Modulus of subgrade reaction fhwa us department of. But there should be one, as both are the measurements of soil capacities and any of these two parameters can be used to design a regular foundation. And one of the major functions of a highway pavement is to reduce the. For all new designs, particularly for critical projects, repeated load resilient modulus. Design resilient modulus of subgrade soils from fwd tests. Subgrade and pavement engineering fourth editionchinese. Subbase thickness10 subbase modulus30,000 psi subgrade m r10,000 psi to get k. This uptodate book covers both theoretical and practical aspects of pavement analysis and design. Estimating stiffness of subgrade and unbound materials for pavement design explores the significance of the resilient modulus property, various methods of determining this property of subsoils and unbound bases, and the application of this parameter in the mechanisticempirical pavement design guide. Evaluation of subgrade strength and flexible pavement. An example of design without soil strength test is by using hrb soil classification system, in which soils are grouped from a1 to a7 and a group index is added to differentiate soils within each group. To this end, this study evaluates the modulus of subgrade considering the effect of rap and moisture content at different stress levels in the laboratory. The kvalue can be determined by field tests or by correlation with other tests.
Thompson subgrade soils play an integral part in pavement performance. Indianadepartmentoftransportation 100northsenateavenue room1101 indianapolis. Accordingly, we can use dcp testing to estimate the subgrade resilient modulus for new pavement design and base course and subgrade moduli for rehabilitation design. The upper 500 mm of soil, whether in embankment or in cutting, compacted to a higher density than that of the native soil below it is considered as the subgrade of a flexible pavement as per the current practice in india. A solid subbase is a key to a successful building project. Recommendation give serious consideration to developing generalized resilient modulus relationships to obtain in a practical manner design values for route use. The final iterated value for resilient modulus is the design resilient modulus. The subgrade is extremely essential, as it is the foundation of the pavement. A subbase will go on top of the subgrade, which typically is native soil or improved soil that has been compacted. The modulus of subgrade reaction, which is defined as the ratio between an applied pressure q and the deflection. The parameter is expressed in units of force length 3.
The subgrade modulus, also known as the modulus of subgrade reaction, is a stiffness parameter typically used in defining the support conditions of footings and mat foundations, such as that shown on figure 1. Pavement components, for use in evaluation and design of airport and. Hence the performance of the pavement is affected by the characteristics of the subgrade. The modulus of subgrade reaction is an often misunderstood and misused concept for the. Aci the modulus of subgrade reaction is an often misunderstood and misused concept for the thickness design of slabsonground. It is a required input in the aashto method of flexible pavement design. Subgradefoundation design inputs transportation research board. Historically, numerous techniques have been applied by a multitude of jurisdictions dealing with roadway pavements. A subgrade that is not properly installed or compacted will compromise the pavements structure in the future.
Developing subgrade inputs for mechanisticempirical. Pavement subgrade, unbound materials, and nondestructive. Nov 09, 2015 accordingly, we can use dcp testing to estimate the subgrade resilient modulus for new pavement design and base course and subgrade moduli for rehabilitation design. Characterization of subgrade soil mixed with recycled. There is a better correlation in huangs pavement design book, but thats reasonably close. Design outputs are compared for mean, maximum likelihood and median rvalue inputs in terms of reliability and thickness using different design procedures. Adjustments are made and iterations continue until the values used to predict subgrade modulus reasonably match the calculated stresses in the pavement system.
The subgrade is the in situ material upon which the pavement structure is placed. Characterization of subgrade resilient modulus for mepdg and. The resilient modulus of the underlying material supporting the pavement is now considered as a key material property in the aashto mechanisticempirical design procedure. Attempts have been made by researchers to predict the subgrade resilient modulus from laboratoryfield experimental methods based on the soil properties. Strength indices like the california bearing ratio cbr have been commonly measured in the past as an overall indication of material quality in terms of stiffness and resistance to permanent deformation. Pavement design and materials is a practical reference for both students and practicing engineers that explores all the aspects of pavement engineering, including materials, analysis, design, evaluation, and economic analysis. If deflection testing is not performed, laboratory tests of subgrade samples should be performed to determine the resilient modulus of subgrade soil. A spring constant, or spring value, is defined as the ratio of vertical load to vertical. Base and subgrade layers must provide adequate and moisture resistant strength that meets the design modulus, in addition to durability and stability. Physically however, it is defined as the contact bearing pressure of the. It consists of superimposed layers of selected and processed. Resilient modulus mr is a fundamental material property used to characterize unbound pavement materials. This is a subgrade modulus method with nonlinear depth dependent.
It is a measure of material stiffness and provides a mean to analyze stiffness of materials under different conditions, such as moisture, density and stress level. The resilient modulus of subgrade soils is a required input parameter for the aashto method of flexible pavement design and is also used to compute the modulus of subgrade reaction for the aashto rigid pavement design equations. The dominant geotechnical factors for many pavement distresses isare the stiffness andor strength of the unbound subgrade materials. Selection of subgrade modulus for pavement overlay design. The modulus of subgrade reaction k is used as a primary input for rigid pavement design. This is a subgrade modulus method with nonlinear depth dependent loaddeformation characteristics representing the pilesoil interaction.
Therefore applicability of the resilient modulus for the design. The analytical relationship between a soils resilient modulus and it modulus, of subgrade reaction is a follows. Characterization of subgrade soil mixed with recycled asphalt. It estimates the support of the layers below a rigid pavement surface course the pcc slab.
This geotechnical special publication contains 10 papers on timely and important issues related to characterization of pavement subgrade and unbound materials using new analytical and experimental techniques. Pavement performance can be largely attributed to the care given in designing and preparing its foundation, which is comprised of the subgrade and base layers. The american petroleum institute api code prescribes a methodology known as py method, which is widely used for design of offshore piles. The effective modulus of the pavement structure is determined by m r and deflection at the center of loading area. All subgrade and unbound pavement layers for all pavement types are characterized using m r in the nchrp 7a design methodology. The modulus of subgrade reaction has been traditionally used in pavement design as a representation of the stiffness of the subgrade soils under short duration, transient loading. The introduction of the resilient modulus into routine pavement design caused considerable concern and discussion among engineers re. The 1986 aashto guide for design of pavement structures 1 adopted the resilient modulus as the subgrade soil property controlling the design of flexible pavements. Estimating stiffness of subgrade and unbound materials for. All that being said, the modulus of subgrade reaction doesnt greatly affect the thickness of the slab in reasonable increments. Cut across the e sb cut across m r to the tl vertically meet other line read kvalue k600pci topic 10 aashto rigid pavement design figure 12. Laboratory determination of resilient modulus for flexible pavement design 2004 chapter.
Since pavement life and surface deflection are strongly related, resilient modulus is a fundamental and rational material property that needs to be included in pavement design. Because lower values of subgrade resilient modulus result in more pavement damage, lower values of subgrade resilient modulus are weighted more heavily. This manual is neither a textbook nor a substitute for engineering. It is recommended that this design value be used to calculate pavement thickness requirements for all pavement types under consideration for the project. The resilient modulus mr of a subgrade soil is an essential input into the flexible pavement design models contained in the american association of state highway and transportation officials new pavement design guide, the mechanisticempirical pavement design guide mepdg. Structure magazine correlation between soil bearing. In the current design and redesign of driving surfaces like pavement, it is crucial to understand the limitations of the underlying subgrade ground beneath the surface. Common subgrade theories used for concrete pavements. The soil bearing capacity is 50 knm2 and soil is soft clay soil but to analyze this foundation in safe i need to know the subgrade modulus k value so any one can suggest the conservative k value range for this type of soil and. Design of pavement structures 1993 requires selecting a value for the design subgrade resilient modulus.
As a result, we felt that the time was right for recapturing the pavement engineering state of the art in a textbook. Thus, a new formula form is developed in this book, as shown in eq. Trbs national cooperative highway research program nchrp synthesis 382. Evaluation of engineering performance of subgrade material mixed with rap is important for pavement design and new constructions.
These stresses are compared to those assumed values used in the initial iteration. The effects of variations in subgrade resilient modulus on various design parameters and on the aashto design thickness are examined. The structural design of concrete pavements according to aashto and pca methods makes use of modulus of reaction k from the subgrade and subbasesubgrade system as parameter to calculate slab. An empirical analysis of flexible pavement design can be done with or with out a soil strength test. Soilpropertybased subgrade resilient modulus estimation. The overall strength and performance of a pavement is dependent not only upon its design including both mix design and structural design but also on the loadbearing capacity of the subgrade soil.
The standard method in the 1993 aashto guide for design of pavement structures involves calculating a weighted average subgrade resilient modulus based on the relative pavement damage. Pavement subgrade, unbound materials, and nondestructive testing. Cbr or modulus value, for the combination of a capping layer and a semiinfinite subgrade. The pavement response model for rigid pavement design, however, is based on a winklerspring foundation model that requires a value for the modulus of subgrade reaction k dynamic see appendix d for more details on. The structural design of concrete pavements according to aashto and pca methods makes use of modulus of reaction k from the subgrade and subbase subgrade system as parameter to calculate slab. This procedure is calibrated to provide the worst case scenario for the foundation. The aastho design guide 1993 recommends a design subgrade resilient modulus equal to 33% of that back calculated from fwd data for flexible pavement and 25% of the backcalculated value for pcc pavement. Modulus of subgrade reaction which one should be used. Subgrade resilient modulus for design purposes is usually less than the value directly from fwd data. Minimum rvalue assessment for making the decision of subexcavation is also performed. Proceedings of sessions of geodenver 2000, held in denver, colorado, august 58, 2000. Take cores and perform lab tests strongly recommended. This paper describes how a lot of resilient modulus research work has been completed recently, mostly in the long term pavement performance ltpp study.
Next, an extensive laboratory testing program, several back calculation analyses, and overlay thickness designs were completed. According to the chinese specifications of asphalt pavement design for highway, 6 the. It includes some of the latest developments in the field, and some very useful computer softwaredeveloped by the authorwith detailed instructions. The tendency for pavement to be more flexible in nature gives increased importance to the properties and condition of the underlying soil subgrade. A number of states have already developed generalized resilient modulus relationships for use in design, particularly for cohesive subgrade soils. The most common and probably the safest answer to the question of correlation between bearing capacity and the modulus of subgrade reaction is that there is no correlation. The modulus of subgrade reaction is an often misunderstood and misused concept for the thickness design of slabsonground.
The subgrade design for the trackbed, however, is primarily relying on the static test results such as and deformation modulus, ev. Jan 09, 2008 pavement design and materials is a practical reference for both students and practicing engineers that explores all the aspects of pavement engineering, including materials, analysis, design, evaluation, and economic analysis. Selection of subgrade modulus for aashto flexible pavement. This value may be based on laboratory testing, back calculation programs using deflection measurements, resilient modulus correlation studies, or the equation presented in the aashto overlay design procedures based on deflection measurements. A slab on ground and pavements normally are designed to be supported by a solid subbase, which needs to be uniform by nature to support the structure above it. In roadway pavement design, one must consider the performance of the pavement structure and mixture design. The resilient modulus value 3,000 psi used to represent the. Subgrade impact to pavement performance benchmark inc.
Selection of subgrade modulus for aashto flexible pavement design. Pdf models to estimate k subgrade reaction modulus. Pavement design manual july 15, 2016 update this file contains. Soilpropertybased subgrade resilient modulus estimation for flexible pavement design kevin 0. Estimating stiffness of subgrade and unbound materials for pavement design explores the significance of the resilient modulus property, various methods of determining this property of subsoils and unbound bases, and the application of this parameter in the mechanisticempirical pavement. Pdf subgrade resilient modulus for pavement design and. Flexible pavement empirical design example pavement interactive. Read laboratory determination of resilient modulus for. This procedure is calibrated to provide the worst case scenario for the foundation behavior under static. Aasho road test subgrade in the aashto flexible pavement design equation is examined. The test involves driving a conetipped rod into the unbound layers by dropping a sliding hammer from a prescribed height onto an anvil attached to the rod as illustrated in. It consists of superimposed layers of selected and processed materials. This file contains the july 15, 2016 update to the pavement design manual pdm.
Estimating stiffness of subgrade and unbound materials for pavement design. Models to estimate k subgrade reaction modulus values based. Although there is a tendency to look at pavement performance in terms of pavement structure and mix design alone, the subgrade can often be the overriding factor in pavement performance. There is no direct laboratory procedure for determining kvalue. With some judgment, k values obtained from field testing can be used for pavement design purposes. Implementation of subgrade resilient modulus for pavement 2.