Characterization of Model Uncertainty for the Vertical Pullout Capacity of Helical Anchors in Cohesive Soils

Po Cheng,Jiang Tao Yi,Fei Liu,Jun Jie Dong

doi:10.3390/jmse8100738

Po Cheng, Jiang Tao Yi + Show 2 more

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https://doi.org/10.3390/jmse8100738

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Abstract

This paper conducts coupled Eulerian–Lagrangian (CEL) analysis to characterize the model uncertainty of using the cylindrical shear method (CSM) to predict the pullout capacity of helical anchors in cohesive soils. The model factor M is adopted to represent the model uncertainty, which is equal to the value of measured capacity divided by estimated solution. The model factor Mcel can be considered to be a random variable with a lognormal distribution, and its mean value and coefficient of variation (COV) are 1.02 and 0.1, respectively. Correction factor η is introduced when comparing CSM and CEL, which is found to be influenced by input parameters. The dependence on input parameters is removed by performing regression analysis and the regression equation f is obtained. Substituting the regression equation f into the original CSM constitutes the modified CSM (MCSM), and the model factor of MCSM can be modeled as a random variable with a lognormal distribution, and its mean value and COV are 1.02 and 0.13, respectively. Finally, 13 filed tests are collected to compare the prediction accuracy, the results show that the prediction error range of MCSM is mostly within 15%. The present findings might be helpful for engineers and designers to estimate the pullout capacity of helical anchors in cohesive soils more confidently.

Highlights

In the past research literature, a major focus on the pullout capacity of helical anchors in cohesive soils is the performance of helical anchors with different plate configurations [3,4,5,6,7], i.e., number of helical plates, n, the embedment depth of the uppermost helical plate, H, helical plate diameter, D, the ratio of helical plate spacing to diameter, S/D (See Figure 1)
The results indicate that Mcsm cannot be directly considered to be a random variable due to its association with the input parameters
This indicates that when predicting the pullout capacity of helical anchors in cohesive soil, the use of modified CSM (MCSM) can provide a relatively more accurate prediction result

Summary

Introduction

Installation of the helical anchors is through applying a calculated torque to the top of the central steel shaft, which in turns transmit loads to helical plates. In the past research literature, a major focus on the pullout capacity of helical anchors in cohesive soils is the performance of helical anchors with different plate configurations [3,4,5,6,7], i.e., number of helical plates, n, the embedment depth of the uppermost helical plate, H, helical plate diameter, D, the ratio of helical plate spacing to diameter, S/D (See Figure 1). Helical anchors manufacturers propose two possible failure modes that depend on the relative spacing of helical plate [8]. Each failure mode corresponds to an empirical method to predict pullout capacity

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