Structural Analysis of Tie Back Retaining WallTie-Back Retaining Wall

ByNick Crane Brett Morrow

ForCE 331, Spring 2007

Project 2

The Tie-Back Retaining Wall is 885 Feet Long and Varies in Height from 5 – 40 Feet

ContractorWyatt Construction, LLC

Structural EngineerSchnabel Foundation Company

Location

OwnerUniversity of Alabama

LocationRidgecrest South Residential Community, University of Alabama

Beginning Nowg g

The Tie-Back Retaining wall is C t t d f 114 12 53 H PilConstructed of 114 - 12x53 H-Piles

Driving PilesDriving Piles

The Wall is Constructed from Top to Bottom, Temporary Lagging is Placed Between the e po a y agg g s aced et ee t e

H-Piles in Order to Hold Back the Soil

Drainageg

Tie-Back DetailThe Tie-Backs Anchor the Piles Which Creates a Force That Pulls

A i t th L i O i th L t l S il P d K iAgainst the Lagging Overcoming the Lateral Soil Pressure and Keeping the Soil in Place

Soil Boring at H-Pile Number 37

15°

Ti B k

Brownish-Red Clayey Sand with Gravel

Loose to Firm, Moist 21ft.

Tie-Back

Brownish-Red Silty Sand with Gravel

Firm, Moist 10 ft.Light Gray Fat Clay

Firm to Very Stiff, Moist 4 ft.

H-Pile

Calculations of Lateral Soil Pressure

Drained Shear

Active Lateral Soil Pressure

Specific Weight of

Vertical Soil

Horizontal Soil

Type of SoilStrength

(Φ)Coefficient

(Ka)Depth

(ft.)

gSoil (γ) (lb/ft^3)

Pressure (Pv) (psf)

Pressure (Ph) (psf)

Clayey Sand, Loose to Firm 28° 0.361 21 115 2415 871.815

Silty Sand & Gravel, Medium 32° 0.307 10 115 3565 1094.455

Homogeneous Inorganic Clay, Sandy or SiltySandy or Silty Clay, Medium

Stiff to Stiff 28° 0.361 4 115 4025 1453.025

Typical Calculations

)sin(1)sin(1

Φ+Φ−

=Ka

)28sin(1361 −

DepthPv *γ= PvKaPh *=

2415=(115pcf)*(21’) 872=( 361)*(2415))28sin(1)(361.

+= 2415=(115pcf) (21 ) 872=(.361) (2415)

We Analyzed A Particular Beam (# 37) in th R t i i W llthe Retaining Wall

Free to Move

8.5 ft

#37

Roller Boundary Conditions Representing

35 ft#37Tiebacks16.5 ft

Fixed Boundary Condition

RISA Analysis and Unity Checks for H-Pile

Mu (kft) = (1.6)(Max Moment (kft))

29.345 kft = (1.6)(18.34 kft)

Unity Check

MnMuφ kft

kft5.277

35.29=

Unity Check

= .1058kft < 1, OK

Distributed Load (lb/ft) Moment Diagram (lb-ft)

Analysis of Shotcrete On Face of Wallf CLRFD Method Used for Concrete Design

Max Moment From the Worst Case Earth Pressure Load: 9.22 K-ft

))(')(85(.))((bfcf

fyAsa =)"12)(3)(85(.

)60)(6(."176.12

ksiksiin

=

)12/1)](2

()[)()(9.0( adfyAsMn −=φ

"1761

Mn < ΦMn 9 22<11 91 OK

)12/1)](2

"176.1("5)[60)(6)(.9.0( 2 −= ksiinMnφ

9.22<11.91, OK

a = depth of stress block (in.)As = area of steel (in^2)fy = yield strength of steel (ksi)f’ i t th f t (k i)f’c = compressive strength of concrete (ksi)Bf = effective flange width (in.)d = distance from extreme compression fiber to centroid of steel (in.)

Any Questions?