This paper presents the procedure of evaluation of the modulus of elasticity e and the modulus of subgrade reaction k s value based on the california bearing ratio cbr tests and fem analysis. The california bearing ratio cbr test is commonly used to determine the suitability of a soil as a. Westergaards modulus of subgrade reaction kvalue is used for designing rigid concrete pavements. Resilient modulus is a measure of the elastic response of a soil e. 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 like those experienced by pavements. A subbase will go on top of the subgrade, which typically is native soil or improved soil that has been compacted. In the field, the determination of k for concrete pavement design is gen erally done for a deformation of 0. Cbr, rvalue and index tests were performed on tropical residual soils from four locations on the island of oahu in the state of hawaii. E, subgrade reaction modulus k kvalue, and california bearing. The increase in stiffness with the increase in cement kiln dust due to the reaction of the stabilizer with the clay material and the. The modulus of subgrade reaction k is used as a primary input for rigid pavement design. Subgrade reaction modulus k s of clayey soils based on field tests 2025 the ultimate soil pressure is at a settlement of. A sdvosb service disabled veteran owned small business. The modulus of subgrade reaction, which is defined as the ratio between an applied pressure q and the deflection.
Evaluation of subgrade stabilization on pavement performance. Comparison of the dynamic cone penetrometer with other. California bearing ratio cbr, plate load test plt, modulus of elasticity e, modulus of subgrade reaction k. The modulus of subgrade reaction k used in the aashto guides is also correlated to mr. The correlations were presented in blowsinch cbr curves from dcp tests, and the bearingcapacity cbr curve from static cone penetration tests. Why use the modulus of subgrade reaction it was previously stated that to design a flexible mat foundation, the modulus of subgrade reaction is used instead of bearing capacity of soil. Very little work has been reported for the correlation between modulus of subgrade reaction ks and cbr test though the mechanism of deformation is similar. In this case, the ratio between contact pressure and displacement of pile referred to as the coefficient of horizontal subgrade reaction, kh terzaghi 1955. Cbr, rvalue and index tests were performed on tropical residual soils from four.
The subgrade reaction modulus is determined as the ratio between the normal stress and the settlement from 0 to 1. The california bearing ratio or cbr test table 527 is an indirect measure of soil. Development of a chart for preliminary assessments in. Transportation researcii rtcord i 196 resilient modulus and aashto pavement design ronrnr p. The kvalue can be determined by field tests or by correlation with other tests. Modulus of subgrade reaction which one should be used. It means that as the consistency of soil decreases the modulus of subgrade reaction decreases. Subgrade characterization plays a key role in the thickness design of airport pavements.
It also presents how evd can be linked with cbr and thus be useful for pavement design, but also with the subgrade reaction modulus k of the assessed soils. Hence, the modulus of subgrade reaction, which is the function of soil settlement and the external pressure,is used for flexible foundation design. I have found some information related to this while. Subgrades be composed of a wide range of materials although some are much better than. Correlation between subgrade reaction modulus and cbr for.
Using the e values, modulus of subgrade reaction can be calculated and vice versa as well. The frequency or distance of sampling depends on the level of investigation, uniformity of soils, and the potential for detrimental reaction from chemical. Resilient modulus and aashto pavement design ronrnr p. Tsonuron in the 1986 aa shto guide for the design of pavement strucores, subgrades and granular base layers are evaluated by the resilient modulus test. Pdf evaluation of modulus of elasticity and modulus of. The correlation of modulus of elasticity e with california bearing ratio cbr is developed based on the elastic properties of the soil sample.
This correlation is conservative in the sense of overestimating the subgrade reaction for a given cbr value, which encourages designers to unnecessarily increase the design. The modulus of subgrade reaction is not a soil property. Ufc 325001 pavement design for roads and parking areas. The modulus of subgrade reaction ks is a function of the contact pressure and allowable settlement on an unit area of soil. The dcp penetration index dp1 was conwertcd to modulus using previously established1 coneli%tion between the i 111, california bearing ratio cbr, and rnoduliis standairtl fwid tesls were also pcrformed at some locations and the moduli. The usual practical way to deal with heterogeneous. To evaluate the subgrade strength is important during construction and design stage. The life cycle output can only be as reliable as the input parameters. The results showed that the 28day qu, the soaked cbr, the modulus of rupture mr and the modulus of subgrade reaction k of the 3 stabilized subgrade materials increased with an increase in. The need for cbr testing you need to perform cbr testing in order to evaluate the strength of the subgrade which is beneath the road or pavement in order to determine the thickness of the road and its sub component layers, in order to carry the required loads. 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. The 80 pci would have both the reduction of wide area loading and the reduction for longterm soil consolidation. In the current study, the particular soil parameters under consideration are youngs modulus e, subgrade reaction modulus k kvalue, and california bearing ratio cbr.
Evaluation of in situ pavement layers with the dynamic. The modulus of subgrade reaction has a direct relation with clayey soils consistencies. Pdf models to estimate k subgrade reaction modulus values. Inclusion of the resilient modulus test rvas prompted by the need for a rational evaluation method. The correlation between the cbr and shear strength in. Cementmodified soil cms is a soilaggregate material that has been treated with a relatively small proportion of portland cement in order to amend its undesirable properties so that they are suitable for use in subgrade or foundation construction. For soils, the following equation 2 is frequently used and recommended by aashto. Relationship between cbr and k, from tests at erdc developed by gonzalez. Pdf correlation between subgrade reaction modulus and. Estimation of subgrade resilient modulus using the. Among the various methods of evaluating the subgrade strength, cbr test is important but quick estimate of cbr is very. Approximate equivalent cbr values can be derived from the modulus of sub grade reaction by use of mathematical relationship. In order to promote public education and public safety, equal justice for all, a better informed citizenry, the rule of law, world trade and world peace, this legal document is hereby made available on a noncommercial basis, as it is the right of all humans to know and speak the laws that govern them. Correlation between subgrade reaction modulus and cbr for airport pavement subgrades.
The conversion from resilient modulus of the subgrade to kvalue was updated in the fall of 2011 to better reflect published test results. It estimates the support of the layers below a rigid pavement surface course the pcc slab. Modulus of subgrade reaction geometrically standard. The correlations were presented in blowsinchcbr curves from dcp tests, and the bearingcapacitycbr curve from static cone penetration tests. In highway formations the subgrade layer, where acts as a pavement foundation should be well designed. As the title states i am looking to convert the cbr value of a poorly graded sand and gravel into a modulus of subgrade reaction to be used in foundation design not pavement design. As a result, it cannot be determined using a cbr test, plate load test or any other test, for that matter. Laboratory and field methods where appropriate for determining the stiffness and other relevant mechanical properties of unbound materials in pavement systems are described in the following subsections and tables. Determining the effective modulus of subgrade reaction for design. Trackbed design programs, such as kentrack and geotrack selig and waters, 1994, require the input of a subgrade modulus for structural analysis. Evaluation of modulus of subgrade reaction ks in gravely. Ziaie moayed and janbaz 12 proposed equation 5 which. This web applet, based on the conversion factors included in nchrp report 128, evaluation of aashto interim guide for the design of pavement structures, allows you to quickly estimate the subgrade resilient modulus m rsg from either a california bearing ration cbr or resistance value rvalue measurement.
Cbr value for subgrade cbr testing uk nationwide cbr. Modulus of subgrade reaction to calculate the modulus of subgrade reaction, plate bearing test is conducted. A solid subbase is a key to a successful building project. Correlation between soil bearing capacity and modulus of.
Soils engineer materials division virginia department of transportation introduction. Evaluation of modulus of elasticity and modulus of subgrade reaction of soils using cbr test. In this a compressive stress is applied to the soil pavement layer through rigid plates of relatively large size and the deflections are measured for various stress values. Furthermore, the correlation between e and cbr is proposed. Stabilization of subgrade soil using additives a case study.
Senior research scientist virginia center for transportation innovation and research wan soo kim, ph. Identifying critical parameters, such as the maximum deflection and maximum bending moments of a street supported by an elastic subgrade, is key to designing safe and reliable roadways. Characterisation of in situ soils based on the resilient. This corrected k eff is the value to be used for design. A comprehensive laboratory study was undertaken to determine engineering properties of cementitiously stabilized common subgrade soils in oklahoma for the design of roadway pavements in accordance with the aashto 2002 mechanisticempirical pavement design guide mepdg. A materials resilient modulus is actually an estimate of its modulus of elasticity e. E s can be derived from the results of triaxial tests. Evaluation of modulus of elasticity and modulus of subgrade reaction of soils using cbr test free download as pdf file.
Comparative study of methods of determination of coefficient. Determining modulus of subgrade reaction k value txdot designation. Models to estimate k subgrade reaction modulus values based on deflection basin parameters conference paper pdf available june 2009 with 2,110 reads how we measure reads. He undertook a considerable number of tests in australia for obtaining the cbr,using staticdynamic cone penetrometersdcpscala, 1956. The modulus of subgrade reaction kvalue is defined as that measured or. It also discusses the fundamental principles behind the. Evaluation of modulus of elasticity and modulus of. Historical modulus of subgrade reaction kvalue primary subgrade design variable for concrete pavement design in the good old days westergaard models pca design procedure, etc. The pressuredisplacement response of the soil in the cbr mould is simulated using cosmosworks fem model where the soil, the load plunger, and the steel mould of cbr are. Cementmodified soil cms is a soilaggregate material that has been treated with a relatively small proportion of portland cement in order to amend its undesirable properties so that they are suitable.
Performing organization name and address ohio research institute for transportation and the environment orite 141. Subsequent soaking condition of subgrade the modulus of subgrade found by this method depends on the moisture content of the soil at the time of testing. The modulus of subgrade reaction k is calculated from the relation k p0. Effective parameters on modulus of subgrade reaction in. What is the value of the modulus of subgrade reaction of. Aci the modulus of subgrade reaction is an often misunderstood and misused concept for the thickness design of slabsonground.
Converting a cbr value into a modulus of subgrade reaction ih8xc geotechnical op 25 jun 15 20. Measure of soil resistance to vertical pressure pressure deflection k 18. Table 546 summarizes the recommended design values for the modulus of subgrade reaction from the lowvolume road section of the 1993 design guide. An approximate, empirical relationship between the modulus of subgrade reaction k s and california bearing ratio cbr are presented. On the other hand, the safe bearing capacity is the maximum pressure which the soil can carry safely without risk of shear failure. Unfortunately, the intricacy and logistics of performing a large number of in situ bearing capacity measurements or collecting. Evd with the static soil modulus ev obtained from static plate load tests. The 80 psi would be 35% 80 pci230 pci x 100% of the plate subgrade reaction value. The federal aviation administrations faa faarfield thickness design program embeds a simple mathematical correlation between kvalue and cbr. Evaluation of subgrade stabilization on pavement performance louisiana transportation research center mark morvant, p. Pdf correlation between subgrade reaction modulus and cbr. However, the strain modulus is determined by the curve fitting method for the overall normal stresssettlement data. The unified facilities criteria ufc system is prescribed by milstd 3007 and provides planning, design, construction, sustainment, restoration, and modernization criteria, and applies. 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.
There is no direct laboratory procedure for determining kvalue. Structure magazine correlation between soil bearing. The modulus of subgrade reaction k used in the aashto guides is also correlated to m r. The modulus of subgrade reaction is defined as the pressure per unit deformation of the subgrade. Railroad subgrade support and performance indicators. In the current study, the particular soil parameters under consideration are youngs modulus. Results from the test shall consist of raw data, loadsettlement curve, yield pressure, recommended allowable pressure for foundation design, and modulus of subgrade reaction k for road design. Using figure 527 and table 545, correct the effective modulus of subgrade reaction k eff for loss of support due to subbase erosion.
Expanded polystyrene eps geofoam has been used as lightweight subgrade for rigid pavement construction over weak soils. Rfreund, its an equation from plate bearing test by terzaghi. Converting a cbr value into a modulus of subgrade reaction. Inclusion of the resilient modulus test rvas prompted by the need for a rational evaluation. The resilient modulus is a basic subgrade soil stiffnessstrength characterization commonly used in structural design of pavements. Modulus subgrade reaction ks is conceptual only, not soil parameter. From the result of this study, the modulus of elasticity derived from cbr tests is higher than the modulus of elasticity obtained from uct test. The results showed that the 28day qu, the soaked cbr, the modulus of rupture mr and the modulus of subgrade reaction k of the 3 stabilized subgrade materials increased with. Pdf evaluation of modulus of elasticity and modulus of subgrade. Pdf models to estimate k subgrade reaction modulus. The output of kentrack is a life cycle estimate of the trackbed structure.
California bearing ratio cbr, plate load test plt, modulus of. The subgrade resilient modulus m r is an essential engineering parameter for the mechanistic empirical pavement design. With constant width and with constant load intensity, the modulus of subgrade reaction in strip foundation has the. Research paper comparison between soaked and unsoaked cbr 1sathawara jigar k. Modulus of subgrade reaction and deflection abstract differential equations govern the bending and deflection of roads under a concentrated load.
Use of dynamic cone penetrometer in subgrade and base acceptance 5. Design methods require modulus of subgrade reaction as input parameter for characterizing subgrade materials underlying rigid pavement structures. Since 1920, the theory of subgrade reaction has also been used for computing stresses in piles and sheet piles, which are acted on by horizontal forces above the ground surface. The story began when terzaghi tried to relate the vertical deflection d of a shallow foundation to the load that applied on that foundation q. Estimation of subgrade resilient modulus using the unconfined.
From a mechanical point of view, a subgrade soil represents a highly diverse heterogeneous structure. For our example, the equivalent modulus of subgrade reaction was determined to be 80 pci. The cbr california bearing ratio value is a penetration test that evaluates the mechanical strength of subgrades and basecourses that lay beneath new road constructions or pavements. The subgrade reaction modulus k30 having 30cm diameter is calculated using the following equation. Evaluation of modulus of elasticity and modulus of subgrade. Engineering properties of stabilized subgrade soils for. The answer lies in the underlying assumptions of how a foundation might behave.