Comparisons Between behaviors of Undisturbed and Remolded Swelling Soil

A.H. Hammam, A.E. Abdel Salam

Dans les comptes rendus d’articles de la conférence: GeoMontréal 2013: 66th Canadian Geotechnical Conference; 11th joint with IAH-CNC

Session: Soil and Rock Mechanics I

ABSTRACT: Swelling potential of expansive soils depends mainly on the microstructure, physical and chemical properties of naturalsoils. This study investigated the swelling characteristics of undisturbed and remolded swelling clay. Seventy-fiveundisturbed samples were collected from three locations in Egypt, among them are Hurghada city at 27• 30' 29"N, 33•34' 38" E, Suize city at 29• 59' 59" N, 32• 28' 42" E and Maadi city at 29•57' 36" N, 31• 16' 47"E. All samples weresubjected to the necessary tests similar to water content, Atterberg limits, bulk density, gradation and 24-hour free swell.Disturbed samples were also collected from the same citiesfrom which remolded samples were prepared according toASTM (D4829). Expansion Index and swelling pressure were measured for the undisturbed samples according tomethod A of ASTMD4546. The undisturbed samples divided totwo to four groups according to its moisture content.The first group represented the natural moisture contents whileothergroups subjected to air-drying to control its degreeof saturation. A comprehensive comparison has been achieved between swelling characteristics of the remolded andundisturbed samples. In general, the swelling behaviors of remolded samples are obviously higher than that ofundisturbed.The ratiobetween Expansion Index of remolded and those of undisturbed samplesranged between 1.6 and1.9.The effectsof poor drilling onmoisture contents ofundisturbed samples were discussed during analyzing the effectof degree of saturation on the swelling behavior.R†SUM†Potentiel des sols gonflants gonflement d‡pend principalement de la microstructure, les propri‡t‡s physiques etchimiques des sols naturels. Cette ‡tude a examin‡ les caract‡ristiques de gonflement de l'argile gonflement nonremani‡ et remani‡s. Soixante-cinq ‡chantillons intacts ont ‡t‡ collect‡es … partir de trois endroits en Egypte, parmi euxsont-ville d'Hurghada, … 27 • 30 '29 "N, 33 • 34' 38" E, ville Suize … 29 • 59 '59 "N, 32 • 28' 42 "E et Maadi ville … 29 • 57'36" N, 31 • 16' 47 "E. Tous les ‡chantillons ont‡t‡ soumis aux tests n‡cessaires semblables … la teneur en eau, leslimites d'Atterberg, la densit‡ apparente, la gradation et de la houle libre de 24 heures. †chantillons perturb‡s ont‡galement ‡t‡ recueillies … partir des m—mes villes o– les ‡chantillons remoul‡s ont ‡t‡ pr‡par‡s conform‡ment … lanorme ASTM (D4829). Indice d'expansion et de pression de gonflement ont ‡t‡ mesur‡es pour les ‡chantillons intacts,selon la m‡thode A de la norme ASTM D4546. Les ‡chantillons intacts divis‡es deux … quatre groupes en fonction de sateneur en humidit‡.Le premier groupe est repr‡sent‡ le taux d'humidit‡ naturel alors que les autres groupes soumis aus‡chage … l'air pour contrƒler son degr‡ de saturation. Une comparaison d‡taill‡e a ‡t‡ r‡alis‡e entre lescaract‡ristiques de gonflement des ‡chantillons remoul‡s et paisible. En g‡n‡ral, les comportements de gonflement des‡chantillons remoul‡s sont ‡videmment plus ‡lev‡ que celui des non perturb‡e. Le rapport entre l'indice d'expansion deremani‡s et ceux des ‡chantillons intacts variait entre 1,6 et 1,9. Les effets d'une mauvaise forage sur la teneur enhumidit‡ des ‡chantillons non remani‡s ont ‡t‡ discut‡s au cours de l'analyse de l'effet de degr‡ de saturation sur lecomportement de gonflement.1INTRODUCTIONExpansive soils in many parts of the world pose asignificant hazard to foundations not only for lightbuildings but also sometimes for high-rise buildings.Expansive soils attribute their characteristics to thepresence of swelling clay minerals. As they get wet, theclay minerals absorb water molecules and expand;conversely, as they dry they shrink, leaving large voids orcracks in the soil. Swelling clays can control the behaviorof virtually any type of soil if the percentage of clay ismore than about 12 percent by weight. Soils with activeclay minerals, such as montmorillonite, exhibit the mostdangerous swelling properties.Potentially expansive soils in Egypt can typically berecognized in the lab by their motley color, usually hasgreenish, yellowish, reddish or multi color in addition tohigh plasticity. Expansion of soils can initially bemeasured in the lab directly, by immersing a remoldedsoil sample and measuring its volume changethrough 24-hour free swell test.The situation at field is different from the lab because ofsite engineer misses to the experience to discover thisproblematic soil. Different projects encountered seriousproblems due to lack of soil investigation. Since 1980,Egyptian starts to invade the desert for land reclamationand establishing new communities and industrial areas.So, swelling clay was encountered at most of new urbandevelopments. Swelling soils that distributed all overEgypt are not similarin natureand each zone has itsdistinguishswelling characteristics. In general, swellingbehavior has been determined in Egypt through odometertests carried out on undisturbed samples. Due to the poortechnique of single core drilling, soil samples generallyexpose to drilling fluids and hence its natural moisturecontent or degree of saturation increases which can reach

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