Lime-cement columns were constructed to improve soft ground at the I-95/Route 1 Interchange in Alexandria, Virginia. As part of the test embankment program, two different commercial laboratories performed laboratory tests on treated soil, and they produced strikingly different unconfined compression test results. Further, both sets of results are different from test results for similar soils available in the published literature. This situation created uncertainties and a conservative design philosophy, accompanied by increased construction costs compared to typical lime-cement column projects. The goals of this research project were to assess factors that influence strength gain of lime-cement-soil mixtures and to develop a detailed laboratory test procedure that produces consistent results. Key findings from the research are that a laboratory test procedure that produces consistent results has been developed, drying and subsequent restoration of soil moisture prior to treatment can decrease the strength of the mixture, the mixture strength decreases as the ratio of soil water content to cement content increases for 100 percent cement-soil mixtures, the addition of lime can increase the mixture strength for some soils and decrease the strength for others, and presenting the test results in the form of contour plots of unconfined compressive strength can be very useful. / Master of Science

<p>The thesis is dealing with mixing processes havingapplication to ground improvement by deep mixing. The mainobjectives of the thesis is to make a contribution to knowledgeof the basic mechanisms in mixing binding agents into soil andimprove the knowledge concerning factors that influence theuniformity of stabilised soil.</p><p>A great part of the work consists of a literature surveywith particular emphasis on literature on the processindustries. This review forms a basis for a profounddescription and discussion of the mixing process and factorsaffecting the process in connection with deep mixingmethods.</p><p>The thesis presents a method for a simple field test for thestudy of influential factors in the mixing process. A number offactors in the installation process of lime-cement columns havebeen studied in two field tests using statistical multifactorexperiment design. The effects of retrieval rate, number ofmixing blades, rotation speed, air pressure in the storagetank, and diameter of the binder outlet on the stabilisationeffect and the coefficient of variation determined byhand-operated penetrometer tests for excavated lime-cementcolumns, were studied.</p><p>The literature review, the description of the mixingprocess, and the results from the field tests provide a morebalanced picture of the mixing process and are expected to beuseful in connection to ground improvement projects and thedevelopment of mixing equipments.</p><p>The concept of sufficient mixture quality, i.e. theinteraction between the mixing process and the mechanicalsystem, is discussed in the last section. By means ofgeostatistical methods, the analysis considers thevolume-variability relationship with reference to strengthproperties. According to the analysis, the design values forstrength properties depends on the mechanical system, the scaleof scrutiny, the spatial correlation structure, and the conceptof safety, i.e. the concept of sufficient mixture quality isproblem specific.</p><p><b>Key words:</b>Deep Mixing, Lime cement columns, Mixingmechanisms, Mixture quality, Field test, ANOVA, Variancereduction.</p>

The thesis is dealing with mixing processes havingapplication to ground improvement by deep mixing. The mainobjectives of the thesis is to make a contribution to knowledgeof the basic mechanisms in mixing binding agents into soil andimprove the knowledge concerning factors that influence theuniformity of stabilised soil. A great part of the work consists of a literature surveywith particular emphasis on literature on the processindustries. This review forms a basis for a profounddescription and discussion of the mixing process and factorsaffecting the process in connection with deep mixingmethods. The thesis presents a method for a simple field test for thestudy of influential factors in the mixing process. A number offactors in the installation process of lime-cement columns havebeen studied in two field tests using statistical multifactorexperiment design. The effects of retrieval rate, number ofmixing blades, rotation speed, air pressure in the storagetank, and diameter of the binder outlet on the stabilisationeffect and the coefficient of variation determined byhand-operated penetrometer tests for excavated lime-cementcolumns, were studied. The literature review, the description of the mixingprocess, and the results from the field tests provide a morebalanced picture of the mixing process and are expected to beuseful in connection to ground improvement projects and thedevelopment of mixing equipments. The concept of sufficient mixture quality, i.e. theinteraction between the mixing process and the mechanicalsystem, is discussed in the last section. By means ofgeostatistical methods, the analysis considers thevolume-variability relationship with reference to strengthproperties. According to the analysis, the design values forstrength properties depends on the mechanical system, the scaleof scrutiny, the spatial correlation structure, and the conceptof safety, i.e. the concept of sufficient mixture quality isproblem specific. Key words:Deep Mixing, Lime cement columns, Mixingmechanisms, Mixture quality, Field test, ANOVA, Variancereduction.

Excavations in soft clays come with a number of specific challenges. The use of lime-cement columns in the passive zone of such works represents a promising solution to some of these problems, such as basal heave stability or excessive deformations. Nevertheless, lime-cement columns in the passive zone of excavations in soft clays are not yet widely used and studied. Knowledge about this improvement method is still limited, particularly when it comes to numerical modelling. They have mostly been studied numerically using simple geometries or constitutive models that do not allow to represent the key features of the material, that could influence the behaviour of the structure. Thus, there is a need for more investigations regarding precise modelling tools for this type of problems. In this study, an advanced constitutive model named the Concrete model was employed to capture the mechanical behaviour of the lime-cement improved soil material. A boundary value problem representing an excavation in soft clay supported by sheet pile walls and lime-cement columns was studied using a three dimensional finite element model that included the Concrete model for lime-cement column panels. The results show that the Concrete model is able to capture the behaviour of lime-cement improved clay very well. Key features such as strain hardening and strain softening are well represented. The results of the boundary value problem were compared to field measurements and it was showed that the Concrete model employed in a three dimensional finite element representation of the problem is able to give realistic results. / Schakter i lös lera medför ett antal specifika utmaningar. Användningen av kalk-cementpelare i den passiva zonen i sådana fallen är en lovande lösning på några av dessa problem, t.ex. jordhävning eller stora deformationer. Kalk-cement pelare i den passiva zonen av schakter i lös lera har dock ännu inte använts och studerats i någon större utsträckning i Sverige. Kunskapen om denna metod är fortfarande begränsad, särskilt när det gäller numerisk modellering. Denna förstärkningsmetod har studerats numeriskt med hjälp av enkla geometrier eller konstitutiva modeller som inte gör det möjligt att representera materialets viktigaste egenskaper som kan påverka konstruktionens beteende. Det finns därför ett behov av mer forskning för en precis modellering för denna typ av problem. I den här studien användes en avancerad konstitutiv modell (Concrete model) för att simulera det mekaniska beteendet hos det kalkcementstabiliserade jordmaterialet. Ett gränsvärdesproblem som representerar en schakt i lös lera som stöds av spontväggar och kalkcementpelare studerades med hjälp av en tredimensionell finita elementmodell. Resultaten visar att den advancerade konstitutiva modellen kan simulera beteendet hos kalkcementstabiliserad lera mycket väl. Viktiga egenskaper som t.ex. töjningshärdning och töjningsuppmjukning är väl representerade. Resultaten av gränsvärdesproblemet modellering jämfördes med fältmätningar och det visades att konstitutiva modellen som används kan ge realistiska resultat. / Les excavations dans les argiles molles présentent de nombreuses difficultés. L’utilisation de colonnes en chaux-ciment dans la zone passive de ces structures représente une solution prometteuse à certains de ces défis, tels que le soulèvement de la base ou les déformations excessives. Néanmoins, l’utilisation et l’étude des colonnes en chaux-ciment dans la zone passive des excavations dans les argiles molles ne sont pas généralisées et les connaissances à ce sujet sont encore limitées, notamment en ce qui concerne la modélisation numérique. La plupart des études numériques se basent sur des géométries simples ou des modèles constitutifs ne permettant pas de représenter certaines particularités du comportement du matériau, qui pourraient influencer le comportement de la structure. Il est donc nécessaire d’approfondir les recherches sur les outils de modélisation pour ce type de problème. Dans cette étude, un modèle constitutif avancé (Concrete model) a été utilisé pour reproduire le comportement mécanique de l’argile stabilisée à la chaux et au ciment. Un problème de valeurs aux limites représentant une excavation dans de l’argile molle soutenue par des murs de palplanches et des colonnes en chaux-ciment a été étudié à l’aide d’un modèle d’éléments finis tridimensionnel. Les résultats montrent que le modèle employé permet de reproduire le comportement de l’argile stabilisée à la chaux-ciment de manière très satisfaisante. Les particularités du comportement du matériau, telles que l’écrouissage et l’adoucissement, sont bien représentées. Les résultats du problème de valeurs aux limites ont été comparés aux mesures sur le terrain et il semble que ce modèle constitutif, employé dans une représentation tridimensionnelle par éléments finis du problème, soit capable de donner des résultats réalistes.