《高等土力学》课程教学资源（书籍文献）United States Steel - Steel Sheet Piling Design Manual.pdf_大学文库

LATERALPRESSURESONSHEETPILEWALLSEARTHPRESSURETHEORIESEarth pressure is the force per unit area exerted by the soil on the sheet pile structure.Themagnitudeoftheearthpressuredependsuponthephysical propertiesofthesoil,theinteraction at the soil-structure interface and the magnitude and character of thedeformations in the soil-structure system. Earthpressure is also influenced by thetime-dependent nature of soil strength,whichvaries due to creep effects and chemicalchanges in the soil.Earth pressureagainst a sheet pile structure is nota unique function for each soil,butratherafunctionofthesoil-structure system.Accordingly,movementsofthestructureare a primary factor in developing earth pressures. The problem, therefore, is highlyindeterminate.Two stages of stress in the soil are of particular interest in the design of sheet pilestructures,namely theactiveand-passivestates.When avertical plane,such as a flexibleretainingwall,deflects undertheactionof lateral earthpressure,eachelementof soiladjacent to the wall expands laterally,mobilizing shear resistance in the soil and causing acorresponding reduction in the lateral earth pressure.One might say that the soil tends tohold itself upby its boot straps;that is, by its inherent shear strength.The lowest state oflateralstress,whichisproducedwhenthefull strengthofthesoil isactivated(astateofshearfailure exists),is called the active state.Theactive state accompanies outwardmovement of the wall. On the other hand, if the vertical plane moves toward the soil,such as the lower embedded portion of a sheet pile wall, lateral pressure will increase asthe shearing resistance of the soil is mobilized.When the full strength of the soil ismobilized,thepassivestateof stress exists.Passive stresstends toresistwall movementsand failure.Thereare two well-known classical earth pressure theories;the Rankine Theory and theCoulomb Theory.Each furnishes expressions for active and passive pressures fora soilmassatthestateoffailure.Rankine Theory-The Rankine Theory is based on the assumption that the wallintroduces no changes intheshearing stresses at the surface of contact between the walland thesoil.Itis alsoassumedthatthegroundsurfaceisastraight line(horizontal orslopingsurface)andthataplanefailuresurfacedevelopsWhentheRankinestateoffailurehasbeenreached,activeand passivefailurezoneswilldevelopasshowninFigure1.AARailureZoneailureZoneWallWallMovementMovement0-045*+@/2FAFFEFFAFACTIVECASEPASSIVE CASEof soil (degreesFig.1-Rankinefailurezones

LATERAL PRESSURES ON SHEET PILE WALLS EARTH PRESSURE THEORIES Earth pressure is the force per unit area exerted by the soil on the sheet pile structure. The magnitude of the earth pressure depends upon the physical properties of the soil, the interaction at the soil-structure interface and the magnitude and character of the deformations in the soil-structure system. Earth pressure is also influenced by the time-dependent nature of soil strength, which varies due to creep effects and chemical changes in the soil. Earth pressure against a sheet pile structure is not a unique function for each soil, but rather a function of the soil-structure system. Accordingly, movements of the structure are a primary factor in developing earth pressures. The problem, therefore, is highly indeterminate. Two stages of stress in the soil are of particular interest in the design of sheet pile structures, namely the active and-passive states. When a vertical plane, such as a flexible retaining wall, deflects under the action of lateral earth pressure, each element of soil adjacent to the wall expands laterally, mobilizing shear resistance in the soil and causing a corresponding reduction in the lateral earth pressure. One might say that the soil tends to hold itself up by its boot straps; that is, by its inherent shear strength. The lowest state of lateral stress, which is produced when the full strength of the soil is activated (a state of shear failure exists), is called the active state. The active state accompanies outward movement of the wall. On the other hand, if the vertical plane moves toward the soil, such as the lower embedded portion of a sheet pile wall, lateral pressure will increase as the shearing resistance of the soil is mobilized. When the full strength of the soil is mobilized, the passive state of stress exists. Passive stress tends to resist wall movements and failure. There are two well-known classical earth pressure theories; the Rankine Theory and the Coulomb Theory. Each furnishes expressions for active and passive pressures for a soil mass at the state of failure. Rankine Theory - The Rankine Theory is based on the assumption that the wall introduces no changes in the shearing stresses at the surface of contact between the wall and the soil. It is also assumed that the ground surface is a straight line (horizontal or sloping surface) and that a plane failure surface develops. When the Rankine state of failure has been reached, active and passive failure zones will develop as shown in Figure 1. ACTIVE CASE PASSIVE CASE where = angle of internal friction of soil (degrees) Fig. 1 - Rankine failure zones

can (45+)PpZtan （45号）+2ctan (45+号tan(45-Cohesive Soil-Active PressureCohesive Soil -Passive PressureFig. 2 - (Continued)Coulomb Theory-An inherentassumption of theRankineTheory is that thepresenceof thewall does not affectthe shearing stressesatthe surface ofwall contact.However,since the friction between the retaining wall and the soil has a significant effect on thevertical shear stresses in the soil,thelateral stressesonthe wall are actuallydifferentthanthose assumed by the Rankine Theory. Most of this error can be avoided by using theCoulomb Theory,which considers the changes in tangential stress along the contactsurface due to wall friction.As the wall yields,thefailurewedge tends to move downward for the active case.Forthe passive case, where the wall is forced against the soil, the wedge slides upward alongthe failure plane.These differential movements involve vertical displacements betweenthe wall and backfill and create tangential stresses on theback of the wall due to soilfriction and adhesion. The resulting force on the wall is,therefore,inclined at an angle tothe normal to thewall.This angleis known asthe angle of wall friction,.For theactivecase,whentheactivewedge slides downward relative to thewall,is taken as positiveForthepassive case,whenthepassivewedge slidesupwardrelativetothewall,istakenas negative.If the angleof wall friction is known,the following analytical expressionsforK, and K, in the horizontal direction for a vertical wall are:cos'SKasin(+の）sin(@-β)cosScoso cosβcos"dFsin(@+8)sin(@+β)COSOcosScosβwhereΦ=angle of internal friction of soil=angle of wall frictionβ =angle of the backfill with respect to horizontalFigure 3(a) is included for ease in obtaining Ka and KpAsintheRankine Theory,theCoulombTheoryalso assumesaplanesurfaceoffailure.However,theposition of thefailureplaneisafunctionofboththe-angleofthesoilandthe angle of wall friction,.The position of the failure plane for the active and passivecases fora level backfill isgiven by:tang+tanp(tanp+cotp)(1+tang.cotp)αa = 90°--arctan1+tang (tanp+cotp)tang+tanp(tanp+cot$)(1+tan.cotp)αp=90°+α-arctan1+tano (tanp+cot)