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# A Novel Estimation of Axial Pullout Capacity of Suction Caisson in Sand Flow Failure Mode

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A brief summary of Jinfu Xiao's research work on suction caisson.

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### A Novel Estimation of Axial Pullout Capacity of Suction Caisson in Sand Flow Failure Mode

1. 1. A Novel Estimation of Axial Pullout Capacity of Suction Caisson in Sand Flow Failure Mode Jinfu Xiao jxiao3@ncsu.edu Department of Civil, Construction and Environmental Engineering, North Carolina State University Doctoral Preliminary Oral Presentation
2. 2. Pullout Capacity Components: • Caisson weight/ Caisson + Core soil weight • Internal wall friction • External wall friction • Reverse end bearing capacity The actual pullout capacity is the combinations of the components depending on the failure mode. However, in current study, the soil in all the failure modes is assumed to be in solid state and the pullout capacity is independent to the pullout rate! Current Estimation Methods and Failure Modes (Randolph and Gourvenec 2011) orE G     Soil in solid state Soil-caisson interface  tann   
3. 3. In the sand flow zone, the constitutive model of sand flow is Where 𝜏 is shear stress, G is shear modulus, 𝛾 is shear strain, 𝛾 is the shear strain rate, 𝜏0 is the yield stress, 𝜇 is viscosity of sand flow For sand flow, the shear stress is dependent to the shear strain rate, consequently the pullout capacity is dependent to the pullout rate! Estimation Considering Sand Flow Occurrence I II III I – Suction caisson II – Core soil plug III – Sand flow zone IV – Sand at rest IV Core Soil Soil Flow Soil Flow Soil at Rest 0 0 0 for for G            
4. 4. Model test - Failure wedge in soft marine clay (Rao 1996) Field test - Failure surface under cyclic eccentric load in clay (Dyvik et al. 1993) Model test - Failure surface under axial load in cemented siliceous sand (Chen 2013) The sand flow occurrence was observed in literature but mistaken for solid failure wedge of soil I II III I – Suction caisson II – Core soil plug III – Sand flow zone IV – Sand at rest IV
5. 5. Methodology I Analytical solution for Bingham plastic flow in straight annular domain
6. 6. Methodology II Numerical simulation in multi-physics program COMSOL Axisymmetric model
7. 7. Pressure and Velocity Profile from Numerical Analysis
8. 8. Numerical Results vs. Analytical Solution                       2 2 2 0 1 2 2 0 2 2 2 1 2 2 2 0 2 1 ln 2 1 ln 1 1 2 1 ln 1 1 1 2 o z r C r B r r r r U r r B r r r r r r r B r r r r                                   1 0 z rz rz z z rz dUB B dU dz dr dU B dr                  Analytical solution Numerical data
9. 9. Analytical Solution Vs. Experimental data (Kelly et al. 2006) & Houlsby’s prediction (Houlsby et al. 2005)
10. 10. Analytical Solution Vs. Experimental data (Kelly et al. 2006) & Houlsby’s prediction (Houlsby et al. 2005)
11. 11. Summary The method proposed here makes a better estimation of axial pullout capacity of suction caisson in the sand flow failure mode*. *This statement is ONLY for sand flow failure mode. In other failure modes, the soil can be still in solid state. In that case, the conventional method is still valid. The criterion for determination of failure modes of suction caisson in sand under axial pullout load is discussed in another section.
12. 12. Thank You!