Design of a free-fall penetrometer for geotechnical characterisation of saturated sediments and its geological application [Elektronische Ressource] / Sylvia Stegmann

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Design of a free-fall penetrometer for geotechnical characterisation of saturated sediments and its geological application Doctoral Thesis Submitted for the doctoral degree in natural sciences at the Faculty of Geosciences of Bremen University Zur Erlangung des Doktorgrades der Naturwissenschaften im FachbereichGeowissenschaften der Universität Bremen byvorgelegt von Sylvia Stegmann Bremen, September 2007 AbstractAbstract Cone Penetration Testing (CPT) is a versatile, time efficient method to characterise sediment strength and pore pressure in offshore settings and on land. The majority of the penetrometers rely on heavy trucks or rigs to provide the necessary force to push the CPT probe into the ground. This laborious process usually deforms or otherwise affects the uppermost deposits, whose physical properties are in turn vital to understand processes related to scour, burial of mines, cable or pipeline laying, silting of water ways and harbours, or sediment transport and remobilisation. Owing to the shortcomings of heavy seagoing CPT gear, this thesis aimed to develop and use a cable-led marine penetrometer lance which profiles the uppermost sediments in a less destructive manner. The study summarises the development and deployment of a marine cone penetrometer system.

Informations

• Publié par: universitat_bremen
• Publié le: 01 janvier 2007
• Nombre de lectures: 168
• Langue: English
• Poids de l'ouvrage: 23 Mo

Extrait

etDesign of a free-fall pen

ter for geotechnical erom

rated sediments and its geological characterisation of satu

application

Doctoral Thesis

natural sciences at the r the doctoral degree inSubmitted fo

Faculty of Geosciences of Bremen University

Zur Erlangung des Doktorgrades der Naturwissenschaften im Fachbereich

r Universität Bremen eGeowissenschaften d

by

n t vovorgeleg

amSylvia Stegnn

ber 2007 ptemen, SeBrem

Abstract

Abstract Cone Penetration Testing (CPT) is a versatile, time efficient method to characterise
sediment strength and pore pressure in offshore settings and on land. The majority of the
eters rely on heavy trucks or rigs to provide the necessary force to push the CPT penetrom or otherwise affects the sms usually deforprobe into the ground. This laborious procesrn vital to understand processes related properties are in tuost deposits, whose physical upperms, cable or pipeline laying, silting of water ways and harbours, or neito scour, burial of msediment transport and remobilisation. Owing to the shortcomings of heavy seagoing CPT
gear, this thesis aimed to develop and use a cable-led marine penetrometer lance which
nner. aents in a less destructive most sedimprofiles the uppermeter ent of a marine cone penetroment and deploymarises the developmThe study summsystem. It consists of an instrument for shallow-water application (200 m) and, based on the
experience of the first, a second version operable down to 4000 m water depth. Design and
construction of the instruments occurred at the Research Centre Ocean Margins, Bremen
Kopf, Matthias collaboration between AchimUniversity (RCOM) in close and productive initial phase of researching for sensors and Lange and myself during the first year. After an entsr construction, a total of 338 CPT experimponents, I contributed to the design. Aftecom] device) were carried out to date. ] and deep-water [DW(both with the shallow-water [SWFrom the wealth of deployments, 300 of them were performed by me while 204 raw data sets
were processed by me over the course of this thesis (mostly 2nd and 3rd year). The CPT
ent testing, and later focused on ents were initially dedicated largely to instrumdeploymgeological application. A total of ten manuscripts, on six of which I am lead author, were submitted for
publication and are contained in this thesis. Five of them serve as a proof-of-concept of the
two CPT lances, which are operable on winches as well as in free drop. Two of these texts,
one each on the SW- and DW-instrument, are rather generic in nature and introduce the
munity. A third and fourth paper ent design and its benefit to a broader scientific cominstruments in different modes of operation, summarise the initial results from various deploymcomprising both short-term CPT profiling and mid-term deployments to also study pore
parison ofprehensive systematic compressure response. The fifth paper provides a comvelocity-controlled CPT deployments and, after having built an adapter for our lance,
38 selected data sets, the strain-rate ents. Fromhydraulically pushed constant-rate deploymeffects of the dynamic tests were assessed and, based on earlier empirical solutions from the
ingly, the results with the RCOM lance agree well for. Overwhelmre, correctedCPT literatu

2

Abstract

with those from the pushed tests, and further help to accentuate them. Within the spectrum of
/s), it is found that the faster the rate of initial penetration is velocities tested (35 – 135 cmdeviations caused by layering and variations in chosen, the larger the discrepancy between the y be vital when carrying out CPTaents. This observation mphysical properties of the sedimexperiments in geomaterials where lithological variability is small, because it helps
/s. identifying features otherwise undetectable by pushed profiling at the standard rate of 2 cmAnother five manuscripts summarise the geological application of the CPT devices. The
ents as diverse as the Baltic Sea, Lake Lucerne, l environmed in geologicatests were performan activRegardless of the regioe mud volcanonal scenario, some overa in Azerbaijan, and the Cretan Sea in the Eastern Medrching consistent results were obtained during iterranean.
the CPT deploymsignals are recorded by CPT lance when deploents. As an outstanding finding, three types of characteriyed in “free-fall” mode on a cable. In granular, stic pore pressure
normexponential decay back to amally consolidated material, a pore pressure spike upon imbient values (if sufficient time is allopact is usually followwed for dissipation).ed by an
Alternatively, a secondfollowed by an increase in pressure to am pattern often met is a negative (i.e. sub-hydrostatic) pressure spike bient pore pressure values. The sub-hydrostatic
signal is caused by displacement of pore fluid by the profiling CPT instrument, which results
high permin flow away fromeability. The third characteristic signa the probe. This second pattern l generally shows supra-hydrostatic pressures is restricted to coarse-grained deposits with
upon impact and during profiling, but then climbs to even higher pressures with time. Graphs
ents of variable grain size distribution and are related to fluid like this are found in sedim g-bearinird type is observed in clays as well as silt- or sandoverpressures. Interestingly, the thdeposits, and appears no matter what the cause of the excess pore pressure is. In the various
rves are seen although the reason for the field studies, very similar pore pressure cu ading (and potentially EQ tremor; Lake Lucerne), presence ofoverpressures were glacial loation in folded and faulted shales of the crobial gas (Baltic Sea), hydrocarbon formiment and ovemation (Azerbaijan, Greater Caucasus), or neo-tectonic mMaykopian Formlandsliding (Cretan Sea). ” CPT lances are an ary, this study has shown that velocity-controlled “free-fallIn summ deposits. eans to characterise geotechnically shallow sub-bottomefficient, user-friendly mThey obtain reproducible results that can be linked with standard pushed tests, but have the frictionadded advantage of producing m as well as characteristic poore pressure responses inre pronounced excursions in cone resistance and sleeve dicative of geological conditions.

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Zusammenfassung

Zusammenfassung Cone Penetration Tests (CPT) stellen eine vielseitig einsetzbare, zeitgünstige Methode zur
nd und aentfestigkeit und des Porendrucks an L der Sedimgeotechnischen Charakterisierungim Wasser dar. Die Mehrzahl der Penetrometer basiert hierbei auf LKWs oder schweren
Metallrahmen als notwendiges Widerlager, um die CPT-Sonde in den Untergrund zu drücken.
ation und Beeinträchtigung der Dieser arbeitsaufwendige Prozess führt generell zur Deformobersten Sedimentlagen, deren physikalische Zustandsgrößen umgekehrt wichtig sind, um
pelines, ibeln oder PProzesse wie Auskolkung, Versandung von Minen, Verlegung von KaVerschlickung von Wasserstrassen und Häfen sowie Sedimenttransport und –remobilisierung
rine Tests hatte diese aen für men CPT-Rahmzu verstehen. Aufgrund der Nachteile der schwereterlanze zu entwickeln, die die rine PenetromaDoktorarbeit zum Ziel, eine drahtgeführte mglichst ungestört profiliert. öente mobersten Sedimrinen aDie vorliegende Studie beinhaltet die Entwicklung und Anwendung eines mPenetrometer-Systems. Dieses besteht aus einem Instrument für den flachmarinen Bereich
it dieser Lanze, eine zweite m) und, aufbauend auf den Erfahrungen massertiefen bis 200 (Wssertiefe einsetzbar ist. Das Design und die Konstruktion beider am WLanze, die bis in 4000 en (RCOM) in anränder der Universität Brem OzeGeräte fanden am DFG-Forschungszentrum Projektjahr statt. r im ersteni Lange und menger Kooperation zwischen Achim Kopf, Matthiasenten arbeitete ich ponNeben einer umfassenden Marktanalyse geeigneter Sensoren und Komin der Initialphase am Entwurf mit. Nach dessen Umsetzung wurden bis heute insgesamt 338
eführt. Von dieser rchgTiefwasserlanze) duente (sowohl Flach- als auch CPT-Experimrsönlich durch und arbeitete bei 204 von ihnen Vielzahl an Geräteeinsätzen führte ich 300 pelich 2. und 3. auf der Dissertation (vornehm Verlan der Aufbereitung der Rohdaten im Projektjahr). zur Einreichung net zehn Manuskripte, auf derer sechs ich Erstautorin bin, kamInsgesamär als rtation enthalten. Fünf Manuskripte dienten primund sind in der vorliegenden Disseente, die an Seilwinden und Nachweis des Funktionsverhaltens der beiden CPT-Instrum können. Zwei der Publikationen, je eine zur freien Fall eingesetzt werdenKränen oder imn die Geräte und ihre Vorzüge tur und stellea generischer NFlach- und Tiefwasserlanze, sindeiner breiteren wissenschaftlichen Öffentlichkeit vor. Der dritte und vierte Artikel fassen die odi zusammen, die ersten vorläufigen Ergebnisse von Tests in unterschiedlichen Operationsmilierung als auch längere Messungen zum entprofdimesowohl kurze CPT-Einsätze zur Sfassenden Porendruckverhalten beinhalten. Das fünfte Manuskript stellt einen umit den atischen Vergleich der geschwindigkeitskontrollierten CPT-Einsätze msystem

4

Zusammenfassung

Vorschub dar, für die eigens ein Adapter an die it konstantemhydraulisch gedrückten Tests m

Lanze gebaut wurde. An einer Auswahl von 38 CPT-Tests konnten die Effekte der

Verformungsrate bei dynamischer Eindringung der Freifall