Subgrade modulus of laterally loaded piles in clays. The displacement diagram shows a dishing effect as discussed earlier. Modulus of subgrade reaction and deflection abstract differential equations govern the bending and deflection of roads under a concentrated load. The compressive pressure was applied to the sample in the box mold through the rigid plate of relatively large size. Subgrade reaction modulus k s is a conceptual relationship between soil pressure and deflection, which is widely used in structural analysis of various foundations. The subgrade modulus was related to the percent clay, pi, and optimum moisture content.
For each test, the pavement surface deflections were measured at the distance of 0, 8. 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. The present paper deals with the experimental analysis study involving model plate load tests plt. Scale effect study on the modulus of subgrade reaction of.
Table 546 summarizes the recommended design values for the modulus of subgrade reaction from the lowvolume road section of the 1993 design guide. Effective parameters on modulus of subgrade reaction in. No footing, rafts, pavement design westergaards work in 1920s q k d used by structural engineers q applied or contact pressure fl2 d settlement of footing under q l k qd slope linear spring. Modulus of subgrade reaction for eps geofoam expanded polystyrene eps geofoam has been used as lightweight subgrade for rigid pavement construction over weak soils. Subgrade reaction modulus k s of clayey soils based on field tests 2025 the ultimate soil pressure is at a settlement of. Subgrade reaction method srm, finite element method fem, all of which are mentioned in the relevant literature 6, 12, 15. For this exercise, the software default value for the modulus of subgrade reaction was used. 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. Randolph 1991 also takes up the same argument in his lecture series. Assessment of mechanical properties of cement stabilized.
The elastic modulus of subgrade reaction k is a required design input that represents the response of the subgrade to traffic loads. The ltpp models did not yield good results compared to the models proposed by this study. It means that as the consistency of soil decreases the modulus of subgrade reaction decreases. Effect of fwd testing position on modulus of subgrade reaction. Soilpropertybased subgrade resilient modulus estimation for. The subgrade reaction modulus for rock foundations under axial loading is investigated by model footing tests. The theory of subgrade reaction assumes that the unit soil reaction p with respect to a laterally loaded pile increases linearly with the lateral deflection y, as expressed in the fol lowing equation. Correlation between soil bearing capacity and modulus of. Experience from this study proves that the dcp is a viable alternative device to evaluate insitu base and subgrade materials during construction. The modulus of subgrade reaction is an often misunderstood and misused concept for the thickness design of slabsonground. Subgrade reaction modulus k s of clayey soils based on field tests. A comparative study was made with different subgrade modulus from three different methods. Bureau of reclamation usbr conducted soil tests to determine modulus of soil reaction values for a wide variety of soils having differing compaction levels. The present study is an experimental analysis using plate load test to determine the effect of foundation depth, size as well as the shape on the modulus of subgrade reaction k s of cohesionless soils.
Dass books for instance have tables throughout with coorelations using n values, dr and so forth. A series of modelscale footing tests are performed to investigate the effects of the unconfined compressive strength, discontinuity spacing and inclination of the rock joint. Prediction of subgrade reaction modulus of clayey soils. This corrected k eff is the value to be used for design. From this figure it can be seen that the modulus of subgrade reaction increases with increasing the relative density of the soil. The sub grade reaction at any point along the beam is assumed to be proportional to the vertical displacement of the beam at that point. The modulus of sub grade reactions are ca lculated with different standard penetration number spt n values in the interval of 5 up to 100. A composite modulus of subgrade reaction was determined from the combined effective roadway modulus for use in design of rigid pavements for various working platforms as a function of thickness. Pdf subgrade reaction modulus k s of clayey soils based. It is used to study the effect of footing shape on the coefficient of subgrade reaction of cohesion less soils. Pdf rational assessment of modulus of subgrade reaction. Once a subgrade modulus is known, the behavior of a laterally loaded pile may be eval. The modulus of subgrade reaction determined from the initial linear portion of the curve was 120 mpa see fig. Engineering properties of stabilized subgrade soils for.
Subgrade reaction an overview sciencedirect topics. Estimation of subgrade resilient modulus using the. 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. This is reflected by the availability on the market of numerical programs, such as geo5 sheeting check, deepxcav. In other word, the soil is assumed to obey hooks law. Subgrade modulus ppp stress mechanics stiffness free. Journal of chemical and pharmaceutical sciences issn. Westergaard was the first to introduce the terms modulus of subgrade reaction and radius of relative stiffness to describe the relative stiffness of the concrete slab to that of the subgrade 1. It is important to consider how these parameters apply to the design of floor slabs. Using figure 527 and table 545, correct the effective modulus of subgrade reaction k eff for loss of support due to subbase erosion. Use of the methods and values suggested can reasonably predict the initial no time effect deflection of buried flexible pipe under fills up to 15 m 50 ft. In engineering design of structures, the subsoil can be simulated by a much simpler system called subgrade reaction model. Say, you know a racking system will be installed in the completed building. It is used for continuous footings, mats, and various types of pilings to be.
In this study, effective parameters on modulus of subgrade reaction in clayey soils are studied with use of numerical modeling. Effect of fwd testing position on modulus of subgrade. I understand that accurately estimating the modulus of subgrade reaction is a bit of a loose term however. Prediction of subgrade reaction modulus of clayey soils using. The value of reaction modulus decreases when both the footing width and settlement increase. The modulus of subgrade reaction is a conceptual relationship between soil pressure and deflection that is widely used in the structural analysis of foundation members. Purpose and scope the purpose of this study was to develop a correlation to estimate resilient modulus values for subgrade soil from uc test results for use in mepdg level 2 or 3 analysis. With the concept of soil shear strength nonlinearly mobilized with shear strain, an analytical solution of p k is.
The modulus of subgrade reaction of soil depends upon various factors such as the size, shape as well as the depth of the foundation. Modulus of subgrade reaction foundation engineering engtips. The modulus of subgrade reaction is a basis for structural engineers to evaluate deformation from point loads that may or may not be applied to the slab. Design methods require modulus of subgrade reaction as input parameter for characterizing subgrade materials underlying rigid. 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. A simple new method is proposed to determine an approximate value of subgrade reaction modulus in. 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. In this paper the results of spt and plt tests on gravely soils of tehran alluvium are evaluated. Phase ii of the study, the data from phase i are also included for completeness. Estimation of subgrade resilient modulus using the unconfined.
Effect of rigidity of foundation the subgrade modulus is not a soil property but it is a function of the following. Determination of typical resilient modulus values for. The key points made are that the modulus of subgrade reaction k is not a fundamental soil property, but varies with the foundation type, foundation dimension, and type of loading. Subgrade modulus predictive equations were developed for repeated deviator stress levels of 27. Design pamphlet for the determination of design subgrade in support of the 1993 aashto guide for the design of pavement structures publication no. Evaluation of subgrade stabilization on pavement performance. Flexural strength modulus of rupture subgrade strength, or subgrade subbase combination modulus of subgrade reaction, kvalue weights, frequencies, and types of truck axle loads load transfer load safety factor design period design factors. Nonlinear subgrade reaction solution for circular tunnel.
Jan 23, 2016 the subgrade reaction modulus for rock foundations under axial loading is investigated by model footing tests. However, the strain modulus is determined by the curve fitting method for the overall normal stresssettlement data. Effect of modulus of sub grade reactions on the static. An experimental study on the effect of foundation depth, size. Soil models selected for investigation in the study were soft clay 2, stiff clay above the water table 3, and stiff clay below the water table 5. One of the most important engineering challenges in the design of structure, is the reaction of soil in contact with structure. A table of modulus of soil reaction e values for use in the iowa formula has been empirically developed by the bureau of reclamation. Soilpropertybased subgrade resilient modulus estimation. Subgrade reaction approach the subgrade reaction approach by broms 1981 is based on idealisation of the soil as a series of horizontal layers, which provide spring supports.
Also, the modulus of subgrade reaction for the crushed stone is greater than that of the sand material. Experimental study of estimating the subgrade reaction. This study focuses on quantifying a new subgrade reaction modulus by considering rock discontinuities. This paper presents a nonlinear solution of a radial subgrade reactiondisplacement p k u r curve for circular tunnel lining design in undrained clay. Evaluation of resilient modulus of subgrade and base. The influence of geogrid length on subgrade modulus is negligible and only the effective depth is affected it. The modulus of subgrade reaction k is the reaction pressure sustained by the sample layer under a rigid plate of standard diameter per unit settlement measured at a specified pressure or settlement. Design methods require modulus of subgrade reaction as input parameter for characterizing subgrade materials underlying rigid pavement structures. Several researchers have considered some forms of interaction among the spring elements that indicate the soil continuum, and tried to make the winkler model more realistic and practical 18. Pdf estimation of the coefficient of subgrade reaction. Soil subgrade modulus subgrade subbase strength soil bearing capacity, soil compressibility, and soil modulus of subgrade reaction are various measures of strengthdeformation properties of soil. The modulus of subgrade reaction has a direct relation with clayey soils consistencies. Evaluation of modulus of subgrade reaction ks in gravely.
With constant width and with constant load intensity, the modulus of subgrade reaction in strip foundation has the. Department of transportation federal highway administration research and development turnerfairbank highway research center 6300 georgetown pike mclean, va 221012296. The compressive pressure was applied to the sample in the box. Vertical modulus of subgrade reaction modulus of subgrade reaction k is it a soil property. The rack load may be applied anywhere in the building, so the structural engineer needs to account for these point. Due to the results obtained the correlation between spt results n 1 60 and modulus of subgrade reaction k s are also presented for gravely soils. Experimental evaluation of the subgrade reaction and soil. Note that the plate load test results only reflected the condition of the upper layer of 1. In order to inspect the performance of the models developed in this study, comparison with the models developed based on ltpp database was made. Design pamphlet for the determination of design subgrade in. Ziaie moayed and janbaz 12 proposed equation 5 which. Study the effect of layer thickness on modulus of subgrade reaction and bearing capacity of soil estimated by plate load test conference paper pdf available march 2008 with 8 reads. The raft was analyzed using safe 2014 software by varying the values of modulus of sub grade reaction.
Pdf study the effect of layer thickness on modulus of. In this study, effective parameters on modulus of subgrade reaction in clayey soils. Soil subgrade modulus subgradesubbase strength soil bearing capacity, soil compressibility, and soil modulus of subgrade reaction are various measures of strengthdeformation properties of soil. The present paper deals with the experimental analysisstudy involving model plate load tests plt. Evaluation of subgrade modulus and bearing capacity with. The resilient modulus data used in developing the predictive equations represented soils at ap.
Experimental evaluation of subgrade modulus and its. Data collected shows that engineers can use the dcp to quantify the construction quality of the asbuilt materials. The subgrade reaction method is often used for structural calculation of embedded walls. The modulus of subgrade reaction k s depends on several factors such as the size and shape of the foundation as well as the embedment depth of the foundation. Stabilization of subgrade soil using additives a case study. The pavements constructed on these type of soil are normally subjected to deterioration. Also, the modulus of subgrade reaction for the crushed. Modulus of subgrade reaction k foundation engineering. Perhaps the best known are is that of a continuous, horizontal beam or footing resting on an elastic sub grade.
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