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published_or_final_version / toc / Applied Geosciences / Master / Master of Science

Thesis (PHD)--University of Montana, 2010. / Contents viewed on April 30, 2010 Title from author supplied metadata. Includes bibliographical references.

Stag Hill is an example of a slope failure in London Clay. In 1964 it was proposed to develop the area, so the slope was stabilized using a drainage system and heavy buildings were constructed on piled foundations. Piezometers were also installed to establish the pore pressure pattern. In 1985 a general evaluation of the history of the failure, stabilization and development of the area was undertaken. This gave rise to the view that this area would be a very suitable place to establish a system for studying the efficiency of drainage systems. The presence of the drainage system, which initiates rapid fluctuation of ground water pressure in response to infiltration, brought about the necessity of attention to the errors associated with time lag which would be involved in monitoring of pore water pressure. Later on, when the ground water pressure was being monitored, it was observed that changes of atmospheric pressure significantly affects the records of vibrating wire piezometers. In this way the necessity of the evaluation of difficulties and errors associated with atmospheric pressure in monitoring of ground water pressure automatically merged into the research. Accordingly, to fulfill the above mentioned aspects, all available piezometer records since 1964 were collected and plotted. All piezometers which survived were tested to see if they were still reliable. Drainage trenches were located at appropriate locations and over 60 new piezometers of different types were installed at different depths, in drained and non-drained areas, and in the trenches. Two types of pore water pressure measurements, daily and weekly, were taken. To record the duration and intensity of daily rainfall, an automatic tilting bucket system was installed in the area. To include the effect of the atmospheric pressure on the evaluation of the pore water pressure pattern, records of atmospheric pressure, taken at Gatwick airport were used. The main conclusions are that: Monitoring of ground water pressure, using stand pipe piezometers, in drained areas may lead to serious errors, say 1.0 meter head of water. Application of rigid piezometers is necessary but not enough, unless a reasonable correlation is established between piezometer reading times and rainfall periods. Changes of atmospheric pressure are a significant source of error in monitoring of ground water pressure techniques. A method to correct piezometer readings for changes in atmospheric pressure was established. At Stag Hill, the ground water pressure pattern, and in turn the stability of slopes is governed by layers of higher permeability in the range of 10[-5] - 10[-6] cm/sec. The main drainage system having a spacing to depth ratio of S/D = 3.4 - 3.8 has not efficiently improved the stability of the slopes. Surface covering (buildings and paving), however, has a dominant effect on the improvement of safety factor. At Wates House, the drainage system having S/D = 1.1, has lowered the ground water pressure with 92% efficiency. It takes some years before the ultimate efficiency of a drainage system takes effect. The efficiency of drainage trenches below invert level varies between the maximum and minimum efficiency of drains at invert level, in the long term. The theoretical methods for design of drainage trenches do not agree with practice. A practical design curve was suggested.

M.Ing. / Please refer to full text to view abstract

as one of three explanations of a prominenttine delay in the 6.5 km/s branch of their seismic refraction survey in the Rocky Mountain Trench, Eennett et al (1975) suggested a high-angle crustal fault crossing the trench near Radium. If the density contrast between basement and cover rocks is 0.1 g/cm3, a gravity anomaly of approximately 18 mgal should be observed. To test the fault hypothesis, a gravity survey has been carried out in and adjacent to the trench in the Radium area. The resultant data are not consistent with the proposed fault model. The principal feature of the data is a pronounced low which coincides with the trench throughout the survey area. The low is due to Cenozoic fill and interpretation by two-dimensional modeling indicates the thickness of fill is about 550 m to the north and 420 m to the south of Radium. An analysis has also been performed of the shear-wave data recorded during the seismic survey of Bennett et al (1975). Although the quality of the S save data is poor, they show consistent behavior with the P save data. There is weak evidence suggesting a basement refractor velocity of 3.5 km/s and a Moho refractor velocity of 4.2-4.5 km/s. The corresponding Poisscn's ratios are 0.30 and 0.28-0.32. To determine maximum and minimum depth limits to the Hcho allowed by the seismic data, an extremal analysis was performed on both the P and S wave record sections. From the P wave data, the limits on crustal thickness beneath the Rocky Mountain Trench are 52 km and 60 km; from the S wave data, the limits are 47 km and 59 km. Is a result of these additional studies, the tao alternative hypotheses of Bennett et al (1975) to explain the seismic data must be reconsidered. These are (1) the existence of a crustal low velocity zone and (2) a major deformation of the basement and overlying rocks due to the trench being an ancient zone of weakness which coincides with the western limit of the continental Precambrian craton. As reflections from the top of the low velocity zone are not observed by Bennett et al (1975), the second alternative is preferred. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

A proposed modeling technique that yields a best fit to observed wide-angle reflection profiles incorporates (1) the use of migrated vertical reflection profiles to provide topographic control, (2) ray tracing to produce theoretical wide-angle reflection profiles for hypothetical crustal sections, and (3) the iterative adjustment of crustal layer dip, thickness and velocity. The technique, applied to four successive wide angle reflection profiles located due west of Callao, Peru, and extending from 50 km west of to 80 km east of the axis of the Peru-Chile trench, suggests (1) that a 5 km thick oceanic crust thickens to 7 km at the trench axis, (2) that the oceanic plate underthrusts the continental plate, and (3) the existence of a previously undetected 7.8 km per sec oceanic layer. Migrated vertical reflection profiles show (1) a series of block faults across 20 km of the trench edge of the continental plate and (2) oceanic basement underthrusting 6 km of the trench edge of the continental plate. / Graduation date: 1974

Detailed surveys of several segments of the Peru Trench show that the region between 6° to 10⁰ S is an area of recent deformation. Seismic reflection records across the axis of the trench show faulting, uplift, and tilting of the sedimentary fill and the acoustic basement. Uplift of the acoustic basement beneath the trench is greatest at 7°40'S and 9°20'S where ridges are elevated above the trench floor. Turbidites occur on top of the ridge at 9°20'S and seaward of the ridge in a basin which is elevated 300 m above the main trench floor. Based upon a hemipelagic sedimentation rate of 1.7 cm/1000 yr, the age of uplift of the ridge is dated at less than 10,000 yrs. B.P. Similarly, the age of uplift of the elevated basin seaward of the ridge is dated at less than 34,000 yrs. B.P. near the ridge and at less than 53,000 yrs. B.P. at the seaward edge of the basin. The trench shoals and turns eastward as one proceeds from south to north along the axis. It divides naturally into three segments separated by the axial ridges at 7°40'S and 9°20'S. The southern segment trends N31W and has an axial depth of 6300 m; the middle segment trends N24W at 6200 m; and the northern segment trends N11W at 5800 m. The upper continental slope is characterized by submarine canyons which funnel sediments into the trench axis. The lower slope is characterized by benches. These benches may define old imbricate thrust sheets. Ridges in the axis are thought to be new imbricate thrust sheets which are forming at the boundaries between segments of the subducted lithosphere. An apparent fracture zone trending N45E enters the area from the southwest. Two turbidite basins (B1 and B2) trending N9E occur northeast of this fracture zone. Turbidite deposition ended in these basins 5100 yrs. ago. The basins intersect the trench axis just north of the ridge at 7°40'S and are presently 700 m above the trench axis. This relative difference in depth is attributed to a combination of subsidence of the trench and uplift of the oceanic plate upon initiation of thrust faulting which presumably occurred 5100 yrs. B.P. There is still insufficient data to determine the exact origin of these basins. From the regional structure, it appears that the lower continental slope of South America is underthrusting the upper continental slope along old imbricate thrust faults beneath the Peruvian continental slope. This overthrusting has caused uplift and accretion of the continental slope and shelf edge and subsidence and sediment infilling of the area between the shelf edge and the coastline. The author suggests that the seismic gap (present lack of large magnitude shallow earthquakes in this area) may be in part due to the highly fractured and deformed nature of the subducted Nazca Plate. Finally, using variable motion along old imbricate thrust faults, the imbricate thrust model provides mechanisms for reorientation of the trench and for episodic subduction of the oceanic plate beneath the trench axis. / Graduation date: 1974

The hardened inner city community of trench town represents one of several impoverished communities that form the heart of the Jamaican capital city, Kingston. As wealth and influence have moved inland, off the coastal plains on which the city was originally settled on, to the slopes of the surrounding mountains, the once vibrant downtown core has decayed. With this urban decay came the social ills that usually accompany failing communities such as crime, violence, shadow economies, health and sanitation issues. As has been the case with many urban centres worldwide, this problem was further exacerbated by an ever present influx of rural immigrants in search of a better life in the city. These associated urban problems not only affect the inhabitants of these communities, but they stifle the growth of the larger national economy. This thesis aims to explore and propose urban design interventions to the inner city community of Trench Town, that not only address the issues of providing viable shelter to the residents of the community, but also begin to set up a frame work of self reliance and economic sustainability and growth, so that the community members can begin to develop their lives for themselves. It also begins to look at ideas of communal living that have been experimented with at on a small scale over the years, but have never been fully integrated into the urban fabric. This thesis looks to examine one specific community within the urban fabric of the city, but all the while cognisant of the fact that this one community is but one in the overall urban fabric, yet recognising that as each informal inner-city community has developed out of a unique set of conditions and thus must be treated individually as such. Throughout the years, several interventions have been implemented to address the overall need to house the population of the expanding urban centres, with many variations of urban housing solutions being used, with varying degrees of success. This thesis will explore the implications of these solutions on the proposed site, and explore viable modifications and variations. Firstl an in depth exploration into the historical and cultural context of the case site will be explored to gain important background knowledge of known factors of spatial development and community needs, and this will form the foundation of any further development going ahead in the case study, which will provide the analytical breakdown of the site and influences. The thesis will then explore international case studies of various approaches to similar situations to identify challenges that have been experienced elsewhere and that may inform the design site. From this research information, parameters and principles will be distilled to inform the overall design intervention. Finally, the proposed design intervention will be reflected upon, and evaluated to try to determine any shortcomings and indentify how the design might be replicated in other communties in Kingston facing similar social and economic conditions.

The hardened inner city community of trench town represents one of several impoverished communities that form the heart of the Jamaican capital city, Kingston. As wealth and influence have moved inland, off the coastal plains on which the city was originally settled on, to the slopes of the surrounding mountains, the once vibrant downtown core has decayed. With this urban decay came the social ills that usually accompany failing communities such as crime, violence, shadow economies, health and sanitation issues. As has been the case with many urban centres worldwide, this problem was further exacerbated by an ever present influx of rural immigrants in search of a better life in the city. These associated urban problems not only affect the inhabitants of these communities, but they stifle the growth of the larger national economy. This thesis aims to explore and propose urban design interventions to the inner city community of Trench Town, that not only address the issues of providing viable shelter to the residents of the community, but also begin to set up a frame work of self reliance and economic sustainability and growth, so that the community members can begin to develop their lives for themselves. It also begins to look at ideas of communal living that have been experimented with at on a small scale over the years, but have never been fully integrated into the urban fabric. This thesis looks to examine one specific community within the urban fabric of the city, but all the while cognisant of the fact that this one community is but one in the overall urban fabric, yet recognising that as each informal inner-city community has developed out of a unique set of conditions and thus must be treated individually as such. Throughout the years, several interventions have been implemented to address the overall need to house the population of the expanding urban centres, with many variations of urban housing solutions being used, with varying degrees of success. This thesis will explore the implications of these solutions on the proposed site, and explore viable modifications and variations. Firstl an in depth exploration into the historical and cultural context of the case site will be explored to gain important background knowledge of known factors of spatial development and community needs, and this will form the foundation of any further development going ahead in the case study, which will provide the analytical breakdown of the site and influences. The thesis will then explore international case studies of various approaches to similar situations to identify challenges that have been experienced elsewhere and that may inform the design site. From this research information, parameters and principles will be distilled to inform the overall design intervention. Finally, the proposed design intervention will be reflected upon, and evaluated to try to determine any shortcomings and indentify how the design might be replicated in other communties in Kingston facing similar social and economic conditions.