Caisson Drilling Fluid Interaction with Fine Grained Bedrock
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Applied Research and Innovation Branch Caisson Drilling Fluid Interaction with Fine Grained Bedrock Authors Mitul Sisodiya Shubjot Singh Yida Zhang, Ph.D. Ronald Pak, Ph.D. Report No. CDOT-2020-04 February 2020 The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views of the Colorado Department of Transportation or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation i Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. CDOT-2020-04 4. Title and Subtitle 5. Report Date Caisson Drilling Fluid Interaction with Fine Grained Bedrock February 2020 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Mitul Sisodiya, Shubjot Singh, Yida Zhang, Ronald Y.S. Pak 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Department of Civil, Environmental & Architectural Engineering University of Colorado Boulder, CO 80309-0428 11. Contract or Grant No. 218.03 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Colorado Department of Transportation - Research Final 2829 W. Howard Pl. Denver CO, 80204 14. Sponsoring Agency Code 15. Supplementary Notes Prepared in cooperation with the US Department of Transportation, Federal Highway Administration 16. Abstract This report presents a comprehensive evaluation on the effect of drilling fluid infiltration in claystone bedrock on the axial capacity of drilled caissons. The methodology of this research combines experimental testing and numerical simulations. The results obtained in the experimental phase are used to inform the numerical study. In the experimental phase, extensive laboratory experiments are conducted on claystone samples from three sites near Denver; I-70 & Colfax, I-70 & Wadsworth and C-470 & Wads (referred as site-1, 2 and 3 hereafter) to quantify the abovementioned hydro-mechanical interactions. In the second phase, Finite Element Analyses (FEA) on drilled caisson has been performed to quantify the bearing capacity reduction due to excessive wetting of the bedrock. It is predicted that for all three sites with various permeability and strength reduction characteristics, the pile capacity reduction for 4-hour wetting is less than 15%, despite several very conservative assumptions adopted in the study. It is therefore concluded that the 4-hour limitation is quite reasonable and perhaps on the conservative side for the construction of drilled caissons. 17. Keywords 18. Distribution Statement Denver Blue claystone, Shear strength, Water This document is available on CDOT’s website retention, Fluid weakening, Slaking, Pile axial http://www.coloradodot.info/programs/research/pdfs capacity, Finite element method, ABAQUS 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified Form DOT F 1700.7 (8-72) Reproduction of completed page authorized ii Final Project Report for Research Project 218.03 Caisson Drilling Fluid Interaction with Fine Grained Bedrock by Mitul Sisodiya Shubjot Singh Yida Zhang, Ph.D. Ronald Y.S. Pak, Ph.D. Department of Civil, Environmental & Architectural Engineering University of Colorado Boulder CO 80309-0428 February 2020 CDOT PROJECT COORDINATOR: Amanullah Mommandi, P.E. CDOT TECHNICAL PANEL LEADER: David Thomas, Ph.D., P.E. iii ACKNOWLEDGEMENTS The authors like to thank CDOT’s DTD Applied Research and Innovation Branch for funding and support of this study. The Study Panel includes David Thomas, Andy Pott, Trever Wang, Teddy Meshesha, David Vara, and Dustin Robbins. Their input and suggestions throughout the project are gratefully acknowledged. iv EXECUTIVE SUMMARY This report presents the results form a research project to evaluate the effects of drilling fluid infiltration in claystone bedrock on the axial load bearing capacity of drilled caissons in the Denver area. The methodology of this research combines laboratory soil testing and finite element simulations. In the first stage of this study, we performed extensive laboratory experiments to quantify the shear strength variation at different water saturation and the hydraulic characteristics of the claystone samples obtained from three different sites near Denver: I-70 & Colfax, I-70 & Wadsworth and C-470 & Wads. To evaluate the reduction in ultimate axial load capacity for different wetting times, extensive numerical simulations of drilled caissons were conducted through elastoplastic finite element analysis. Adopting the coupled unsaturated flow and mechanical analysis module provided by the commercial code ABAQUS, a versatile numerical simulation framework is developed for modeling the full process of drilling, fluid wetting, caisson construction, and in-situ axial loading. The material parameters obtained from the experimental phase are used to calibrate the material model in numerical simulation. The saturation-dependent shear strength parameters are introduced using a user-defined subroutine USFIELD developed in this project. It is predicted that for all three sites with various permeability and strength reduction characteristics, the pile capacity reduction for 4-hour wetting is less than 15%, despite several very conservative assumptions adopted in the study. It is therefore concluded that the 4-hour limitation is quite reasonable and perhaps on the conservative side for these sites. In addition to the site- specific simulations, parametric studies are conducted to isolate the effect of hydraulic conductivity and initial saturation of the in-situ claystone on the axial capacity reduction curves. These studies show that highly weathered or fissured claystone with low in-situ saturation can experience rapid and significant strength reduction upon wetting. Thus for this situation the constructor should limit the wetting time as much as possible. Future studies are needed to remove some of the conservative assumptions in this study and to investigate the capacity reduction if polymer fluid or slurry is used during drilling instead of water. v TABLE OF CONTENTS 1. Introduction ............................................................................................................................. 1 2. Experimental investigation ...................................................................................................... 2 2.1 Overview .......................................................................................................................... 2 2.2 Vapor equilibrium ............................................................................................................ 3 2.3 Soil water retention curve (SWRC) ................................................................................. 5 2.4 Direct shear test ................................................................................................................ 9 2.4.1 Shear box design ................................................................................................... 9 2.4.2 Sample preparation .............................................................................................. 10 2.4.3 Procedure ............................................................................................................. 10 2.4.4 Results ................................................................................................................. 11 2.5 Interface direct shear test................................................................................................ 17 2.6 Hydraulic conductivity ................................................................................................... 19 3. Finite element model ............................................................................................................. 20 3.1 Introduction .................................................................................................................... 20 3.2 Model geometry and mesh type ..................................................................................... 21 3.3 Input parameters ............................................................................................................. 22 3.4 Steps used in the finite element simulation .................................................................... 23 3.4.1 Geostatic balance................................................................................................. 23 3.4.2 Wetting phase ...................................................................................................... 28 3.4.3 Pile activation ...................................................................................................... 32 3.4.4 Friction activation and pile axial loading step .................................................... 33 4. User defined field (usdfld) ..................................................................................................... 33 4.1 Equations for strength parameters .................................................................................. 33 4.2 Workflow of USDLFD................................................................................................... 34 vi 5. Results and discussion ........................................................................................................... 36 5.1 Simulation results for Site-1 ..........................................................................................