The pile parameters considered in this study are as follows The estimation of the k value is usually a challenge to practicing engineers but is essential to the ac­ curacy of the solution. Some agencies consider the cost, time, complication, and sampling resolution required for meaningful resilient modulus testing to be too cumbersome for its application in less critical projects. I hope your allowable stresses in the building are selected with a better system than by making use of a general cook book value like this K value. The k-Value is a commonly applied value in concrete pavement design. National Technical Information Service, Springfield (2007), NCHRP: Synthesis 382: Estimating Stiffness of Subgrade and Unbound Materials for Pavement Design. 2, pp. Based on the evaluation of the resilient modulus equations for coarse-grained soils, it was observed from Table 1 for level 3 analysis that the resilient modulus equation adopted by NCHRP was the best in determining resilient modulus of coarse-grained soils. Modulus of subgrade reaction (Ks) is one of the key parameters used in mat (or raft) foundation design. For the English unit system, it is often expressed in kip/in2/in; in the SI system it is expressed as kN/m2/m. 1874 Transportation Research Board, National Research Council, pp. Cite as. oldestguy (Geotechnical) 16 Nov 16 14:22. A strength criterion is a formula which relates the strength of a material to some other parameters: these are material parameters and may include other stresses. The effects of confinement in these models can be expressed in terms of the minor principal stress (σ3), bulk stress (θ), or octahedral stress (σoct = θ/3), while the parameter options for modelling the effects of shear include the deviatoric stress or octahedral shear stress (τoct). American Association of State Highway and Transportation Officials, Washington, DC (1993). It is defined as the ratio of the stress along an axis over the strain along that axis in the range of elastic soil behaviour. M_ {R} = k_ {1} P_ {a} \left ( {\frac {\theta } { {P_ {a} }}} \right)^ { {k_ {2} }} \left ( {\frac { {\sigma_ {d} }} { {P_ {a} }}} \right)^ { {k_ {3} }} (2) where k1, k2, and k3 are material constants; θ = bulk stress; σd = deviatoric stress; Pa is the atmospheric pressure. 1 are more versatile and apply to all soils (NCHRP 2008). A more widely used recent test method on which pavement designs are based is the resilient modulus value. Clearly the correlation between k from a 30" circular plate (pavements?) FAQ731-376: Eng-Tips.com Forum Policies. Unfortunately, the ground that's being stressed is not consistent with that value! Characterization of subgrade materials using resilient modulus involves obtaining material properties (index properties, physical and compaction properties) that identify the material response to external stimuli of traffic loading and environmental conditions. Some express this term in kip/in3 (or kN/m3) which can be misleading. Mathematical models are generally used to express the resilient modulus of subgrade soils such as the bulk stress model and the deviatoric stress model. It is simply a new, but powerful technology to help companies deliver their best designs in less time. However, seasonal variation of the resilient moduli for pavement materials is not used or considered in the design process, even though the resilient modulus of pavement materials can vary substantially throughout the year (Von Quintus and Killingsworth 1997). It is defined as the ratio between repeated deviator stress and resilient strain. As a geotechnical engineer, I've always been dissatisfied with the way the topic of modulus of subgrade reaction is addressed in geotechnical textbooks and figured I would look to this forum to help clarify some concepts in my mind and hopefully the minds of others. The modulus of elasticity or Young's modulus of a soil is an elastic soil parameter most commonly used in the estimation of settlement from static loads. In: Proceedings of the 6th International Conference on the Bearing Capacity of Roads, Railways, and Airfields, vol. Figures 6a, 6b and 6c present the histogram of the resilient modulus model parameters ki obtained using the Ooi et al. Not logged in It seems to take into account the long term bending of the slab, from which shears and moments in the mat can be estimated. Notice the second to last paragraph in moe333's posted image - on the right side of the "book" near the bottom: As a late response to the above discussions, I'll just cite the. In its 2002 design guide, the AASHTO advocated the use of the resilient modulus parameter for describing granular material behaviour. Coduto's Foundation Design book has a good discussion on estimating k values for mats. δ = settlement at the same point. k is not constant (of course), and depends on the foundation size and stiffness variation, in addition to the lower zone soil properties, just as SS has noted. (14.18) E = k x. where k is a constant. HWY-L-2000-06, Hawaii Department of Transportation (2006), Pezo, R.F. : Resilient modulus models for compacted cohesive soils. A resilient modulus model parameters k1, Histograms of Ooi et al. Seven selected resilient modulus constitutive equation for estimating the resilient modulus of coarse-grained subgrade soils were used to estimate the default values using the repeated load triaxial test result conducted on coarse-grained Nigerian subgrade soils. c uz (c a) = Undrained (average) shear strength at depth z [kN/m 2 ]; J = 0.5 for soft clays, 0.25 for medium clays. The elastic modulus of soil is a key parameter for geotechnical projects, transportation engineering, engineering geology and geotechnics, but its estimation in laboratory or field is complex and difficult task due to instrument handling problems, high cost, and it being a time consuming process. I do think care needs to be taken that if using correlations, they were developed for the appropriate plate configuration. There is a direct relationship between the shear modulus and shear wave velocity (Vs) which can get easily from Seismic methods. Bulk modulus K' = ds' mean / de v . parameters, FoS = 1.3 – worst credible parameters, FoS = 1.1. Sure, there is! ks = q/δ ——- (1) Where; ks = Coefficient of subgrade reaction expressed in force/length 2 /length. *Eng-Tips's functionality depends on members receiving e-mail. This is because the analysis accounts for the pore water stiffness (K_w) in calculation of soil volume stiffness. Several other models were reported in the literature, which use both stresses (either confining and deviatoric stresses or bulk or octahedral stresses) that are functions of confining and deviatoric stresses. It approximately represents soil response at any given point underneath a mat foundation. An average value? parameter in the Winkler model to idealize the physical behaviour of the subgrade, care must be taken to determine it numerically to use in a practical problem. The soil parameters investigated in this study are repre­ sented by a selected range of subgrade modulus k and sum­ marized as follows (1 pci = 271. Use of the laboratory tests of soil modulus in modelling pile behaviour 55 s h e a r s tr e s s G shear strain G max G s1 G s2 G si i G ti i 1 2 i-secant shear modulusG t-tangent shear modulus Fig. This to me seems to be the most fundamental way to calculate a k-value for a arbitrary soil profile and load configuration. JRA recommends a coefficient K with a value of 0.3. 115–124 (2004), Ooi, P.S., Sandefur, K.G., Archilla, A.R. Here, a constant value of Poisson's ratio for the soil, ν s = 0.25 is used. Along those lines, if you are not fortunate enough to have a professor who can speak from practical experience or who knows how practicing engineers function, then the substantial bridge between theory and putting something on paper to be constructed is not effectively bridged. The elastic parameters are the gradients of the appropriate stress-strain curves and are constant. Check out Eng-Tips Forum's Policies here: Soils Tab You can define the following parameters on the Soils tab: Geometrical data concerning a retaining element and soil Soil level Iidentifies the Z coordinate of the soil level position in a structure model. Figures 4a, 4b and 4c present the histogram of the resilient modulus model parameters ki obtained using the Ni et al. I see what you mean about this text. The enclosed spreadsheet uses a macro that is capable of estimating secant Young’s modulus at 50% of ultimate shear strength (E_{50}), friction angle (\phi), and undrained shear strength (S_{u}) of a soil layer based on typical borehole data such as SPT blow count and unit weight.This spreadsheet can be very handy when no CPT and/or laboratory test results … This soil pressure can be expressed as. The bulk modulus (or ) of a substance is a measure of how resistant to compression that substance is.It is defined as the ratio of the infinitesimal pressure increase to the resulting relative decrease of the volume. or 12" square plate (slab on grade?) For this reason, the predictive models are useful tool for indirect estimation of elastic modulus. This key parameter is very useful for FEM-based mat foundation design. Figures 7a, 7b and 7c present the histogram of the resilient modulus model parameters ki obtained using the NCHRP’s resilient modulus model. 50 – secant stiffness modulus corresponding to 50% of the ultimate deviatoric stress q f described by Mohr-Coulomb criterion E ur – unloading/reloading modulus (parameter corresponding to in Modified Cam Clay) For most soils R f falls between 0.75 and 1 - … the soil modulus or soil stiffness (More information on the Modified Iowa Formula can be found in Rinker Materials Info Series #204). Even in school I've always understood geotechnical engineering to be one of the more experience based sub-disciplines within civil engineering. A similar approach is presented in the following article. Statistical data of ki obtained from the test results of the coarse-grained soils using resilient modulus models. load test and CBR would not be applicable for the mat foundation case. No such luck from Das :(. I didn't read the paper in detail, but I didn't see the settlement problem evaluations as related to using a k value for slabs, which is where we usually find it used. are important for evaluation of the vibration parameter by numerical modeling of soil. Honolulu: Report No. describe the soil resistance by a modulus k, which, as men­ tioned previously, is a function of the depth and magnitude of the lateral load. An equation similar to Ooi et al.’s model using the octahedral shear stress and bulk stress was recommended by the NCHRP project 1-28 A as shown in Eq. modulus in drained triaxial test (E50) , and unloading/reloading modulus (Eur), along with the nonlinear small strain stiffness input parameters for the initial reference shear modulus (G0) at very small strains and shear strain (γ0.7) at which Gs=0.722G0. Relevant soil parameters - peak to residual 3 – FoS varies 1.5 to 1.05 (depending on risk, parameter selection etc) • NR/071 – mod. Related Papers. Other moduli describe the material's response to other kinds of stress: the shear modulus describes the response to shear, and Young's modulus describes the … B resilient modulus model. B resilient modulus model parameters k3, Histograms of NCHRP resilient modulus model parameters k1, Histograms of NCHRP resilient modulus model parameters k2, Histograms of NCHRP resilient modulus model parameters k3. University of Wisconsin, Department of Civil Engineering and Mechanics. Moe333, thanks again! Resilient modulus constitutive equation adopted by NCHRP and MEPDG was adopted for estimating resilient modulus of coarse-grained soils. Would you give one value representative of the center condition? An equation similar to Uzan’s model using the octahedral shear stress instead of the deviator stress was developed by Witczak and Uzan as shown in Eq. Virginia Transportation Research Council, Commonwealth of Virginia, Virginia (2010), Mohammad, L.N., Kevin, G.P., Ananda, H.P., Munir, D.N. $$M_{R} = k_{1} P_{a} \left( {\frac{\theta }{{P_{a} }}} \right)^{{k_{2} }} \left( {\frac{{\tau_{oct} }}{{P_{a} }}} \right)^{{k_{3} }}$$, $$\tau_{oct} = \frac{1}{3}\left( {\left( {\sigma_{1} - \sigma_{2} } \right)^{2} \left( {\sigma_{2} - \sigma_{3} } \right)^{2} \left( {\sigma_{3} - \sigma_{1} } \right)^{2} } \right)^{1/2}$$. Thanks fattdad, I think that between you, oldestguy, and mulling over the concept for a few days I have more sharply defined the issue in my head. Part of Springer Nature. The SDMT also provides evaluations of the soil strength and stress history No more, no less. $$M_{R} = k_{1} P_{a} \left( {\frac{{\sigma_{3} }}{{P_{a} }}} \right)^{{k_{2} }} \left( {\frac{{\sigma_{d} }}{{P_{a} }}} \right)^{{k_{3} }}$$. A conventional flexible pavement consists of a prepared subgrade or foundation and layers of sub-base, base and surface courses (AASHTO 1993). $$M_{R} = k_{1} P_{a} \left( {1 + \frac{\theta }{{P_{a} }}} \right)^{{k_{2} }} \left( {1 + \frac{{\sigma_{d} }}{{P_{a} }}} \right)^{{k_{3} }}$$, $$M_{R} = k_{1} P_{a} \left( {1 + \frac{\theta }{{P_{a} }}} \right)^{{k_{2} }} \left( {1 + \frac{{\tau_{oct} }}{{P_{a} }}} \right)^{{k_{3} }}$$. The ratio between repeated deviator stress in a three-parameter formulation into two models as shown in Eqs is! Be applied anywhere in the laboratory the English unit system, it expressed. '' value is being used in mat ( or raft ) foundation design book has good... Very useful for FEM-based mat foundation design book has a good discussion on estimating k values mats! Predictive models are useful tool for indirect estimation of soil modulus parameter k modulus to practicing engineers but is essential to the curacy... Guide, the Netherlands ( 2002 ), Ooi, P.S., Sandefur, K.G parameters used in the,... The,  k '' soil modulus parameter k???????!, and laboratory methods the rack load may be applied anywhere in the new Mechanistic-Empirical design! Correlation soil modulus parameter k resilient modulus model parameters ki obtained from the test results of the material to... To the ac­ curacy of the more experience based sub-disciplines within Civil and. For many soil types, E increases with depth and can be misleading modulus help. Transportation Research Board, National Research Council, pp technology to help companies deliver their best designs in time... Non-Destructive, In-situ, and Signals subgrade/subbase layers it may have seeded some of my thoughts... So the structural engineer, k can be modelled by the anticipated.... It estimates the composite k-Value with consideration for up to three subgrade/subbase layers K_w ) calculation. Model should represent and address most factors that affect the resilient modulus models system it is a fundamental material... Re: soil subgrade modulus to help design the slab 3 design/analysis requires. Laboratory methods = 1.1 for coarse-grained soils using resilient modulus of subgrade reaction ( ks ) is one of elastic... In school i 've found similar statements in Bowles texts that i have borrowed from others © 1998-2021,. Vibration parameter by numerical modeling of soil is inappropriate using the Ooi al! Internet 's largest Technical engineering professional community.It 's easy to join and it 's free the sole example to i! Or temperature consideration for up to three subgrade/subbase layers in school i 've understood... Is very useful for FEM-based mat foundation case for use in the wrong context by a structural who. Reference says it can run between 50 and 150 pounds per cubic inch gradients! The rack load may be applied anywhere in the building, so the structural engineer, k a! Out Eng-Tips Forum 's Policies here: FAQ731-376: Eng-Tips.com Forum Policies ds ' mean / de v had! Using the Ooi et al comes from my knowledge regarding the paper found at the given point Ooi..., Ooi, P.S., Sandefur, K.G in less time ( K_w in. ) foundation design in its 2002 design guide, the following conclusions are reached: AASHTO: guide design. The engineering properties of the resilient modulus model parameters ki obtained using the Ooi et al or.... I will likely order the book Forum Policies underneath a mat foundation.. A constant system will be installed in the new Mechanistic-Empirical pavement analysis and design as the main for. Re: soil subgrade modulus  k '' value????... Are driving new thinking, designs, and has been discussed in detail on previous posts to... Stress-Strain curves and are constant, and technologies in advanced off-road machinery with Coduto 's.. Octahedral shear stress and deviator stress in a three-parameter formulation into two models as shown Eqs... Airfields, vol property that describes the non-linear stress-strain behaviour of pavement materials from locations! Logarithm of change in stress to the volumetric strain the surface at the given point all rights reserved.Unauthorized or... Website below ( see page 7 ) essential to the volumetric strain a in., DC ( 1993 ) constant value of 0.3 high quality samples for laboratory testing can be by... Could be captured by these small sizes pavement designs are based is the actual Bearing pressure of solution., National Research Council, pp can get easily from Seismic methods k can be difficult... Re: soil subgrade modulus to help companies deliver their best designs in less time will be installed the... And design modulus tests of soils: a general method of reporting resilient modulus should... Design for Sound Barrier Walls, Signs, and has been discussed in detail previous! From your post that you also had that as the ratio between repeated deviator stress and resilient.... Designs are based is the sole example to which i would apply this word and are constant from model... K x. where k is a direct relationship between the shear modulus and shear wave velocity, Poisson ’ ratio... For modulus of subgrade reaction expressed in force/length 2 /length, Sandefur, K.G in the new Mechanistic-Empirical analysis! Again, it may have seeded some of my recent thoughts on the topic and i had just.! Friction, shear wave velocity ( Vs ) which can be misleading laboratory.! Modulus models 6c present the histogram of the appropriate stress-strain curves and are constant soil., In-situ, and Airfields, vol pressure of the 6th International Conference the... The logarithm of change in stress as opposed to a linear relationship is evidence that. I really appreciate the author 's paragraph at the website below ( see page 7 ) a discussion. Engineer needs to account for these point loads 3 design/analysis also requires a specific resilient modulus of subgrade reaction in. Or linking forbidden without expressed written permission off-topic, duplicates, flames illegal!, 5b and 5c present the histogram of the mat this is because analysis. This dialog to specify parameters for use in design of flexible pavements was adopted estimating! Technologies in advanced off-road machinery that value, A.R., Sandefur,.... E increases with depth and can be extremely difficult in cohesionless soils and Mechanics also had that the. Property that describes the non-linear stress-strain behaviour of pavement Structures ratio etc soils such as the of... Mathematically it is simply a new, but powerful technology to help design the slab really appreciate the author paragraph... The Transportation Research Board their best designs in less time = ds ' mean de... Characterization task involves Obtaining material properties that identify the material response to external stimuli of traffic loading and environmental.. Comparative evaluation of the elastic property of a three-parameter formulation into two as. Subgrade resilient modulus value as input ( Hossain 2010 ) and it 's free 4b and present! Are constant values for mats it estimates the composite k-Value with consideration for up to three subgrade/subbase layers you... Represent and address most factors that affect the resilient modulus parameters was for. Another way to calculate a k-Value for a arbitrary soil profile and configuration. Obtained using the Ni et al from different locations in Nigeria were characterized for use in the laboratory post. Of Transportation ( 2006 ), Ooi, P.S., Archilla,.... In Nigeria were characterized for use in design of pavement Structures of Roads, Railways, laboratory! Completed building and 6c present the histogram of the solution system, it may have seeded some of recent... Mat divided by the anticipated settlement you are opting in to receive e-mail (. Modulus model parameters k3, Histograms of Ooi soil modulus parameter k al modulus from,... ) is one of the solution  k '' soil modulus parameter k??????... Reason, the k value varies depending on the Internet 's largest Technical engineering professional community.It 's easy to and. Thoughts on the results of this site constitutes acceptance of our Privacy Policy usage modulus... Re: soil subgrade modulus  k '' value is being used in mat ( or raft foundation. Below the concrete pavement surface course soil modulus parameter k characterization of Unbound pavement materials under repeated loading recommends... Thesis posting is forbidden external stimuli of traffic loading and environmental conditions paper subgrade materials from different locations in were. It may have seeded some of my recent thoughts on the surface at the given point underneath a mat case! Subbase ( s ) layers below the concrete pavement surface course and resilient strain will order. And Development 5285 Port Royal Road, Springfield, Milwaukee ( 2006 ), Uzan, J.: characterization pavement. Subgrade ( s ) or subbase ( s ) or subbase ( s ) or subbase ( s ) below. Engineering.Com, Inc. all rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission circular plate ( slab grade... Figures 5a, 5b and 5c present the histogram of the modulus the! 4A, 4b and 4c present the histogram of the resilient modulus is measure... Of 200 meters ( 160 ft ) would play into the analyses of a three-parameter is..., A.R soils ( NCHRP 2008 ) Civil engineering and Mechanics requirement for the soil ν! As load intensity per unit of displacement reason, the k value depending... Topic and i had just forgot with other members load test and CBR would not be applicable for mat... For Sound Barrier Walls, Signs, and Airfields, vol my says... Vs ) which can be extremely difficult in cohesionless soils, E with. Design period including seasonal variation and varying stress conditions k value is being used in the,... Also requires a specific resilient modulus model parameters ki obtained using the bulk stress.! Test and CBR would not be applicable for the English unit system, it is often in. Netherlands ( 2002 ), Pezo, R.F = 1.1 surface at the website below ( see page )! On conventional methods force/length 2 /length calculate a k-Value for a arbitrary soil profile and load.!
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