This blog presents a case study for the test piles driven into interbedded sand and stiff clay layers based on the single pile testing results reported in Rollins et. al. (2006). The configuration of the steel pipe pile subject to a lateral force at the top is extracted from Rollins et. al. (2006) and shown in the figure below.
The soil profile generally consists of over-consolidated stiff clays with some sand layers to a depth of 5 m. The sand layers are in a medium compact density state. Groundwater is located a t a depth of 1.07 m during the testing. The stiff clay is underlain by softer sensitive clays which are in turn underlain by interbedded layers of silty clay and sand.
The test pile is 324 mm o.d. steel pipe piles with 9 mm wall thickness and is driven closed ended to a depth of approximately 11.9 m below the ground surface. The moment of inertia of the pile is 1.16 x 10^8 mm^4. Two angle irons were attached to each pile to protect the strain gages, which increased the moment of inertia to 1.43 x 10^8 mm^4. The detailed soil parameters, p-y curve model and layer thickness inputs are summarized in the table below for the analysis using PileLAT program.
Since the testing load is applied at 0.49 m above the ground surface, a “Null material” model in the PileLAT program is adopted to model this cantilever portion of the pile above the ground surface. The total pile length adopted in the analysis is therefore 12.39 m (11.9 m + 0.49 m). The p-y curve model of modified stiff clay without water is adopted to model the clay layers as the initial subgrade modulus can be considered by this model. Reese sand model is used for the sand layers. Matlock soft clay model is used to model the soft clay layer.
The figure below shows the inputs for the steel pipe pile with the section type of “Pipe Section”. The outside diameter is 0.324 m and the inside diameter is 0.3 m. Note that the inside diameter is not based on the wall thickness of 9 mm. Instead, it is determined on the base that the moment of inertia matches the value of 1.43 x 10^8 mm^4 to consider the contribution from two angle irons attached to the pile during the testing. Young’s modulus is adopted as 200 GPa for steel and the Poisson’s ratio is 0.2.
The following figures show the typical soil parameter inputs for clay and sand layers. Note that the p-y curve models for clays are under the category of cohesive material type whereas the p-y curve models for sand are under the category of cohesionless material type.
The ground profile and groundwater table inputs are shown in the figure below. Note that the depth of water table below pile head is 1.56 m which includes the cantilever length of 0.49 m. The option of soil-layering correction for all layers is selected.
The figure below shows the overview of geotechnical model with ground profile, water table, pile length, loading and soil parameters information.
The figure below shows the typical analysis outputs when the applied horizontal force at the pile head is 211 kN.
The figure below shows the applied horizontal load versus deflection curves for this example. The testing results reported in Rollins et al (2006) are also included for comparison purposes. It can be seen that the deflection results obtained from the analysis carried out with the PileLAT program show a strong agreement with the measured results reported in Rollins et al. (2006).
Additionally, the figure below illustrates a comparison between the measured pile head load deflection curves and those computed by LPile and Florida Pier programs, as documented in Rollins et al. (2006). The remarkable consistency between the outcomes of various programs indicates that the results generated by the PileLAT program are nearly identical to those produced by LPile and Florida Pier programs.