Lateral pile load test calibration for Helical pile software HelixPile
This section includes a number of tests that were considered in the verification of lateral pile analyses with HelixPile. A few tests include known piles, and last two lateral load tests directly on helical piles are presented. Soil properties for the lateral load analysis were estimated based on published information.
Lateral pile load test verification with experimental results – Case C1: Cox et al (1974)
The Cox et al (1974) experimental investigations on single piles under lateral excitation are included in the verification process of the cohesionless P-Y models implemented in the HelixPile software. In regard to the experimental configuration, the test site consisted of sandy clay seams underlain by a layer of firm gray clay and a layer of silty fine sand. Before the lateral load test, 2.44 m of clay layer were removed and backfilled with 0.76 m of sand. The sand at the test site varied from clean fine to silty fine, both exhibiting high relative density. The angle of internal friction, φ, was determined to be 39o degree, and the value of the submerged unit weight, γ′, was 1.06 tn/m3. The water table and ground levels were the same after the placement of the backfill. The test pile was hollow circular steel pile with a diameter of 0.61 m and a thickness of 9.5 mm.
In regard to the simulation of the experimental configuration in the HelixPile software, the Reese proposal was selected as the most efficient P-Y model for the specific soil properties. The subgrade modulus was derived by the HelixPile through the empirical correlation of Ksub with the angle of internal friction of the cohesionless soil as proposed in (Reese 1974). The comparison of the pushover results for the experimental data and the P-Y simulation are illustrated in figure 1b.
Figure 1: a) site and experiment configuration C1 b) comparison of measured results with P-Y simulation in the Helixpile Software
Lateral pile load test verification with experimental results – Case C2: Price and Wardle (1981)
The Price and Wardle (1981) experimental investigations on single piles under lateral excitation are included in the verification process of the cohesive clay P-Y models implemented in the HelixPile software. The experiment measured the response of a steel pipe pile with diameter equal to 0.406m embedded in an overall length of 16.5m. The soil properties of the cohesive soil of the site were defined through in site measurement tests. According to the results of the tests the following undrained shear strength values of 44.1, 85.2, 80.6 and 133.3 KPa have been reported for the depths 0, 4.6, 6.2 and 19 m respectively.
In regard to the simulation of the experimental configuration in the HelixPile software, four intermediate layers with constant properties were defined in order to appropriately simulate the increase of the undrained shear strength relative to the depth of the site. The calculation of the strain parameter which occurs at one half the maximum stress on laboratory undrained compression tests ε50 is accomplished through the empirical correlation to the undrained shear strength function for overconsolidated Clay deposits as proposed by (Reese and Van Impe 2001) . The appropriate stiff or soft clay P-Y models are selected for each individual layer according to the layers properties. The comparison of the pushover results for the experimental data and the P-Y simulation are illustrated in the following figure.
Figure 2: a) site and experiment configuration C2 b) comparison of measured results with P-Y simulation in the Helixpile Software
Lateral pile load test verification with experimental results – Case C3: (Davisson and Gill 1963)
The multilayer capabilities of the HelixPile software are verified through the two layer site test performed in Austin, Texas (Davisson and Gill 1963). The experimental test consisted of the cyclic lateral loading of a 152mm diameter and 3.2mm thickness pipe section pile with embedded length equal to 4.9 meters. The soil profile is comprised by an initial stiff clay layer of 380mm thickness overlying medium dense sand. According to measurements on site the clay layer undrained shear strength was found to be equal to 96 KN/m2 while the medium dense sand layer is defined by an angle of friction equal to 35o and subgrade modulus equal to 15.5MN/m3.
In regard to the simulation of the experimental configuration in the HelixPile software, the Reese P-Y model was selected for the simulation of the cohesionless layer while the cohesive clay layer was simulated through the stiff clay model with no free water model. The comparison of the pushover results for the experimental data and the P-Y simulation are illustrated in figure 3b.
Figure 3: a) site and experiment configuration C3 b) comparison of measured results with P-Y simulation in the Helixpile Software
Lateral helical pile load test verification with experimental results – Case C4 (Mohammed Sakr 2010):
The (Sakr 2010) single pile experiments under lateral excitation are implemented in the verification process of the HelixPile software in order to estimate the accuracy of the numerical P-Y helical pile configuration. The comparison of the experimental and numerically simulated behavior of the single helical pile is calculated for two different piles and site locations included in the Sakr research paper. The ST23 experimental configuration consists of a 0.406m diameter steel pipe pile with double helixes of diameter equal to 0.813m, located in a four layer soil site. The ST18 experimental configuration consists of the same diameter but different thickness steel pipe pile with one helix of diameter equal to 0.914m, located in a four layer site with different soil properties and layer thickness.
In regard to the simulation of the experimental configuration in the HelixPile software, the Reese P-Y model was selected as the modeling representation of the cohesionless soil layers while Matlock and Reese models where used for the cohesive soil layers simulation, where the stiff or soft clay model selection was accomplished in accordance to the undrained shear strength of each cohesive soil layer. The subgrade modulus essential to the cohesionless soils was derived by the HelixPile according to an empirical correlation with the angle of internal friction as proposed by (Reese 1974). The comparison of the pushover results for the experimental data and the P-Y simulation are illustrated in the following figures.
Figure 4: a) site and experiment configuration C4 – ST23 b) comparison of measured results with P-Y simulation in the Helixpile Software
Figure 5: a) site and experiment configuration C4-ST18 b) comparison of measured results with P-Y simulation in the Helixpile Software
References
Cox, W. R., Reese, L. C., and Grubbs, B. R. (1974). “Field testing of laterally loaded piles in sand,” Proceedings
of the Offshore Technology Confeence”,Houston,Texas,paper 2079
Davisson, M. T., and Gill, H. L. (1963). “Laterally loaded piles in a layered soil.” J. Soil Mech. and Found.
Div., ASCE, 89(3), 63-94.
Mohammed Sakr (2010) ” Lateral Resistance of High Capacity Helical Piles – Case Study “,GEO2010 -
63rd Canadian Geotechnical Conference, Calgary, Canada
Price, G. and Wardle, I.F. 1981. “Horizontal load tests on steel piles in London clay”, Proceedings of the X international Conference on Soil Mechanics and Foundation Engineering, Stockholm, Sweden:803:808
Reese, L. C., and Van Impe, W. F. (2001). Single Piles and Pile Group under Lateral Loading. A. A. Balkema, Rotterdam, 463 p.
Reese, L. C., Cox, W. R., and Koop, F. D. (1974). “Analysis of laterally loaded piles in sand,” Proc. 6th Offshore
Technology Conference, Paper 2080, Houston, Texas, 473-483.
