Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Civil Engineering. / Bibliography: leaves 158-163. / M.S.

In geotechnical engineering, soil is subject to shear stress, as well as normal stress. In many cases, soil is sheared along multiple directions, such as an embankment under earthquake loading and foundation soil of a structure under a complex loading. In recent years, significant research has been devoted to understanding the static and cyclic shear behaviour of sand under complex stress conditions. To investigate the shear behaviours of soils, a few testing devices have been specifically developed. The most commonly used apparatuses are direct shear, direct simple shear, and hollow cylinder apparatuses. While each has its own merits, they share one common limitation. That is the soil specimens are sheared along only one direction in these devices, making it impossible to study the soil responses under multiple shear stresses encountered in many geotechnical engineering problems. It is widely acknowledged that testing stress path has a significant effect on shear stress, so specimens must be examined under a stress path similar to in-situ. In many cases, a simple shear apparatus closely duplicates the stress conditions in soil elements, and a bi-directional direct simple shear apparatus can create complex stress conditions. To investigate the shear behaviour of soils subject to complex loading conditions, several studies of multidirectional simple shear testing were performed on the first commercially available Variable Direction Dynamic Cyclic Simple Shear (VDDCSS) system. In the VDDCSS, the secondary shear actuator acting at 90 degrees to the primary shear actuator enables it to add shear stress in any horizontal direction. Various previously unexplored complex stress paths were tested in this study using the VDDCSS. Sand samples of Leighton Buzzard sand (Fraction B) were first subjected to consolidation shear stresses under drained conditions along different directions (from 0° to 180° to the X direction of the apparatus), followed by monotonic or cyclic secondary shear stresses along 0° until failure occurs. The magnitude and direction of the consolidation shear stress on the static and cyclic secondary shear behaviours of sand were systematically studied. In undrained static tests, soil strength was the lowest when the angles between the two shears stresses were near 90°, and the strength was the highest at 0°. In addition, a smaller angle produced a more brittle response, and a greater angle led to a more ductile response. The effect of stress path (the direction of consolidation shear stresses) was found to be more significant in tests with a greater magnitude of consolidation shear stresses, and the relationship between the angles (between the first shear stresses and secondary shear stresses) and shear behaviours was much more complex when the magnitude of consolidation shear stresses was increased. In drained static tests, the evidence of non-coaxiality was obtained. The non-coaxiality was the greatest at the initial stage of shearing, and it decreased to zero at higher shear strains. The degree of non-coaxiality was affected by the relative density of the specimen, vertical stress, level and direction of consolidation shear stress. In addition, the non-coaxiality was significantly affected by the consolidation shear stress, and the effect increased at a greater magnitude of consolidation shear stresses. The non-coaxiality increased as the angle was increased. In stress-controlled undrained dynamic tests, there was no significant difference in pore water generation rate among samples with consolidation shear stresses in different directions. However, samples with different directions of consolidation shear stresses failed at different numbers of cycles and in different directions. Liquefaction resistance was decreased by the increased magnitude of consolidation shear stress. In most of the tests with consolidation shear stress, the levels of liquefaction resistances were lower than that without consolidation shear stress. In strain-controlled undrained dynamic tests, liquefaction resistance (shear strength) was decreased from 0° to 90°, and increased from 90° to 180°. Liquefaction resistance in tests with consolidation shear stresses were lower than those without consolidation shear stress.

The Patonga Claystone, a red bed facies in the Narrabeen Group of the Sydney Basin, is one of the most unfavorable rock units in the basin from a geotechnical point of view. This rock unit is composed of sandstone, siltstone, mudstone and claystone. One of the unfavorable characteristics is the low shear strength, which causes instability of cut slopes; another is its slaking-prone behaviour. Numerous measurements of geotechnical properties, along with extensive mineralogical and geochemical determinations, were carried out to identify cause of this slaking behaviour. Key techniques were the use of quantitative X-ray diffractometry for mineralogical analysis, and the determination of slake durability index and related properties to evaluate the slaking behaviour under both standard and more extended conditions. Standard (two cycle) slake durability test results indicate a range from low to high slake durability index values, with some mudstone samples having very low durability and some sandstones having very high slake durability indices. Jar slake test results indicate that the rock samples break rapidly and/or develop several fractures (Ij = 4) in an as-received state, but degrade to a pile of flakes or mud (Ij = 1) if the samples are oven dried before testing. The results for jar slake testing of oven-dried material are comparable, for individual samples, to those obtained from the more comprehensive slake durability tests. The mineralogy of the samples was evaluated by quantitative X-ray diffraction techniques using the Rietveld-based Siroquant processing system. Comparison to independent chemical data show a generally good level of agreement, suggesting that the mineralogical analysis results are consistent with the chemical composition of the individual rock samples. Good correlations were also obtained between clay mineralogy determined from orientedaggregate XRD analysis of the &lt2 micron fraction and the results from powder diffractometry and Siroquant analysis of the whole-rock samples. Evaluation of the slake durability characteristics and other geotechnical properties in relation to the quantitative mineralogy suggests that quartz and feldspar form a rigid framework in the rocks that resists the disruptive pressures that cause slaking. Expansion of the clay minerals by various processes, including the incorporation of water into the interlayer spaces of illite/smectite as well as changes in pore pressures associated with entry of water into micro-fractures in the clay matrix, are thought to produce the disruptions that cause slaking and degradation. An abundant clay matrix also reduces the strength of the rock materials, probably because of the less rigid nature of the clay minerals relative to the quartz and feldspar particles. As well as the mineralogy, the loss on ignition (LOI) and water absorption percentage were found to provide good indicators of longer-term slaking behaviour. Both properties are also related to the overall clay content. Rock samples with water absorption values of &lt10, 10-15 and &gt15% behave as highly durable, intermediate and less durable materials respectively. Rocks with LOI values of greater than 5% by weight behave as less durable rock materials, at least for the strata encompassed by the present study. The water absorption and LOI values were also used to develop a predictive model of slake durability characteristics for the different rock materials in the Patonga Claystone, providing a relatively simple basis for predicting longer-term stability in a range of geotechnical studies.

The site investigation phase plays a vital role in any foundation design where inadequate characterisation of the subsurface conditions may lead to either a significantly over designed foundation that is not cost-effective, or an under-designed foundation, which may result in foundation failure. As such, the scope of an investigation should be dependent on the conditions at the site and the importance of the structure. However, it is common for the expense dedicated to the site investigation to be a fraction of the total cost of the project, and is typically determined by budget and time constraints, and the experience and judgement of the geotechnical engineer. However, additional site investigation expenditure or sampling is expected to reduce the financial risk of the design by reducing the uncertainties in the geotechnical system and protecting against possible foundation failures. This research has quantified the relative benefits of undertaking site investigations of increased and differing scope. This has been achieved by simulating the design process to yield a foundation design based on the results of a site investigation. Such a design has been compared to an optimal design that utilises the complete knowledge of the soil, which has only been possible due to the use of simulated soils. Comparisons between these two design types indicate the performance of the site investigation to accurately or adequately characterise the site conditions. Furthermore, the design based on the results of the site investigation have been analysed using the complete knowledge of the soil. This yields a probability of failure and, therefore, has been included in a risk analysis where the costs associated with the site investigation have been measured against the financial risk of the design. As such, potential savings in financial risk for increased site investigation expenditure have been subsequently identified. A Monte Carlo analysis has been used in this research to incorporate the uncertainties in the foundation design process. Uncertainties have been included due to soil variability; sampling errors; measurement and transformation model errors; and errors related to the use of a simplified foundation response prediction method. The Monte Carlo analysis has also provided the means to obtain results in a probabilistic framework to enable reliability and risk analyses. Computer code has been specifically developed with an aim to: generate a simulated soil that conforms to the variability of soil properties; simulate a site investigation to estimate data for a foundation design; simulate the design of a foundation and conduct a reliability and risk analysis of such a design. Results indicate that there are significant benefits to be derived from increasing the scope of a site investigation in terms of the risk and reliability of the foundation design. However, it also appears that an optimal site investigation scope or expenditure exists where additional expenditure leads to a design with a higher financial risk due to the increased cost of the site investigation. The expected savings in terms of financial risk are significant when compared to the increased investigation cost. These results will assist geotechnical engineers in planning a site investigation in a more rational manner with knowledge of the associated risks. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1255275 / Thesis(Ph.D.) -- School of Civil and Environmental Engineering, 2006

How can the suitability of a clay to act as a barrier to the flow of a specified fluid be determined? This question is directly related to the different mechanical and chemical stresses to which a clay barrier will be exposed. In spite of these mechanical and chemical stresses it must be guaranteed that the clay will fulfil its barrier function during the entire required containment period. This required technical life could be very long in engineering terms: 100-10000 years. During this period the clay barrier can neither be repaired nor maintained. Therefore it must be known which chemical or physical reactions will occur and how these reactions will influence the geomechanical properties of the clay. Because there was no standard approach to test the suitability of natural clays as barrier on the long-term, this had to be developed. Based on literature it was shown that the reactions between clays and fluids could be decomposed in reactions on the particle level, the interlayer level and the TOT/TO level of clay minerals: - Micrometer: Reactions on the particle level are the most frequent, the fastest to accomplish (instantaneous when leachate arrives) and have the least impact on the geomechanical properties of clays. It was shown that the double layer theory presents a valuable framework to analyse the changes in geomechanical properties upon clay-leachate contact. The properties of the fluid that are taken into account are the concentration of cations and the relative dielectric constant. Other processes on the particle level not captured by the double layer theory are e.g. the dissolution of calcitic cement and the oxidation of pyrites. The acids produced by the latter process influence reactions on the lower interlayer and TOT/TO level as well. It was shown that the natural clays possess themselves a rich variety of cations. These concentrations must be included in the analysis. New tools developed on the particle level were: - Integration of the chemical composition of the natural fluid contained in the clay in further analyses. - The discretisation of clay samples into a discontinuous but homogeneous assembly of discrete clay particles (finite element mesh) with the use of information from petrographical studies of thin sections and oedometer tests. - The implementation of a constitutive law into a numerical code to simulate the interparticle distance to interparticle fluid chemistry and mechanical stress. - Nanometer: Reactions on the interlayer level include clay mineral alteration processes. To link these processes to geomechanical properties, the clay mineral sample preparation was modified to include all clay minerals and not only the fraction smaller than two micrometers. Next a method was developed to link clay mineralogy to geomechanical properties (equivalent basal spacing). New tools developed on the interlayer level were: - The equivalent basal spacing (EBS) - Relation between the equivalent basal spacing and the liquid limit With these tools a link can be made between the clay mineralogy and geomechanical properties. Leachate - clay interactions can be analysed as well as other processes like the mixing of clays and the reactions of clays upon heating etc. - Ångström: Reactions on the TO/TOT level include the disintegration of TO arrangements, which will result in a complete destruction of a clay mineral. Of all three levels considered, changes on the TO/TOT level will cause the greatest change in geomechanical properties. Fortunately the processes on this TOT/TO level take a long history of subsequent physical and chemical reactions (hundreds to thousands of years in situ). Because changes on this level fail to be reproduced in the laboratory one must rely on natural analogues. New tools developed on the TO/TOT level were: - The link between the clay leached in the laboratory to natural analogues using thin sections and XRD diffraction analysis. Examples are shown that the aforementioned approach can be applied in any geomechanical problem involving clays.

Insufficient information on the host medium can cause serious problems, even collapse, during construction in a tunnel. This study focuses on understanding the reasons behind the collapse of the Tunnel BT24 to be opened within the framework of Ankara-Istanbul High Speed Railway Project. The tunnel is located near Boz&uuml / y&uuml / k in the Bilecik Province. The collapsed section of the tunnel was driven into a highly weathered, weak to medium rock mass. Unanticipated geological/geotechnical circumstances caused excessive deformations at the section on which the primary support system was applied, leading eventually to collapse. To understand the response of the tunnel and the collapse mechanism, the construction sequence is simulated using two-dimensional plane-strain and axisymmetric finite element models. The analyses were carried out for the section with and without invert closure of the shotcrete liner. To implement the effects of likely unfavorable ground conditions on the tunnel response, a number of fault scenarios and possible creep effects were also considered with those two alternatives. Displacements in the tunnel periphery, forces and moments in the primary liner as well as the plastic deformation zones in the surrounding ground were determined for each case and comprasions were made accordingly. It is concluded that the unforseen ground circumstances might have substantially aggravated the deformations in the section and that the lack of ring closure of the primary liner at invert played the key role in the collapse.

Niksar (Tokat), is an urban area located in a seismically active zone of Turkey. The aim of this thesis is to prepare GIS-based microzonation map of Niksar settlement area for the purpose of urban planning. Liquefaction, activity, slope, aspect, fault proximity, ground amplification and lithology are considered during the overlay analysis by using Multicriteria Decision Making Analysis (MCDA) of Simple Additive Weighing (SAW) and Analytical Hierarchical Process (AHP) methods. Based on the evaluations, the study area is divided into four different zones, namely, (1) areas suitable for settlement / (2) provisional settlement areas / (3) areas requiring detailed geotechnical investigation / (4) unsuitable areas. Two microzonation maps obtained from analyses are compared. Maps prepared by SAW and AHP methods are found to be consistent with each other. However, the microzonation map prepared by AHP method is recommended for the purpose of urban planning because it has the ability to check consistency itself.

Weakening and liquefaction of sands with increasing excess pore water pressures under repeated loads is well-known. Occurrence of extensive damage to the built environment also at the sites underlain by fine soils during earthquakes have led the researchers to focus on the seismic response of such soils more recently. The primary objective of this study is to investigate the factors affecting cyclic behavior of saturated low-plastic fine soils through laboratory testing. An extensive laboratory testing program including conventional soil mechanics tests, consolidation tests, reconstituted sample preparation, monotonic and cyclic triaxial tests was carried out for this purpose. Laboratory program was conducted within two parts, one of which includes the tests performed with the silt specimens reconstituted in the laboratory and the other consisting of the tests performed with the undisturbed soil samples retrieved from Adapazari. The effects of the inherent soil properties and the effects of loading characteristics on the cyclic response of saturated low plastic silty soils were examined separately. Based on the test results, models were introduced (i) to predict the relationship between excess pore pressure ratio (ru), number of cycles (N) and cyclic stress ratio (CSRtx), (ii) to estimate the effect of initial shear stress on cyclic response, and (iii) to show the effects of initial void ratio (ei), initial shear stress ratio (

We study timing effects of carbon mitigation and solar radiation management (SRM) policies for correlated pollutants, CO₂ and SO₂. We show that national levels of carbon and sulfur emissions quotas and SRM implementation are positively correlated with each other. First-mover advantages exist when deciding both carbon quotas and SRM levels. Moreover, we use an example to illustrate that if international equity is considered, governments would be willing to choose SRM levels before carbon quotas since it yields higher payoffs and less acid rain and droughts damages. This timing was neglected by all previous theoretical economic models on geoengineering.

published_or_final_version / Applied Geosciences / Master / Master of Science