Piedmont residual soils, commonly found in the southeastern United States, are formed through in-situ weathering of parent rock, resulting in a complex mixture of soil and partially weathered rock fragments. These soils retain characteristics of both soil and rock, displaying significant variability in stiffness, strength, and structure over short distances. Due to these properties, conventional p-y curves developed for more uniform soil types, such as sand or clay, may not accurately capture the lateral response of piles embedded in Piedmont residual soils.
Simpson and Brown (2003) addressed this issue by developing specific p-y curves tailored to the behaviour of Piedmont residual soils under lateral loading. Their study incorporated field and laboratory data to capture the variability in stiffness and strength that is characteristic of these soils. The modified p-y curves they developed consider the tendency of Piedmont soils to display anisotropic behaviour due to the presence of relict rock structures and varied particle sizes. This approach enables more accurate predictions of pile deflections, bending moments, and lateral resistance in Piedmont soils.
The p-y curve is based on the equations below:
where:
p = Actual lateral resistance
D = Pile diameter
λ = Dimensionless constant (= -0.23)
Esi = Initial soil modulus.
EDMT = Dilatometer modulus (kPa)
qc = Cone penetration tip resistance (kPa)
NSPT = Standard penetration blow count (blows/cm)
EPMT = Menard pressuremeter modulus (kPa)
The required input parameters for Piedmont Residual Soils are shown in the figure below and summarised as below:
Total Unit Weight, γ: The total unit weight of the soil material.
Initial Soil Modulus, Esi : Initial soil modulus at the top of the soil layer. The value of initial soil modulus can be determined based on the equations above.
Initial Soil Modulus, Esi – Rate of change: The increase rate of initial soil modulus with the depth from the top of the soil layer.
Reference:
Simpson, M. and Brown, D.A. (2003). Development of P-Y Curves for Piedmont Residual Soils. Project No. B-424 (2). Highway Research Center, Harbert Engineering Center, Auburn University.
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