Probabilistic Evaluation of the Uplift Capacity of Transmission Tower Foundations Using Reinforced Anchors
Publication: International Journal of Geomechanics
Volume 23, Issue 11
Abstract
The present study pertains to the probabilistic assessment for analysis and design of uplift capacity of transmission tower foundation reinforced with horizontal anchor using the radial basis function (RBF)-based response surface method. The deterministic uplift capacities of horizontal anchors in both unreinforced and reinforced soils were obtained using a finite difference numerical scheme. For the case of reinforced soil, geogrid was used and placed on top of the anchor plate. The improvement in uplift capacity due to the inclusion of geogrid reinforcement is first discussed. Next, RBF-based response surface models were constructed using the observed uplift resistance from the deterministic numerical model. The reliability of the foundation subjected to uplift forces was assessed using the Monte Carlo simulation, considering uncertainties of the soil and geogrid properties. The influence of safety factors on the failure probability of the foundation for both unreinforced and reinforced cases was shown. Variation of the probability of failure with different coefficients of variation of input variables was also investigated. The reinforcement stiffness was the most influencing parameter, having a pronounced effect on the failure probability of the reinforced foundation. Significant improvement in the uplift capacity and reduction in failure probability of the foundation were observed when a reinforced anchor was used, showing the effectiveness of reinforcement on top of the anchor plate. The results indicated that for the same failure probability, the reinforced anchors require much lower depth compared to unreinforced anchors.
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Data Availability Statement
All data, models, or codes that support the findings of this study are available from the corresponding author upon reasonable request.
Acknowledgments
The authors gratefully acknowledge the financial support provided by the Central Power Research Institute (CPRI), Bangalore, India for this study under the project titled “Analysis of Performance of Inclined Plate Anchors Embedded in Geosynthetics Reinforced Soils for Transmission Tower Foundations” (File Number: CPRI0007) at the Department of Civil Engineering, Indian Institute of Science, Bangalore.
Notation
The following symbols are used in this paper:
- B
- width of the anchor plate (m);
- BT
- width of the tower at base;
- b
- width of the reinforcement;
- c
- cohesion of soil (Pa);
- ci
- interface cohesion (Pa);
- d
- axial uplift displacement of the anchor plate (m);
- Es
- elastic modulus of soil (Pa);
- Frp
- wind load acting on the tower with a return period of rp (N);
- exact value of a function of ;
- approximation of ;
- HT
- height of the tower;
- J
- stiffness of the reinforcement (N/m);
- K
- deterministic constant for the wind load;
- k
- number of additional coefficients for the augmented RBF model;
- ki
- interface stiffness per unit area (Pa/m);
- l
- length of the reinforcement;
- m
- number of variables in the RBF model;
- N
- number of input data points;
- Nf
- number of simulations for failure events;
- Ns
- total number of MC simulations;
- Nq
- breakout factor;
- Pf
- probability of failure;
- QL
- uplift load acting on the anchor plate;
- Qu
- uplift capacity of the anchor plate;
- r
- distance between two data points;
- r0
- radius of the compact support domain;
- s
- spacing between anchors;
- Vb
- basic wind speed (m/s);
- Vrp
- wind velocity having a return period of rp (m/s);
- X
- vector of random variables;
- Ymean
- mean of the observed responses;
- Yobs
- observed response from the numerical model;
- Ypre
- predicted response from the response surface model;
- Poisson’s ratio of soil;
- γ
- unit weight of soil (N/m3);
- λi
- unknown coefficient for the ith basis function;
- ρa,b
- correlation coefficient between variables a and b;
- σm
- effective confining stress (Pa);
- ϕ
- internal friction angle of soil (°);
- ϕi
- interface friction angle (°); and
- ψ ()
- basis function.
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Published In
International Journal of Geomechanics
Volume 23 • Issue 11 • November 2023
Copyright
© 2023 American Society of Civil Engineers.
History
Received: Apr 11, 2022
Accepted: May 20, 2023
Published online: Sep 4, 2023
Published in print: Nov 1, 2023
Discussion open until: Feb 4, 2024
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