LKAB and Trafikverket want to increase the maximum allowed axial load from 30 tons to 32,5 tons for the northern part of Malmbanan. There are ongoing investigations of the condition of the railway with the current axial load of 30 tons. The investigations do not include one of Trafikverket's concerns about the condition of the railway. That question is how the periodical load from trains affect the stability and maintenance cost of the railway embankment. The aim of this thesis is therefore to do a preliminary investigation of how the excess pore pressure is developed in the railway embankment during periodical loading and an attempt to model it the help of PLAXIS2D, a finite element software. PLAXIS2D has been used to model a simplified section of section km 1449+820 that is subjected by periodical loading with an axial load of 30 tons. There are 6 created models in the thesis where model 2-6 origin from model 1 but with some minor changes. The changes between the models are the train speed, groundwater level, width of the embankment and load. The periodical load applied in all models has been assumed to load the embankment with a periodical shape of a sinus curve. From the models, the distribution of the effective stress and excess pore pressure have been measured. The total displacement and the magnitude of excess pore pressure in different measuring points in the embankment have also been measured. These results have been used to analyze why there are certain points in the embankment which accumulate excess pore pressure. In the models, measuring points have also been created beneath the sleeper and in the embankment toe where total displacement and effective stress have been measured to relate and see if the response in stress and displacements are trustworthy. It was concluded that accumulation of excess pore pressure is relative high in the embankment toe due to the stress distribution and slope stability. The embankment is developing large shear stresses in the embankment toe to resist against slope failure. The excess pore pressure is recommended to be measured in the embankment toe, but it is also recommended to develop the model further since it does not consider any dynamics and neither soil stiffening or soil softening which limit the possibility to analyze liquefaction in detail.

Masters of Science / The Bredasdorp basin is situated off the south coast of the Republic of South Africa, southeast of Cape Town and west-south-west of Port Elizabeth. It covers approximately 18,000 sq. km beneath the Indian Ocean along the southern coast of South Africa, which is in the southwest of Mosselbay. Bredasdorp basin contains South Africa’s only oil and gas production facilities and has been the main focus for oil and gas exploration in South Africa. It is one of the largest hydrocarbon producing block in South Africa, rich in gas and oil prone marine source rocks of kimmeridgian to berriasian age. The wells of interest for this study are located within block 9 which is made up of 13 wells but for this study the focus is only on 3 wells, which are well F-01,F-02 and F-03. The goal of this study is to predict as accurately as possible the areas within and around the sandstone reservoir intervals of these wells with abnormal pressure, using well logs and production test data. Abnormal pore pressure which is a major problem for drillers in the oil industry can cause serious drilling incidents and increase greatly drilling non-production time if the abnormal pressures are not predicted accurately before and while drilling. Petrophysics log analysis was done to evaluate the reservoirs. The intervals of the reservoir are the area of interest.Pore pressure gradient, fracture gradient, pore pressure and fracture pressure model were run. Pressures of about 6078.8psi were predicted around the zone of interest in well F-01, 7861 psi for well F-02 and 8330psi for well F-03. Well F-03 was the most pressured of the three wells. Abnormal pressures were identified mostly at zones above and below the area of interest and predicted pressure values were compared to actual pressure values to check for accuracy.

Understanding the behavior of charring or decomposing materials exposed to high temperature environments is an essential aspect in rocket design. In particular, the tip of re-entry vehicles and sacrificial rocket nozzle liners are both exposed to extremely high temperatures. This thesis is specifically concerned with better understanding the reaction of sacrificial rocket nozzle liners to these high temperature environments. The sacrificial liners are designed to shield the rocket nozzle from the thermal and chemical effects of the heated exhaust gas that flows through the nozzle. However, in the design process space and weight of the rocket are at a premium. The sacrificial liners need to be designed to be as light and thin as possible, while properly shielding the nozzle from the heated exhaust gases. The sacrificial liner material is initially impermeable in its virgin state; however, as the liner is exposed to the heated exhaust gases, it chars and the liner material begins to decompose. The decomposition of the liner by heating in the absence of oxygen is known as pyrolysis. At high temperatures, the virgin material will decompose into a solid material (charred liner) and a vapor (pyrolysis gas). The pyrolysis process leads to the flow of pyrolysis gases throughout the porous charred liner. As a result, significant pressures can build within the liner. If the pressures within the liner are high enough, mechanically weak portions of the liner may fracture and break off. Fracturing of the liner could expose the nozzle to the heated exhaust gases, thus jeopardizing the structural integrity of the nozzle. Therefore, it is important to understand the pressure distribution within the sacrificial liners that occurs as a result of the pyrolysis process. This work describes the code PorePress, which solves for steady state and transient pressure distributions in 1- and 2-D axisymmetric geometries that represent sacrificial liners. The PorePress code is essentially a 1- and 2-dimensional differential equation solver for mixed, unstructured geometries. Specifically, the code is used for solving a coupled form of the Ideal Gas Law, Conservation of Mass, and Conservation of Momentum Equations, which describe the flow and resulting pressures within liner geometries. The code centers around using Taylor Series expansions to approximate derivatives needed to solve the appropriate differential equations. The derivative approximation process used in PorePress is grid transparent, meaning the same method can be used for any combination of quadrilateral (4-sided) or triangular (3-sided) elements in a mesh, without any changes to the code. Stability issues arise in both the 1- and 2-D PorePress solution processes, as a result of the non-linear nature of the coupled equations, high spatial gradients, and large variations in material properties. In the 1-D case stabilization techniques such as: upwinding, dynamic differencing, under-relaxation, and preconditioning are applied. Meanwhile, in the 2-D case, stabilization techniques such as: inverse weighting and QR factorization of the coefficient matrix, under-relaxation, and preconditioning are applied. The steady state and transient solution processes for both the 1- and 2-D pore pressure solution processes used in PorePress are covered in this thesis, as well as discussion of the resulting pressure distributions. Certain sacrificial liner design considerations that arise as a result of PorePress models for sample liner burns are also covered. / Master of Science

Moisture damage is one of the major causes of deterioration of pavements. An example is the damage caused by flooding. While the effects of pore water pressure in pavement have been studied using finite element modeling, few of the models consider a realistic moving tire and the viscoelastic behavior of the asphalt layer. Consequently, a three-dimensional finite element simulation based on Biot consolidation theory and Schapery's non-linear viscoelasticity model, was developed to accurately simulate and analyze the detrimental effects of saturated layers in asphalt pavements. In addition, a parametric study is conducted to analyze the response of pavements with varying surface and base thickness, base and subgrade permeability, and vehicle speeds under different level of saturation. The results indicate that the effects of pore water pressure be considered in the design of pavements in flood-prone areas and in the proposal of flood management plans. Ultimately, the implementation of a "flood resilient" asphalt pavement could be effective in reducing the cost of road restoration and repair in flood-prone areas. / Master of Science / Moisture damage is one of the major causes of deterioration of pavements. An example is the damage caused by flooding. While the effects of pore water pressure in pavement have been studied using finite element modeling, few of the models have accurately modeled the behavior of the asphalt concrete and have not considered the realistic loading conditions. Consequently, a three-dimensional finite element simulation was developed to accurately simulate and analyze the detrimental effects of saturated layers in asphalt pavements. In addition, a parametric study is conducted to analyze the response of pavements with varying surface and base thickness, base and subgrade permeability, and vehicle speeds under different level of saturation. The results indicate that the effects of pore water pressure be considered in the design of pavements in flood-prone areas and in the proposal of flood management plans. Ultimately, the implementation of a "flood resilient" asphalt pavement could be effective in reducing the cost of road restoration and repair in flood-prone areas.

This thesis describes a numerical modelling methodology to interpret dynamic fluctuations in pore-pressures to isolate the effects of loading associated with changes in total soil moisture (site water balance) alone. The methodology is required to enhance the data-interpretation and performance-assessment for potential applications of a novel piezometer-based, large-scale, geological weighing lysimeter. This interpretative methodology is based on a method of superimposing computer-based numerical analyses of independent causes of pore-pressure transients to separate the different pore-pressure responses. Finite element coupled load-deformation and seepage numerical models were used to simulate field-observed piezometric responses to water table fluctuations and loading induced by surface water balance (using meteorological data).<p> Transient pore-pressures in a deep clay-till-aquitard arising from variations in the water table within a surface-aquifer were modelled and removed from the measured pore-pressure record (corrected for earth tide and barometric effects) to isolate and identify pore-pressure fluctuations arising from loading associated with site water balance. These estimates were compared to simulated pore-pressure responses to an independently measured water balance using meteorological instrumentation. The simulations and observations of the pore-pressure responses to surface water balance were in good agreement over the dry years of a 9-year period. Some periods of significant differences did occur during wet years in which runoff, which is not accounted for in the current analyses, may have occurred.<p> The identification of pore-pressure response to total soil moisture loading using the developed numerical modelling methodology enhances the potential for the deployment of the piezometer-based geological weighing lysimeter for different applications which include real-time monitoring of site water balance and hydrological events such as precipitation and flooding. Interestingly, the disparity occurring during the wet years even suggests the potential to adapt the method to monitor runoff (net lateral flow).<p> The methodology also demonstrated the capability to accurately estimate in situ elastic and hydraulic parameters. Calibration of the model yielded equivalent properties of the aquitard (hydraulic conductivity, Kv, of 2.1E-5 m/day and specific storage, Ss, of 1.36E-5 /m) for a Skemptons B-bar coefficient of 0.91 for an assumed porosity of 0.26. Sensitivity tests also provided insight into the consolidation and pressure propagation (swelling) behaviour of the aquitard under parametric variations. The parameters obtained are consistent with range of values reported for glacial clay till soil. Therefore, this work also provides a unique case history of a method for determining, large scale, in situ material properties for geo-engineers and scientists to explore by simply using piezometric and meteorological data.

This thesis describes a numerical modelling methodology to interpret dynamic fluctuations in pore-pressures to isolate the effects of loading associated with changes in total soil moisture (site water balance) alone. The methodology is required to enhance the data-interpretation and performance-assessment for potential applications of a novel piezometer-based, large-scale, geological weighing lysimeter. This interpretative methodology is based on a method of superimposing computer-based numerical analyses of independent causes of pore-pressure transients to separate the different pore-pressure responses. Finite element coupled load-deformation and seepage numerical models were used to simulate field-observed piezometric responses to water table fluctuations and loading induced by surface water balance (using meteorological data).<p> Transient pore-pressures in a deep clay-till-aquitard arising from variations in the water table within a surface-aquifer were modelled and removed from the measured pore-pressure record (corrected for earth tide and barometric effects) to isolate and identify pore-pressure fluctuations arising from loading associated with site water balance. These estimates were compared to simulated pore-pressure responses to an independently measured water balance using meteorological instrumentation. The simulations and observations of the pore-pressure responses to surface water balance were in good agreement over the dry years of a 9-year period. Some periods of significant differences did occur during wet years in which runoff, which is not accounted for in the current analyses, may have occurred.<p> The identification of pore-pressure response to total soil moisture loading using the developed numerical modelling methodology enhances the potential for the deployment of the piezometer-based geological weighing lysimeter for different applications which include real-time monitoring of site water balance and hydrological events such as precipitation and flooding. Interestingly, the disparity occurring during the wet years even suggests the potential to adapt the method to monitor runoff (net lateral flow).<p> The methodology also demonstrated the capability to accurately estimate in situ elastic and hydraulic parameters. Calibration of the model yielded equivalent properties of the aquitard (hydraulic conductivity, Kv, of 2.1E-5 m/day and specific storage, Ss, of 1.36E-5 /m) for a Skemptons B-bar coefficient of 0.91 for an assumed porosity of 0.26. Sensitivity tests also provided insight into the consolidation and pressure propagation (swelling) behaviour of the aquitard under parametric variations. The parameters obtained are consistent with range of values reported for glacial clay till soil. Therefore, this work also provides a unique case history of a method for determining, large scale, in situ material properties for geo-engineers and scientists to explore by simply using piezometric and meteorological data.

An investigation was conducted as a preliminary effort to develop a methodology to predict pore pressure in a rock formation during drilling, for all types of rocks and situations. Specifically, it was investigated whether or not the virgin pore pressure (the pore pressure of the undisturbed rock) can be determined at the drill bit from drilling and environmental parameters, as well as solid and pore fluid properties. Several drilling situations were analyzed to develop models relating pore pressure to drilling and environmental parameters, as well as solid and pore fluid properties. Three approaches to the modeling of such drilling situations were considered, which were used to predict pore pressure and compare the predictions to actual drilling data. The first approach used the concept of the effective stress in conjunction to the Mohr-Coulomb failure criterion. The second approach used the concept of the mechanical specific energy. The third approach made use of basic principles to relating virgin pore pressure to drilling and environmental parameters, as well as solid and pore fluid properties. This third approach resulted in the proposal of a more fundamental way of viewing mechanical specific energy (MSE) and the use of Biot's poroelasticity theory to describe the cutting process of rock. The first approach did not provide an adequate prediction of virgin pore pressure for all types of rocks and situations. The second approach showed promising results with limited actual drilling data. A sensitivity analysis of the model resulting from the third approach indicated that pore pressure, type of rock, and back rake angle of the cutter are the most significant factors affecting the energy required to break the rock. Moreover, rate of cutting stress, depth of cut, and type of pore fluid become significant factors of the cutting process only when a low-porosity, low-permeability rock is considered. It was concluded that there exists a relationship among pore pressure, drilling and environmental parameters, as well as solid and pore fluid properties. Therefore, it is possible in principle to determine the virgin pore pressure at the drill bit from drilling parameters, environmental parameters, and material properties. However, further work is required to establish a quantitative relationship among the significant parameters before a methodology to predict virgin pore pressure for all types of rocks and situations can be developed.

Uniaxial consolidation tests of resedimented mudrocks from the offshore Gulf of Mexico reveal compression and permeability behavior that is in many ways similar to those of intact core specimens and field measurements. Porosity (n) of the resedimented mudrock also falls between field porosity estimates obtained from sonic and bulk density well logs at comparable effective stresses. Laboratory-prepared mudrocks are used as testing analogs because accurate in-situ measurements and intact cores are difficult to obtain. However, few direct comparisons between laboratory-prepared mudrocks, field behavior, and intact core behavior have been made. In this thesis, I compare permeability and compressibility of laboratory-prepared specimens from Gulf of Mexico material to intact core and field analysis of this material. I resediment high plasticity silty claystone obtained from Plio-Pleistocene-aged mudrocks in the Eugene Island Block 330 oilfield, offshore Louisiana, and characterize its compression and permeability behavior through constant rate of strain consolidation tests. The resedimented mudrocks decrease in void ratio (e) from 1.4 (61% porosity) at 100 kPa of effective stress to 0.34 (26% porosity) at 20.4 MPa. I model the compression behavior using a power function between specific volume (v=1+e) and effective stress ([sigma]'v): v=1.85[sigma]'v-⁰̇¹⁰⁸. Vertical permeability (k) decreases from 2.5·10-¹⁶ m² to 4.5·10-²⁰ m² over this range, and I model the permeability as a log-linear function of porosity (n): log₁₀ k=10.83n - 23.21. Field porosity estimates are calculated from well logs using two approaches; an empirical correlation based on sonic velocities, and a calculation using the bulk density. Porosity of the resedimented mudrock falls above the sonic-derived porosity and below the density porosity at all effective stresses. Measurements on intact core specimens display similar compression and permeability behavior to the resedimented specimens. Similar compression behavior is also observed in Ursa Basin mudrocks. Based on these similarities, resedimented Gulf of Mexico mudrock is a reasonable analog for field behavior. / text

Hydrocarbon exploration involves drilling into or near salt deposits in the Gulf of Mexico, Brazil, Egypt, and the Middle East. Drilling these systems has proven to be quite dangerous, challenging, and expensive due to the pressure and stress perturbations that exist around the salt. My study focuses on characterizing the pressure and stress distribution at the Mad Dog field, which is a large oil field below an allochthonous salt body in the deepwater Gulf of Mexico. The Mad Dog field lies beneath the Sigsbee Escarpment, which represents the surface and seaward-most indicator of a mobile salt in Green Canyon blocks 781, 782, 825, and 826, 190 miles southwest of New Orleans in 4,500-6,500 feet of water. I characterize the pressure distribution within the Lower Miocene sandstone reservoir which has produced over 100 million barrels to date. I map the reservoir horizon using 3D seismic data and that the reservoir is a complex regional anticlinal structure that is separated by numerous normal faults that cause it to be segmented into compartments. The in-situ pore pressures show that the compartments are not in pressure communication across the field and that multiple aquifer phase pressures are present. The in-situ pore pressure measurements are used to characterize the pressure distribution in the Miocene sediments below the salt body and in front of the mobile salt body. These measurements show that between the upper Miocene to middle Miocene there is an absolute pressure decrease and between the middle to lower Miocene there is a large pressure increase. This pressure distribution is seen both within the Miocene sediments below salt and in front of salt. A porosity and effective stress relationship from shallow Pleistocene sediments was developed to predict the pressure behavior observed within the Miocene and compare the predicted pressure with in-situ pore pressure measurements. The mudstone pressure prediction overestimates the in-situ sand pore pressure. The mudstones bounding regional sandstone have a constant porosity throughout the field, suggesting that the vertical effective stress is constant. These observations can be used to estimate the mudstone pore pressure in a new well location. If the vertical effective stress in an offset well is known and given knowledge of the total vertical stress in the new well location, the mudstone pore pressure can be estimated. / text

I estimate overpressure in a seismic cross-section along a 12km traverse associated with a 2D/4C OBC line in the Columbus Basin, Trinidad, West Indies, where shallow gas reduces both data quality and apparent seismic velocity for P-waves, using a modified Eaton's equation for PS-waves. Pore pressure prediction using the modified Eaton's method involves velocity analysis, conversion of the stacking velocities to interval velocities via the Dix's equation, converting the interval velocity trends to pressures and mudweights, and comparison of the predictions to 3 wells surrounding the seismic line. In the presence of shallow gas, the magnitude and areal extent of seismically derived P-wave and PS-wave velocity deviates from regional trends along the seismic line. PS-waves show a more accurate areal extent of velocity deviation due to overpressure than the P-wave, which is also affected by the presence of shallow gas. I verify my derived velocities and predicted-pressure values using sonic log data and observed pressure from 3 wells. Direct comparison between the sonic-derived velocities and the seismic-derived velocities shows that shallow gas reduces P-wave velocity, and that PS-wave velocity is less affected. Pressure prediction is verified using mudweights and formation tests from well logs and drilling reports. I find pressure predictions associated with P-waves, especially in areas of shallow gas are less reliable than for pressure predictions using PS-waves. I conclude that PS-wave velocity provides a superior map of overpressure in this region in areas with shallow gas clouds. / text