SPR-4230: Alternative Quality Assurance Methods for Compacted Subgrade

Transcription

1 SPR-4230: Alternative Quality Assurance Methods for Compacted Subgrade Peter J. Becker, PhD Indiana Department of Transportation Division of Research & Development

2 Presentation Layout Project background Research approach Research Findings to Date Laboratory Testing Field Testing Summary Future Work

3 Performance-Based Specifications Type of quality assurance specification Quality assurance = owner/owner s representative (i.e., INDOT) Quality control = contractor Describes desired level(s) of engineering property(s) Predictor(s) of performance Appear in primary prediction relationship(s) Doyle, G. (2003). Major Types of Transportation Construction Specifications: A Guideline to Understanding Their Evolution and Application. AASHTO Highway Subcommittee on Construction, Quality Construction Task Force. Washington, D.C.: American Association of State Highway and Transportation Officials.

4 Traditional Subgrade Quality Assurance γ d(max) w opt Dry unit weight, γ d Although soil strength and stiffness tends to increase with increasing dry unit weight (density), density/dry unit weight cannot be used to directly predict performance Moisture content, w

5 A More Appropriate Performance Property

6 INDOT Allowed Subgrade Treatment Types Type I Compacted to 100% RC 24 Type IB Chemically Modified 14 Type IC No. 53 Aggregate 12 Type II No. 53 Aggregate 6 Type IIA Chemically Modified 8 Type III Compacted to 100% RC 6 Type IV No. 53 Aggregate 12 Type V No. 53 Aggregate 3 Type IB geogrid

7 Goal of SPR-4230 Specified chemically modified subgrade resilient modulus used in design In situ quality assurance testing Light weight deflectometer (LWD) Rapid Easy to use Provides stiffness meaurement Confirm specified chemically modified subgrade resilient modulus during construction

8 Light Weight Deflectometer (LWD) 10 kg drop weight imparting 1,589 lbf maximum force Accelerometer measuring peak deflection 28-⅜ in. drop height Data collector Loading plate (11.81 in. diameter)

9 LWD Elastic Modulus Backcalculation Boussinesq s solution: r o F o y z r x σ z σ θ y z τ zr τ σ rz r x In Situ Stresses: σσ zz = ff FF oo, rr, zz σσ rr = ff FF oo, rr, zz σσ θθ = ff FF oo, rr, zz In Situ Vertical Strain: εε zz = 1 EE σσ zz νν σσ θθ + σσ rr ν is Poisson s ratio (0.2 to 0.4 typical) Vertical Deflection at Surface: δδ zz = εε zz dddd 0 δδ zz = FF oo 1 νν 2 kk ππrr oo EE k is applied stress shape factor EE LLLLLL = FF oo 1 νν 2 kk ππrr oo δδ zz E is elastic Modulus F o is applied force r o is loading plate radius ν is Poisson s ratio k is applied stress shape factor δ z is surface deflection

10 Applied Stress Shape Factor (k) Is stress applied uniformly? Probably not (loading plate is too stiff) F o σσ oo σσ oo 0.4δ z δ z Stress applied over an inverse-parabolic stress distribution is a better assumption σσ oo rr σσ oo rr = δ z FF oo 2ππrr oo rr oo 2 rr 2 EE LLLLLL = FF oo 1 νν 2 kk ππrr oo δδ zz kk = ππ 2

11 LWD Elastic Modulus 50,000 Subgrade Treatment Type IB Material Maximum Allowable Deflection (mm) 40,000 INDOT Standard Specification No LWD Elastic Modulus (psi) 30,000 20,000 10,000 F o = 1,589 lb r o = 5.91 in. ν = 0.3 k = π/ Measured Deflection (mm)

12 LWD Elastic Modulus Resilient Modulus (Strain) σσ dd h Δh εε = h h σσ dd εε = εε pp + εε rr EE = σσ dd εε = σσ dd εε pp + εε rr lim εε pp = 0 NN lim NN EE = σσ dd εε rr = MM rr Strain, ε 10,000 cycles Resilient Strain (ε r ) Resilient Strain (ε r ) Plastic Strain (ε p ) Loading Cycles, N Plastic Strain (ε p )

13 LWD Elastic Modulus Resilient Modulus (Stress) AASHTO T 307 (Resilient Modulus Lab Test) σσ dd = 6 psi Light Weight Deflectometer γ = 120 pcf νν = 0.3 σσ rr = σσ θθ MM rr = kk 1 pp aa θθ pp aa kk 2 θθ = σσ 1 + σσ 2 + σσ 3 ττoooooo pp aa + 1 kk 3 One Plate Diameter (11.81 in.) σσ zz ττ oooooo = 1 3 σσ 1 σσ σσ 1 σσ σσ 2 σσ 3 2 σσ 2 = σσ 3 = 2 psi σσ 1 = 8 psi σσ 3 = 2 psi θ is bulk stress τ oct is octahedral shear stress p a is atmospheric pressure k 1, k 2, k 3 are material constants On average = 0.4 psi = 0.2 psi σσ zz oo σσ rr oo σσ zz = 6.5 psi σσ rr = 1.9 psi σσ zz ff σσ rr ff = 6.9 psi = 2.1 psi σσ 2 = σσ 3 = 2.1 psi σσ 1 = 9.0 psi

14 Previously Established E LWD and M r Correlations Untreated A-6 subgrade Untreated A-4 and A-7-5 subgrades MM rr = kk 1 pp aa θθ pp aa kk 2 ττoooooo pp aa + 1 kk 3 D. J. White, M. Thompson, and P. Vennapusa, Field validation of intelligent compaction monitoring technology for unbound materials, Final Report MN/RC , Minnesota DOT, St. Paul, Minn, USA, S. H. Mousavi, A. G. Gabr, and R. H. Borden, Subgrade resilient modulus prediction using light-weight deflectometer data, Canadian Geotechnical Journal, 54(3), 2017.

15 This Study s E LWD and M r Correlation 5 kg drop weight imparting up to 871 lbf maximum force Laboratory LWD Loading plate (5.91 in. diameter) CBR-sized sample (7 in. high, 6 in. diameter) A-6 subgrade Nominal 4% cement content Nominal relative compactions of 90%, 95%, & 100% Nominal moisture contents of 2% dry of optimum, optimum, & wet of optimum

16 Relationship Between E LWD and Axial Stress (σ a ) LWD Elastic Modulus, E LWD (psi) 80,000 60,000 40,000 4% PC, OMC, 95% RC 4% PC, OMC, 100% RC 4% PC, 2% wet, 95% RC 4% PC, 2% dry, 95% RC 4% PC, OMC, 90% RC R² = R² = R² = ,000 R² = R² = EE LLLLLL = aaee bbσσ aa Axial Stress, σ a (psi)

17 Predicting In Situ E LWD In the lab In the field h σσ aa Δh EE LLLLLL = aaee bbσσ aa σσ aa = εε LLLLLL EE LLLLLL εε LLLLLL = 1 EE LLLLLL σσ zz νν σσ rr +σσ θθ εε LLLLLL EE LLLLLL = σσ zz νν σσ rr +σσ θθ σσ aa εε LLLLLL = h h EE LLLLLL = aa exp bb εε LLLLLL EE LLLLLL For symmetric loading σσ rr = σσ θθ εε LLLLLL EE LLLLLL = σσ zz 2ννσσ rr EE LLLLLL = aaee bb σσ zz 2ννσσ rr

18 Predicting In Situ E LWD Example: 0 4% cement; optimum moisture content; 95% relative compaction; ν = 0.3 (assumed) F o = 1,589 lb; r o = 5.91 in. EE LLLLLL = 25800ee σσ zz 2ννσσ rr σ z (psi) σ r (psi) σ z 2νσ r (psi) E LWD (psi) με LWD (μin/in) ,000 40, Depth (in.) δδ LLLLLL = 0 εε LLLLLL dddd = mm EELLLLLL = FF oo 1 νν 2 2rr oo δδ zz = 29,033 psi

19 Correlating Predicted In Situ E LWD with M r Resilient Modulus per AASHTO T 307 σ 3 = 2 psi, σ d = 6 psi 20,000 Resilient Modulus, M r (psi) 15,000 10,000 5,000 log(m r ) = log( * E LWD ) r 2 = S.E. = log(psi) ,000 20,000 30,000 40,000 Predicted In Situ LWD Elastic Modulus, * E LWD (psi)

20 Field Testing (2018 construction season) I-65 near Frankfort (Crawfordsville District) Target 4% cement A-4 and A-2-4 subgrades 4 test sections I-469 near Fort Wayne (Fort Wayne District) Target 5% cement A-6 subgrade 2 test sections US-6 near Brimfield (Fort Wayne District) Target 4% cement A-1-b and A-4 subgrade 1 test section Cleveland Road in South Bend (La Porte District) Target 4% cement A-1-b 1 test section CR 400 S near Clymers (La Porte District) Target 4% cement A-4 1 test section I-69 near Anderson (Greenfield District) Target 4% cement A-6 1 test section

21 Results of LWD Field Testing (LWD Deflection) Average mm mm mm mm mm mm Standard Deviation mm mm mm mm mm mm Count LWD Deflection (mm) I-65 I-469 US-6 Cleveland Rd. CR 400 S I-69 Average of all sections: mm Standard Deviation of all sections: mm

22 Results of LWD Field Testing(LWD Elastic Modulus) Average 14,213 psi 11,266 psi 18,081 psi 10,967 psi 13,150 psi 12,857 psi Standard Deviation 4,147 psi 3,147 psi 7,396 psi 5,066 psi 2,894 psi 4,514 Count ,000 30,000 LWD Elastic Modulus (psi) 20,000 10,000 0 I-65 I-469 US-6 Cleveland Rd. CR 400 S I-69 EE LLLLLL = FF oo 1 νν 2 2rr oo δδ zz Average of all sections: 13,268 psi Standard Deviation of all sections: 4,867 psi

23 Results of LWD Field Testing (LWD correlated resilient modulus) Average 12,903 psi 12,241 psi 13,535 psi 12,020 psi 12,716 psi 12,586 psi Standard Deviation 873 psi 813 psi 1,309 psi 1,347 psi 657 psi 940 psi Count ,000 15,000 LWD Elastic Modulus (psi) 10,000 5,000 0 I-65 I-469 US-6 Cleveland Rd. CR 400 S I-69 MM rr = 1480 EE LLLLLL Average of all sections: 12,654 psi Standard Deviation of all sections: 1,039 psi

24 Falling Weight Deflectometer (FWD) Applies 7 kip, 9 kip, & 11 kip nominal loads (load cell measures actual loads) in. diameter loading plate Geophones measuring surface deflection basin to nearest 0.01 mil

25 Backcalculation of Subgrade Resilient Modulus from FWD Deflection, d (mil) Example: I-469 NB STA Distance from loading plate, r (in.) Subgrade is primary source of deflection far away from the loading plate ( 36 in.) MM rr = CC 0.24FF oo dd rr AASHTO (1993) M r is resilient Modulus F o is applied force r is distance from loading plate d is surface deflection C is a correction factor (equals 0.33)

26 LWD and FWD Resilient Modulus Agreement Foundations of these stations along I-469 (Fort Wayne) were chemically modified ( double treatment ) 30,000 FWD Backcalculated Resilient Modulus, Mr (FWD) (psi) 20,000 10, % agreement interval I-65 (Frankfort) I-469 (Fort Wayne) US-6 (Brimfield) Cleveland Road (South Bend) 0 10,000 20,000 30,000 LWD Correlated Resilient Modulus, M r(lwd) psi These stations along US-6 (Brimfield) experienced a downpour of rain shortly after construction ( moisture treatment )

27 Key Findings The LWD measures in situ soil stiffness (LWD elastic modulus) that relate to pavement subgrade performance Although LWD elastic modulus and resilient modulus are not one and the same, they do correlate well with one another Field LWD tests provide validation of proposed LWD elastic modulus and resilient modulus correlation Resilient moduli correlated from LWD testing are in agreement with resilient moduli backcalculated from FWD testing

28 Future Work Improve correlation between predicted LWD deflection and resilient modulus (more samples from more soil types) LWD and FWD measurements from INDOT contracts during the 2019 construction season o Use better model for backcalculating resilient modulus from FWD Provide recommendations for subgrade construction acceptance o Maximum LWD deflection o Testing frequency o Effect of curing time Publish findings in JTRP technical report

29 Acknowledgements SPR-4230 Study Advisory Committee o Athar Khan o Nayyar Siddiki INDOT Research & Development o Tony Johnson o Ross Bucher o Maurice Hendryx INDOT Construction o Terry Olding o Greg Hole Engineering Consultants o Dale Wills (Lochmueller Group) o Gary Fox o Tom Harris o Hobie Deaton o Daniel Tran o Allen Truax o Charles Schueler o Kyle Van Meter o Myron Cohagan (Lochmueller Group) o Tom Duncan o Lyle Burkhalter o Chris Weinard o Steve Lindway o Josh Tinkle (Alt & Witzig Engineering)

30 Peter J. Becker, PhD Soil Foundation Research Engineer Indiana Department of Transportation Division of Research and Development P.O. Box Montgomery Street West Lafayette, IN Phone: (765) Fax: (765) Thank you for your attention