Unformatted text preview: Cone Penetration Test (CPT) Friction Sleeve fc = sleeve resistance Filed Tests (Cont’d)
Friction ratio = fc /qc Conical tip qc = cone tip stress cone CPT Correlations
1. Relative density of Sand, Dr : Sand, 2. Drained friction angle of Sand, φ’ : Sand, ⎡q ⎤ c ⎢ ⎥ ⎛ ⎞ ⎢ pa ⎥ 1 Dr = ⎜ ⎜ 305 Q ( OCR ) 1.8 ⎟ ⎢ ' 0.5 ⎥ ⎟ c ⎝ ⎠⎢ ⎛ σ o ⎞ ⎥ ⎜⎟ ⎢ ⎜ pa ⎟ ⎥ ⎣⎝ ⎠ ⎦
qc and are the cone tip resistance and vertical effective stress. Pa = atmospheric pressure (100 kN/m2) OCR = over consolidation ratio Qc = 0.9 to 1.1 is the compressibility factor σ’o φ ' = tan −1 ⎢0.1 + 0.38 log10 ⎜ ⎜
⎣ ⎡ ⎛ qc ⎞ ⎤ ⎟ '⎥ σ o ⎟⎦ ⎝⎠ qc and σ’o are the cone resistance and effective vertical stress. 3. Undrained shear strength of Clay, cu: Clay, cu = qc − σ o NK Consistent units is required σo is the total vertical stress. NK = 15 for electronic cone, and 20 for mechanical cone. 1 4. Pre-consolidation pressure for Clay σ’c : PreClay 6. Correlation of soil types Based on qc and Fr type of soil can be anticipated σ 'c = 0.243(qc )
(MN/m2) 0.96 (MN/m2) 5. Over-consolidation Ratio for Clay, OCR : OverClay, ⎛ q −σ ⎞ OCR = 0.37 ⎜ c ' o ⎟ ⎜σ ⎟ o ⎝ ⎠ 1.01 σo and σ’o are the total and effective vertical stress. Fr = fc qc Example In the shown soil profile, the cone penetration resistance, qc, measured at point A, using electronic friction cone penetrometer, is 0.8 MN/m2. penetrometer, Observation of Water Table
Water Table: Significantly affects the soil bearing capacity and Settlement. It is necessary to establish the highest and lowest Levels of water during project period. Fined: 1. undrained cohesion, cu. 2. The over consolidation ratio, OCR. 3. Pre-consolidation Prepressure, σ’c. For Highly permeable soil, ground water stabilized after 24 hours of borehole completion. For Highly impermeable soil, it may take several weeks for the water level to stabilized inside the borehole. Therefore we need to used a Piezometer to Piezometer periodically check the water level and pressure. 2 Coring Rock
Rock coring is necessary when a rock layer is encountered. A core barrel with a diamond cutting edge is attached to a drilling rod. Rock Quality is evaluated based on: Reck Quality Designation RQD = Length of core recovered Theoretical length of rock cored
Recovered core with lengths less than 101.6 mm (4 in) are not counted. RQD = 1 (Excellent Rock) RQD = 0.25 (very poor Rock)
Drill Rod Boring Logs Typical example Subsoil Exploration Report
Text Book, p 76 3 ...
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This note was uploaded on 02/22/2010 for the course CVE 333 taught by Professor Magdy during the Spring '10 term at American Dubai.
- Spring '10