Effect of Suction on the Resilient Modulus of Compacted Fine- Grained Subgrade Soils

Size: px

Start display at page:

Download "Effect of Suction on the Resilient Modulus of Compacted Fine- Grained Subgrade Soils"

Britton Palmer
5 years ago
Views:

1 THE UNIVERSITY OF WISCONSIN-MADISON Effect of Suction on the Resilient Modulus of Compacted Fine- Grained Subgrade Soils by Auckpath Sawangsuriya, Ph.D. Tuncer B. Edil, Ph.D., P.E. Craig H. Benson, Ph.D., P.E. TRB 88 th Annual Meeting Jan 14 th, 2009

2 Outline Introduction Test Materials Testing Program Results & Analysis Conclusions

3 Typical flexible pavement structure Asphalt Layer Base Course Subbase Course Natural Subgrade Soils Pavement subgrade moisture in MN

4 Introduction NCHRP 1-37A addresses this issue by employing the resilient modulus (M r ) at an equilibrium degree of saturation for pavement design, and provides a model to predict changes in modulus due to changes in moisture content.

5 Conceptual Relationship Resilient Modulus, M r Resilient Modulus, M r Matric suction Moisture content Modulus of unsaturated soils is strongly influenced by matric suction, particularly for compacted fine-grained soils. However, simple predictive relationships between M r and matric suction have not been defined.

6 Objectives To investigate M r of compacted finegrained subgrade soils having a wide range of plasticity index over a range of matric suctions To develop empirical relationships between M r and matric suction

7 Soil Properties Red Wing, MN Red Lake Falls, MN MnRoad, MN Duluth TH 23 Slopes, MN USCS ML CL CL CH % Sand % Clay % Fine LL PI G s O.M.C. (%) ρ d,max

8 10 6 Net confining pressure = 34.5 kpa 10 5 Matric suction (kpa) MnRoad DI TH 23 Slopes Red Lake Falls 10 1 Red Wing Volumetric water content

9 Testing Program Phase I: Suction Conditioning Saturation (zero suction) Inducing Target Suction (154 and 350 kpa) Phase II: Resilient Modulus (M r ) Testing Tests were conducted in accordance with NCHRP 1-28A using Procedure II for soils with at least 35% fines Phase III: Post-Test Measurement of Matric Suction

10 Phase I: Saturation Followed ASTM D 5084 (ASTM 2004) B-check (not less than 90%) ~ 2-6 weeks saturation time

11 Phase I: Inducing Target Suction u w = 0 To graduated cylinder or horizontal capillary tube Top drainage line Top cap u a Soil Specimen Triaxial cell Thick rubber band with adjustable steel clamp D = 10.2 cm H = 20.3 cm High air-entry ceramic disk Pedestal Bottom drainage line u w = 0 To graduated cylinder or horizontal capillary tube Schematic of suction cell Drawing of pedestal

12 Phase II: Resilient Modulus (M r ) Testing Five-parameter power function: k a oct k a b a r k p p k p k M + = τ σ

13 Resilient Modulus-External (M r,e ), kpa k = k = k = k = 0 6 k = Measured Matric suction = 83 kpa Bulk Stress (σ ), kpa b

14 Resilient Modulus-External (M r,e ), kpa k = k = k = k = 0 6 k = Measured Matric suction = 83 kpa Octahedral Shear Stress ( τ ), kpa oct

15 Resilient Modulus-Internal (M r,i ), kpa k = k = k = k = k = Measured Matric suction = 83 kpa Bulk Stress (σ ), kpa b

16 Resilient Modulus-Internal (M r,i ), kpa k = k = k = k = k = Measured Matric suction = 83 kpa Octahedral Shear Stress ( τ ), kpa oct

17 Red Wing MnRoad Red Lake Falls Duluth TH23 Slopes M r,i /M r,e M r,i /M r,e = x10-5 M r,i R 2 = M r,i (kpa)

18 Phase III: Post-Test Measurement of Matric Suction Soil specimen Data and excitation cable Thermal dissipation sensor 60 mm 32 mm 15 mm Plastic head Steel needle Porous block Thermocouple Heating element Schematic of Thermal Dissipation Sensor Model 229 by Campbell Scientific Inc.

19 10 5 Red Wing Induced Target Suction = 350 kpa Matric suction (kpa) Top Middle Bottom Elaspe Time (min)

20 Results & Analysis

21 Summary Resilient Modulus, M rs (kpa) 2.5x x x x x Red Wing-103% Red Wing-98% MnRoad-103% MnRoad-98% Red Lake Fall-103% Red Lake Fall-98% Duluth Th23 Slopes-103% Duluth TH23 Slopes-98% Water Content (%)

22 2.5x10 5 Summary Resilient Modulus, M rs (kpa) 2.0x x x x10 4 M r = -54, ,000 log (u a - u w ) R 2 = ,000-24,000 Red Wing MnRoad Red Lake Falls Duluth TH23 Slopes Matric Suction (kpa)

23 1.0 M rs /M rs,opt M rs /M rs,opt = log(u a - u w ) R 2 = 0.76? ? 0.2 Red Wing MnRoad Red Lake Falls Duluth TH23 Slopes Matric Suction (kpa)

24 20 15 Red Wing MnRoad Red Lake Falls Duluth TH23 Slopes M rs / M rs,sat 10 M rs /M rs,sat = log(u a - u w ) R 2 = 0.81? ? Matric Suction (kpa)

25 Conclusions A series of tests was conducted on four fine-grained subgrade soils representing a wide range of plasticity to evaluate how M r is affected by matric suction. M r test was conducted on each specimen after matric suction conditioning using methods described in NCHRP 1-28A. After M r test, target matric suction was checked using thermal dissipation sensors. Independent direct measurement of matric suction obtained with thermal dissipation sensors was used to define relationship between modulus and suction.

26 Conclusions Summary M r of all four soils increased with increasing matric suction within a narrow band. A modulus ratio (MR) was computed as the ratio of the summary M r at any suction to a reference summary M r. Two reference moduli were considered: summary M r at optimum compaction conditions and summary M r at saturation. MR varied linearly with logarithm of matric suction in a relatively narrow band for all soils and using both normalization schemes.

27 Conclusions These trends can be used to estimate summary M r of a well compacted sample at a given suction if the summary M r at optimum compaction conditions or at saturation is known.

28 Acknowledgments Study funded by the Minnesota Department of Transportation (MnDOT) through a subcontract with the University of Minnesota under the direction of Professor Satish Gupta. Help and support of Mr. John Siekemier of the MnDOT.

Pavement Design Using Unsaturated Soil Technology

2007-11 Pavement Design Using Unsaturated Soil Technology Take the steps... Research...Knowledge...Innovative Solutions! Transportation Research Technical Report Documentation Page 1. Report No. 2. 3.