【正文】 il is given free access to water, it may decrease in volume,increase in volume, or do soil that increases in volume is called a swelling or expansive soil, and a soil that decreases in volume is called a collapsible amount of volume change that occurs depends on the soil type and structure, the initial soil density, the imposed stress state, and the degree and extent of materials prised of soils that change volume upon wetting have caused distress to highways since the beginning of the professional practice and have cost many millions of dollars in roadway prediction of the volume changes that may occur in the field is the first step in making an economic decision for dealing with these problem subgrade project will have different design considerations, economic constraints, and risk factors that will have to be taken into , with a reliable method for making volume change predictions, the best design relative to the subgrade soils bees a matter of economic parison, and a much more rational design approach may be example, typical techniques for dealing with expansive clays include:(1)In situ treatments with substances such as lime, cement, or flyash。(2)seepage barriers and/ or drainage systems。or(3)a puting of the serviceability loss and a modification of the design to “accept” the anticipated order to make the most economical decision, the amount of volume change(especially nonuniform volume change)must be accurately estimated, and the degree of road roughness evaluated from these , alternative design techniques are available for any roadway emphasis here will be placed on presenting economical and simplemethods for:(1)Determining whether the subgrade materials are collapsible。and(2)estimating the amount of volume change that is likely to occur in the 39。., Advanced Transp., Arizona State Univ., Tempe, AZ open until April 1, extend the closing date one month,a written request must be filed with the ASCE Manager of manuscriptfor this paper was submitted for review and possible publication on February 3, paper is part of the Journal of , , ,November, , ISSN 0733947X/88/00060673/$ + $.15 per 3field for the collapsible this information will place the engineerin a position to make a rational design soils are frequently encountered in an arid depositional process and formation of these soils, and methods for identification and evaluation of theamount of volume change that may occur, will be discussed in the following SOILSFormation of Collapsible SoilsCollapsible soils have high void ratios and low densities and are typicallycohesionless or only slightly an arid climate, evaporation greatlyexceeds , only the nearsurface soils bee wettedfrom normal is the bination of the depositional process andthe climate conditions that leads to the formation of the collapsible collapsible soils exist in nondesert regions, the dry environment inwhich evaporation exceeds precipitation is very favorable for the formationof the collapsible the soil dries by evaporation, capillary tension causes the remainingwater to withdraw into the soil grain interfaces, bringing with it soluble salts,clay, and silt the soil continues to dry, these salts, clays, andsilts e out of solution, and “tackweld” the larger grains leads to a soil structure that has high apparent strength at its low, naturalwater , collapse of the “cemented” structure may occurupon wetting because the bonding material weakens and softens, and the soilis unstable at any stress level that exceeds that at which the soil had beenpreviously , if the amount of water made available to the soilis increased above that which naturally exists, collapse can occur at fairlylow levels of stress, equivalent only to overburden soil loads, such as traffic loading or the presence of a bridge structure, add tothe collapse, especially of shallow collapsible triggering mechanismfor collapse, however, is the addition of Problems Resulting from Collapsible SoilsNonuniform collapse can result from either a nonhomogeneous subgradedeposit in which differing degrees of collapse potential exist and/or fromnonuniform wetting of subgrade differential collapse ofsubgrade soils occurs, the result is a rough, wavy surface, and potentiallymany miles of extensively damaged have been several reported cases for which differential collapse has been cited as the cause ofroadway or highway bridge few of these in the Arizona and NewMexico region include sections of 110 near Benson, Arizona, and sectionsof 125 in the vicinity of Algadonas, New Mexico(Lovelace et 。Russman 1987).In addition to the excessive waviness of the roadway surface, bridge foundations failures, such as the Steins Pass Highway bridge,110, in Arizona, have frequently been identified with collapse of foundation of Collapsible SoilsThere have been many techniques proposed for identifying a collapsiblesoil methods range from qualitative index tests conducted on4disturbed samples, to response to wetting tests conducted on relatively undisturbed samples, to in situ meausrement all cases, the engineer must first know if the soils may bee wetted to a water contentabove their natural moisture state, and if so, what the extent of the potentialwetted zone will methods for identifying collapsible soils are onlyqualitative in nature, providing no information on the magnitude of the collapse strain qualitative methods are based on various functions of dry density, moisture content, void ratio, specific gravity, and Atterberg situ measurement methods appear promising in some cases, in that manyresearchers feel that sample disturbance is greatly reduced, and that a morenearly quantitative measure of collapse potential is ,in situ test methods for collapsible soils typically suffer from the deficiency of an unknown extent and degree of wetting during the field makes a quantitativ