In this way for calibrating model, the studied case is based on results of 0. Prediction of subgrade cbr using fwd for thin bituminous. In recent years, software has been developed to calculate aircraft pavement strength ratings from modulus values that are back calculated from deflections measured by a falling weight deflectometer. This report provides a users manual for the new windows version of modulus 6. Analysis of track support and determination of track modulus. This paper presents a back calculation analysis to evaluate pavement layer moduli by using a threedimensional numerical model developed using the flac3d finite difference software. A spring constant, or spring value, is defined as the ratio of vertical load to vertical.
Forwardcalculation can be used to estimate layer moduli for the subgrade and bound. Issues pertaining to backcalculation of stiffness modulus. In order to calibrate subgrade back calculation modulus, the correction method of subgrade back calculation modulus was put forward based on theoretical analysis and indooroutdoor experiments, and the detailed implementation process was analyzed combined the latest results of subgrade dynamic modulus and subgrade moisture forecast. Back analysis of the falling weight deflectometer bowls can be used to estimate the stiffness modulus of the subgrade from software packages such as.
The back calculation is a userdependent procedure and produces a nonunique resilient modulus estimation. The back analysis algorithm solves for both a two layer elastic system and the thickness of subgrade, or a three layer elastic system and the thickness. The modulus of the subgrade can be converted into a subgrade rvalue. The conversion from resilient modulus of the subgrade to kvalue was updated in the fall of 2011 to better reflect published test results. Soil subgrade modulus subgradesubbase strength soil bearing capacity, soil compressibility, and soil modulus of subgrade reaction are various measures of strengthdeformation properties of soil. To alleviate this limitation, this paper focuses on the recent development of a systematic back calculation protocol for subgrade resilient modulus using modcomp6 software. Most backcalculation software requires an initial value of modulus, known. Presentation of calculation report with sufficient details.
If a subgrade modulus in units of fl3 is multiplied by a footing tributary area in units of l 2, the result is a standard spring constant in units of fl. The program first calculates the tributary area for each node of the footing and then multiplies the modulus of subgrade reaction by the corresponding tributary area for each node to get the. A comparison of nondestructive testing backcalculation. The protocol is intended for use on a flexible pavement with a.
In this research, three software programs, modulus 6. The program incorporates a stiff layer modulus of elasticity of 1,ooo,ooo psi and infinite thickness, below the subgrade, into the. Back analysis of the falling weight deflectometer bowls can be used to estimate the stiffness modulus of the subgrade from software packages such as efromd2. Estimating base layers and subgrade modulii for me. Using the subgrade modulus and depthtostiff layer estimates in the backcalculation. Generally, there are two groups of backcalculation programs. If the user opts to fix the calculated dtb to a value in the 120 to 240in. Study on correction method of subgrade modulus based on. Anastasios ioannides for making backcalculation software. Substantial improvements have been made to the programs, data editing, and segmentation routines.
Performing organization name and address applied research associates, inc. When characterizing a subgrade layer with the mepdg software, a factor of 0. Estimating resilient modulus choosing the right method for. Index backcalculation of layer parameters for ltpp test. As the area gets smaller, the spring constant gets smaller i. This number was compared to typical values found in stabilized soil cement 200 k. Estimating base layers and subgrade modulii for me pavement. Contract dtfh6195c00029 as part of task b backcalculate resilient modulus. For finegrain soils the ratio of e back e lab was back e lab ratio for the coarsegrain soil was found to be higher with an average value of 2. Systematic backcalculation protocol and prediction of. Show full abstract a theoretical strength rating for. In the mepdg computation models, pavement response computation models incorporated into the mechanisticempirical design approach require the input of values to represent the stiffness of supporting layers, which include unbound granular base materials and subgrade soils.
Issues pertaining to backcalculation of stiffness modulus in. The common theory for calculating the modulus of subgrade reaction is the winkler theory, which cannot take the effect of elasticity and plasticity of soils. The coefficient of horizontal subgrade reaction kh. Nov 09, 2015 as discussed below, deflection testing and back calculation analysis provides considerably more data at less cost and results in a more comprehensive estimation of subgrade resilient modulus at the expense of the accuracy inherent in the laboratory test. The first is the iterative approach in which a forward calculation scheme typically a linear elastic program is used within the iterative process chua, 1989. In flexible pavement design, resilient modulus is one of five variables used to. It should be understood that many different software packages can be used to calculate the elastic modulus of pavement layers and subgrade soils from deflection basins, as demonstrated in report fhward97086, back calculation of layer moduli of ltpp gps sites. Evaluation of insitu stiffness of subgrade by resilient. Classical pavementsubgrade system analysis is based on multilayer linear.
The subgrade modulus is a lumped constant of integration of the differential equation of a beam supported by elastic springs. Backcalculation of resilient modulus of lightly stabilized. Recently, a deflection analysis of pavement structures daps software has been developed, which enables the rapid calculation of layer stiffness moduli using a singular decomposition technique. Systematic backcalculation protocol and prediction of resilient. Comparison of static and dynamic backcalculation of.
Top 4 download periodically updates software information of modulus full versions from the publishers, but some information may be slightly outofdate using warez version, crack, warez passwords, patches, serial numbers, registration codes, key generator, pirate key, keymaker or keygen for modulus license key is illegal. Calculation of settlement corresponding to the allowable pressure. In other cases, the back calculation yields very high asphalt stiffness and very low subgrade stiffness modulus. Pdf consistency and accuracy of selected fwd backcalculation.
The correction factor is applied to adjust the backcalculated resilient modulus to those obtained from laboratory testing. Falling weight deflectometer fwd mndot pavement design. Concrete mixture proportioner iphone concrete mixture proportioner ipad evaporation rate calculator. This report details how the backcalculation program was selected, lists the. So, it seems as though you will get a different spring stiffness for a given subgrade modulus depending on the area of soil that you assume the spring to cover. The modulus backcalculation program, which uses databases generated. Design methods require modulus of subgrade reaction as input parameter for characterizing subgrade materials underlying rigid pavement structures.
Evaluation of resilient modulus of subgrade and base. Both techniques are able to comprehensively investigate the elastic modulus of the subgrade layer in existing pavement nondestructively. Effective parameters on modulus of subgrade reaction in. Recent advances in hardware and software technology have significantly improved ndt equipment, data collection, and analysis software. Evaluation of modulus of subgrade reaction ks in gravely. The faas back calculation program, bakfaa, can be downloaded from the faa website and can be used to analyze ndt data, subject to the limitations discussed herein. Estimation of subgrade resilient modulus using the. Used to evaluate the subgrade modulus based on soil bearing capacity, allowable soil settlement, and safety factor. The highest value of modulus of subgrade reaction is in the corner of flexible foundation and the side points have middle value of modulus of subgrade. More accurate modulus backcalculation by reducing noise. Clarifying the application of subgrade modulus in structural.
Structure magazine correlation between soil bearing. 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. Daps deflection analysis of pavement structures back calculation of layer stiffness from deflection data using the singular value decomposition technique construction data pavement construction information must be defined to enable back calculation. Winter fwd modulus is about 40% higher than early summer fwd modulus. Modulus software free download modulus top 4 download offers free software downloads for windows, mac, ios and android computers and mobile devices. In this paper the results of spt and plt tests on gravely soils of tehran alluvium are evaluated. Study on correction method of subgrade modulus based on fwd. Calculation and generation of modulus of subgrade reaction contour on the footing surface. Based on a back calculation procedure with the elmod software, the elastic modulus of each flexible pavement layer can be obtained. Estimating resilient modulus choosing the right method. Key words modulus, backcalculation, layer moduli, remaining life 18. Subgrade soil properties gravel g stones pass 75 mm sieve, retained on 2 mm 0 excellent 5075 a1 gpgm 70 assumed sand sa will form a cast when wet.
Subgrade modulus of reinforced concrete kootk structural 3 jun 15 21. The above described tributary area calculation is the key procedure used internally by the commercial software to calculate the linear spring constant. Opens when the calculate subgrade modulus from soil bearing capacity button is clicked on the soil property form is clicked. The structural engineers need an appropriate way to represent the soil in the structural analysis. Estimation of subgrade resilient modulus using the unconfined. The modulus of subgrade reaction is an often misunderstood and misused concept for the thickness design of slabsonground.
The subgrade modulus takes its theoretical origins from the formulation of winklertype beamsonelasticfoundations hetenyi 1946. Correlation between soil bearing capacity and modulus of subgrade reaction computer and structures, inc. Modcomp, back calculation, modulus, youngs modulus, elastic. The fwd data gathered from different test sites, including the zanjantabriz, eivanekeygarmsar and garmsarsemnan freeways and also rafsanjan. 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. Although resilient modulus values could be determined through laboratory testing of actual subgrade soil samples, such testing would require significant resources including a high level of technical capability to conduct the test and interpret results. Consistency and accuracy of selected fwd backcalculation.
Development of a computer program for dynamic backcalculation of. It is important to consider how these parameters apply to the design of floor slabs. Correlation between soil bearing capacity and modulus of. E elastic modulus of the beam, i second moment of area of the beam, z deflection at a point x from the applied load, x distance along the beam from the point of application of the load, and u modulus of the elastic support commonly known as the track modulus note that the track mod. The mepdg identifies a threelevel hierarchical approach for resilient moduli based on.
Soil office bearing capacity software sofoundation. The variability of each layers back calculation modulus without correcting the basin is much larger. X j is the unknown variables, including modulus of elasticity, poissons ratio, thickness of layer, pressure, contact area, j varies from 1 to n. Subgrade modulus of reinforced concrete structural. Backcalculation of flexible pavement layers moduli, using four software. According to the authors, the inaccuracy of the subgrade reaction method results from. The results show that the equivalent resilient modulus of.
Expanded polystyrene eps geofoam has been used as lightweight subgrade for rigid pavement construction over weak soils. Comparison of static and dynamic backcalculation of flexible. When the overall modulus of subgrade reaction for two 32,000 pound loads spread six feet apart is given by the following equation timoshenko, p. Modulus software free download modulus top 4 download. Calculate subgrade modulus from soil bearing capacity dialog. Software has also been developed allowing the estimation of layer modulus, including the subgrade, and in some cases the calculation of. The tonn program may be downloaded from the pavement design software webpage. Another clue that the default solution is suspect would be if the ratio of the flexible base modulus unstabilized layers only to the subgrade modulus is very high 5. Calculation of subgrade reaction modulus considering the. Index using falling weight deflectometer data with mechanistic. Nazzal and mohammad 6 carried out a study to develop regression models to predict the resilient modulus of. Measurements of the elastic modulus of pavement subgrade. Subgrade reaction modulus k s can be considered as an appropriate interface between the geotechnical and structural engineers.
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