CE 115 Intro to Civil Eng: Geotechnical Engineering Soil Pressure Acting on Wall

Transcription

1 CE 115 Intro to Civil Eng: Geotecnical Engineering Soil Pressure Acting on Ground Surface Soil Pressure Were: σ = soil pressure acting on wall φ k a = tan 2 45, active eart pressure coefficient 2 γ = unit weigt of soil (approximately 100 lb/ft 3 ) = dept below ground surface σ = γ (Eq. 1) k a Given: Find: φ = 30 degrees Soil pressure acting on wall at depts of 10 feet and 20 feet below te ground surface. CE 115 Intro to Civil Eng: Geotecnical Engineering Lecture Notes 1

2 Surcarge Pressure Acting on A retaining wall wit veicles located beind te top of te wall is sown below. Te veicle weigt imposes additional pressure on wall. A simplification of te surcarge load used to determine te induced surcarge pressures on te wall is sown below. Surcarge Load, q (psf) Surcarge Pressure on σ k a q (Eq. 2) Were: σ = surcarge pressure on wall k a = active eart pressure coefficient q = surcarge load in pounds per squar foot = CE 115 Intro to Civil Eng: Geotecnical Engineering Lecture Notes 2

3 Given: surcarge load, q = 100 lb/ft 2 φ = 30 degrees Find: Te surcarge pressure acting on te wall at depts of 10 feet and 20 feet. Total Pressure Acting on Soil and Surcarge Pressure σ + σ CE 115 Intro to Civil Eng: Geotecnical Engineering Lecture Notes 3

4 Calculate Pullout Force on Reinforcement 2 ft Layer 1 Lf Le Layer 2 Layer 3 Failure Plane Layer 4 Reinforcement Layer 5 ( σ + σ ) A t F pi = (Eq. 3) Were: F pi = pullout force for reinforcement layer i ( σ + σ ) = oriontal pressure at dept of reinforcement layer i A t = tributary area for reinforcement layer A t = SvS (Eq. 4) Were S v = vertical spacing between reinforcement layers S = oriontal distance between reinforcement strips Given: Pressure distribution calculated for te retaining wall above, and a oriontal reinforcement spacing, S, of 3 ft, Find: Te pullout force for layer 3 (F p3 ) CE 115 Intro to Civil Eng: Geotecnical Engineering Lecture Notes 4

5 Determine Reinforcement Lengt to Resist Pullout Reinforcement resists pullout troug te development of friction forces between te reinforcement and soil beind te failure plane. 2 ft Layer 1 Lf Le Layer 2 Layer 3 Failure Plane Layer 4 Reinforcement Layer 5 Lf = distance from wall to failure plane Le = distace from failure plane to end of reinforcement Lf = tanα (Eq. 5) Were: Were: = distance from base of wall to reinforcement layer i α = angle between wall and failure plane ( F ) pi FS Le = 2 2bγ tan φ 3 F pi = pullout force for layer i FS = factor of safety b = widt of reinforcement γ = soil unit weigt = dept below ground surface φ = soil friction angle (Eq. 6) Ten te total reinforcement lengt, L, is Lf + Le. CE 115 Intro to Civil Eng: Geotecnical Engineering Lecture Notes 5

6 Given: Te retaining wall sown above, data from previous calculations (i.e. pullout force), reinforcement wit of 0.5 ft, and a factor of safety of 1.5 Find: Te reinforcement lengt for layer 3 CE 115 Intro to Civil Eng: Geotecnical Engineering Lecture Notes 6

7 CE 115 Intro to Civil Eng: Geotecnical Engineering Lab Location: BEL 123 Objective: Design and build te most economical mecanically stabilied eart (MSE) wall. Tasks: 1. In your assigned group, create a Matcad workseet to determine te required reinforcement lengt for te MSE wall. Tis must be completed before te lab class begins. Bring your Matcad workseet to te lab on a ip disk or CD-ROM. 2. Determine te soil friction angle by building a wall witout reinforcement and measuring te angle of te failure plane beind te wall. Bring a protractor to measure te angle of te failure plane. Failure Plane Angle, θ = Soil Friction Angle, φ = 3. Use your Matcad workseet from Task 1 and te friction angle from Task 2 to determine ow muc reinforcement you will need to build your wall. Bring a scale to measure your reinforcement lengt. Layer No. 4. Construct te MSE wall Distance from Top of (inces) Reinforcement Lengt, L (inces) MSE Design Data Heigt: 11.5 inces Soil Unit Weigt, γ: 100 lb/ft 3 Surcarge Load, q: 20 lb/ft 2 Factor of Safety: You coose Reinforcement Widt, b: 0.5 inces Horiontal Spacing, S : 4 inces (Te soil box is 4 inces wide and tere is only one reinforcement strip at eac dept) Vertical Spacing, S v : You coose (I recommend 3 or 4 equally spaced reinforcement layers along te eigt of te wall) Soil Friction Angle, φ: Obtained from Task 2 (Wile creating te Matcad workseet, assume φ = 36 degrees) Failure failure for tis project is defined as 0.5 inces of outward movement/rotation of te wall face.