Centrifuge Tests on Rock-Socketed Piles: Effect of Socket Roughness on Shaft Resistance
J.G. Gutiérrez-Ch, G. Song, Heron, C.M., Marshall, A., Jimenez, R.
Abstract
Preliminary estimations of shaft resistance of rock-socketed piles are usually conducted using empirical formulations that relate to the uniaxial compressive strength (𝜎𝑐) of the weaker material involved (intact rock or pile). However, there are other factors, such as the degree of socket roughness, that could affect the shaft resistance of rock-socketed piles. In this paper, results from geotechnical centrifuge tests are presented to demonstrate the effect of socket roughness on the pile shaft resistance. Aluminum model piles with different degrees of shaft roughness were fabricated and embedded within an artificial rock mixture composed of sand, cement, bentonite, and water. Pile loading tests were conducted within the centrifuge and axial forces along the model piles were measured using fiber Bragg grating (FBG) sensing technology. Results are used to demonstrate that centrifuge testing provides a suitable experimental method to study and quantify the effect of socket roughness on the shaft shearing mechanism of rock-socketed piles. Finally, the centrifuge test measurements are compared with several formulations published in the literature, suggesting that centrifuge measurements tend to agree with the overall trend, despite the variability of predictions obtained with different formulations.
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Discrete element modelling of rock creep behaviour using rate process theory
J.G. Gutiérrez-Ch, S. Senent, E. Estebanez, R. Jimenez
Abstract
Rock creep behaviour is crucial in many rock engineering projects. Different approaches have been proposed to model rock creep behaviour; however, many cannot reproduce tertiary creep (i.e., accelerating strain rates leading to rock failure). In this work, the distinct element method (DEM) is employed, in conjunction with the rate process theory (RPT) of M.R. Kuhn and J.K. Mitchell (published in 1992) to simulate rock creep. The DEM numerical sample is built using a mixture of contact models between particles that combines the Flat Joint Contact Model and the Linear Model. Laboratory uniaxial compression creep tests conducted on intact slate samples are used as a benchmark to validate the methodology. Results demonstrate that, when properly calibrated, DEM models combined with the RPT can reproduce all creep stages observed in slate rock samples in the laboratory, including tertiary creep, without using constitutive models that incorporate an explicit dependence of strain rate on time. The DEM results also suggest that creep is associated with damage in the samples during the laboratory tests, due to new microcracks that appear when the load is applied and maintained constant at each loading stage.
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A DEM-Based Factor to Design Rock-Socketed Piles Considering Socket Roughness
J.G. Gutiérrez-Ch, S. Senent, S. Melentijevic, R. Jimenez
Abstract
The Distinct Element Method (DEM) has gained recent attention to study geotechnical designs with rock-concrete or rock–rock interfaces, such as rock-socketed piles. In this work, 3D DEM models with non-standard contacts laws (the Smooth-Joint and Flat-Joint contact models) are proposed to analyze the response of axially loaded rock-socketed piles with different sockets roughness, since socket roughness is a key factor affecting their side shear resistance that is not usually considered for pile design. DEM models are calibrated using experimental data, and the consequences of applying 2D models for calibration, to be subsequently used in a 3D analysis, are studied. Numerical results suggest that such DEM models can be employed to reproduce key aspects of the behavior of rock-socketed piles, such as their load and global stiffness-settlement response, their side shear resistance, and the damage at the rock-pile interface. Finally, an empirical factor 𝛼𝑅𝐹,1%𝐷 is proposed to estimate the side shear resistance of rock-socketed piles considering the socket roughness and the uniaxial compressive strength (UCS) of the weaker material (rock or pile) at the interface
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