LADOTD DRIVEN PILE DESIGN & VERIFICATION. Jesse G Rauser, PE USING LRFD

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1 LADOTD DRIVEN PILE DESIGN & VERIFICATION Jesse G Rauser, PE USING LRFD

2 OBJECTIVES Not all of our policies, guidelines, and SOP s are in the same location Answer commonly asked questions about LADOTD pile design & verification procedures Address misconceptions about pile design & verification processes used by LADOTD Identify relevant research projects associated with driven piles Highlight changes to Section 804 in the upcoming 2016 Standard Specifications Provide links to useful information and codes

3 PRESENTATION OUTLINE Geotechnical Investigations In-House vs. Consulted Site investigation guidelines Lab testing requirements Soil boring logs Driven Pile Design Methods Scour Design procedures Constructability Specification changes Field Verification Test Piles Monitor Piles Indicator Piles Pile Setup Resistance Factor Selection Research Projects

4 USEFUL LINKS FHWA Geotechnical Library: Louisiana Transportation Research Center (LTRC) Downloads: LADOTD Bridge Design Section e_design/pages/default.aspx LADOTD Pavement & Geotechnical Section ment_geotechnical/pages/default.aspx

5 GEOTECHNICAL INVESTIGATIONS

6 PROJECT ASSIGNMENT HIERARCHY Project Management (or other) Pavement/ Geotechnical Section Bridge Design Section Geotechnical Consultant LADOTD In- House Crew Geotechnical Retainer Contract Bridge Retainer Contract LADOTD Materials Lab Geotechnical Subconsultant

7 SITE INVESTIGATION GUIDELINES What are the LADOTD boring and laboratory testing requirements? GEC No. 5 Evaluation of Soil & Rock Properties (FHWA-IF ) Table 3 provides guidelines for minimum investigation Also in LRFD Bridge Design Specification Table GEC No. 5 Cover Page

8 SITE INVESTIGATION GUIDELINES Number of Borings When foundation layout is known: At least one boring at every substructure (bent or pier) Two borings per substructure, for widths greater than 100 When foundation layout is unknown: At least one boring every 100 of alignment Depth of Investigation Use the greater of: At least 20 below anticipated tip 2x maximum pile group dimension In general, we use 120 for bridge foundations Subgrade borings should terminate at least 8 below finished roadway elevation

9 SITE INVESTIGATION GUIDELINES For embankment/fill, consider depth of influence (based on width), not only height of fill It may be appropriate to drill to depths over 2B Penetrate through weak strata into denser material to terminate boring, when possible Stress Distribution Beneath Continuous Strip (from Coduto) No SPT s in clay!

10 LAB TESTING REQUIREMENTS Deep Borings 75% of all cohesive samples tested with Atterberg Limits and UU Triaxial tests This easily covers costs of testing sand instead of clay Perform some consolidation tests in fill areas Data submitted electronically in gint format and printed in the LADOTD log format Subgrade Borings Test enough samples to classify using AASHTO system This should include hydrometer tests to identify silt content ph & resistivity in culvert areas Data submitted in gint format, log format varies among consultants

11 SOIL BORING LOGS 10-2GT Geotechnical Database Phase 2 standardized the gint database format Soil boring log format was also standardized We can now plot consultants data directly into charts, fences, etc. This cuts down on errors introduced by retyping data & saves time Double check -200 results before classifying (SP versus SP -SM, etc.) Make sure SPT termination is reported properly ( Standard Penetration Test) Stratify the soil borings: Only group 2 adjacent consistencies (i.e., very soft to soft, med. to stiff) Do not group different USCS types to avoid drawing additional layers

12 DRIVEN PILE DESIGN METHODS

13 DESIGN CONSTRAINTS Certain constraints are set before pile design begins Type & size of pile Unsupported length & slenderness ratio Type of field verification available due to budget or accessibility Scour Considerations Scour often has a major impact upon the pile design BDTM 21 Describes DOTD Policy for Predicting Scour Elevation Bridge Profile with Scour Information

14 SCOUR CONSIDERATIONS For permanent structures: Subtract Contraction & Local Scour from the lowest point in channel Apply this calculated elevation to all piers/bents and end bents Abutment scour is not usually calculated this does not mean to ignore scour at abutments! Minimum tip elevation for scour: 20 below scour elevation for piles less than 24 in diameter 25 below scour elevation for piles 24 in diameter or greater From old Bridge Design Manual, not in new Bridge Design Manual For detour bridges, apply local scour from the design ground surface at each bent location

15 AXIAL PILE DESIGN #1 Question: What is the status of DRIVEN? FHWA does not want to be in the software development business Other software exists, including DrivenPiles (successor to DRIVEN) You could run DRIVEN in a Virtual Machine running an older Win OS Create your own spreadsheet/software LADOTD has no current plans to vet/endorse any specific software package A future research proposal may address this later no timeline Ultimately, we will accept methods providing results consistent with the DRIVEN methods Cohesionless soil Nordlund Method Cohesive soil Tomlinson/α Method

16 AXIAL PILE DESIGN Does guidance exist for designing driven piles? DOTD generally tries to adopt methods described in the NHI course manuals An older (1998) version of the manual is available on the FHWA website Newer versions (2006) are available to those who take the associated NHI course FHWA HI Cover Page

17 AXIAL PILE DESIGN BY CPT Louisiana Pile Design by CPT Software We have had success designing piles with CPT on recent projects LTRC developed the PILE- CPT software to design piles A new research proposal aims to evaluate newer CPT methods & update software To develop experience, we recommend evaluating CPT & borings side by side for any projects with both

18 RESISTANCE FACTORS

19 RESISTANCE FACTOR SELECTION Selection of φ must consider tradeoff between pile length & cost of field verification Table is a starting point for φ Region-specific research is also used to refine our selection of φ values Site-specific φ calibration may be warranted on large projects LRFD Bridge Design Specifications

20 RESISTANCE FACTOR SELECTION From Table (LRFD Bridge Design Spec - 6th Edition w/2013 Revisions) Resistance Factor Determination Method Static Load Testing of at least 1 pile per site condition, plus Dynamic Testing on at least 2% of production piles (minimum 2/site) Static Load Testing of at least 1 pile per site condition, no Dynamic Testing Resistance Factor (φ) Dynamic Testing conducted on 100% of production piles 0.75 Driving criteria established by Dynamic Testing, plus Dynamic Testing of at least 2% of production piles (minimum 2/site) 0.65 Wave Equation Analysis, no Dynamic Monitoring or Load Testing 0.50 FHWA-modified Gates dynamic formula at end-of-drive only 0.40 Static Methods (α-method/nordlund method) 0.35/0.45 Note: Dynamic Testing includes restrike testing and signal matching analyses

21 RESISTANCE FACTOR CALIBRATION 07-2GT Calibration of Resistance Factors Needed in the LRFD Design of Driven Piles Completed May GT Calibration of Region-Specific Gates Equation for LRFD Draft report reviewed, implementation is imminent 11-2GT Field Instrumentation and Testing to Study Set -up Phenomenon of Piles Driven into Louisiana Clayey Soils Draft report reviewed, implementation plan in progress 03-1GT, 10-2GT, 15-1GT Geotechnical Database Projects Phases 1 & 2 complete, Phase 3 underway

22 RESISTANCE FACTOR SELECTION Resistance Factor Determination Method LRFD LADOTD Static: 1 pile/site Dynamic: 2% production piles ( 2/site) Static: 1 pile/site Dynamic: None AASHTO LRFD Bridge Design Manual vs. Typical LADOTD Practice Static: None Dynamic: 100% production piles Dynamic: Used to establish driving criteria Dynamic: 2% production piles ( 2/site) Wave Equation Analysis only, no Dynamic/Static FHWA-modified Gates dynamic formula at end-of-drive only * Static Methods (α-method/nordlund method) 0.35/ * Implementation of new research should increase to 0.55

23 CONSTRUCTABILITY

24 CONSTRUCTABILITY Remember, conservative strength parameters in design become the opposite when considering drivability Designs must be constructible and capacity must be verifiable We need to find a better way for consultants to maintain oversight during construction phase testing For 200-ton Strength Load Static Test: 200t / 0.75 = 267 tons Indicator Pile: 200t / 0.65 = 308 tons Gates Method: 200t / 0.40 = 500 tons Can the same hammer be used to verify 267 tons and 500 tons?

25 OVERBURDEN EFFECT Why do you overdesign your piles? The Required Pile Resistance is almost 5x greater than the Factored Load! Common with high scour & sandy soils Pile Data Table with Significant Overburden Effect Feasibility of design must consider overburden effect In some cases, drilled shafts may be a better choice

26 Pile 1: 24 Square PPC Pile Pile 2: 24 Square PPC Pile OVERBURDEN EFFECT 20 Design Case: Pile 1 = 122 tons Pile 2 = 122 tons Clay (Scour Zone) Clay Sand No Predrill Case: Pile 1 = 187 tons Pile 2 = 320 tons Predrill Case: Pile 1 = 150 tons Pile 2 = 206 tons 20 of Overburden: 56 tons 46% of nominal resistance

27 PILE DRIVING SPEC CHANGES Alternate hammer approval method has been removed from Specs Contractor s Pile Driving Plan must include WEAP analysis Many were already doing so DOTD will continue to look at a basic drivability analysis during design process Contractor is responsible for the specifics of his proposed driving system GRLWEAP Software

28 PILE DRIVING SPEC CHANGES Contractor is responsible for Pile Construction Log Documents all pile installation activities including predrilling Provides a record of driving resistance for every foot of drive Practical refusal broadly defined as 20 blows/inch at maximum stroke, for 3 consecutive inches Hammer must be in working order Dynamic monitoring may be needed to verify hammer efficiency We will not accept a refusal condition on a hammer that is malfunctioning Dynamic Load Test item renamed to Dynamic Monitoring Assistance Dynamic Monitoring Instrumentation moved from nonstandard item into the Specification

29 FIELD VERIFICATION

30 PILE CATEGORIES Test Pile (φ= ) Driven in advance of the permanent piles Load tested Dynamic testing is typically done as well Indicator Pile (φ=0.65) Same as test pile, dynamic testing only Monitor Pile Permanent pile with dynamic monitoring Preparing to Drive a Test Pile

31 TEST PILES How many test piles are needed? 1 per site condition 1 per pile size (unless similar enough to back out unit resistances) Consider additional piles if end bearing conditions differ Consider additional piles if additional information is needed for design What is the maximum pile test load under LRFD? Old way was to use 300% of the design load Now, use 150% of the Required Nominal Resistance (with predrilling) in plans Spec Change: Spec now references ASTM D -1143, Procedure A, with minor modifications: Load is applied in 20 equal increments, or as directed by engineer Load is removed in 5 equal increments, based on max test load Deflection is measured with 3 independent gauges accurate to +/

32 TEST PILES Testing schedule should be flexible Some static tests done as early as 7 days Restrike tests do not have to be exactly at 24 hours Load Test Reaction System Load test plus dynamic testing allows us to verify design methodology, calibrate PDA, establish setup criteria, and verify hammer performance

33 INDICATOR & PERMANENT PILES Indicator Piles How many Indicator Piles are needed? Same criteria as Test Piles Can be used to establish setup criteria but not calibrate PDA to a load test Permanent Piles Spec Change Modified Gates to be used only when specified in the plans Based on research, we hope to change φ from 0.40 to 0.50 or 0.55

34 PILE SETUP We use test piles and indicator piles to Confirm static calculations Reduce uncertainty Assess pile setup behavior Establishing setup rates may allow for accelerated field verification In some cases, we can provide acceptance before reaching the nominal resistance 20-hr restrikes on LA-1 project (65% to 75% of capacity) Pile Setup Curve Compared to Static Test Results

35 MACARTHUR BLVD. PROJECT No room to do static testing Used restrikes on monitor piles to establish setup behavior Late restrikes had to be eliminated due to vibrations In some piers, early restrikes saved the contractor time and allowed pile acceptance prior to 24 hours Pile Setup Curves Setup curves were used to estimate pile capacity deficiency and determine pile extension lengths

36 QUESTIONS? FHWA Geotechnical Library: Louisiana Transportation Research Center (LTRC) Downloads: LADOTD Bridge Design Section e_design/pages/default.aspx LADOTD Pavement & Geotechnical Section ment_geotechnical/pages/default.aspx