MSCAGR (Soil Science) / Department of Soil Science / Soil resilience is the ability of a soil to recover its function or capacity after applied stress such as crusting. Some soils have high potential for recovery while others have poor resilience. Soils with poor resilience are much more vulnerable to degradation. Many soils in South Africa are susceptible to crust formation, which affects many soil surface properties and processes and hence productivity. The objectives of this study were to demonstrate how soil resilience to crust formation is affected by conventional tillage and conservation agriculture in selected soils in South Africa. Soil samples were collected from four different soils (Hutton, Shortland, Glenrosa and Dundee) using PVC pipes with the length of 20 cm and diameter of 5cm and scanned using micro xray computed tomography for total pores. Total porosity from Luvisols, Ferrosols, Leptsols and Fluvisols under both conventional tillage and conservation agriculture was used to find soil resilience index. Soil crusting was influenced by both soil texture and clay mineralogy. The dominance of kaolinitic mineral caused the soil to be more stable as compared to soil dominated by quartz. Luvisols, Ferrosols and Leptsols were more stable and had aggregate stability of 57%, 69,5% and 32,7%, respectively. On the other hand, Fluvisols had poor aggregate stability with the value of 14,2%. Total porosity was in the order of 34,3%>32,2%>23,5%>16,3% for Ferrosols, Luvisols, Leptsols and Fluvisols, respectively. Soil crusting influenced the total porosity. Tillage practices had influence on soil crust formation hence, total porosity of the soils. Total porosity was higher under conservation agriculture as compare to conventional tillage. Resilience total porosity was in the order of 37,5> 23,9> 4,1> -30,1 on Luvisols, Ferrosols, Leptsols and Fluvisols, respectively. Soil resilience to crust formation was influenced by tillage practices. Soil resilience of Luvisols, Ferrosols and Leptsols can be achieved through conservation agriculture however, soil resilience of Fluvisols can be achieved through conventional tillage. / NRF

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20327号 / 工博第4264号 / 新制||工||1661(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 三村 衛, 教授 大津 宏康, 准教授 肥後 陽介 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

No description available.

In this investigation, seismic response of retaining walls constructed with cohesive and cohesionless backfill materials was studied. Fully dynamic analysis based on finite difference method was used to evaluate the performance of retaining walls during the earthquake. The analysis response was verified by the experimental study conducted on a retaining wall system with cohesive backfill material in the literature. The effects of cohesion and free-field peak ground acceleration (PGA) on seismic earth thrust, the point of action of earth thrust, and maximum wall moment during the earthquake were compared with analytical and experimental solutions. The numerical results were compared with various analytical solutions. The motion characteristics of the retaining wall during the earthquake were also considered. The relative displacement of the walls with various backfill cohesions, under different ground motions, and free-field PGAs were investigated. Current analytical and empirical correlations developed based on Newmark sliding block method for estimating retaining wall movement during earthquakes were compared with the numerical approach. Consequently, fragility analyses were conducted to determine the probability of damage to the retaining walls. To evaluate the fragility of the studied models, specific failure criterion was chosen for retaining walls based on the suggested methods in practice. Using numerical approaches, the effects of soil-wall interaction and wall rigidity on the seismic response of retaining walls were also evaluated in earthquake conditions for both cohesive and cohesionless backfill materials. According to the findings, practical correlations were presented for conducting the seismic design of retaining walls.

Settlement-Induced Bending Moments (SIBM) are an important design condition that must be considered whenever battered piles are placed in settling soils. The objective of this research was to investigate various parameters which can affect SIBM in battered piles within a levee embankment. The results from the current study were compared and verified against those obtained from centrifuge testing and alternative numerical simulations. A series of centrifuge testing as well as finite difference numerical simulations in Fast Langrangian Analysis of Continua (FLAC) were conducted. Different parameters which may affect the bending moments were investigated including pile connection fixity, batter, and stiffness of the pile as well as the magnitude of settlement. The simulations show that these parameters can have large impacts on the magnitude and location of the bending moments. Findings of this research can be used to validate or identify the need for adjustment of the current modeling/design approach.

La presente investigación, desarrollará la interacción dinámica suelo estructura IDSE con y sin amortiguamiento aplicado a 3 modelos denominados modelo A, modelo B y modelo C con 4, 8 y 12 pisos respectivamente. Estos modelos serán evaluados en tres tipos de perfiles de suelo S1, S2 y S3 con características (peso específico, coeficiente de poisson y carga admisible) obtenidas de los libros del Sr. Braja M. Das y Willian Rodriguez Serquen. La evaluación de la IDSE se realizará mediante las ecuaciones simplificadas propuestas por la Norma Americana (EEUU) NIST GCR 12-917-21 Soil-Structure Interaction for Building Structures donde se desarrolla la interacción inercial que se hace referencia a los desplazamientos y rotaciones en la base de la estructura (fundación) debido a la respuesta de la estructura cuando da lugar un sismo. Asimismo, la flexibilidad de la fundación y suelo son representados mediante 6 rigideces (3 de traslacionales y 3 de rotación) con y sin amortiguamiento. Para cada modelo se realizará una comparación de cortante basal, momento, desplazamientos, derivas, periodos, frecuencias, modos de vibración, fuerzas internas máximas, y fuerzas internas en un pórtico con la finalidad de observar el comportamiento de las estructuras en los distintos tipos de suelo y tamaños de las modelos propuestas. / This research will develop dynamic floor structure IDSE interaction with and without damping applied to 3 models called model A, model B and model C with 4, 8 and 12 floors respectively. These models will be evaluated in three types of soil profiles S1, S2 and S3 with characteristics (specific weight, poisson coefficient and permissible load) obtained from the books of Mr. Braja M. Das and Willian Rodriguez Serquen. The evaluation of the IDSE will be carried out using the simplified equations proposed by the American Standard (USA) NIST GCR 12-917-21 Soil-Structure Interaction for Building Structures where inertial interaction is developed that refers to displacements and rotations at the base of the structure (foundation) due to the response of the structure when an earthquake occurs. In addition, the flexibility of the foundation and soil are represented by 6 rigidities (3 translational and 3 rotation) with and without damping. For each model, a comparison of basal shear, timing, displacements, drifts, periods, frequencies, vibration modes, maximum internal forces, and internal forces will be made on a gantry in order to observe the behavior of structures in the different soil types and sizes of the proposed models. / Tesis

The focus of this study is on potential problems resulting from construction on expansive soils in Kibaha region, Tanzania. For the fact that most of the affected structures are founded on expansive soils, a clear understanding of the soil behaviour and their interaction with structures, specifically as they relate to shallow foundations, has been of more interest to the study in order to evaluate properly the source of the problem. The geotechnical behaviour of expansive clay soils is investigated by looking into the geomorphologic, geological and climatic conditions and mineralogical composition of the soils in the study area. The geotechnical results are linked with the performance of the foundation as well as structures. Two sites, representative of known problem-areas in Kibaha were selected for geotechnical tests. Geotechnical site investigation consisted of open trial pits, profile description and the collection of both disturbed and undisturbed samples. The collected samples were submitted to soil laboratories at KTH and DIT for mineralogical composition tests, natural water content, density, Atterberg limits and swell tests (free swell and swelling pressure). The results of this investigation indicate that soil in Kibaha contains clay (31%), have high liquid limit (59%) and plastic limit (37%) which indicate high potential swell. Since swell potential and swell pressure are key properties of expansive soils, the swell parameters were measured by free swell tests and one-dimensional oedometer swell tests respectively. The free swell ranged from 100% to 150% and the swell pressure was in the region of 45 kPa. The properties of expansive soils were confirmed by the x-ray diffraction test which showed the presence of montmorillonite in the soil. It is from this fact that the source of the problem is in the expansive soils coupled with poor building materials. Physical conditions of the surveyed properties in the area confirmed the hypothesis of building damages due to poor building materials triggered by expansive soils. In support of the obtained data, the actual behaviour of the foundations is supplemented with prototypes of strip foundations whose performances are to be monitored over a long period. Finally, suggested are the ways forward to solve the problem of foundation on expansive soil. / QC 20101118

Conventional farming systems create socio-economic problems through increased production costs and loss of the soil and chemicals that are washed from the farmlands. Even though no-till farming systems can increase farm profit and reduce environmental degradation, soil compaction can negate the advantages of no-till farming when no-till systems are used continuously under certain soil and climatic conditions. One objective of this study was to evaluate the long-term effects of the no-till method on bulk density, capillary porosity, noncapillary porosity, void ratio, and cone index of the soil. Although tillage affected cone index significantly, moisture variations caused difficulty in interpreting the results. No statistically significant differences in other parameters were found among no-till, conventional till, and control fallow treatments within each of three cropping seasons. However, within each tillage treatment these parameters showed significant variations between test seasons. When the soil bulk density data is required at close depth intervals, the core sample method becomes laborious while its use is limited by soil type and moisture conditions. The neutron probe densitometer is difficult to use in tillage studies due to practical problems. Among the predictive models for bulk density, some require parameters determined through expensive laboratory procedures while others have not been proven to work in field conditions. Therefore, the second objective was to develop a model to predict soil bulk density using cone index and moisture content data for a Virginia soil. Two separate models have been developed for top and subsoil layers using remolded natural soil samples. The topsoil model predicted bulk density close to the actual data taken in recently disturbed soils. One cropping season after plowing, predicted values were about 10% higher than the actual, a result which could be due to the aging effect. The subsoil model, on the other hand, under-predicted soil bulk density by about I5% After the model coefficients for a particular soil are determined through laboratory tests, cone index and moisture data can be used to predict bulk density in that soil. This procedure may save time and expense in future research on soil compaction. / Ph. D.

Highway bridges are considered to be one of the most susceptible constituents of transportation networks when they are subjected to severe natural hazards such as earthquakes and environmental exposures like subfreezing temperatures. To facilitate and enhance pre-hazard event mitigation and post-hazard emergency response strategies, probabilistic risk assessment methodologies have attracted increased attention, recently. Seismic fragility assessment is one of the probabilistic techniques which predicts the damage risk of the structure for a given hazard level. While fragility curves can be developed using different methods, such as expert-based, empirical, experimental, analytical, and hybrid, analytical fragility curves are perceived to be the most reliable and least biased technique. Seismic isolation systems are prevalently used in bridge structures to mitigate the damage risk of bridge components against natural hazards. However, the effectiveness of implementing recently emerged isolators such as Stable Unbonded Fiber Reinforced Elastomeric Isolators (SU-FREI) should be examined by developing analytical fragility curves of retrofitted bridges and quantifying the mitigation in the damage probability of different bridge components. In this regard, incorporating the Soil-Structure Interaction (SSI) is critical since the lateral response of bridges relies on the relative stiffness of bridge components, such as columns and isolators and the supporting soil. In addition, all bridge components are exposed to environmental stressors like subfreezing temperature that can alter the seismic response of bridges. In the first phase of this thesis, a seismic fragility assessment is carried out on an existing multi-span continuous reinforced concrete bridge. Two bridge representations are developed to simulate the as-built bridge along with its retrofitted counterpart utilizing SU-FREI. An Incremental Dynamic Analysis (IDA) is conducted using 45 synthetic ground motion records developed for eastern Canada and damage limit states are applied to generate fragility curves and determine the probability of damage to different bridge components. Bridges are analyzed in longitudinal and transverse directions, independently, and component- and system-level fragility curves are developed. In the second phase, the previously generated bridge models are expanded to incorporate the SSI effects by introducing the pile groups under piers and abutments. Several interactions including deck-abutment, abutment-embankment, pile-soil, and pile-soil-pile interactions are considered. A significant challenge in this phase is the accurate simulation of the lateral and vertical behavior of pile groups since all pile groups comprised of closely-spaced vertical and battered piles. A ground motion suite consisting of 45 ground motions has been selected, which reflects the seismicity of the bridge site. IDA is conducted to monitor the seismic performance of the bridge from the elastic linear region up to collapse. Fragility curves, which serve as an important decision-support tool have been developed to identify the potential seismic risk of the bridge. In the third phase, a multi-hazard assessment is carried out by conditioning the previously developed bridge models (i.e. monolithic fixed-base, isolated fixed-base, monolithic with SSI, and isolated with SSI) to a range of room and subfreezing temperatures and applying a seismic excitation, simultaneously. The cold temperature behavior of the constitutive materials of different bridge components, namely, concrete, reinforcing steel, rubber, and the supporting soil are studied and reflected in the bridge models. IDA is performed and damage potential of different bridge components are quantified. In summary, it is demonstrated that SU-FREI is a competing alternative for seismic isolation of bridges by offering potentially less manufacturing time and cost, lower weight, and easier installation which is an attractive feature for accelerated bridge construction applications. In all three phases, it is shown that the bridges which are isolated using SU-FREI have improved seismic performance in comparison with monolithic bridges by exhibiting lower probability of damage to the primary bridge components like columns and pile caps and transferring the damage to less important components such as abutments at which damage does not cause bridge closure. In addition, it is shown that seismic isolation using SU-FREI can effectively mitigate the seismic demand and damage potential of the constitutive components of a bridge supported by weak soil. While occurrence of seismic events along with an environmental stressor such as cold temperature can drastically jeopardize the functionality of a bridge supported by weak soil, it is demonstrated that seismic isolation using SU-FREI can significantly alleviate the probability of damage to bridge components. / Dissertation / Doctor of Philosophy (PhD)

No description available.