended for more arid climates
3. Freeze tolerant species may be recommended for colder climates
Local vegetation experts should always be consulted
Engineer’s Design Manual - 9
Design Method Earth Pressures
Active pressure SRW’s yield slightly Coulomb’s or Rankine
Tied back wedge
Tiers Most complex designs
Create steep slopes
Setback 2:1
Closer spacing surcharges External Overturning Stepping Six inch increments
Stability Sliding Bearing
Global
Walls Make top steps symmetrical Returns for steep steps
Stepped base affects grid
Internal Pullout Adjoining Posts behind wall preferred
Stability Over-stress Sliding
Structures Allow for movement Units cannot cantilever
Facial Stability Connection
Shear
Overturning at top
Design Limits Grid length Grid spacing
Shoreline Requires more drainage Scour protection Foundation concerns Rapid draw down
Rules of Thumb Embedment for Engineered Walls
At least one-tenth the height of the wall should be buried below the final grade in front of the wall when grade is
level. Embedment depth increases for special conditions. Tiers
The lateral distance between the tiered walls should be at least twice the height of the lower wall. If horizontal
spacing must be closer than this, the lower wall(s) should be designed and reinforced to withstand additional load
from the upper walls.
Maximum Height Without Geogrid
In best site and soil conditions, we recommend a maximum of 4-6 feet, though this does depend on specific juris-
diction requirements.
Geogrid Lengths
Lengths for level backfill walls are generally 0.6 to 0.7 times the wall height. Lengths increase with increased
slopes and increased wall loads.
Maximum Geogrid Spacing
Vertical spacing between geogrid layers should not exceed 2 feet in general.
Engineer’s Design Manual - 10
Questions and Answers Question 1: How high can Terra-Gen walls be built without the use of geogrid?
Terra-Gen walls can be constructed between 2’ and 6’ high without geogrid depending on soil conditions,
amount of batter used, and surcharge on top of the wall. Typically, under good soil conditions, we recommend
geogrid be used for walls exceeding 4’ in height.
Question 2: Are concrete footings necessary?
No. The Terra-Gen GTX bags are soft and can adapt to imperfections in the base. Therefore a leveled
surface is usually sufficient unless the design engineer requires further sub-base.
Question 3: How high can I build a Terra-Gen wall?
It can be built as high as you need to. Terra-Gen walls can be built as high as any concrete modular block wall
because it is based on the same MSE principles. Terraces are often incorporated into tall walls.
Question 4: How many Terra-Gen GTX bags should be buried at the base?
Typically the ratio is 1:10 (one course should be buried for every 10 courses above the surface). In most
cases, other than where the grade slopes away from the wall at the base, 3 to 4 units are the maximum to be
buried on tall walls. More than that does not create an added benefit. For extreme ground water conditions
and in frost conditions we recommend filling the sand/soil bags with crushed stone.
Question 5: Should construction be started at one end of the wall or is it acceptable to start in the
middle?
Construction of the wall should begin at your lowest point whenever possible. Question 6: How do I finish the top of the wall off (capping)?
For the final row of taller walls, rotate the bags 90 degrees such that they extend further into the backfill to
provide an effective capping solution if required. Another capping method is to build a self-standing wall at the
top as per the Design Drawings.
Question 7: How high can Terra-Gen GTX bags be stacked before placing the backfill?
We recommend placing and compacting backfill every two courses at least. This aids in keeping the wall
straight and helps ensure good compaction.
Question 8: What type of material should be used for backfill?
Granular materials such as rock and sand are best if available. These types of materials compact fairly easily
and will not hold excessive moisture. Terra-Gen walls can be built with silty material and lean clays, but these
types of soils require more compaction and care should be taken not to place these materials when they are
wet. High clay soils that shrink and swell rapidly as well as organic soils should be avoided.
Question 9: How often do I need to compact the fill soils?
We recommend placing and compacting fill every two courses at least to avoid putting unnecessary pressure
on the wall. Thick lifts of soil require more compaction effort and create a greater force at the back of the wall,
generally 8 inch (20 cm) lifts is the recommended maximum. Consult with a geotechnical engineer for further
compaction criteria based on specific site soil.
Engineer’s Design Manual - 11
External Stability Failures
BEARING OVERTURNING GLOBAL
Internal Stability Failures
PULLOUT INTERNAL SLIDING BREAKAGE Facial Stability Failures
SHEAR STRENGTH CONNECTION STRENGTH Basic Reinforcing Design Methodology for the Engineer
To properly stabilize a segmental retaining wall system the reinforced soil mass must be designed large enough to
resist loads from outside the wall system (external stability) and must contain enough soil reinforcement to keep
the soil mass together (internal stability).
For external stability, the reinforced soil mass must have sufficient width to resist sliding, overturning, and bearing
failure. For internal stability, soil reinforcement must have sufficient strength and layers to resist tensile overstress
(breakage) and sufficient length to resist pullout from stable soil.
Various wedges of soil which could move forward, away from stable soil, are analyzed to ensure that soil rein-
forcement layers have sufficient anchorage to hold these wedges in place.
External soil loads are calculated by traditional earth pressure theories used for design of any retaining walls. In-
ternal forces on geosynthetic soil reinforcement are calculated using two soil properties – internal angle of friction
and soil unit weight.
Accurate knowledge of these properties is needed for proper wall design. Generally, the cohesion of any fine-
grained soils is conservatively ignored to simplify design.
Passive resistance against sliding, provided by soil in front of wall bases, is also conservatively ignored.
Engineer’s Design Manual - 12
Applications
The Terra-Gen System has a wide variety of applications including: Environmental Applications
Erosion Control
Steep Slope Stabilization
Storm water & Drainage
Fisheries Sensitive Creeks and Streams
Trail Enhancement
Culvert Headwalls
Riverbank Protection & Remediation
Slope and Slip Repairs
Open Pit Mining Restoration
Infrastructure Applications
Retaining Walls
Highway Walls
Bridge Abutments
Levees/Dikes & Berms
Noise and Roadside Barriers
Military & Emergency Applications
Flood Protection
Ammunition Storage Points (ASP’s)
Blast Walls/Bunkers
Commercial & Residential Applications
Garden Walls
Landscaping
Golf Courses
Advantages
The Terra-Gen System offers many advantages including:
Lightweight components
Easy to transport, store and handle
Variety of natural wall faces are possible
Modular construction ensures long term performance, soil containment keeps fines intact
Minimal site preparation; builds faster than other systems, resists settlement activity and hydrostatic pressure, no sagging, bulging, cracking or staining…graffiti proof
No footing or leveling pad required
Engineer’s Design Manual - 13
Maintenance
The Terra-Gen System does not require any maintenance if appropriate seeds are selected for the wall face. Proper engineering design, installation and site preparation will ensure a maintenance free wall.
Technical Services
Terra-Gen System distributors are trained and knowledgeable of the product and installation, and can answer most questions. Please contact us if additional detail and information are required.
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