A new analytical method for stability analysis of rock blocks with basal erosion in sub-horizontal strata by considering the eccentricity effect

The basal cavity of a rock block formed due to differential weathering is an important predisposing factor for rockfall in hard–soft interbedded rocks, which induces an eccentricity situation at the base of the rock block. Rock block falling due to the non-uniform distribution with the failure modes of toppling or sliding is defined as biased rockfall in this study. Taking into account the non-uniform stress distribution due to the eccentricity effect, a new analytical method is proposed for three-dimensional stability analysis of biased rockfall. The development of non-uniform stress distribution stress calculated by this analytical method was verified by numerical simulation. The biased rockfall progresses from partial damage of the soft underlying layer, caused by non-uniform distributed stress, to toppling and sliding of overhanging hard rock block due to overall unbalanced force. Therefore, a set of factors of safety (Fos's) against partial damage (compressive and tensile damage of the soft underlying layer) and overall failure (toppling and sliding of the hard rock block) are used to determine the rockfall susceptibility level. The analytical method is applied and validated using biased rockfalls on the northeastern edge of the Sichuan Basin in southwest China, where a significant number of rockfalls consisting of overhanging thick sandstone and underlying mudstone occur. The evolution process of biased rockfalls is divided into four stages, initial state, basal cavity formation, partially unstable and failure. The proposed method is validated by calculating Fos's of the typical unstable rock blocks in the study area. As the cavity continues to grow, the continuous retreat of mudstone causes stress redistribution between the hard and soft rock layers. This results in damage to the underlying soft rock layer due to the development of the non-uniform distribution, ultimately leading to the failure of the hard rock block. The critical retreat ratio is determined to be 0.33, which is used to classify the low and moderate rockfall susceptibility in the eastern Sichuan Basin. The proposed analytical method provides insights into the evolution of biased rockfall and a means for early identification and susceptibility assessment of rockfall.</p

Future Trends in Advanced Materials and Processes

The Special Issue “Future Trends in Advanced Materials and Processes” contains original high-quality research papers and comprehensive reviews addressing the relevant state-of-the-art topics in the area of materials focusing on relevant or innovative applications such as radiological hazard evaluations of non-metallic materials, composite materials' characterization, geopolymers, metallic biomaterials, etc

Survivability assessment of fastnet lighthouse

Historic rock lighthouses are unusual structures that are situated in hostile marine environments to provide warning to mariners. Even in an era of satellite navigation their role continues to be an important one, but their survivability into the future is not assured. Out of concern for their ongoing service, the multidisciplinary STORMLAMP project is assessing their survivability under wave loading. This paper presents the various stages of investigations into the structural integrity and stability assessment of the Fastnet lighthouse, situated just off the coast of Ireland. The paper describes: Extreme Bayesian analysis to quantify waves of particular return periods resulting in a 1 in 250 year return period wave with H 0.1% of 17.6 m and an associated maximum force of 20,765 kN; logistically challenging field modal tests revealing the key modal parameters, like the modal masses of 1822 t and 1 675 t for 4.8 Hz and 5.0 Hz modes respectively, the cantilevered nature of the overall lighthouse and the directional effects due to the asymmetric contact with the granite rock; and details of a discontinuous finite element model that is used to determine the stability of the tower under the 1 in 250 year return period breaking wave condition, which is well within stability and material strength limits, causing maximum horizontal displacements in the order of 1 mm at the top of the tower. The overall assessment is that the sheer mass of the lighthouse and its interconnected joints are able to withstand the worst of the Atlantic storms. Coastal Engineerin

The fluid mechanics of floating and sinking

This thesis is concerned with the fluid mechanics of floating and sinking. More specifically, the majority of this thesis considers the role played by surface tension in allowing dense objects to float. We first derive the conditions under which objects can float at an interface between two fluids. We obtain the conditions on density and size for various objects to float and show that being ‘super-hydrophobic’ does not generally help small, dense objects to float. Super-hydrophobicity does, however, dramatically reduce the energy required to remove an object from the interface. We then show that two floating objects can sink if they come into close proximity with one another. We extend this to show that a raft consisting of many interfacial objects can become arbitrarily large without sinking, providing that its density is below a critical value. Above this critical value, there is a threshold size at which sinking occurs. We then consider the surface tension dominated impact of an object onto a liquid–gas interface. We determine a similarity solution, valid shortly after impact, for the shape of the interface and study the asymptotic properties of the capillary waves generated by impact. We also show how the interfacial deformation slows down the impacting body. We use a boundary integral simulation to study the motion at later times and determine the conditions under which the object either sinks or is trapped by the surface. We find that for an object of a given weight there is a threshold impact speed above which it sinks. We study the waterlogging of a floating porous body as a model for the waterlogging of the pumice ‘rafts’ that often form on bodies of open water after a volcanic eruption. We study the inflow of water that is driven by capillary suction and hydrostatic pressure imbalances, and determine the time taken for this inflow to cause the object to sink. Finally, we study the effects of a natural slope on the spreading of carbon dioxide sequestered into aquifers. We use laboratory models and numerical techniques to study the spreading of the resulting gravity current. Initially the current spreads axisymmetrically, while at later times it spreads predominantly along any slope in the overlying cap rock. We show that in industrial settings the time scale over which this asymmetry develops is typically a few years. This effect may have important practical implications since the current propagates faster in the asymmetric state

Analysis of a ventilation network in a multiple fans limestone mine

As mining progresses the total resistance of an excavation is increased, the mine characteristic curve becomes steeper, and the operating point moves up the fan curve, reducing the total air quantity and increasing the system pressure. For multi-level ventilation networks with a number of fans the process can be tedious, and on a count of numerous dependent factors the optimal combination of fans is very hard to be achieved. The design of a ventilation network in conjunction with multi surface fans and booster fans entails a complex procedure. The objective of this study is to provide a plan to improve the ventilation network of a mine for use in the future with consideration to the source of losses through the network, design of network with multi fans and fire analysis. The guidelines listed in this paper were formulated based on current U.S. and international standards, safe operating practices developed by the mining industry, and recommendations provided by fan manufacturers. The problems proposed can be solved using ventilation and fire simulators and usage of computational fluid dynamics. Some key design factors which, if not accounted for properly, may result in ventilation system inefficiencies are shown. A pressure and quantity ventilation survey has been conducted. The Hardy Cross method using switching parameters has been found to be a good tool to solve a multi fan network. The modified Hardy Cross method is faster and more flexible than other methods. Ventsim Visual software modeling has been used for network analysis to determine suitable surface and booster fans locations, blade settings, and speeds. No underground peril has greater potential for large loss of life than a mine fire or explosion. A study has been carried out in order to get a better understanding of fire behavior in unpredicted incidents. A Bobcat vehicle burning at the working faces has been investigated. Various possible ways to control the fire have been considered. Main mine fans are often connected to underground workings through bends or elbows. These connections may include damper controls or louvers. Leakage and shock losses in different parts of mine airways are of major concern. Comprehensive analyses has been undertaken of these ventilation shock losses experimentally, numerically and computationally to increase understanding and optimize air flow through the mine. --Abstract, page iii

The Impact of Oil Price Instability on the Growth Process of the Nigerian Economy

The oil sector has not always been of importance as it is now. Moreover, beginning with the twentieth century, the importance of oil has increase tremendously a decade or two ago it over took coal as the major source of energy in the world. Petroleum crude oil as we all know today is a dark, evil smelling, vicious liquid composed of a mixture of a number of chemical product mainly carbon and hydrogen hence he name hydrocarbon. There are other minerals such as oxygen and sulphur. Nigeria was not depending on the oil sector as the major source of revenue. Prior to its advent, agriculture has been the backbone of the Nigeria economy. in fact between 1960 and 1966, agriculture contributed about 58.9% of the GDP while it was providing employment for more than 90% of the nation’s labour force. However, following the discovering of oil and the sub-sequent oil boom in 1970s agriculture lost its pre-eminent position to mining and specifically petroleum. In terms of export earnings, oil contributed 509.6 million (about 57.6%) to the Nigeria economy in 1970. Production also grew from over 3 billion barrels in 1956 to about 823.3 billion in 1974. Within the last 50 years, while total consumption has risen fourfold, world consumption of oil has risen by a factor of 16, currently gas and oil accounts for almost 70% of the world energy consumption. The energy transition from coal to oil was partly a response to technological development but even more significant was the steady decline in the real prices of oil. Nigeria has a very large reserve of crude oil and mineral gas. Oil was first found in commercial quantities at Oloibiri in the Niger Delta. There were further discoveries at Afam and Boma which established the country as an oil producing nation. Its oil fields are located in a territory south of a line that can be drawn through Benin City in Edo State, Owerri in Imo State and Calabar in Cross River State. The highly concentrated drilling areas and the greatest oil producing areas are around Port-Harcourt in Rivers State, and Ughelli and Escravos in Delta State. The analysis of oil exploration in Nigeria dates back to 1908 with the coming of a German firm called the Nigeria Bitumen Corporation whose activities terminated with the outbreak of the first World War in 1914, Shell D’ Archy which in 1956 was transformed into Shell-BP resumed prospecting activities in Nigeria, and was covering the entire country. On 4th November, 1938, until 1955, Shell-BP was the only company that had a license to serach for oil in many parts of the country. With time more companies have joined in prospecting for oil and among them are: Mobil oil, Chevron oil, America Oversea Petroelum Company, Agip Oil, Esso Oil, Tennesse, Ashland, and Phillips, Nigeria owned National Oil Co-operation and Henry Stephens which is a joint venture between Nigeria and Japan. The output of crude oil in Nigeria since its discovery by Shell-Bp has risen from 229,629 million barrel of a record of 815 million barrel in 1974. The dramatic rate of increase in production has been the result of a higher success rate in the oil companies’ search for new oil fields particularly after 1965, and the increased output rate from the existing oil wells. In 1958, estimated resources given by Shell-BP stood at 22.23 million barrel with a life span of 12 years. Since then with increased production of crude as a result of prospecting, drilling and exploration by some other companies estimates of reserves have been increasing yearly and by 1989 production had hit 625,456,000 barrel while export stood at 525,869,000 barrel. It is important to point out that because of the need to conserve foreign exchange, job opportunities were created to some extent, in addition to other multiplier effects derivable from setting refineries locally, the federal government in 1962 in awarded a contract for the construction of a refinery at Alesa Eleme, Port-Harcourt, River State. Prior to the construction of oil refinery in Port-Harcourt in 1964 all oil produced was exported. However, after completion of the refinery, part of it was retained to be refined domestically and the other part exported. Between 1970 and 1978, the nation experienced an upsurge in demand for petroleum product averaging a yearly increase of 23.4 percent. Thus in 1978, the Warri refinery was officially opened with a total capacity standing at 100,000 barrels per day. Continued demand pressures led to the building of a third refinery at Kaduna in 1980 with initial capacity of 100,000 Bd but with a potential capacity of 260,000Bd. A fourth refinery has been constructed near Port Harcourt. Since the first discovery in 1956, with initial production of about 6,000Bd Nigeria’s oil production had been on steady increase from 0.55 million Bd in 1966 to 0.96 million Bd in 1970 and to 2.0 million Bd in 1972 till it reach a peak of 2.4 million Bd in 1979. This steady increase in oil production corresponded with the rise in the importance of petroleum in the Nigeria economy. Today, petroleum provides more than 90% of our export earnings and Nigeria has grown to become the sixth largest oil producing country within the Organization of petroleum countries (OPEC). Hence, Nigeria like other oil exporting countries, using the traditional national accounts framework has confused oil proceeds as income against the correct interpretation of being as asset and a component of wealth. This conceptual confusion is a serious issue embodied with implications and signals for making policies and taking decisions that affect several important variables that have national and international significance Anyanwu (1993). Since the arrival of oil in Nigeria, petroleum has remained the backbone of the Nigeria Economy. In other words, Nigeria as a nation is fully dependent on the revenue generated from oil exports. This revenue is a function of price oil in the international market. Empirical analyses have proved that there are instabilities in world’s oil prices and these instabilities have different impacts on various countries depending on how dependent the economy is on oil. So, in a country like Nigeria which this study is based on, more than 80% of her export revenue is generated from oil. As a result of this oil price instabilities have adverse effects on its economy. While positive changes leads to an increase in government revenue its negatives counterpart manifest in form of budget deficit. The oil sector in Nigeria is an enslave sector employing an infinitesimal portion of the labour force and having little forward and backward linkages with the rest of the economy. There is need for government to diversify the economy to reduce the adverse effects of oil instabilities on the economy. The impact of petroleum in the overall economy of Nigeria is so great that when petroleum sneezes, the nation not just the economy alone catches cold and trembles to crumbling point. This has become more pronounced because of the over-dependence of the economy on this sector. In the oil boom ear of the 1970s, the government spree on consumption activities and execution of white elephant projects, the result had been chronic budget deficit. But since the global glut and subsequent fall in the price of oil, the Nigerian government has been finding it difficult to adjust with the economy realities of the time. The now permanent feature of belt tightening and belt loosening inherent in the country’s budgeting planning and policies is as a result of the over reliance in the petro-oil culmination in the implementation of the structural adjustment programme (SAP) in 1986. The impact of oil instabilities on government revenue is so great that the fourth development plan almost hit the rock. For example in that which was to last for four years (1981-1985) with a capital investment target of 82.2 billion all the resources needed to accomplish this plan was based on a projected oil production of over 2 million barrel per day and selling price of over $40 per barrel during the plan period. Not fast was the plan launched in 1981 than the world oil market weakened. By 1983, the level of Nigeria’s oil production had dropped from 2.1 million barrel per day in 1983 while the selling price also fell from$40 to $30 per barrel during the period; the plan had to be reviewed. This study is expected to assist the government, policy makers, individuals and development planners to plan for the future especially in the diversification of the productive base of the economy with a review to averting the danger of over dependence of oil as the major source of foreign exchange earning. That there is need to diversify the production base of the Nigerian economy cannot be overemphasized. This has become necessary in view of the current move by the international community especially the west to impose economic section especially oil sanction on Nigeria. the goals of this study however, is to examine the genesis of oil price instabilities, to examine the instability in oil price and the condition for stability, to examine ways and means of diversifying the economy with a view to removing the over dependence of government on this sector and to show the extent to which fluctuation of oil prices affect the Nigeria economy in terms of GDP, government revenue, balance of payment equilibrium and economic growth

Mathematical Modelling of the Drilling Process for Real-time Applications in Drilling Simulation, Interpretation and Assistance

For the last thirty years, mathematical modelling has been used to develop software solutions that support drilling engineering activities at the planning stage of drilling operations. But it is only for the last decade that mathematical models have been used for the real-time support of drilling operations. Moving from a pure engineering perspective to having models that can respect real-time requirements, necessitates many improvements of the subjacent mathematical modelling of the drilling process. First, it is not anymore possible to ignore transient behaviors that were somewhat irrelevant at the planning stage. Second, there is a need for solutions that should be fast enough to cope with the real-time constraints of the drilling process. With the perspective of creating applications that can support the drilling process in real-time, the following mathematical models have been developed: • Drilling fluid behavior. The properties of drilling fluids depend on their composition and pressure-temperature conditions. For instance, the pressure-temperature dependence of the mass density of drilling fluids, depends on the individual PVT-properties (Pressure-Volume-Temperature) of each of the components and their relative volume fractions. Therefore, the addition of drill-cuttings in the drilling fluid also changes the drilling fluid PVT-behavior. Furthermore, the rheological behavior of drilling fluids depends also on its composition. We have found that the rheological behavior of a KCl/polymer water-based mud is simultaneously modified by the relative proportion of barite and sand. Furthermore, it is known that drilling fluids are thixotropic. Yet, we found that the thixotropic behavior of drilling fluids is different from the one of other thixotropic fluids and we have determined that one of the causes for the discrepancy is related to the presence of solids in the fluid mix. We have developed a method to estimate the rheological behavior and its associated uncertainty, as a function of the modification of the solid proportions. • Drill-string mechanical sub-models coupled with hydraulic effects. Hydraulic pressure has also an impact on drill-string mechanical forces not only because the fluid mass density modifies buoyancy but more generally because viscous pressure gradients generate net forces along the drill-string. These hydraulic related forces are superposed to those engendered by mechanical friction and elastic deformation. • Steady state and transient drill-string mechanical models. Steady state torque and drag models utilizing the above-mentioned drill-string mechanical sub-models can be used to assess some characteristics of the drilling process when constant velocities are prevalent. But, during a drilling operation, there are many moments during which the drill-string displacement is in transient mode. Therefore, it is also important to have access to transient torque and drag models with a fast response time. • Transient cuttings transport model. The transport of cuttings is obviously influenced by hydraulic circulation but also drill-string rotational speed, at least in the deviated parts of a well. On the other hand, the presence of drill-cuttings in suspension or settling on the low-side of the borehole, influences pressure losses and mechanical forces along the drill-string. Therefore, the estimation of the transient displacement of drill-cuttings plays an important role in the overall estimation of the actual drilling conditions during a drilling operation. However, a transient cuttings transport model shall also be sufficiently fast, especially when it is used in real-time applications. Equipped with such models of the drilling process that are compatible with real-time constraints, then it is possible to solve problems that are relevant for the assistance of drilling operations. A first domain of application is related to the estimation, in real-time, of surface and downhole sensor values as a function of external commands like the block position and speed, the top-drive rotational velocity and the pump rates. We will refer to this domain of application as “drilling simulation”. However, comparison of measured values with simulated ones, require the proper modelling of the sensors and the impact of their actual position on the readings. For instance, drilling fluid is retained in the flowline and mud treatment equipment. Therefore, to simulate pit volumes, it is important to model the retention mechanism. Transient hydraulic, mechanical and heat transfer models, associated with precise modelling of sensor measurements, can then be used to interpret the current actual drilling conditions, because if their estimated parameters differ from the measurements, then a possible reason is that something unexpected is happening downhole. However, such drilling symptom detection method necessitates two additional conditions to be fulfilled: • The models shall be calibrated. Regardless of the quality of the drilling models, the inputs to these models are always known with a limited degree of accuracy and therefore their outputs may differ from measurements for that simple reason. However, it is important to distinguish between uncertainties that are related to properties that do not change substantially during a given drilling operation, from those that can change at any time. To avoid influencing the calibration of time invariant properties with possible side effects of the deterioration of the drilling condition, it is important to utilize drilling conditions by which undesirable side effects have no or little influence on the measurements that are used to calibrate the property. • Uncertainty of the modelled outputs shall be estimated. Calibration may reduce the uncertainty on the model outputs, but it does not eliminate it completely. It is therefore important to estimate the uncertainty of the predicted values. To achieve this, it is necessary to capture the precision by which the inputs of the process are known and to propagate that uncertainty throughout the modelling of the outputs. With continuously calibrated models and an estimation of the current downhole conditions, then it is possible to address some preliminary drilling process assistance functions: • Safety triggers. During the execution of automation functions, the situation awareness of the driller is reduced as he does not drive the drilling machines himself. Therefore, it shall not be attempted to automate any functions before a minimum set of protection functions are in place. Such safety triggers shall detect and react to incidents related to the axial and rotational movement of the drill-string and, of course, associated with pressure. Example of such safety triggers are: o Reactions to overpulls and set-down weights. o Reactions to abnormal torques. o Reactions to abnormal pressures. • Safeguards. Any drill-string or drilling fluid movements shall not generate a drilling incident. Therefore, commands to the drilling machines shall be kept within safe operational envelopes. For instance, upward movement of the drill-string shall not decrease the downhole pressure below the pore pressure or the collapse pressure of the open hole formations. Similarly, the applied flowrate combined with a possible downward movement and rotation of the drill-string shall not overpass the fracturing pressure of open hole formation rocks. • Automated procedures. Protected by safety triggers and operating within acceptable safeguards, then it is possible to automate some standard procedures. However, such automatic procedures must continuously be adapted to the current drilling conditions. For instance, the length of a friction must be modified to account for the current drill-string length and mechanical friction, or the flowrate applied during the ream-down sequence of a reciprocation procedure shall be reduced as a function of the current potential surging risk

Workshop on the Early Earth: The Interval from Accretion to the Older Archean

Presentation abstracts are compiled which address various issues in Earth developmental processes in the first one hundred million years. The session topics included: accretion of the Earth (processes accompanying immediately following the accretion, including core formation); impact records and other information from planets and the Moon relevant to early Earth history; isotopic patterns of the oldest rocks; and igneous, sedimentary, and metamorphic petrology of the oldest rocks