Thesis--M. Sc.(Eng.), University of Hong Kong. / Mimeographed.

Shallow foundations are used when designing subsea structures on the seafloor of deep water Gulf of Mexico. In order to design these subsea shallow foundations it is important to understand the behavior of the undrained shear strength of the shallow soils (i.e. upper ten to twenty feet of soil). The objective of this research is to analyze a database of soil data from deep water Gulf of Mexico originally produced by Cheon (2011) with a focus on shallow soils. The purpose of this analysis is to gain a better understanding of the soil and how it will be usable with regards to shallow foundation design. The methodology of this analysis involves studying raw data collected from different measurements taken to aid in the creation of design profiles of undrained shear strength versus depth. Within the existing database there are 18 locations with a high resolution of point data from in-situ tests (Halibut Vane) and non in-situ tests (Minivane and Torvane) that provide the clearest picture of undrained shear strength in the shallow region. The data shows that the design profiles originally created for these locations for deep foundations are generally not representative of the strength in the shallow region. They also show that in-situ test data show more variability than non in-situ data. There are also 25 Cone Penetration Tests in the existing database that show very high resolution data in the shallow region. These Cone Penetration Tests also indicate a crust that appears to be about 1 ft thick and exists along the edge of the continental shelf. Recommended future activities to build upon this work include re-evaluating the design profiles at these 43 locations at which high resolution studies have been performed in the shallow region, collecting these design profiles as well as any new design profiles and organizing them into a new database focused on shallow soils, generating a new generic profile base on the data within the new database, and creating a model that uses spatial variability analysis to calculate undrained shear strengths at new locations based on the data in the database. / text

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The University of Aberdeen has conducted research into ground anchorage systems since the early 1980's. During this time, the non-destructive GRANIT system (GRound ANchorage Integrity Testing) has been developed for anchorages in rock. The system is based on observing the dynamic response from anchorages to which an impulse of a known intensity has been applied. This technique has been proven to be a reliable system to assess the integrity of rock anchorages, which is then used as a base to study the integrity of soil anchorages. This research aims to implement a non-destructive testing system at small scale size and full scale stress levels by means of centrifuge modelling at the University of Dundee. Accordingly, centrifuge modelling was undertaken to monitor and assess the dynamic response of soil anchorages installed in dry sand reinforcing a retaining wall in 3x3 anchorage array sets, subject to different post tension levels within different bonding ratios and different inclinations. In order to perform non-destructive testing, an In-flight Robotic Manipulator, previously developed, was used to apply a post tension load followed by an impact load to the anchorage head to obtain the dynamic response of the system. Anchor frequency response signatures were then evaluated in order to validate the consistency of results obtained. The practical importance of this research is that non-destructive testing may be usable to assess the soil anchors integrity to define the relationship between both anchor load and geometrical characteristics with frequency response accomplished using centrifuge modelling. This research presents a further development of the physical model in which additional instrumentation is included in order to obtain load/deflection information of the anchor head, which has been proven crucial for monitoring load on rock anchorage. Additionally, load distributions along scaled model soil anchors are measured and found to reduce gradually within the fixed length, similarly as it was reported for the fixed length of rock anchorages. Furthermore, a lumped parameter model for a single soil anchorage was adapted to investigate the dynamic response under the same physical and geometrical characteristics studied during centrifuge modelling. Mode shapes helped to understand the origin of some of the frequency modes present in the frequency response of the centrifuge results. The results from the numerical and centrifuge models were compared and good agreement was observed. Soil anchorage does not show as much frequency shift as was observed for rock anchorages under different post tension load, suggesting that the bonding strength of the fixed length with the surrounding ground plays an important role on the dynamic response of the system. The accomplishment of the assessment of soil anchorage can not be exclusively judged on its ability to diagnose controlled changes under centrifuge and numerical modelling. Therefore a preliminary phase to assess a soil anchorage under field conditions was carried out deploying the GRANIT system. This research showed that the GRANIT non-destructive testing technique has potential for use in soils, but that the results are not as well defined as in rock, necessitating more careful characterization of each anchorage signature response.

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