TI Design Standards_v1_Chapter 2_Sept 2012.pdf

Tactical Infrastructure Design Standards September 2012 (Version V.1)

Chapter 2 – Fence Design Standards

Chapter 2 –

Fence Design Standards

INTENTIONALLY LEFT BLANK

CHAPTER 2 - FENCE DESIGN STANDARD

SECTION 1. FENCE TYPES

SECTION 2. PRIMARY PEDESTRIAN FENCE DESIGN STANDARDS

2.1 PRIMARY PEDESTRIAN FENCE TYPES

2.1.1 Picket Fence (Type P-1)

2.1.2 Bollard Fence (Type P-2)

2.1.3 Bollard Fence With Steel Plate (Type P-3)

2.1.4 Floating Bollard Fence (Type P-4)

2.1.5 Floating Picket Fence (Type P-5)

2.2 PRIMARY PEDESTRIAN FENCE DESIGN CRITERIA

SECTION 3. SECONDARY FENCE DESIGN STANDARDS

3.1 SECONDARY FENCE TYPES

3.1.1 Mesh Fence (Type S-1)

3.2 SECONDARY FENCE DESIGN CRITERIA

SECTION 4. TERTIARY FENCE DESIGN STANDARDS

4.1 TERTIARY FENCE TYPES

4.1.1 Chain Link Fence (Type T-1)

4.1.2 Barbed Wire Fence (Type T-2)

4.2 TERTIARY FENCE DESIGN CRITERIA

SECTION 5. PRIMARY VEHICLE FENCE DESIGN STANDARDS

5.1 PRIMARY VEHICLE FENCE TYPES

5.1.1 Post & Rail Fence (Type V-1)

5.1.2 Normandy Fence (Type V-2)

5.2 PRIMARY VEHICLE FENCE DESIGN CRITERIA

SECTION 6. FENCE DRAINAGE PROTECTION DESIGN STANDARDS

6.1 DRAINAGE, SCOUR & EROSION CONTROL DESIGN

SECTION 7. REFERENCES

SECTION 1. FENCE TYPES

Up to three layers of fence are currently used by Border Patrol across the Southwest Border. The first layer of fence is considered the primary fence, and includes pedestrian fence (PF) and vehicle fence (VF).

While Primary PF, Figure 29 – Primary Pedestrian Fence (Type P-3), is designed to resist vehicular impact, its focus is to slow down and deter the flow of pedestrian traffic. Included under these standards are five types of approved PF (P-1 through P-5) that are constructed using square steel tubes or solid steel square pickets as means for impedance. See Appendix B, Fence & Gate

Standard Details, for PF details.

Figure 29 – Primary Pedestrian Fence (Type P-3)

The VF on the other hand is solely intended to resist vehicular passage across the border, Figure 30

– Vehicle Fence (Type V-2). Included under these standards are two types of approved VF (V-1 and

V-2). The VF types are constructed using steel tubing and wide flange sections as the main fence components. See Appendix B, Fence & Gate Standard Details, for VF details.

Figure 30 - Vehicle Fence (Type V-2)

The next layer of fence used by CBP is called the secondary fence, Figure 31 – Secondary Fence (Type

S-1). The sole purpose of the secondary fence is to resist and deter pedestrian traffic. Included under these standards is one type of SF (S-1), with the option of either mesh or perforated metal sheeting. See

Appendix B, Fence & Gate Standard Details, for SF details.

Figure 31 - Secondary Fence (Type S-1)

The final layer of fence used by CBP is the tertiary fence. The tertiary fence is used as a means to delineate property limits and is constructed using open fence fabric without the intent to impede pedestrian traffic. See Appendix B, Fence & Gate Standard Details, for tertiary fence details.

Following are descriptions of the various TI fence types and design criteria. For a list of standard specifications, see Appendix A, Standard Specifications. For standard fence details for the fence types, see Appendix B, Fence & Gate Standard Details.

SECTION 2. PRIMARY PEDESTRIAN FENCE DESIGN STANDARDS

2.1 PRIMARY PEDESTRIAN FENCE TYPES

PF uses steel bollards or pickets to impede illegal pedestrian and vehicular traffic. The standard height for PF is 18 feet; however, specific operational requirements can allow for the fence to be designed to greater heights. In order to facilitate construction of the 18-foot tall PF, the fence types are detailed to allow for panelized installation methods. Fence panels are designed and detailed using horizontal steel angles and bars that are strategically placed so to allow the members to remain after the fence is erected, while minimizing the ability for the horizontal members to be used as ladder rungs for climbing the fence. To further resist climbing, various anti-climb and/or anti-perch measures are added to the tops of the PF. Where hollow members are used for the design of the PF, grout and a single #6 rebar are placed inside up to 10 feet above grade in order to resist cutting. PF are typically supported by a 6-foot deep by

16-inch wide reinforced concrete trench. Grade beams with drill shafts can be used for support of the

PF; however, this foundation system must first be approved by CBP due to the 6-foot under-dig criteria required for PF. For a full description of the design criteria required for PF, see Section 2.2, Primary

Pedestrian Fence Design Criteria.

2.1.1 PICKET FENCE (TYPE P-1)

P-1 Fence consists of vertical 1-inch by 1-inch solid steel bars (pickets) that are supported on steel hollow structural sections HSS 4x2x3/16 (rails) that are connected to steel HSS

6x6x1/2 (columns). The clear space between pickets is 3 inches and the maximum center-to-center spacing of the columns is 6 feet 8 inches in areas of gently sloping terrain of less than 30 percent. For terrain with slopes greater than or equal to 30 percent the post spacing is reduced to 3 feet 4 inches. There are four rails that support the pickets directly that are placed at equal spacing along the height of the columns. To meet the anti-perch criteria, the columns are either mitered at 45 degrees, and a plate is tack welded on or capped with pre-formed pyramid caps.

2.1.2 BOLLARD FENCE (TYPE P-2)

P-2 fence consists of vertical HSS 6x6x3/16 steel tubes (bollards). The bollards are typically fabricated and installed in nominal 8-foot wide panels for gently sloping terrain of less than 30 percent. For terrain with slopes greater than or equal to 30 percent, the nominal panel width is reduced to 4 feet. Bollards within a panel are aligned in a rotated pattern with 4 inches of minimum clearance between any bollards.

To meet the anti-perch criteria, the columns are either mitered at 45 degrees, and a plate is tack welded on or capped with pre-formed triangular enclosed caps.

2.1.3 BOLLARD FENCE WITH STEEL PLATE (TYPE P-3)

P-3 fence consists of vertical HSS 6x6x3/16 steel tubes (bollards) panels with 11-gage solid steel plate (steel sheathing) at the top. The bollards are typically fabricated and installed in nominal 8-foot wide panels for gently sloping terrain of less than 30 percent.

For terrain with slopes greater than or equal to 30 percent, the nominal panel width is reduced to 4 feet. Bollards within a panel are aligned in a rotated pattern with 4 inches of minimum clearance between any bollards. The 11-gage steel sheathing is 5 feet in height and is continuous across the top of the fence. The sheathing is attached to the bollards using a ½-inch by 4-inch steel bar and a notched 4-inch by 4-inch by ¼-inch steel angle. To meet the anti-perch criteria, the columns are either mitered at 45 degrees and a plate is tack welded on or capped with pre-formed triangular enclosed caps.

2.1.4 FLOATING BOLLARD FENCE (TYPE P-4)

P-4 fence consists of reinforced concrete barriers with vertical HSS 6x6x 3/16 steel tubes

(bollards). The reinforced concrete barriers are pre-cast in 10-foot long sections with an approximate cross sectional area of 11.4 square feet. The concrete barriers are placed at grade and the bollards are inserted into concrete barriers by means of a steel sleeve set during casting of the section. The sleeves are positioned so as to provide 4-inch clear spacing between the bollards, which are aligned on the diagonal. The bollards are held rigid and plumb by placing steel shims on the U.S. side of the fence. The Type P-4 PF is typically specified where the fence is required to be removable such as, but not limited to, placement on levees.

2.1.5 FLOATING PICKET FENCE (TYPE P-5)

P-5 fence consists of reinforced concrete barriers with vertical 1-inch by 1-inch solid steel bar (pickets) fence panels. The reinforced concrete barriers are pre-cast in 10-foot long sections with an approximate cross sectional area of 11.4 square feet. The concrete barriers are placed at grade and a single W 6x15 wide flange section (w-section) is inserted into each concrete barrier by means of a steel sleeve set during casting of the section. The sleeves are positioned at 10-foot spacing to allow for placement of the picket panels across the length of the concrete barriers. The w-sections are held rigid and plum by placing steel shims on the U.S. side of the fence. The Type P-5 PF is typically specified where the fence is required to be removable such as, but not limited to, placement on levees.

2.2 PRIMARY PEDESTRIAN FENCE DESIGN CRITERIA

Design of the primary PF shall utilize standard details P-1 through P-5 and comply with the following design criteria, unless specifically directed or approved otherwise:

Vehicular impact applied to the fence design as a static 10-kip load per AASHTO 17 th

Edition, Chapter 2.7.1.

Vehicular impact loading shall be applied to the fence design and combined with all applicable load groups per the International Code Council

, latest edition.

The minimum compressive concrete strength for foundations shall be 3,000 psi.

The primary PF shall be aligned on a 3-foot offset parallel to the international border, and border monuments, between the U.S. and Mexico, see Appendix D, Miscellaneous Standard Details.

All hollow fence members (tubes, pipes, etc.) shall be filled with concrete up to 10 feet above grade.

All fence members shall be plain, un-painted steel except where existing sites consist of corrosive soils or where the fence is either known or anticipated to be underwater for prolonged durations.

In such cases, the appropriate measures shall be taken to protect the fence members from corrosion.

Fence shall be anti-perch at all locations and shall be resistant to climbing without special climbing tools. Straight fence without large corrugations, seams, horizontal ridges, or a cantilever panel on top.

Fence shall have the ability to survive temperatures applicable to the Southwestern border of the

U.S. including diurnal and seasonal extremes with temperature deltas in excess of 120 degrees

Fahrenheit.

Continuous openings in the fence, such as space between adjacent tubes, pickets, plates, etc., shall have a clear spacing of no more than 4 inches, except at drainage crossings where spacing between members shall be no more than 5 inches, and shall be uniform in appearance.

Fence shall disallow ponding of water on either side of the border.

Fence shall, where it is necessary, allow migration of all species and shall have minimal impact on habitat and animal dwelling patterns per environmental requirements. The need for and spacing of migratory features within a fence shall be determined on a project-by-project basis.

Fence shall provide deterrence to common/basic under-digging of up to 6 feet below grade.

Floating fence types are exempt from under-digging criteria.

Fence drainage impact shall be designed in accordance with criteria presented in Section 6, Fence

Drainage Protection Design Standards.

Provide construction workers and maintenance crew room to build/maintain fence without breaching border.

The 30-year service life requires planned maintenance, but no more frequently than every 10 years.

Planned maintenance includes application of coatings, minor concrete repair such as surface cracks and surface spalling, and replacement of hinges.

All fence materials shall conform to the following:

o Reinforcing Steel, ASTM A615 Grade 60 o Welded Wire Fabric Reinforcing, ASTM A185. Flat sheets only.

o Deformed Welded Wire Reinforcing, ASTM A497.

o Structural Steel Shapes (W-Shapes), ASTM A992, Grade 50 o Structural Steel Shapes (Angles, Bars, Plates), ASTM A36 o Steel Sheet (Sheet, Strip), ASTM A570.

o Galvanizing, ASTM A153 o Welding, AWS D1.1., E70XX Electrodes

15 Reference 15, page 48

SECTION 3.SECONDARY FENCE DESIGN STANDARDS

3.1 SECONDARY FENCE TYPES

Secondary Fence (SF) as a means of TI uses fence fabric to impede illegal pedestrian traffic that has breached the PF. The standard height for SF is 15 feet; however, specific operational requirements can allow for the fence to be designed to greater heights. In order to facilitate construction of the 15-foot tall

SF, the SF is detailed to allow for panelized installation methods. SF details use horizontal rails in the form of steel tubes and fence fabric of either mesh or perforated metal sheeting. The individual panels of fence fabric are spliced together using steel unions. To resist climbing, the openings in the fence fabric are specified at small openings at tight intervals, and various anti-climb and/or anti-perch measures are added to the tops of the SF at column locations. SF is typically supported by 4-foot deep by 16-inch wide reinforced concrete trench foundation. Drill shafts can be used for support of the SF; however, analysis should be completed to determine the most cost-effective solution. For a full description of the design criteria required for SF, see Section 3.2, Secondary Fence Design Criteria.

3.1.1 MESH FENCE (TYPE S-1)

S-1 fence consists of vertical HSS 6x6x½ steel tubes (bollards) that are typically installed at 8 feet on-center. 4 rows of HSS 3x3x3/16 horizontal rails are mounted to the bollards to allow for continuous support of the SF fence fabric to the vertically mounted bollards. The fence fabric consists of either 6-gage steel mesh or 6-gage perforated metal sheeting with maximum opening of 0.5 inch by 0.5 inch. To meet the anti-perch criteria, the columns are either mitered at 45 degrees and a plate is tack welded on or capped with pre-formed pyramid caps.

3.2 SECONDARY FENCE DESIGN CRITERIA

Design of SF shall utilize standard details S-1 and comply with the following design criteria, unless specifically directed or approved otherwise:

Fence shall be designed to withstand critical load combination per the International Building

Code, latest edition.

The minimum compressive concrete strength for foundations shall be 3,000 psi.

All fence members shall be plain, un-painted steel except where existing sites consist of corrosive soils or where the fence is either known or anticipated to be underwater for prolonged durations.

In such cases, the appropriate measures shall be taken to protect the fence members from corrosion.

Fence shall be anti-perch at all locations and shall be resistant to climbing without special climbing tools. Straight fence without large corrugations, seams, horizontal ridges, nor a cantilever panel on top.

Fence shall have the ability to survive temperatures applicable to the southwestern border of the

U.S. including diurnal and seasonal extremes with temperature deltas in excess of 120 degrees

Fahrenheit.

Continuous openings in the fence, such as space between adjacent tubes, pickets, plates, etc., shall have a clear spacing of no more than 4 inches, except at drainage crossings where spacing between members shall be no more than 5 inches, and shall be uniform in appearance.

Fence shall be of compatible design applicable to desert, mountain, floodplains, open range, and remote conditions.

Fence shall not allow ponding of water on either side of the fence.

Fence shall, where it is necessary, to allow migration of all species and shall have minimal impact on habitat and animal dwelling patterns per environmental requirements. The need for and spacing of migratory features within a fence shall be determined on a project-by-project basis.

The 30-year service life requires planned maintenance, but no earlier than every 10 years. Planned maintenance shall include re-application of coatings, minor concrete repair such as surface cracks and surface spalling, and replacement of hinges.

Fence design shall allow for expedient repair of damage or breaching to be completed within 24 hours.

All fence materials shall conform to the following:

o Reinforcing Steel, ASTM A615 Grade 60 o Welded Wire Fabric Reinforcing, ASTM A185. Flat sheets only.

o Deformed Welded Wire Reinforcing, ASTM A497.

o Structural Steel Shapes (W-Shapes), ASTM A992, Grade 50 o Structural Steel Shapes (Angles, Bars, Plates), ASTM A36 o Steel Sheet (Sheet, Strip), ASTM A570.

SECTION 4.TERTIARY FENCE DESIGN STANDARDS

4.1 TERTIARY FENCE TYPES

Tertiary Fence (TF) uses open fence fabric to delineate property limits and/or the limits of the TI corridor. The fence fabric for TF consists of either standard chain link or barbed wire. Chain link fence fabric for TF is typically used in more urban environments, while barbed wire is typically used in more rural environments. For a full description of the design criteria required for TF, see Section 4.2, Tertiary Fence Design Criteria.

4.1.1 CHAIN LINK FENCE (TYPE T-1)

T-1 fence consists of 10-foot tall, 9-gage, 2-inch chain link material. The chain link fabric is connected to round schedule 80 steel posts at 10-foot maximum spacing with top and bottom round steel rails.

4.1.2 BARBED WIRE FENCE (TYPE T-2)

T-2 fence consists of 4.5-foot tall, 3-strand barbed wire material. The barbed wire fabric is connected to round wood posts at 16-foot maximum spacing. Steel posts may be substituted for wood posts, upon approval by CBP.

4.2 TERTIARY FENCE DESIGN CRITERIA

Design of the TF shall utilize standard details T-1 and T-2 and shall comply with the following design criteria, unless specifically directed or approved otherwise.

Fence shall be designed to withstand critical load combination per the International Building

Code, latest edition.

The minimum compressive concrete strength for foundations shall be 3,000 psi.

Fence shall have the ability to survive temperatures applicable to the southwestern border of the

U.S. including diurnal and seasonal extremes with temperature deltas in excess of 120 degrees

Fahrenheit.

Fence shall be site adaptable where necessary to allow migration of all species and have minimal impact on habitat and animal dwelling patterns per environmental requirements. The need for and spacing of migratory features within a fence shall be determined on a project-by-project basis.

The 30-year service life requires planned maintenance, but not earlier than every 10 years. Planned maintenance shall include re-application of coatings, fence fabric connection repairs, minor concrete repair such as surface cracks and surface spalling, and replacement of hinges.

Concrete mow strip under fence shall be provided.

All fence materials shall conform to the following:

o Steel Pipe, ASTM F1083 schedule 40 pipe, hot-dip zinc-coated after fabrication with 1.8 ounces of zinc per square foot of coated surface area.

o Fence Mesh, chain link fence with zinc coated 9-gage steel wire mesh (before any coatings) with maximum 2-inch opening per side.

o Barbed Wire, ASTM A121, metallic-coated carbon steel barbed wire, strand of two wires.

SECTION 5. PRIMARY VEHICLE FENCE DESIGN STANDARDS

5.1 PRIMARY VEHICLE FENCE TYPES

VF as a means of TI uses steel bollards and wide flange sections to resist illegal vehicular traffic across the border but does not impede illegal pedestrian traffic. VF is typically used in rural or isolated locations that have a low occurrence of illegal pedestrian traffic. As the primary purpose for VF is to stop vehicular traffic, all VF types are designed to meet the vehicle loading standard. For a full description of the design criteria required for VF, see Section 5.2, Primary Vehicle Fence Design

Criteria.

5.1.1 POST & RAIL FENCE (TYPE V-1)

V-1 fence consists of HSS 6x6x1/2 steel tubes installed vertically and spaced at 4 feet with a single wide flange section horizontally attached to the tubes. The height of each steel tube alternates between 4 feet 8 inches and 6 feet 2 inches above ground line, and the tubes are filled with grout to the top of each tube. Additionally, a single #6 rebar is embedded in the grout for the full height of each tube. A single W 6x9 section is welded to each steel tube at 3 feet above the ground line and is 15 feet 10 inches long. V-1 Fence is supported by 6-foot deep by 18-inch diameter reinforced concrete shaft footing. The

HSS 6x6x1/2 and W 6x9 may be assembled in a shop and delivered to the site in 15 feet

10 inches sections, which are then installed horizontally and stepped up to 1 foot to accommodate varying terrain. Exceeding the 1-foot step may require special detailing and the rail height above ground shall not exceed 3 feet 6 inches or be lower than 2 feet

6 inches. Alternatively, posts may be installed plumb and the W 6x9 rail field attached parallel to the ground at the 3 feet height.

5.1.2 NORMANDY FENCE (TYPE V-2)

V-2 fence is constructed of HSS 6x6x1/2 steel tube, W 6x25 section, and HSS 2x2x3/16 steel tube members. This fence type consists of three “X” shaped legs joined together by a long beam and placed in a continuous procession. The “X” is created by welding two 6 feet 8 inches long W 6x25 together. V-2 Fence is typically fabricated and installed in 24-foot long sections with each section consisting of three “X”s stood on edge and spaced 8 feet apart. They are connected by a 24-foot long HSS 6x6x1/2 welded into the saddle of each “X”. Additionally, three 24-foot long HSS 2x2x3/16 steel tubes are welded to two of the legs for each “X” to reduce the ability for local ranch cattle to pass over or under the

V-2 barrier. A minimum of eight of the 24-foot long segments must be continuously joined to meet the design vehicle loading requirements. Segments are joined by a 2-foot long HSS 7x7x1/4 steel tube sleeve which is welded to the end of the HSS 6x6x1/2 steel tubes. When crossing a wash or on grades steeper than 20 percent, the V-2 fence should be anchored to an H-pile driven into the ground or to concrete drilled shaft spaced 24 feet apart. The fence will be tied to the anchor by ½-inch steel cable through an eye bolt or 1 ½-inch hole.

5.2 PRIMARY VEHICLE FENCE DESIGN CRITERIA

Design of primary VF shall utilize standard details V-1 and V-2 and shall comply with the following design criteria, unless specifically directed or approved otherwise.

Vehicular impact applied to the fence design as a static 10-kip load per AASHTO 17th Edition, Chapter 2.7.1.

Vehicular impact loading shall be applied to the fence design and combined with all applicable load groups per the International Building Code, latest edition.

The minimum compressive concrete strength for foundations shall be 3,000 psi.

All fence members shall be plain un-painted steel except where existing sites consist of corrosive soils. In such cases, the appropriate measures shall be taken to protect the fence members from corrosion.

Fence shall have the ability to survive temperatures applicable to the southwestern border of the

U.S. including diurnal and seasonal extremes with temperature deltas in excess of 120 degrees

Fahrenheit.

Compatible design applicable to desert, mountain, floodplains, open range, and remote conditions.

The need for big game passage panels shall be determined on a project-by-project basis per CBP requirements.

No portion of any new fence above grade shall be constructed within 3 feet of the base of any existing USIBWC Border Monument.

No portion of any new fence above grade shall be constructed within 3 feet of the base of any existing USIBWC Border Monument.

The USIBWC Border Monument 3-foot clearance shall extend approximately 8 feet each side of the border monument and then transition gradually over 40 feet minimum to the primary VF offset from the international border between the U.S. and Mexico.

Fence shall allow construction workers and maintenance crews room to build/maintain fence without breaching the border.

Fence shall have a 30-year service life requiring planned maintenance to occur not earlier than every 10 years.

Fence shall have a design that allows for expedient repair of damage or breaching to be completed within 24 hours.

Construction shall take place within temporary construction easement.

All fence materials shall conform to the following:

o Reinforcing Steel, ASTM A615 Grade 60 o Welded Wire Fabric Reinforcing, ASTM A185. Flat sheets only.

o Deformed Welded Wire Reinforcing, ASTM A497.

o Structural Steel Shapes (W-Shapes), ASTM A992, Grade 50 o Structural Steel Shapes (Angles, Bars, Plates), ASTM A36 o Steel Sheet (Sheet, Strip), ASTM A570.

SECTION 6.FENCE DRAINAGE PROTECTION DESIGN STANDARDS

Any alteration to existing conditions requires consideration of drainage effects as they relate to the installation or improvement of primary pedestrian, secondary, tertiary and primary vehicle fence (TI fence). TI fence shall be protected from erosion due to stormwater run-off and allow the conveyance of stormwater run-off design across the site. In addition, any TI fence constructed or improved within the

Roosevelt Reservation, or 60 feet north of the land border, as well as any TI fence constructed within the Rio Grande and Colorado River floodplains, are required to comply with various border related treaties between the U.S. and Mexico. General drainage design criteria that shall be used for sizing erosion protection and conveyance measures as well as USIBWC treaty requirements is discussed in

Chapter 1, Road, Bridge & Signage Design Standards, Section 7.1, USIBWC Floodplain, and

Section 7.2, General Drainage.

6.1 DRAINAGE, SCOUR & EROSION CONTROL DESIGN

To meet the USIBWC requirements for impacts to WSE within drainage crossings, three means of increasing drainage conveyance through the primary pedestrian fence types P-1, P-2 and P-3 have been accepted by CBP and USIBWC. The first means of increasing drainage conveyance (applicable only to primary pedestrian fence types P-2 and P-3) is to increase the spacing between fence vertical members from 4 inches to 5 inches and rotate the fence vertical members so the flat face is parallel with the border. See drawings for primary pedestrian fence Types P-2 and P-3 Section B located in Appendix B, Fence & Gate Standard Details, for additional clarification. This will maximize the amount of open space per foot of TI fence while still meeting CBP’s maximum clearance requirement between fence vertical members. The second means of reducing the WSE is to grade at the fence location so as to lower the existing grade. However, this approach can only be used if the proposed grading can be shown to daylight, thus allowing the water to drain away from the fence. The third means of reducing the WSE at the fence location is to install drainage gates in the fence at drainage locations. See Chapter

3, Gate Design Standards, for additional drainage gate requirements. Where primary pedestrian fence types P-4 and P-5 are the specified fence type to be installed, the primary fence will be required to transition to Type P-1, P-2 or P-3 at all drainage crossings.

While drainage crossings at secondary, tertiary and primary vehicle fence types can have significantly less impact at the border compared to primary pedestrian fence types, the designer shall still comply with USIBWC treaty requirements. Whereas upon completion of the analysis, the results show that the fence in question, impacts the water surface elevation above acceptable limits, the designer shall implement means of drainage conveyance through or under the fence by means of culverts with grates and/or LWC.

In addition to meeting USIBWC requirements, the fence shall also be protected from scour and erosion.

In many cases the 6-foot deep foundation required to meet the primary PF under-digging criteria will provide sufficient depth for both scour protection and fence stability. However, where scour calculations combined with fence stability design require additional foundation capacity, deepening the concrete trench footing, installation of a scour apron to the north of the fence or sheet piling south of the fence are acceptable means of protecting the fence foundation. Once fence scour requirements are met, erosion control shall be evaluated at both upstream and downstream locations of the fence.

Typically, erosion control is in the form of LWC and/or grouted rip-rap. The minimum gradation size for rip-rap is D50 of 6 inches, and the maximum size of rip-rap depends on the result of drainage analysis. All rip-rap with a D50 of less than 18 inches shall be grouted. Other forms of erosion control, such as erosion control mats, concrete slope protection, or soil cement shall be permitted as final design dictates and subject to CBP approval.

SECTION 7.REFERENCES

Reference 15: International Code Council (ICC), <http://www.iccsafe.org/Pages/default.aspx> http://www.iccsafe.org/Pages/default.aspx