technical bulletin mse-4

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The Reinforced Earth Company 8614 Westwood Center Drive

Suite 1100Vienna, Virginia 22182-2233

Telephone: (703) 821-1175Telefax: (703) 821-1815www.reinforcedearth.com

Use of MSE Walls for Acute Corners Less than 70 Degrees

TECHNICAL BULLETIN: MSE-4

MAY 1, 1992

Atlanta Boston Dallas/Ft. Worth Irvine, CA Lafayette, IN Orlando Seattle Vienna, VA



TABLE OF CONTENTS

Page No.

I. Introduction....................................................................…………..… 1

II. Backgorund..........................………………………..…………….…… 1

III. Design Method…...................................................................…......... 2

IV. Recommendation……………………………………………….……… 2

V. List of Reinforced Earth Structures With Acute Corners

Less than 70°…………………………………………………………. 3

VI. Typical Acute Corner Drawings……………………………………….. 6

VII. Special Provision For MSE Walls at Acute Corners………………… 8



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I. Introduction

MSE structures offer significant economic benefits, especially in tight urban areas

where rights-of-way are severely restricted. Skewed bridges and acute corners,in particular, benefit from MSE construction. The design and construction of Reinforced Earth structures with acute corners considerably less than 70o hasbeen standard practice since 1986, and they have performed exceptionally well.The use of MSE structures in these applications requires a proper designprocedure such as the one described below.

II. Background

A design method was developed in 1986 based on experience gained on the firstacute corner project, on I-277 at Mint and Morehead Streets in Charlotte, North

Carolina. In plan, the structure is a triangular closed cell, with one side being anordinary retaining wall and the other two sides being "true" (no piles) bridgeabutments. The bridge loads are distributed through a beam seat that restsdirectly on the reinforced soil.

At one end of one of the beam seats, the abutment and the retaining wall form anacute angle of 26o. The site is underlain by compressible foundation soils,resulting in approximately 5 inches of settlement of the overall structure.However, the acute corner, which is relatively light in comparison to the mass of the entire structure, only settled 1-1/2 inches. The resulting differentialsettlement of nearly 4 inches occurred over a distance of approximately 15 feet,and the panel movements caused some panels to bear against adjacent panelsalong their edges and corners.

The panel contact resulted in cracking of panel ears and opening of a vertical joint approximately 1-1/2 inches wide from top to bottom of the wall. All the paneldamage and the open joints were in one location on the abutment side of thestructure at the transition from the tied-across acute corner to the normally-reinforced structure. Concerns were raised by the FHWA regional office in

Atlanta with respect to the performance of this new use of Reinforced Earthtechnology and, therefore, it was agreed to load test the structure to 115% of itsmaximum design load. A large loading frame and hydraulic jack, restrained byvertical rock anchors drilled and grouted into bedrock, was used to load theaffected end of the abutment. The wall was carefully monitored for vertical andlateral wall movements during this loading process. No movements weredetected. The structure was subsequently completed and placed in service in1987 and has performed as intended.

Since that time, dozens of Reinforced Earth structures with acute cornersconsiderably less than 70o have been constructed, and all are performing asintended. A partial listing of these completed projects is enclosed.



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III. Design Method

The design of the earth reinforcement system for acute corners less than 70o isunique. The nose portion of the structure is designed as an internally tied bin

structure with at-rest earth pressures from top to bottom. The reinforcing stripsare designed as tension members only and are generally at low stress due to thebin effect (soil arching) and the conservative number of strips used. Theconnections to the panels are all double shear structural connections. The tiedbin section is separated from the adjacent normally reinforced portion of thestructure by slip joints. The slip joints allow the relatively light bin section to actindependently of the rest of the structure. In addition, reinforcing strips areextended back from the nose portion of the structure to tie this relatively lightsection back into the major portion of the mass. Details of two different types of acute corners are enclosed, one with a 29o point and the other with a squared-off end forming a 36o acute corner. Note the abundance of strips tied across (at

each level) and the large number of strips to anchor the nose into the mass.

The performance of this system has been remarkably good due to its highstrength and flexibility. In addition, the individual reinforcing strips and numerousconnection locations on the backs of the panels make the system very versatileand constructible in the presence of obstructions such as piles.

No structural problems have been reported on any acute corner projectsconstructed with Reinforced Earth. It follows logically that acute cornersconstructed with any MSE systems (reinforced with strips, bar mats, welded wiremesh or geogrids), will perform adequately if designed and detailed to take intoaccount the three-dimensional stresses and geometrical constraints. However,the design and details cannot be addressed in the field merely by cuttingreinforcement members to clear obstructions or to fit in limited spaces. Completecomprehensive calculations and reinforcement layout details must be a part of the final design submittal and must be reviewed and approved prior toconstruction.

IV. Recommendation

When two intersecting walls form an enclosed angle of 70o or less, a sectionshould be added to the project special provisions requiring full details andcalculations to document the design proposed by an MSE wall supplier. Therecommended wording for this special provision is enclosed.



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REINFORCED EARTH STRUCTURES WITH ACUTE CORNERS LESS

PARTIAL LIST 1982 – 1992

RECOPROJECTNUMBER

PROJECT NAME OWNER STRUCTURE TYPE LOCATIONS

849 Rte. 147 over Amtrak NYDOT Ret. Walls Glenville, NY

932 Sweethome Road NYDOT Ret. Walls Amherst, NY

948 Glenwood Canyon CO DPT. HWY Ret. Wall at Bike Path Glenwood Sprg. CO

1350 Summerhill over Conrail PA DOT Ret. Walls Cambria Co., PA

1599 I-277 from I-77 to 3rd NC DOT True Abut. Charlotte, NY

1760 I-20/I-75 Interchange GA DOT Abut. on Piles Atlanta, GA

1806 Lusk Overpass WY DOT Ret. Walls & Abuts. Lusk Co., WY

1865 MUD Project NY DOT Ret. Walls & Abuts. Utica, NY

1909 I-75/85 Segment D & E GA DOT Abut on Piles Atlanta, GA

1998 General Lawrence Bridge Comm. of Mass Ret. Walls Lawrence, MA

2213 I-264 @ Taylorsville Road KY DOT True Abut. Louisville, KY

2216 I-279 LR 1021 (05) PA DOT Ret. Walls Pittsburgh, PA



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REINFORCED EARTH STRUCTURES WITH ACUTE CORNERS LESS PARTIAL LIST 1982 – 1992

RECOPROJECTNUMBER

PROJECT NAME OWNER STRUCTURETYPE

LOCATIONS

2353 I-30 TX DOT Ret. Walls Ft. Worth, TX

2489 Indian Gap Nat’l Cemetery Veterans Admin. Ret. Walls Annville, PA

2711 US 75 TX DOT Ret. Walls Dallas, TX

2715 I-480 over E-N Ramp Dept. of Roads Ret. Walls Omaha, NE

2806 Schuylkill Expressway PA DOT True Abut.Ret. Walls

Philadelphia, PA

2808 LR1010 (D3T) PA DOT Ret. WallsTrue Abut.

Montgomery, PA

2858 Commonwealth Ctr/Rte. 228 V DOT Ret. Walls & Abuts. Chesterfield, CO., VA

2971 I-45 TX DOT Ret Walls Houston, TX

3097 181st Str. Interchange OR DOT Ret. Walls & Abuts. Multnomah Co., OR

3383 Rte. 147 over Conrail NY DOT Ret. Walls Cattaraugus, NY

3484 Georgia 400 Extension GA DOT Abut. on Piles Atlanta, GA



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REINFORCED EARTH STRUCTURES WITH ACUTE CORNERS LESS PARTIAL LIST 1982 – 1992

RECOPROJECTNUMBER

PROJECT NAME OWNER STRUCTURETYPE

LOCATIONS

3504 Tampa Airport Tampa Airport Auth.

Ret. Walls Abut on Piles

Tampa, FL

3519 FA Rte. 586 IL DOT Ret. Walls Abut. On Piles

Madison, CO., IL

3838 I-80 @ Calumet Ave. IN DOT Abut. On Piles Lake Co., IN

3839 Minton Road FL DOT Ret. Walls Abut. on Piles Brevard, FL

3898 Evelyn St. Oxing SPRR OR DOT True Abut. Clackamas Co., OR

4122 PR-22 PRHA Ret. Walls Abut. On Piles

Barceloneta, PR.

4212 49th

Street Bridge Pinelas Co. Abut. On Piles Clearwater, FL.

4261 Washington Ctr. Road IN DOT Abut. On Piles Ft. Wayne, IN



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SPECIAL PROVISION FOR MSE WALLS AT ACUTE CORNERS

1.0 SCOPE

This specification covers the design, detailing, construction, wall system andsubmittal requirements for the use of mechanically stabilized earth (MSE)structures at acute corners.

2.0 DESIGN

The design approach shall include the following:

1. Define the critical nose section of the acute corner.2. Design the nose section as a bin structure capable of tolerating differential

settlements.3. Design the nose restraint reinforcements, extending from within the nosesection back into the fill, beyond all potential failure planes.

2.1 DEFINING THE NOSE SECTION

The nose section of the acute corner shall be defined as the smallestblock extending back from the point(s) of intersection of the wall faces withsufficient mass to be stable against sliding along its base withoutconsidering the restraining effect of soil reinforcements extending beyondthe potential failure plane behind the nose section. See Figure 1. Thecalculation to determine the dimensions of the nose section shall conformto the following:

1. Assume a Rankine failure plane intersecting the base of the wall ata joint between facing units and at an angle of 45 + Ø/2, where Ø isthe backfill angle of internal friction as established for wall designon this project.

2. Assume equal dimensions along the two wall faces extending backfrom the point of intersection to the limit of the nose section.

3. Assume no restraining effect from soil reinforcements extendingbeyond the theoretical Rankine failure surface.



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4. Calculate the driving forces, P A and PS, behind the nose sectiondue to earth pressure and surcharges;

P A = 1/2 x ? x H2 x Ka x d and

PS = q x H x Ka x d where

? = unit weight of wall backfill, lb./cu. ft.,

q = vertical surcharge loading, lb./sq. ft.,

H = height of wall, ft., including distance up to elevation of approach slab for applications at bridge abutments.

Ka = coefficient of active earth pressure,

d = width of block, ft., at section under investigation

5. Calculate the Factor of Safety against sliding of the nose sectionmass along its base:

W = weight of the backfill within the nose section,

lbs.,

R = total available resistance of reinforcementbeyond the theoretical Rankine failure surface.R shall be assumed to be zero for thecalculation to define the extent of the nosesection at the acute corner.

2.2 DESIGNING THE NOSE SECTION AS A BIN

Structural connections of soil reinforcements between the wall elements

within the nose section shall be designed to create an at-rest bin effectwithout eliminating the flexibility of the facing to tolerate differentialsettlements. The design for connections to facing elements and allowablestresses in the connecting members shall conform to the requirements for the wall design in general. The nose section shall be designed with a slip

joint to allow it to settle differentially from the remainder of the structure.

SLIDING

A S

FS =W x + R

P + P

> 1.5 minimum wheretan φ



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2.3 RESTRAINING THE NOSE SECTION

Soil reinforcements shall be designed to restrain the nose section byconnecting directly to each of the facing elements in the nose section and

running back into the backfill to a point at least ten (10) feet beyond theRankine failure surface defined above. Design for facing connections,obstructions, pullout and allowable stress in the reinforcing elements shallconform to the requirements for the wall design in general.

3.0 SUBMITTALS

The Contractor shall submit the following information specific to the acute corner for review and approval by the Engineer prior to construction:

1. Wall design calculations, data and representative construction details and

notes conforming to the above requirements, signed and sealed by aProfessional Engineer directly employed by the wall system supplier andlicensed in this State and who is qualified and experienced in designs of this type.

2. Project information on at least three previous, similar and successfullyperforming applications of the specific wall system proposed, designedand constructed in accordance with the requirements of this SpecialProvision.

3. If the wall construction is found to be inconsistent with the design anddetailing provided for the acute corners, then the Contractor shall resubmitrepresentative design calculations, data and details for review andapproval by the Engineer prior to any further construction in the affectedarea.

4.0 CONSTRUCTION

Construction at the acute corner shall be in accordance with the requirements for the wall construction in general, except as amended by the details and notes for the acute corner as approved by the Engineer.



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