Doctor of Philosophy(PhD) / Soil Stiffness is an important parameter for any geotechnical engineering design. In laboratory tests it can be derived from stress-strain curves or from dynamic measurement based on wave propagation theory. The second method is a more accurate and direct method for measuring stiffness at very small strains. Until now dynamic measurements have usually been obtained manually from the triaxial test. Attempts have been made to automate the procedure but have apparently failed due to the high level of variability in dynamic measurements. Moreover, triaxial tests of soil can be very lengthy and manual dynamic measurements can be very tedious and impractical for long stress-path tests. In this research a computer program has been developed to automate the stiffness measurement (using bender elements) based on the cross- correlation technique. In this method the program records all the peaks and corresponding arrival times in the cross-correlation signal during the test. The stiffness is calculated and displayed on the screen continuously. The Bender Element enabled to get the small strain shear modulus. An arbitrary “Chirp” waveform of 4 kHz frequency was used for this purpose. Subsequently Bender Element test results were checked by ‘Sine’ waveforms of frequencies 5kHz to 20kHz, as well as by manual inspection of the arrival time. This thesis discusses the method and some of the difficulties in truly automating the process. Finally some results from a number of stress path tests on uncemented and cemented calcareous sediments are presented. Bender elements have been used by many researchers to determine the shear modulus at small strain. Most previous studies have used visual observation of arrival time, which is time consuming and often requires some judgement from the operator. This thesis will describe the use of cross-correlation as a method for automation of Gmax measurement. Cross-correlation has been claimed to be unreliable in the past. However, it will be shown that provided several peaks in the cross-correlation signal are monitored it is possible to follow the variation of Gmax throughout consolidation and shearing. The measurement can be made at regular intervals within the software controlling a stress-path apparatus. Details of the apparatus used and practical considerations including selection of waveform and frequency are discussed. A series of drained cyclic triaxial tests was carried out on artificially cemented and uncemented calcareous soil of dry unit weights 13, 15, and 17 kN/m3 and sheared with constant effective confining stress 300 kPa. Gypsum cement contents of 10%, 20% and 30% of the dry soil weight were used. In addition a series of stress path tests were performed on Toyuora sand samples. Results will be presented for two uncemented and one cemented sand. In addition to the bender elements, all tests had internal instrumentation to monitor axial and lateral strains. Results will be presented for Toyura sand to show that the measurements are consistent with those obtained by other methods. Results will also be presented for carbonate sand subjected to a wide range of stress paths. Finally, results will be presented for the carbonate sand cemented with gypsum. The degradation of Gmax of the cemented soil subjected to variety of monotonic and cyclic stress-paths is presented. Analysis of the results includes assessment of the factors influencing Gmax for uncemented sand. Preliminary analysis indicates that in order of importance these are the mean effective stress, the stress history, void ratio and stress ratio. For cemented sand, Gmax is initially constant and independent of stress path. After yielding the modulus degrades, becoming increasingly stress level dependent and eventually approaches the value for uncemented sand. Factors influencing the rate of degradation are discussed. For the Toyuora sand samples the effects of end restraint on the stress-strain response at small strains were investigated. The conventional method of mounting triaxial specimen has the effect of introducing friction between sample and end platen during a compression test. This inevitably restricts free lateral movement of the specimen ends. Frictional restraint at the sample ends causes the formation of 'dead zones' adjacent to the platens, resulting in non-uniform distribution of stress and strain (and of pore pressure if undrained). On the other hand the specimen with 'free' ends maintain an approximate cylindrical shape instead of barrelling when subjected to compression, resulting in a more uniform stress distribution.

Doctor of Philosophy(PhD) / Soil Stiffness is an important parameter for any geotechnical engineering design. In laboratory tests it can be derived from stress-strain curves or from dynamic measurement based on wave propagation theory. The second method is a more accurate and direct method for measuring stiffness at very small strains. Until now dynamic measurements have usually been obtained manually from the triaxial test. Attempts have been made to automate the procedure but have apparently failed due to the high level of variability in dynamic measurements. Moreover, triaxial tests of soil can be very lengthy and manual dynamic measurements can be very tedious and impractical for long stress-path tests. In this research a computer program has been developed to automate the stiffness measurement (using bender elements) based on the cross- correlation technique. In this method the program records all the peaks and corresponding arrival times in the cross-correlation signal during the test. The stiffness is calculated and displayed on the screen continuously. The Bender Element enabled to get the small strain shear modulus. An arbitrary “Chirp” waveform of 4 kHz frequency was used for this purpose. Subsequently Bender Element test results were checked by ‘Sine’ waveforms of frequencies 5kHz to 20kHz, as well as by manual inspection of the arrival time. This thesis discusses the method and some of the difficulties in truly automating the process. Finally some results from a number of stress path tests on uncemented and cemented calcareous sediments are presented. Bender elements have been used by many researchers to determine the shear modulus at small strain. Most previous studies have used visual observation of arrival time, which is time consuming and often requires some judgement from the operator. This thesis will describe the use of cross-correlation as a method for automation of Gmax measurement. Cross-correlation has been claimed to be unreliable in the past. However, it will be shown that provided several peaks in the cross-correlation signal are monitored it is possible to follow the variation of Gmax throughout consolidation and shearing. The measurement can be made at regular intervals within the software controlling a stress-path apparatus. Details of the apparatus used and practical considerations including selection of waveform and frequency are discussed. A series of drained cyclic triaxial tests was carried out on artificially cemented and uncemented calcareous soil of dry unit weights 13, 15, and 17 kN/m3 and sheared with constant effective confining stress 300 kPa. Gypsum cement contents of 10%, 20% and 30% of the dry soil weight were used. In addition a series of stress path tests were performed on Toyuora sand samples. Results will be presented for two uncemented and one cemented sand. In addition to the bender elements, all tests had internal instrumentation to monitor axial and lateral strains. Results will be presented for Toyura sand to show that the measurements are consistent with those obtained by other methods. Results will also be presented for carbonate sand subjected to a wide range of stress paths. Finally, results will be presented for the carbonate sand cemented with gypsum. The degradation of Gmax of the cemented soil subjected to variety of monotonic and cyclic stress-paths is presented. Analysis of the results includes assessment of the factors influencing Gmax for uncemented sand. Preliminary analysis indicates that in order of importance these are the mean effective stress, the stress history, void ratio and stress ratio. For cemented sand, Gmax is initially constant and independent of stress path. After yielding the modulus degrades, becoming increasingly stress level dependent and eventually approaches the value for uncemented sand. Factors influencing the rate of degradation are discussed. For the Toyuora sand samples the effects of end restraint on the stress-strain response at small strains were investigated. The conventional method of mounting triaxial specimen has the effect of introducing friction between sample and end platen during a compression test. This inevitably restricts free lateral movement of the specimen ends. Frictional restraint at the sample ends causes the formation of 'dead zones' adjacent to the platens, resulting in non-uniform distribution of stress and strain (and of pore pressure if undrained). On the other hand the specimen with 'free' ends maintain an approximate cylindrical shape instead of barrelling when subjected to compression, resulting in a more uniform stress distribution.

Submitted by PPG Engenharia e Tecnologia de Materiais (engenharia.pg.materiais@pucrs.br) on 2018-05-03T11:34:42Z No. of bitstreams: 1 disserta??o Roger vers?o biblioteca.pdf: 9741593 bytes, checksum: 510807346e33704b6f1650648b1f1b19 (MD5) / Approved for entry into archive by Sheila Dias (sheila.dias@pucrs.br) on 2018-05-14T11:17:02Z (GMT) No. of bitstreams: 1 disserta??o Roger vers?o biblioteca.pdf: 9741593 bytes, checksum: 510807346e33704b6f1650648b1f1b19 (MD5) / Made available in DSpace on 2018-05-14T11:48:12Z (GMT). No. of bitstreams: 1 disserta??o Roger vers?o biblioteca.pdf: 9741593 bytes, checksum: 510807346e33704b6f1650648b1f1b19 (MD5) Previous issue date: 2018-01-15 / Developing technologies for the capture and geological storage of CO2 has been a constant challenge of the scientific community in the search for solutions that can reduce the environmental impacts caused by the release of this gas into the atmosphere. However, its storage in depleted oil wells has been shown to be a very important point, since the materials applied in wells can suffer degradation in the presence of CO2 in the supercritical state and at high pressures. The objective of this work is to evaluate the performance of the class G cement paste used in cementation of wellbore under conditions of geological carbon storage with replacement of part of the cement by pozoanic materials such as fly ash from the fossil fuel burning of the Candiota Thermoelectric Plant, and synthetic zeolites (4A-1 e 4A-2). The contents of the pozalanas used in substitution of the cement were 5% and 10% in weight. The medium in which samples were submitted for degradation tests was CO2 saturated water at 15 MPa pressure and 90 ?C for 7 and 14 days. Scanning Electron Microscopy (SEM), XRay Diffraction (XRD) and compressive strength tests were the characterization techniques used in this work. The results showed that the use of fly ash increased the compressive strength of the samples after 14 days, mainly for higher percentage of cement replacement by this material (10%), but its chemical degraded layer increased. In case of zeolites 4A-1 use, a lower compressive strength was observed compared to the standard paste, but the degraded layer was reduced. When zeolites 4A-2 were used significant loss of compressive strength was observed from 7 to 14 days, mainly for the proportion of the mixture of 10% and its degraded layer also reduced. / Desenvolver tecnologias para a captura e armazenamento geol?gico de CO2 tem sido um desafio constante da comunidade cient?fica na busca de solu??es que possam reduzir os impactos ambientais provocados pela libera??o desde g?s na atmosfera. Por?m, seu armazenamento em po?os depletados de petr?leo tem se mostrado o ponto mais desafiador, pois os materiais aplicados nestes po?os podem sofrer degrada??o na presen?a de CO2 em estado supercr?tico e em altas press?es. Este trabalho tem como objetivo avaliar o desempenho da pasta de cimento classe G, utilizada na cimenta??o e tamponamento dos po?os, em condi??es de armazenamento geol?gico de carbono com substitui??o de parte do cimento por materiais pozol?nicos. O material utilizado foi as cinzas volantes, oriundas da queima de carv?o mineral da Usina Termoel?trica de Candiota, e ze?litas 4A comerciais sint?ticas (4A-1 e 4A-2). Os teores utilizados das pozalanas em substitui??o ao cimento foram 5% e 10% em massa. O meio em que foram submetidas as amostras foi de ?gua saturada com CO2 a 15 MPa de press?o a 90? C por 7 e 14 dias. A Microscopia Eletr?nica de Varredura (MEV), a Difra??o de Raios X (DRX) e o teste de resist?ncia ? compress?o foram as t?cnicas de caracteriza??o utilizadas neste trabalho. Os resultados obtidos mostram que o uso de cinzas volantes aumentou aos 14 dias a resist?ncia ? compress?o das amostras, principalmente para maior a porcentagem de substitui??o do cimento por este material (10%), por?m a camada alterada quimicamente aumentou. Quando utilizadas as ze?litas 4A-1, notou-se uma menor resist?ncia ? compress?o que a pasta padr?o, mas a camada degradada reduziu. No caso das ze?litas 4A-2, foi constatada a perda significativa de resist?ncia ? compress?o dos 7 para 14 dias, principalmente para a amostra contendo 10% dessa zeolita, sendo que a camada alterada quimicamente tamb?m reduziu.