Introduction
When designing pavements, there are three
Pavement Design Parameters
fundamental external design parameters to consider:
东南大学交通学院 黄晓明 [email protected] Tel:8379 5184
the characteristics of the (1)subgrade and pavement structure upon which the pavement is placed, the (2)applied loads and the (3) environment
Transportation College, Southeast University 东南大学交通学院
Subgrade- Introduction
A subgrade’s performance generally depends on three of its basic characteristics: (1)Load bearing capacity.
Subgrade- Introduction
(2)Moisture content. Moisture content can be influenced by a number of things such as drainage,
The load bearing capacity is often affected by degree of compaction, moisture content, and soil type.
Transportation College, Southeast University 东南大学交通学院
groundwater table elevation, infiltration, or pavement porosity.
Transportation College, Southeast University 东南大学交通学院
Subgrade- Introduction
(3)Shrinkage and/or swelling. Shrinkage, swelling and frost heave will tend to deform and crack any pavement type constructed over them.
Transportation College, Southeast University 东南大学交通学院
Subgrade - Introduction
There are several methods available to improve subgrade performance: (1)Removal and replacement (over-excavation) (2)Stabilization with a cementitious or asphaltic binder (3)Additional base layers.
Transportation College, Southeast University 东南大学交通学院
1
Subgrade-Stiffness/Strength Tests
Subgrade materials are typically characterized
Subgrade-Stiffness/Strength Tests
Three basic subgrade stiffness/strength characterizations are commonly used:
by their resistance to deformation under load, which can be either a measure of their strength or stiffness.
(1)California Bearing Ratio (CBR) (2)Resistance Value (R-value) (3)elastic (resilient) modulus and (4) Subgrade Reaction (k) .
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR) The California Bearing Ratio (CBR) test is a wellgraded crushed stone (thus, a high quality crushed stone material should have a CBR @ 100%). It was developed by the California Division of Highways around 1930 and was subsequently adopted by numerous states, counties, U.S. federal agencies and internationally.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR) The basic CBR test involves applying load to a small penetration piston at a rate of 1.3 mm (0.05") per minute and recording the total load at penetrations ranging from 0.64 mm (0.025 in.) up to 7.62 mm (0.300 in.).
⎛ x⎞ CBR (%) = 100⎜ ⎟ ⎜ y⎟ ⎝ ⎠
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
⎛ x⎞ CBR (%) = 100⎜ ⎟ ⎜ y⎟ ⎝ ⎠
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
material resistance or the unit load on the where: x= piston (pressure) for 2.54 mm (0.1") or 5.08 mm (0.2") of penetration standard unit load (pressure) for well y= graded crushed stone for 2.54 mm (0.1") penetration = 6.9 MPa (1000 psi) for 5.08 mm (0.2") penetration = 10.3 MPa (1500 psi)
Transportation College, Southeast University 东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
2
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
Variation of CBR with Density and Moisture Content for a Clay(from Lay 1998)
Transportation College, Southeast University 东南大学交通学院 Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
50 40 30
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
Typical Presumptive Subgrade Design CBR Values Description of Subgrade Material USC Classification Typical CBR Values (%) Well Drained Poorly Drained
20 15 In s itu C a lifo rn ia B e a rin g R a tio (% )
10 8 6 5 4 3 2 4 5 10 20 30 40 60 80 100 P e n e tra tio n (m m /b lo w )
Highly Plastic Clay Silt Silty Clay Sandy Clay Sand
CH ML CL SC SW, SP
5 4 5-6
2–3 2 3-4
10-15
5-10
Correlation Between Dynamic Cone Penetration and CBR
Transportation College, Southeast University 东南大学交通学院 Transportation College, Southeast University 东南大学交通学院
3
Subgrade-Stiffness/Strength Tests
Resistance Value (R-value) The test procedure expresses a material's resistance to deformation as a function of the ratio of transmitted lateral pressure to applied vertical pressure. It is essentially a modified triaxial compression test.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resistance Value (R-value)
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resistance Value (R-value) The R-value test was developed by F.N. Hveem and R.M. Carmany of the California Division of Highways and first reported in the late 1940's.
Subgrade-Stiffness/Strength Tests
Resistance Value (R-value)
The R-value is calculated from the ratio of the applied vertical pressure to the developed lateral pressure and is essentially a measure of
R-value test was developed as an improvement on the CBR test.
Transportation College, Southeast University 东南大学交通学院
the material's resistance to plastic flow.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resistance Value
⎧ ⎫ ⎪ 100 (R-value) R = 100 − ⎪ ⎪ ⎪ ⎨ ⎬ ⎛ 2.5 ⎞ ⎡⎛ Pv ⎞ ⎤ ⎪ ⎪⎜ ⎟ ⎢⎜ ⎟ − 1⎥ + 1 ⎪ ⎝ D ⎠ ⎣⎝ Ph ⎠ ⎦ ⎪ ⎩ ⎭
Subgrade-Stiffness/Strength Tests
Resistance Value (R-value) Standard R-Value test methods are: AASHTO T 190 and ASTM D 2844: Resistance RValue and Expansion Pressure of Compacted Soils Some typical R-values are: · Well-graded (dense gradation) crushed stone base course: 80+ · MH silts: 15-30
Transportation College, Southeast University 东南大学交通学院
R Pv Where Ph D
resistance value applied vertical pressure (160 psi) transmitted horizontal pressure at Pv = 160 psi displacement of stabilometer fluid necessary to increase horizontal pressure from 5 to 100 psi.
东南大学交通学院
Transportation College, Southeast University
4
Subgrade-Stiffness/Strength Tests
Resilient Modulus The Resilient Modulus (MR) is a subgrade material stiffness test. While the modulus of elasticity is stress divided by strain for a slowly applied load, resilient modulus is stress divided by strain for rapidly applied loads.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus A material is elastic if it is able to return to its original shape or size immediately after being stretched or squeezed. Almost all materials are elastic to some degree as long as the applied load does not cause it to deform permanently.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus
Subgrade-Stiffness/Strength Tests
Resilient Modulus-Stress Sensitivity of Moduli
Changes in stress can have a large impact on resilient modulus.
Example Stress-Strain Plot for Steel
Stress-Strain Plot Showing the Elastic Range
Resilient Modulus vs. Bulk Stress for Unstabilized Coarse Grained Materials
Transportation College, Southeast University 东南大学交通学院 Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus
Subgrade-Stiffness/Strength Tests
Resilient Modulus Tests
There are two fundamental approaches to estimating elastic moduli – laboratory tests and field deflection data/backcalculation: Resilient Modulus bearing plate. Diametral resilient modulus. HMA. Triaxial resilient modulus. here. This test is typically used on unbound materials such as soil and aggregate and is covered This test is typically used on
Resilient Modulus vs. Deviator Stress for Unstabilized Fine Grained Materials
Transportation College, Southeast University 东南大学交通学院 Transportation College, Southeast University 东南大学交通学院
5
Subgrade-Stiffness/Strength Tests
Resilient Modulus bearing plate
Subgrade-Stiffness/Strength Tests
Resilient Modulus bearing plate From elastic half space theory, surface deflection can be written as follow:
lr = 0 =
lr = a =
1)Initial tangent modulus 2)tangent modulus 3)secant modulus 4)Resilient modulus
2 pa (1 − µ02 ) E0
4 pa(1 − µ02 )
l=
2 pa(1 − µ02 ) π p( r ) = 1 pa ⋅ 2 a2 − r2 E0 4
π E0
Rigid bearing plate
Flexible bearing plate
Transportation College, Southeast University 东南大学交通学院 Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus bearing plate In China, we use 1mm linear regression method to calculate the subgrade resilient modulus.
Subgrade-Stiffness/Strength Tests
Resilient Modulus-Triaxial Resilient Modulus Test
In a triaxial resilient modulus test a repeated axial cyclic stress of fixed magnitude.
E=
πa (1 − µ 02 )
2
∑p ⋅ ∑l
i
While the specimen is subjected to this dynamic cyclic
i
stress, it is also subjected to a static confining stress provided by a triaxial pressure chamber.
东南大学交通学院 Transportation College, Southeast University 东南大学交通学院
Transportation College, Southeast University
Subgrade-Stiffness/Strength Tests
Resilient Modulus-Triaxial Resilient Modulus Test
Subgrade-Stiffness/Strength Tests
M R (or E R ) =
σd εr
Resilient Modulus-Triaxial
Resilient Modulus Test
AASHTO T 292: Resilient Modulus of Subgrade Soils and Untreated Base/Subbase Materials
where
MR (or ER) σd εr
resilient modulus (or elastic modulus since resilient modulus is just an estimate of elastic modulus) stress (applied load / sample cross sectional area) recoverable axial strain = ∆L/L
东南大学交通学院
Transportation College, Southeast University
Transportation College, Southeast University
..\FlashEXE\resilient
东南大学交通学院
6
Subgrade-Stiffness/Strength Tests
Resilient Modulus-Triaxial Test
1. The compacted specimen is a cylindrical sample normally 100 mm (4 in.) in diameter by 200 mm (8 in.) high (Figure 1a). 2.The specimen is enclosed vertically by a thin "rubber" membrane and on both ends by rigid surfaces (platens) as sketched in Figure 1b. 3.The sample is placed in a pressure chamber and a confining pressure is applied (s3) as sketched in Figure 1c.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus-Triaxial Test
4. The deviator stress is the axial stress applied by the testing apparatus (s1) minus the confining stress (s3). In other words, the deviator stress is the repeated stress applied to the sample. These stresses are further illustrated in Figure 2a. 5. The resulting strains are calculated over a gauge length, which is designated by "L" (refer to Figure 2b). 6. Basically, the initial condition of the sample is unloaded (no induced stress). When the deviator stress is applied, the sample deforms, changing in length as shown in Figure 2c. This change in sample length is directly proportional to the stiffness.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Subgrade-Stiffness/Strength Tests
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus- Strength/Stiffness Correlations A widely used empirical relationship developed by Heukelom and Klomp (1962) and used in the 1993 AASHTO Guide is: ESG (or MR) = (1500) (CBR) This equation is restricted to fine grained materials with soaked CBR values of 10 or less. Like all such correlations, it should be used with caution.
The proposed new AASHTO Design Guide will likely use the following relationship: MR = 2555 x CBR0.64 The 1993 AASHTO Guide offers the following correlation equation between R-value and elastic modulus for fine-grained soils with R-values less than or equal to 20. ESG (or MR) = 1,000 + (555)(R-value)
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus - Strength/Stiffness Correlations
Transportation College, Southeast University
东南大学交通学院
7
Subgrade-Stiffness/Strength Tests
Resilient Modulus - Strength/Stiffness Correlations
Subgrade-Stiffness/Strength Tests
Resilient Modulus - Strength/Stiffness Correlations
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade Reaction (k) The modulus of subgrade reaction (k) is used as a primary input for rigid pavement design. It estimates the support of the layers below a rigid pavement surface course (the PCC slab). The k-value can be determined by field tests or by correlation with other tests. There is no direct laboratory procedure for determining k-value.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade Reaction (k) The reactive pressure to resist a load is thus proportional to the spring deflection (which is a representation of slab deflection) and k (see Figure 4.11):
P = k∆
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade Reaction (k)
The modulus of subgrade reaction came about because work done by Westergaard during the 1920s developed the k-value as a spring constant to model the support beneath the slab (see Figure 4.10).
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade Reaction (k) Plate Load Test: Diameter
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
8
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade Reaction (k) Plate Load Test:
P=applied pressure (load divided by the area of the 762 mm (30 inch) diameter plate) Δ=measured deflection of the 762 mm (30 inch) diamter plate
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade Reaction (k) Plate Load Test: Relationship
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade- Deflection Testing Back-analysis of the surface deflection bowl data can be used to estimate the elastic modulus of the subgrade. This analysis is conducted using software packages such as EFROMD2 and ELMOD, etc. Some Austroads Member Authorities have developed other methods for estimating subgrade moduli values from deflection data.
Transportation College, Southeast University 东南大学交通学院
What is a FWD?
Comprised of a tow vehicle and trailer or self-contained in one vehicle Designed to impart a dynamic load to a pavement structure Measures deflection of the pavement surfaceSimulates a moving wheel load ..\FlashEXE\fwd[1].exe ..\FlashEXE\fwd area.exe
Transportation College, Southeast University 东南大学交通学院
What is a FWD Used For?
Structural capacity/remaining life estimates Load transfer efficiency between PCC pavement joints Void detection in PCC pavements Network level pavement management Project level pavement investigations Many research applications
Transportation College, Southeast University 东南大学交通学院
AC modulus
Transportation College, Southeast University
东南大学交通学院
9
AC modulus
AC modulus
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
Question and answer
1.论述路面材料对道路路面结构的重要性 2.土的物理性质主要包括哪及方面？物理性质与工程性质得关系如何？ 3.土基压实的重要性，压实标准（重、轻）的确定方法，压实度的控制， 压实度与路面结构稳定性的关系。 4.土基弹性模量的测定方法，土基设计弹性模量的取值，主要应考虑哪些 因素？ 5.ＣＢＲ试验方法，ＣＢＲ与路面结构设计的关系 6.各种土基设计指标的关系，如何考虑？ 7.减数路面结构层模量通过FWD反算的基本过程。 8.如果通过各层铣刨试验测定路面结构层的模量。 9.说明沥青路面各结构层模量的测定方法
Transportation College, Southeast University 东南大学交通学院
10
Introduction
When designing pavements, there are three
Pavement Design Parameters
fundamental external design parameters to consider:
东南大学交通学院 黄晓明 [email protected] Tel:8379 5184
the characteristics of the (1)subgrade and pavement structure upon which the pavement is placed, the (2)applied loads and the (3) environment
Transportation College, Southeast University 东南大学交通学院
Subgrade- Introduction
A subgrade’s performance generally depends on three of its basic characteristics: (1)Load bearing capacity.
Subgrade- Introduction
(2)Moisture content. Moisture content can be influenced by a number of things such as drainage,
The load bearing capacity is often affected by degree of compaction, moisture content, and soil type.
Transportation College, Southeast University 东南大学交通学院
groundwater table elevation, infiltration, or pavement porosity.
Transportation College, Southeast University 东南大学交通学院
Subgrade- Introduction
(3)Shrinkage and/or swelling. Shrinkage, swelling and frost heave will tend to deform and crack any pavement type constructed over them.
Transportation College, Southeast University 东南大学交通学院
Subgrade - Introduction
There are several methods available to improve subgrade performance: (1)Removal and replacement (over-excavation) (2)Stabilization with a cementitious or asphaltic binder (3)Additional base layers.
Transportation College, Southeast University 东南大学交通学院
1
Subgrade-Stiffness/Strength Tests
Subgrade materials are typically characterized
Subgrade-Stiffness/Strength Tests
Three basic subgrade stiffness/strength characterizations are commonly used:
by their resistance to deformation under load, which can be either a measure of their strength or stiffness.
(1)California Bearing Ratio (CBR) (2)Resistance Value (R-value) (3)elastic (resilient) modulus and (4) Subgrade Reaction (k) .
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR) The California Bearing Ratio (CBR) test is a wellgraded crushed stone (thus, a high quality crushed stone material should have a CBR @ 100%). It was developed by the California Division of Highways around 1930 and was subsequently adopted by numerous states, counties, U.S. federal agencies and internationally.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR) The basic CBR test involves applying load to a small penetration piston at a rate of 1.3 mm (0.05") per minute and recording the total load at penetrations ranging from 0.64 mm (0.025 in.) up to 7.62 mm (0.300 in.).
⎛ x⎞ CBR (%) = 100⎜ ⎟ ⎜ y⎟ ⎝ ⎠
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
⎛ x⎞ CBR (%) = 100⎜ ⎟ ⎜ y⎟ ⎝ ⎠
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
material resistance or the unit load on the where: x= piston (pressure) for 2.54 mm (0.1") or 5.08 mm (0.2") of penetration standard unit load (pressure) for well y= graded crushed stone for 2.54 mm (0.1") penetration = 6.9 MPa (1000 psi) for 5.08 mm (0.2") penetration = 10.3 MPa (1500 psi)
Transportation College, Southeast University 东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
2
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
Variation of CBR with Density and Moisture Content for a Clay(from Lay 1998)
Transportation College, Southeast University 东南大学交通学院 Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
50 40 30
Subgrade-Stiffness/Strength Tests
California Bearing Ratio (CBR)
Typical Presumptive Subgrade Design CBR Values Description of Subgrade Material USC Classification Typical CBR Values (%) Well Drained Poorly Drained
20 15 In s itu C a lifo rn ia B e a rin g R a tio (% )
10 8 6 5 4 3 2 4 5 10 20 30 40 60 80 100 P e n e tra tio n (m m /b lo w )
Highly Plastic Clay Silt Silty Clay Sandy Clay Sand
CH ML CL SC SW, SP
5 4 5-6
2–3 2 3-4
10-15
5-10
Correlation Between Dynamic Cone Penetration and CBR
Transportation College, Southeast University 东南大学交通学院 Transportation College, Southeast University 东南大学交通学院
3
Subgrade-Stiffness/Strength Tests
Resistance Value (R-value) The test procedure expresses a material's resistance to deformation as a function of the ratio of transmitted lateral pressure to applied vertical pressure. It is essentially a modified triaxial compression test.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resistance Value (R-value)
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resistance Value (R-value) The R-value test was developed by F.N. Hveem and R.M. Carmany of the California Division of Highways and first reported in the late 1940's.
Subgrade-Stiffness/Strength Tests
Resistance Value (R-value)
The R-value is calculated from the ratio of the applied vertical pressure to the developed lateral pressure and is essentially a measure of
R-value test was developed as an improvement on the CBR test.
Transportation College, Southeast University 东南大学交通学院
the material's resistance to plastic flow.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resistance Value
⎧ ⎫ ⎪ 100 (R-value) R = 100 − ⎪ ⎪ ⎪ ⎨ ⎬ ⎛ 2.5 ⎞ ⎡⎛ Pv ⎞ ⎤ ⎪ ⎪⎜ ⎟ ⎢⎜ ⎟ − 1⎥ + 1 ⎪ ⎝ D ⎠ ⎣⎝ Ph ⎠ ⎦ ⎪ ⎩ ⎭
Subgrade-Stiffness/Strength Tests
Resistance Value (R-value) Standard R-Value test methods are: AASHTO T 190 and ASTM D 2844: Resistance RValue and Expansion Pressure of Compacted Soils Some typical R-values are: · Well-graded (dense gradation) crushed stone base course: 80+ · MH silts: 15-30
Transportation College, Southeast University 东南大学交通学院
R Pv Where Ph D
resistance value applied vertical pressure (160 psi) transmitted horizontal pressure at Pv = 160 psi displacement of stabilometer fluid necessary to increase horizontal pressure from 5 to 100 psi.
东南大学交通学院
Transportation College, Southeast University
4
Subgrade-Stiffness/Strength Tests
Resilient Modulus The Resilient Modulus (MR) is a subgrade material stiffness test. While the modulus of elasticity is stress divided by strain for a slowly applied load, resilient modulus is stress divided by strain for rapidly applied loads.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus A material is elastic if it is able to return to its original shape or size immediately after being stretched or squeezed. Almost all materials are elastic to some degree as long as the applied load does not cause it to deform permanently.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus
Subgrade-Stiffness/Strength Tests
Resilient Modulus-Stress Sensitivity of Moduli
Changes in stress can have a large impact on resilient modulus.
Example Stress-Strain Plot for Steel
Stress-Strain Plot Showing the Elastic Range
Resilient Modulus vs. Bulk Stress for Unstabilized Coarse Grained Materials
Transportation College, Southeast University 东南大学交通学院 Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus
Subgrade-Stiffness/Strength Tests
Resilient Modulus Tests
There are two fundamental approaches to estimating elastic moduli – laboratory tests and field deflection data/backcalculation: Resilient Modulus bearing plate. Diametral resilient modulus. HMA. Triaxial resilient modulus. here. This test is typically used on unbound materials such as soil and aggregate and is covered This test is typically used on
Resilient Modulus vs. Deviator Stress for Unstabilized Fine Grained Materials
Transportation College, Southeast University 东南大学交通学院 Transportation College, Southeast University 东南大学交通学院
5
Subgrade-Stiffness/Strength Tests
Resilient Modulus bearing plate
Subgrade-Stiffness/Strength Tests
Resilient Modulus bearing plate From elastic half space theory, surface deflection can be written as follow:
lr = 0 =
lr = a =
1)Initial tangent modulus 2)tangent modulus 3)secant modulus 4)Resilient modulus
2 pa (1 − µ02 ) E0
4 pa(1 − µ02 )
l=
2 pa(1 − µ02 ) π p( r ) = 1 pa ⋅ 2 a2 − r2 E0 4
π E0
Rigid bearing plate
Flexible bearing plate
Transportation College, Southeast University 东南大学交通学院 Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus bearing plate In China, we use 1mm linear regression method to calculate the subgrade resilient modulus.
Subgrade-Stiffness/Strength Tests
Resilient Modulus-Triaxial Resilient Modulus Test
In a triaxial resilient modulus test a repeated axial cyclic stress of fixed magnitude.
E=
πa (1 − µ 02 )
2
∑p ⋅ ∑l
i
While the specimen is subjected to this dynamic cyclic
i
stress, it is also subjected to a static confining stress provided by a triaxial pressure chamber.
东南大学交通学院 Transportation College, Southeast University 东南大学交通学院
Transportation College, Southeast University
Subgrade-Stiffness/Strength Tests
Resilient Modulus-Triaxial Resilient Modulus Test
Subgrade-Stiffness/Strength Tests
M R (or E R ) =
σd εr
Resilient Modulus-Triaxial
Resilient Modulus Test
AASHTO T 292: Resilient Modulus of Subgrade Soils and Untreated Base/Subbase Materials
where
MR (or ER) σd εr
resilient modulus (or elastic modulus since resilient modulus is just an estimate of elastic modulus) stress (applied load / sample cross sectional area) recoverable axial strain = ∆L/L
东南大学交通学院
Transportation College, Southeast University
Transportation College, Southeast University
..\FlashEXE\resilient
东南大学交通学院
6
Subgrade-Stiffness/Strength Tests
Resilient Modulus-Triaxial Test
1. The compacted specimen is a cylindrical sample normally 100 mm (4 in.) in diameter by 200 mm (8 in.) high (Figure 1a). 2.The specimen is enclosed vertically by a thin "rubber" membrane and on both ends by rigid surfaces (platens) as sketched in Figure 1b. 3.The sample is placed in a pressure chamber and a confining pressure is applied (s3) as sketched in Figure 1c.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus-Triaxial Test
4. The deviator stress is the axial stress applied by the testing apparatus (s1) minus the confining stress (s3). In other words, the deviator stress is the repeated stress applied to the sample. These stresses are further illustrated in Figure 2a. 5. The resulting strains are calculated over a gauge length, which is designated by "L" (refer to Figure 2b). 6. Basically, the initial condition of the sample is unloaded (no induced stress). When the deviator stress is applied, the sample deforms, changing in length as shown in Figure 2c. This change in sample length is directly proportional to the stiffness.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Subgrade-Stiffness/Strength Tests
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus- Strength/Stiffness Correlations A widely used empirical relationship developed by Heukelom and Klomp (1962) and used in the 1993 AASHTO Guide is: ESG (or MR) = (1500) (CBR) This equation is restricted to fine grained materials with soaked CBR values of 10 or less. Like all such correlations, it should be used with caution.
The proposed new AASHTO Design Guide will likely use the following relationship: MR = 2555 x CBR0.64 The 1993 AASHTO Guide offers the following correlation equation between R-value and elastic modulus for fine-grained soils with R-values less than or equal to 20. ESG (or MR) = 1,000 + (555)(R-value)
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Resilient Modulus - Strength/Stiffness Correlations
Transportation College, Southeast University
东南大学交通学院
7
Subgrade-Stiffness/Strength Tests
Resilient Modulus - Strength/Stiffness Correlations
Subgrade-Stiffness/Strength Tests
Resilient Modulus - Strength/Stiffness Correlations
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade Reaction (k) The modulus of subgrade reaction (k) is used as a primary input for rigid pavement design. It estimates the support of the layers below a rigid pavement surface course (the PCC slab). The k-value can be determined by field tests or by correlation with other tests. There is no direct laboratory procedure for determining k-value.
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade Reaction (k) The reactive pressure to resist a load is thus proportional to the spring deflection (which is a representation of slab deflection) and k (see Figure 4.11):
P = k∆
Transportation College, Southeast University 东南大学交通学院
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade Reaction (k)
The modulus of subgrade reaction came about because work done by Westergaard during the 1920s developed the k-value as a spring constant to model the support beneath the slab (see Figure 4.10).
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade Reaction (k) Plate Load Test: Diameter
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
8
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade Reaction (k) Plate Load Test:
P=applied pressure (load divided by the area of the 762 mm (30 inch) diameter plate) Δ=measured deflection of the 762 mm (30 inch) diamter plate
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade Reaction (k) Plate Load Test: Relationship
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
Subgrade-Stiffness/Strength Tests
Modulus of Subgrade- Deflection Testing Back-analysis of the surface deflection bowl data can be used to estimate the elastic modulus of the subgrade. This analysis is conducted using software packages such as EFROMD2 and ELMOD, etc. Some Austroads Member Authorities have developed other methods for estimating subgrade moduli values from deflection data.
Transportation College, Southeast University 东南大学交通学院
What is a FWD?
Comprised of a tow vehicle and trailer or self-contained in one vehicle Designed to impart a dynamic load to a pavement structure Measures deflection of the pavement surfaceSimulates a moving wheel load ..\FlashEXE\fwd[1].exe ..\FlashEXE\fwd area.exe
Transportation College, Southeast University 东南大学交通学院
What is a FWD Used For?
Structural capacity/remaining life estimates Load transfer efficiency between PCC pavement joints Void detection in PCC pavements Network level pavement management Project level pavement investigations Many research applications
Transportation College, Southeast University 东南大学交通学院
AC modulus
Transportation College, Southeast University
东南大学交通学院
9
AC modulus
AC modulus
Transportation College, Southeast University
东南大学交通学院
Transportation College, Southeast University
东南大学交通学院
Question and answer
1.论述路面材料对道路路面结构的重要性 2.土的物理性质主要包括哪及方面？物理性质与工程性质得关系如何？ 3.土基压实的重要性，压实标准（重、轻）的确定方法，压实度的控制， 压实度与路面结构稳定性的关系。 4.土基弹性模量的测定方法，土基设计弹性模量的取值，主要应考虑哪些 因素？ 5.ＣＢＲ试验方法，ＣＢＲ与路面结构设计的关系 6.各种土基设计指标的关系，如何考虑？ 7.减数路面结构层模量通过FWD反算的基本过程。 8.如果通过各层铣刨试验测定路面结构层的模量。 9.说明沥青路面各结构层模量的测定方法
Transportation College, Southeast University 东南大学交通学院
10