Earth pressure and retaining wall basics for nongeotechnical engineers richard p. Spring stiffness may be determined by direct solution of. Instructional materials complementing fema p751, design examples foundation design 3. It can also be noted that all other nodes have same tributary area which explains table 2 as it. Soil stiffness either is constant for all depths below grade or linearly increases with depth below grade. Master of science and hereby certify that, in their opinion, it is worthy of acceptance. Inertial soil structure interaction inertia from vibration of structure and foundation causes foundation translation and rotation u f and. The fundamental problem with the use of this model is to determine the stiffness of elastic springs used to replace the soil. For example, preloaded clay actually has a variation of stiffness with respect to depth as shown in figure 4a. The variation of bearing pressure will also be dependent on the stiffness of your ground beam.
It assumed that the material is elastic and isotropic i. A example calculations b pipe deflection for standard installation method c reclamation deflection equation development. This calculation uses these global springs to compute. In this model, the cracked concrete is regarded as cracks with concrete between cracks. Integral bridge design derivation of the spring constant for modelling the soilstructure interaction sergei terzaghi behons, mipenz. This presentation relates to example computations in chapter 5 of the fema p752, nehrp recommended provisions.
Now, almost 20 years on, this paper revisits the issue of stiffness determination, and in particular is concerned with smallstrain stiffness, which was. The relationship between the vertically applied load and horizontally measured deformation is not straightforward as would be the case, for example, in a. The modelling of the soil as springs comes forth out of the winkler foundation model. Analysis of structure on piled foundation with calculation of pile stiffness in the soil system new fe 57 in this lesson you will learn how to. Soil stiffness measured in oedometer test stress versus strain, rather than as conventional elog graphs. Additionally, using the subgrade reaction winkler foundation has other analytical limitations. This paper focuses on the determination of the soil stiffness and considers the factors that influence this value. Approximating lateral stiffness of stories in elastic frames by arturo e. The gross pressure at the base of the foundation at which soil fails is called ultimate bearing capacity. The behaviour of the concrete between cracks is simulated by the. Assuming that the changes in soil stiffness drive the longterm performance, the average strain next to.
Bridge approach slab analysis and design incorporating elastic soil support presented by. Derivation of the spring constant for modelling the soilstructure. Seismic load assessment is another example of using an elastic approach. Evaluation of shear modulus and damping in dynamic centrifuge tests a. The canvas then shows the pile with a top elevation of 2m and a total length of 17m embedded in soil with a ground surface of 1m. Structures and stiffness engr 10 introduction to engineering. Madabhushi3 cueddsoilstr336 2004 1 research fellow, wolfson college, university of cambridge 2 research student, girton college, university of cambridge 3 senior lecturer, girton college, university of cambridge. As long as the majority of soil beneath the mat behave similarily, the spring constant derived by multiplying the soil elastic modulus and the unit area 1 sf is an acceptable approximation to generate profile of deflectionstresses flow of the mat. This increase in pore pressure leads to drainage of some water from the voids of the soil.
As with most construction today, the emphasis on cost control and quality control of soil is prompting the implementation of mechanistic designs, performance specifications, and contractor warranties. China, were tested under laboratory conditions to determine the influence of. With these spring stiffnesses modeled, if you find that your soil is typically experiencing a bearing reaction of 150kpa22psi, 27kn6. It differs from fluid mechanics and solid mechanics in the sense that soils consist of a heterogeneous mixture of fluids usually air and water and particles usually clay, silt, sand, and gravel but soil may also contain organic solids and other matter. Deflection of flexible pipes is usually calculated using the spangler formula. Stein sture professor of civil engineering university of colorado at boulder contents general concepts and stiffness of sand hookes law emoduli from triaxial testing emoduli from oedometer testing examples on the estimation of e. Soil stiffness can also be derived from laboratory tests.
Pdf numerical study for soilspring stiffness of pile group. Table 1 below summarises a number of commonly used methods used to determine the modulus of horizontal subgrade reaction. Computational geotechnics determination of soil stiffness parameters example 2 unloading. A relation for homogenous and elastic soil is presented to determine the stiffness. Soil mechanics is a branch of soil physics and applied mechanics that describes the behavior of soils. The soil spring stiffness is computed using modulus of subgrade reaction. Pdf determination of reinforced soil stiffness by static. Basic mechanics of soils university of the west of. Awwa m11 quotes the accuracy of predicted deflections for different degrees of soil compaction. Initial soil springs stiffness for laterally loaded piles espace curtins. Correlation between soil bearing capacity and modulus of. The german pipe design method in abwassertechnischen vereinigung e.
Limitations of winkler model a number of studies in the area of soil structure interaction have been conducted on the basis of winkler hypothesis for its simplicity. The bearing capacity of soil is defined as the capacity of the soil to bear the loads coming from the foundation. Calculation of measurement uncertainty for stiffness. Soilstructure interface is a very complicate issue, i dont think anyone been able to formulate it precisely. Weber course content content section 1 retaining walls are structures that support backfill and allow for a change of grade.
Tutorial on lirasapr version 2015 example 22 example 22. Limitations of winkler model since the subgrade stiffness is the only 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 chapter continues by describing the interaction between structure and soil. This generally means that there are no attached collars or footings that are effective in resisting lateral soil forces. Pdf many approaches have been developed to determine the soilspring. The higher the soil stiffness is, the more fatigue damage may occur in the riser pipe, since vibration frequency and stress ranges will be higher. The fast measurement and the good usability of the ssg are great advantages, together with the ability to compute the stiffness modulus of the ground assuming a poissons ratio. Despite advances in the computer analysis of frame buildings for lateral loads, there remains a need for simple models that provide accurate estimates of response. This positions the soil with respect to the already defined pile. A numerical model for material nonlinear analysis of concrete slabs supported on soil is described in this work. In the interest of simplicity, equivalent elastic soil stiffness parameters elastic soil moduli are defined as the ratio of stress along an axis to strain along an axis and often employed in soil characterization and analyses.
Integral bridge design derivation of the spring constant. Secant soil stiffness is generally higher than tangent soil stiffness. We all know soil can be modeled by springs, and for that,stiffness of soil spring has to be. The pressure which the soil can easily withstand against load is called allowable bearing pressure. Calculate lateral loads continued in the additional information provided in the description of the house, the top of footing is 24 in. This pipe stiffness value exceeds common flexible pipe stiffnesses. The fundamental problem with the use of this model is to determine the stiffness of elastic springs used to replace the soil below foundation.
Soil mechanics and foundation engineering conference in florence was a turning point, at which the importance of soil stiffness to both theoreticians and practising engineers became accepted. At present, the stiffness can be easily determined with a soil stiffness gauge ssg that is a light and userfriendly equipment. Placerville, california abstract faced with an increasing number of poor soil sites being considered for new development in california. Structural element approaches for soilstructure interaction. In this paper, a series of 3d numerical analyses are conducted to compute the equivalent soil spring stiffness s according to pile distortion for a pile group located under the central pier of. Applicability of small strain stiffness parameters for. Initial soil springs stiffness for laterally loaded piles a. Analysis of pile foundation simplified methods to analyse the pile foundation under lateral and vertical loads 1kanakeswararao thadapaneni,2sarikonda venkata sivaraju,3ravi teja grandhi 1pg student, lenora college of engineering, rampachodavaram,2pg student, kakinada institute of engineering and technology. Lateral load capacity of piles transportation research board. An analysis is presented of a database of 67 tests on 21 clays and silts of undrained shear stressstrain data of.
In general, soil stiffness is determined by soil shear strength. Janbu has promoted this for many years janbu, 1963, also janbu and senesset, 1979, not only because of the modulus issue, but also because the log scale for pressure gives a distorted picture of the soil. Contents general concepts and stiffness of sand hookes law emoduli from triaxial testing emoduli from oedometer testing examples on the estimation of e. In this chapter, direct stiffness method which is also called the displacement method will be introduced that is a modern method. The first approach uses the set of equations published in the document. This model has some drawbacks which are improved by the pasternak foundation model. Predictive relations to find soil spring stiffness.
For instance a retaining wall can be used to retain fill along a. For the design of structural members, the strain or deformation of an element of. Soil stiffness gauge for soil compaction control by scott fiedler, charles nelson, e. The following relationships can be demonstrated for proofs refer to a text on the strength of materials. Calculation of measurement uncertainty for stiffness modulus of asphalt mixture 28 due to the geometry of the measuring system, the stress pattern in a sample is highly nonlinear and biaxial. Pdf roads and railways are always limited in the amount of allowed settlement. Native soil stiffness little, 2004 may be estimated from spt or other test results with correction for depth or from undrained shear strength. The pile in soil was replaced by a cantilever beam, fixed against rotation but free of soil, and the length of the beam, the depth to the point of fixity, was computed by using the lateral load at the pile head pt, the deflection of the pile head yt, and the bending stiffness of the pile epip. Evaluation of shear modulus and damping in dynamic. The liquefaction phenomenon of soil deposits can be described as the reduction of shear strength due to pore pressure buildup in the soil skeleton. Overview of soilstructure interaction principles jonathan p.
Force on a pile eq on unloaded pile pile supporting structure. In assessing the effects of lateral forces applied to the soil by a shallow post or pier foundation, the latest version of ansiasae ep486. There fore, beamonelasticfoundation theory must be modified to account for variations in the spring stiff ness k. Ground stiffness evaluation using the soil stiffness gauge. Initial soil springs stiffness for laterally loaded piles. Numerical study for soilspring stiffness of pi le group. Modelling the interaction between structure and soil for.
Numerical study for soilspring stiffness of pile group. Soil is homogeneous for the entire embedment depth. The stiffness of both structure and soil has an important role when modelling the interaction. Frost susceptible soil granular soils cant support capillarity clay soils arent permeable enough silts have capillarity and permeability free moisture in the subgrade water table within capillary range of soil freezing line penetrates into the subgrade sustained temperatures below freezing. Determination of reinforced soil stiffness by static plate load test. Atv code, 1984 allows calculation of pipe loads for all types of pipe installations and incorporates the effects of pipe stiffness and the variation of soil moduli in the. Soil to begin with, the ground surface elevation is entered see figure 8.
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