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Earthquake-induced soil liquefaction is a phenomenon in which saturated, sandy soil loses its strength and stiffness during earthquake shaking. Liquefaction can be extremely costly and damaging to infrastructure. The commonly used "simplified" stress-based liquefaction triggering framework is correlated with metrics computed from in-situ tests like the Cone Penetration Test (CPT). While CPT-based procedures have been shown to accurately predict liquefaction occurrence in homogenous, sandy soil profiles, they tend to over-predict the occurrence of liquefaction in challenging, highly interlayered soil profiles. One contributing factor to the over-prediction is multiple thin-layer effects in CPT data, a phenomenon in which data in interlayered zones is blurred or averaged, making it difficult to identify specific layer boundaries and associated CPT parameters like tip resistance. Multiple thin-layer correction procedures have been proposed to convert the measured tip resistance in an interlayered profile (qm) to the "true" or characteristic tip resistance (qt) that would be measured without the influence of multiple thin-layer effects. In this dissertation, the efficacy of existing multiple thin-layer correction procedures is assessed. It is shown that existing procedures are not effective for layer thicknesses equal to or less than about 1.6 times the diameter of the cone. Two new multiple thin-layer correction procedures are proposed. Furthermore, a framework for numerically simulating CPTs in interlayered soil profiles using the Material Point Method (MPM) is developed. A framework for linking uncertainties associated with the numerical analyses and the laboratory CPT calibration chamber tests used to calibrate the numerical analyses is also proposed. Finally, a database of laboratory and numerically-generated CPT data is presented. It is shown how this database can be used to improve existing, and develop new, multiple thin-layer correction procedures. Ultimately, the work detailed in this dissertation will improve the characterization of highly interlayered soil profiles using CPTs to support more accurate liquefaction hazard assessment at challenging soil sites. / Doctor of Philosophy / Earthquake-induced soil liquefaction is a phenomenon in which saturated, sandy soil loses its strength and stiffness during earthquake shaking. Liquefaction can be extremely costly and damaging to infrastructure. Existing procedures used to assess liquefaction hazard were developed specifically for homogenous, sandy soil profiles. These procedures do not perform well in challenging, highly interlayered soil profiles. One reason for this is the inadequate characterization of the soil profile by the chosen in-situ test method. For example, the cone penetration test (CPT) consists of hydraulically advancing a steel probe with a conical shaped tip ("cone") into the ground. Typically, the penetrometer is about 3.6 to 4.4 cm in diameter, and data are recorded at 1 to 5 cm depth intervals. However, data recorded at a specific depth are representative of soil that falls within a zone several times the diameter of the penetrometer ahead of and behind the tip of the cone. In a highly interlayered soil profile, this means the CPT records blurred or averaged data within interlayered zones. Typical liquefaction analyses compute a factor of safety against liquefaction at every depth in the soil profile where CPT data are recorded. Hence, having data that are blurred can result in an inaccurate factor of safety against liquefaction. To account for this blurring (called multiple thin-layer effects), correction procedures have been proposed. This dissertation evaluates the effectiveness of those procedures and develops new procedures. Additionally, a numerical simulation tool is shown to be capable of simulating CPTs in layered soil profiles. This reduces the need for costly laboratory testing to further evaluate multiple thin-layer effects. Finally, a combined laboratory and numerically-generated CPT database is developed to support the improvement of, and development of new, multiple thin-layer correction procedures. The broader impacts of this work support more accurate liquefaction evaluations in challenging soil profiles worldwide, like those in Christchurch, New Zealand, and the Groningen region of the Netherlands.

A thesis submitted to the Faculty of Engineering, Cape Peninsula University of Technology, Cape Town, in partial fulfilment of the requirements for the M-Tech Degree in Civil Engineering” Cape Town 16 MAY 2011 / Dwellings in impoverished and upper class urban areas of the Western Cape have undergone serious structural failure due to problematic underlying sand deposits, generally known as Cape Flats windblown found in areas such as Delft, Blue Downs and the Atlantic Beach Golf Estate. The problem is compounded further when moisture penetrates below the footings and reaches saturation in the winter months. When poorly graded sand with a high fines content is coupled with vibration (through earth tremors), liquefaction may occur and without proper precautions, this can lead to inadequate foundation design, more than expected settlement and eventual structural failure. Some sand deposits are highly contaminated with organic debris, leading to compressible and collapsible conditions. Little knowledge is locally available of liquefiable conditions in windblown dune sand and what long-term settlement can be expected. The Western Cape is not known as an area exposed to serious seismic activity, but an updated (and more locally applicable set of data) is needed to eliminate possible erroneous foundation design. Samples have been extracted from typical sandy sites in the Western Cape where windblown dune sand is evident. Laboratory tests have been carried out on representative samples for closer examination and have been placed inside a purpose built calibration chamber that facilitates easy densification and probe testing. A DMT (flat blade dilatometer) was used to hydraulically penetrate the chamber sand sample to varying depths (up to 800 mm). The device can measure (with reduction formula) horizontal stress, angle of friction, bearing capacity and settlement. An accelerometer was attached to the chamber wall and vibration measured with the sand in varying states of moisture. The DMT is an unexplored in-situ soil testing device in South Africa and so far the outcome indicates favourably compared to other devices such as the Dynamic Cone Penetrometer (DCP. The DMT has the ability to measure the in-situ stiffness, strength and stress history parameters of soil for better site characterisation. Settlement within the chamber is easily measured. The DMT has, for example, indicated that sand from the Philippi area are a problematic founding soil and should be treated with special care at shallow founding levels. The horizontal stress index is low and according to the available knowledge on soil stress history, these sand, coupled with low densities, can liquefy easily and result in structural damage. The West Coast dune sand, being coarser and easily consolidated, poses less of a problem under liquefiable conditions. A suitable terrain device for easy on-site manoeuvrability is required to assist the DMT in further testing.

In order to avoid the occurrence of early-age damage, cement-treated base (CTB) materials must be allowed to cure for a period of time before the pavement can be opened to traffic. The purpose of this research was to evaluate the utility of the soil stiffness gauge (SSG), heavy Clegg impact soil tester (CIST), portable falling-weight deflectometer (PFWD), dynamic cone penetrometer, and falling-weight deflectometer for assessing early-age strength gain of cement-stabilized materials. Experimentation was performed at four sites on a pavement reconstruction project along Interstate 84 near Morgan, Utah, and three sites along Highway 91 near Richmond, Utah; cement stabilization was used to construct CTB layers at both locations. Each site was stationed to facilitate repeated measurements at the same locations with different devices and at different curing times. Because of the considerable attention they have received in the pavement construction industry for routine quality control and quality assurance programs, the SSG, CIST, and PFWD were the primary focus of the research. Statistical techniques were utilized to evaluate the sensitivity to curing time, repeatability, and efficiency of these devices. In addition, the ruggedness and ease of use of each device were evaluated. The test results indicate that the CIST data were more sensitive to curing time than the SSG and PFWD data at the majority of the cement-treated sites during the first 72 hours after construction. Furthermore, the results indicate that the CIST is superior to the other instruments with respect to repeatability, efficiency, ruggedness, and ease of use. Because the CIST is less expensive than the SSG and PFWD, it is more likely to be purchased by pavement engineers and contractors involved with construction of CTBs. For these reasons, this research suggests that the CIST offers greater overall utility than the SSG or PFWD for monitoring early-age strength gain of CTB. Further research is needed to identify appropriate threshold CIST values at which CTB layers develop sufficient strength to resist permanent deformation or marring under different types of trafficking.

An investigation into the load-settlement behavior of two drilled shafts, founded in shale, is presented. The motivation for this research is to advance the understanding on how drilled shafts react under loading in stiff clays and shales. The objectives of the study are to measure the strengths within the subsurface material at the test site, estimate the unit side shear and unit end bearing of the shale-shaft interaction by running two axial load tests, and compare the results to the current design methods that are used to predict the axial capacity of drilled shafts. A comprehensive field investigation, performed by Fugro Consultants, provided strength profiles of the subsurface material at the test site. Through the cooperation of the Texas Department of Transportation (TxDOT), the Association of Drilled Shaft Contractors, and McKinney Drilling Company, two drilled shafts were installed at a highway construction site in Austin, Texas. The load tests were performed by Loadtest, Inc.; using the patented Osterberg-Cell™ loading technique to axially displace the shafts. Ensoft, Inc. installed strain gauges at multiple levels within the shafts, making it possible to analyze the shaft mobilization during loading. Ultimate end bearing values of about 100- and 120-ksf were measured for Test Shafts #1 and #2, respectively. The current methods for estimating unit end bearing, developed by TxDOT and the Federal Highway Administration, provide fairly accurate predictions when compared to the measured information. The ultimate side resistance obtained near the O-Cell™ in each test was about 20-ksf, however, the measured ultimate side resistance steadily decreased nearing the tip of the shaft. For the zones where the side resistance was believed to be fully mobilized, the TxDOT design method accurately predicts the side resistance. A limited amount of information is currently available for load tests performed in soils with TCP values harder than 2-in per 100 blows. Additional load test information should allow for a stronger correlation between TCP tests and unit resistances for very hard clay-shales, as well as, allowing for further evaluation of the shale-shaft interaction near the shaft tip. The results presented herein demonstrate the effectiveness of the current design methods for drilled shafts and the non-uniformity of side resistance within one- to two-diameters of the shaft tip. / text

CPTU is one of the most sophisticated geotechnical investigation methods. However, there is a large amount of uncertainties related to this method. The uncertainties depend on different types of factors, for instance lack of accuracy in performance and equipment. The objective of this master thesis is to compare the CPTU-results from a number of commercial actors in Stockholm/Mälardalen in order to analyze these results with respect to the current standards and guidelines. The comparison was made in order to highlight the difference in results which may appear due to different equipment, performance of the operator and evaluation method. Based on this, an invite was sent to the commercial actors in Stockholm/Mälardalen, resulting in the participation of five different commercial actors in this investigation. Execution in the field was conducted over a six week period. During this time 26 CPTU were performed in total in a small area in Hagby, Stockholm, by these different actors. Once the data was collected from all of the actors, the results were evaluated with the aid of the computer softwares Conrad and Excel. The main conclusions from this study are: Not one of the performed CPTU in this master thesis fulfills the requirements for CPT class 1 according to the European standards. The quality of the education of operators should be improved and geotechnical engineers and the clients need to be more familiar with CPTU. The evaluated results from different commercial actors differ, and this can depend on the choice of equipment and performance of the operator during penetration, but it can also depend on systematic errors in the cone penetrometers / CPTU-sonderingar är en av de mest sofistikerade undersökningsmetoderna för geoteknisk analys och bedömning. Det finns emellertid en hög grad av osäkerhet i denna metod. Osäkerheten beror på olika typer av faktorer, bland annat brist på noggrannhet i handhavande och utrustning. Syftet med detta examensarbete är att jämföra CPTU-resultat från de kommersiella aktörerna i Stockholm/Mälardalen för att senare analysera dessa resultat i förhållande till gällande ramverk och riktlinjer. Jämförelsen gjordes med avsikt att lyfta fram skillnaderna i resultat som kan uppstå på grund av olika utrustning, handhavande och utvärderingsmetod. Baserat på detta skickades en inbjudan till de kommersiella aktörerna i Stockholm/Mälardalen, vilket ledde till att fem olika kommersiella aktörer deltog i undersökningen. Utförande i fält genomfördes under en period på sex veckor. Under denna tid utfördes totalt 26 sonderingar i ett avgränsat område i Hagby, Stockholm, av dessa olika aktörer. När all data samlats in från alla aktörer utvärderades resultaten med hjälp av mjukvarorna Conrad och Excel. De viktigaste slutsatserna i denna studie är: Ingen utav de utförda CPTU-sonderingarna uppfyller kraven för CPT klass 1 enligt den europeiska standarden. Kvaliteten på utbildning av fältgeotekniker bör förbättras och geotekniska ingenjörer och även beställare bör bli mer bekanta med CPT. De utvärderade resultaten från de olika aktörerna skiljer sig åt, och detta kan bero på valet av utrustning och fältgeoteknikerns prestation vid sondering men det kan också bero på systematiska fel i de använda sonderna.

Please read the abstract in the section, 00front, of this document / Thesis (DPhil)--University of Pretoria, 2008. / Civil Engineering / unrestricted

The first objective of this research was to investigate temporal trends in the mechanical properties of base materials stabilized with asphalt emulsion and to assess the rate at which emulsion-treated base (ETB) design properties are achieved. The second objective of this research was to identify construction and environmental factors most correlated to specific mechanical properties of ETB layers and to determine which construction factors exhibit the greatest variability. Additional statistical analysis was performed to determine if significant differences existed between different test sections on a given project. In this research, three experimental sections were established along a pavement reconstruction project near Saratoga Springs, Utah. Field tests were performed to assess the structural properties of the ETB immediately following construction and at 2, 3, 7, and 14 days; 4 months; and 1 year. Measured values were plotted against time to determine trends in ETB strength development. Several statistical analyses were then performed on the collected data. Modulus values were consistently low in all three sections during the first two weeks of testing, increased dramatically by 4 months, and then decreased considerably by 1 year. During the first two weeks following construction, the average ETB structural coefficient was 0.04. Only two of the three sections reached the design structural coefficient of 0.25, which occurred after approximately 3 months; however, the average structural coefficient measured for all three sections after 1 year of curing, which included a winter, was only 47 percent of the design strength. The results of this research show that, while pavement capacity is sufficient at 4 months, it is severely reduced during the first two weeks and at 1 year. Trafficking under these reduced capacities is not recommended. Statistical analysis showed that gradation, binder change during emulsion treatment, and moisture content have the most significant impact on ETB structural properties. Gradation and binder change during emulsion treatment also exhibited significant variability; tighter specifications on material gradations and improved uniformity in emulsion distribution should therefore be considered. Because of the negative impacts of moisture on ETB strength development, construction should not be performed in conditions of excess moisture.