Modulus-Based Field Testing for Design Verification

Transcription

1 Modulus-Based Field Testing for Design Verification Soheil Nazarian, PhD, PE, DGE Center for Transportation Infrastructure Systems The University of Texas at El Paso Center for Transportation Infrastructure Systems - ctis.utep.edu

2 Traditional Density-Based Compaction Dry Density Higher Energy Water Content Center for Transportation Infrastructure Systems - ctis.utep.edu 2

3 Famous Quotes of Ralph Proctor Strength is not achieved by density alone. Optimum moisture is for compaction. Proctor(1945), Trans 110, ASCE No use is made of actual peak dry weight. Measure of soil compaction used is penetration resistance. What is this? Proctor Penetrometer Center for Transportation Infrastructure Systems - ctis.utep.edu 3

4 Structural Design Why Modulus-Based Field Testing We do not check whether the modulus designer assumed is achieved We do not check whether the material selected provides the modulus assumed by designer We assume Lab Moisture- Density Curve represents Field Compaction process Long Lasting Pavement Center for Transportation Infrastructure Systems - ctis.utep.edu 4

5 Field Modulus (psi) Devices Falling Weight Deflectometer (FWD) Light Weight Deflectometer (LWD) More Practical!! E = [(1 n 2 ) F / (p a d)] f n = Poisson s ratio F = peak load a = radius of load plate d = peak deflection f = shape factor, Target Modulus (psi) Center for Transportation Infrastructure Systems - ctis.utep.edu 5

6 Modulus, ksi Impact of Moisture Content CH Subgrade 76 Drying OMC 0.8 OMC 0.9 OMC OMC 1.1 OMC 1.2 OMC Moisture Content at Testing Compacted at OMC Constant Density Specimens prepared at MDD Center for Transportation Infrastructure Systems - ctis.utep.edu 6

7 Modulus, ksi Impact of Moisture Content CH Subgrade Drying OMC 0.8 OMC 0.9 OMC OMC 1.1 OMC 1.2 OMC Moisture Content at Testing Compacted at 1.2 OMC Compacted at OMC Constant Density Specimens prepared at MDD Center for Transportation Infrastructure Systems - ctis.utep.edu 7

8 Modulus, ksi Impact of Moisture Content CH Subgrade Drying OMC 0.8 OMC 0.9 OMC OMC 1.1 OMC 1.2 OMC Moisture Content at Testing Compacted at 1.2 OMC Compacted at OMC Compacted at 0.8 OMC Constant Density Specimens prepared at MDD Center for Transportation Infrastructure Systems - ctis.utep.edu 8

9 Major Steps for Anticipated Specification 1. Selecting Suitable Material 2. Selecting Appropriate Design Parameters 3. Selecting Target Field Moduli 4. Field Quality/Process Control 5. Acceptance Process Center for Transportation Infrastructure Systems - ctis.utep.edu 9

10 Step 1: Selecting Most Suitable Material A stiff material does not correspond to a durable material. Parameters, such as the hardness of aggregates, percent fines and plasticity should be controlled for durability. DOTs should be reminded not to abandon their specifications on this subject Center for Transportation Infrastructure Systems - ctis.utep.edu 10

11 Estimating Appropriate Design Parameters Conducting laboratory resilient modulus tests before structural design Utilizing results from a catalog of most common soils that have been tested Estimating modulus based on calibrated models that are functions of index parameters Using presumptive design values based on experience Most Desirable Option Less Desirable Option MR k k θ τoct 1Pa 1 Pa Pa 2 k 3 θ = bulk stress τ oct = octahedral shear stress P a = atmospheric pressure k 1,2,3 = regression constants Center for Transportation Infrastructure Systems - ctis.utep.edu 11

12 Selecting Target Field Moduli Input Thickness of each layer Poisson s ratio of each layer Modulus of each layer HMA Base Subgrade Can easily be part of design Output Target Deflection Center for Transportation Infrastructure Systems - ctis.utep.edu 12

13 ETesting/ECompaction Moisture-Adjusted Modulus K moist = e η(wc-wt) ω T = moisture content at time of testing (%) ω C = moisture content at time of compaction (%) η = 0.18 for subgrades η = 1.19 for unbound aggregates Unbound Aggregates Subgrades E Testing / E Compaction E Testing / E Compaction Subgrades y = e Unbound Aggregates y = e 1.19x MCCompaction-MCTesting, % MC Compaction -MC Testing, % MC Compaction -MC Testing, % Center for Transportation Infrastructure Systems - ctis.utep.edu 13

14 LTRC Experiments 180' 12' Center for Transportation Infrastructure Systems - ctis.utep.edu 14

15 Dry Density, pcf Moisture Content, % LTRC Field Evaluation: Construction Field Moisture Content-Subgrade OMC-Subgrade Dry Optimum Wet Saturated 150 Field Dry Density-Subgrade Subgrade MDD 140 Subgrade 95%MDD Dry Optimum Wet Saturated Center for Transportation Infrastructure Systems - ctis.utep.edu 15

16 Modulus, ksi LWD Lab vs. Field Saturated Wet Optimum Dry Center for Transportation Infrastructure Systems - ctis.utep.edu 16

17 Field IMplementation Site I.1. US 67 in Dublin, TX Site II.1. FAA Facility, Atlantic City, NJ Site I.2. IH 35 W, Tarrant County, TX Site II.2. US-50, North Vernon, IN Site I.3. Route 22, Bridgewater, NJ Center for Transportation Infrastructure Systems - ctis.utep.edu 17

18 Dry Density, pcf Density-Based Quality Control of Field Sections 160 Field Dry Density 95%MDD ? Center for Transportation Infrastructure Systems - ctis.utep.edu 18

19 Cumulative Distribution, % Cumulative Distribution, % Variability of LWD Under Field Conditions 100% 100% 80% 80% 60% 60% 40% 40% 20% 20% a) Subgrade b) Base/Subbase 0% 0% 10% 20% 30% 40% 50% More 0% 0% 10% 20% 30% 40% 50% More COV, % COV, % Center for Transportation Infrastructure Systems - ctis.utep.edu 19

20 Cumulative Distribution, % Cumulative Distribution, % Cumulative Distribution, % Variability of Modulus and Moisture in Actual Field Production 100% 80% a) Moisture Content 100% 80% b) Dry Density 60% 60% 95%MDD 40% 20% OMC 40% 20% MDD 0% Moisture Content, % 100% 0% Dry Density, pcf 80% 60% 80% Target LWD c) Field Modulus 40% 20% Target LWD 0% Modulus, ksi Center for Transportation Infrastructure Systems - ctis.utep.edu 20

21 M/Mopt Modulus Results: How to Handle Moisture (MC-OMC)/OMC, % Center for Transportation Infrastructure Systems - ctis.utep.edu 21

22 How to Handle Variability?? Select a fast test and test more!! Center for Transportation Infrastructure Systems - ctis.utep.edu 22

23 More info!! Soheil Nazarian ph: (915) Be Glad to Help!! Let us know if you have a site in mind!! Center for Transportation Infrastructure Systems - ctis.utep.edu 23