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Geotechnical engineering is strongly associated with large uncertainties. Exploring a medium (soil) that is almost entirely and completely hidden from us is no easy task. Investigations can be made only at discrete points, and the majority of a specific soil volume is never tested. All soils experience inherent spatial variability, which contributes to some uncertainty in the design process of a geotechnical structure. Furthermore, uncertainties also arise during testing and when design properties are inferred from these tests. To master the art of making decisions in the presence of uncertainties, probabilistic description of soil properties and reliability-based design play vital roles. Historically, the observational method (sometimes referred to as the “learn-as-you-go-approach”), sprung from ideas by Karl Terzaghi and later formulated by Ralph Peck, has been used in projects where the uncertainties are large and difficult to assess. The design approach is still highly suitable for numerous situations and is defined in Eurocode 7 for geotechnical design. In paper I, the Eurocode definition of the observational method is discussed. This paper concluded that further work in the probabilistic description of soil properties is highly needed, and, by extension, reliability-based design should be used in conjunction with the observational method. Although great progress has been made in the field of reliability-based design during the past decade, few geotechnical engineers are familiar with probabilistic approaches to design. In papers II and III, aspects of probabilistic descriptions of soil properties and reliability-based design are discussed. The connection between performing qualitative investigations and potential design savings is discussed in paper III. In the paper, uncertainties are assessed for two sets of investigations, one consisting of more qualitative investigations and hence with less uncertainty. A simplified Bayesian updating technique, referred to as “the multivariate approach”, is used to cross-validate data to reduce the evaluated total uncertainty. Furthermore, reliability-based design was used to compare the two sets of investigations with the calculated penetration depth for a sheet-pile wall. The study is a great example of how a small amount of both time and money (in the pre-investigation phase) can potentially lead to greater savings in the final design. / <p>QC 20160201</p> / TRUST, Transparent Underground Structures

The performance and safety assessment of geo-structures is strongly affected by uncertainty; that is, both due a subjective lack of knowledge as well as objectively present and irreducible unknowns. Due to uncertainty in the non-linear variation of the matric suction induced effective stress as a function of the transient soil-atmosphere boundary conditions, the unsaturated state of the subsoil is generally not accounted for in a deterministic slope stability assessment. Probability theory, accounting for uncertainties quantitatively rather than using "cautious estimates" on loads and resistances, may aid to partly bridge the gap between unsaturated soil mechanics and engineering practice. This research investigates the effect of uncertainty in soil property values on the stability of unsaturated soil slopes. Two 2D Finite Element (FE) programs have been developed and implemented into a parallelised Reliability-Based Design (RBD) framework, which allows for the assessment of the failure probability, failure consequence and parameter sensitivity, rather than a deterministic factor of safety. Utilising the Random Finite Element Method (RFEM), within a Monte Carlo framework, multivariate cross-correlated random property fields have been mapped onto the FE mesh to assess the effect of isotropic and anisotropic moderate heterogeneity on the transient slope response, and thus performance. The framework has been applied to a generic slope subjected to different rainfall scenarios. The performance was found to be sensitive to the uncertainty in the effective shear strength parameters, as well as the parameters governing the unsaturated soil behaviour. The failure probability was found to increase most during prolonged rainfall events with a low precipitation rate. Nevertheless, accounting for the unsaturated state resulted in a higher slope reliability than when not considering suction effects. In a heterogeneous deposit failure is attracted to local zones of low shear strength, which, for an unsaturated soil, are a function of both the spatial variability of soil property values, as well as of the soil-water dynamics, leading to a significant increase in the failure probability near the end of the main rainfall event.

Abstract This thesis discusses strengthening foundations of historic buildings by means of pretested, end-jacked, steel piles; pretested, end-jacked drilled spiral steel piles, as well as the geotechnical and structural design of strip foundations using ultimate limit state methods. Strengthening the foundations of historic buildings is a field of engineering where every site is more or less different from another. The variation of the substructure, foundation, and soil circumstances make every case unique. Preserving heritage buildings by preventing structural decay requires know-how and suitable strengthening methods. Drilled spiral piles and jacked piles were employed as strengthening methods for St. John’s Church of Tartu, because of the sinking and uneven settlement of the building. The strengthening work at St. John’s Church was challenging due to the risk of collapse of this historic church. Underpinning with jacked piles is a preferred method for strengthening historic foundations and where drilled spiral piles were employed, the author of this thesis developed special equipment. The strengthening method employed for the tower complies with the anastylosis principle by preserving the authenticity of the structures. Old block stones are visible upon the floating piled rafts. The empty space was left to give archaeologists and engineers a chance to study the realized work “in situ” in the future. The foundation of the tower was underpinned step by step with end-jacked piles and a concrete raft poured step by step. The weight of the tower is 5&#160;500 tons and it rests on four pillars. Every pillar rests on its own floating piled raft. This thesis proves that by means of lower and upper bound theorems a floating, piled strip-foundation can be designed geotechnically and structurally using one method based on ultimate limit state (ULS) and serviceability limit state (SLS). The method takes the following into account as geotechnical requirements: total settlement and angular distortions; and as structural requirements; admissible plastic rotations, end moments due to displacement angle, as well as control of cracking. The chosen piling methods were suitable for St. John’s Church, and the installed piles work well in addition to the old foundations. The functionality of the strengthening techniques has been verified by test piling. Furthermore, every drilled spiral pile was preloaded twice and end-jacked for soil hardening. / Tiivistelmä Tämä tutkimus käsittelee historiallisten rakennusten perustusten vahvistamista esikuormitetuilla teräksisillä puristuspaaluilla ja esikuormitetuilla, loppupuristetuilla spiraaliporapaaluilla. Tutkimus sisältää myös pitkänomaisen anturaperustuksen mitoitusmenetelmän, joka huomioi sekä murtorajatilan että käyttörajatilan vaatimukset. Historiallisten rakennusten perustusten vahvistaminen on insinööritieteen osa-alue, missä jokainen työmaa on oma, ainutlaatuinen kohteensa johtuen erilaisista maaperäolosuhteista, perustuksista ja rakenteista. Rakennuksen luonteen säilyttäminen edellyttää insinööriltä monialaista kykyä ja tietoa sopivista vahvistamismenetelmistä. Spiraaliporapaaluja ja puristuspaaluja käytettiin Johanneksen kirkon (Jaani Kirik) perustusten vahvistamisessa rakennuksen epätasaisen painumisen ja sortumisvaaran vuoksi. Perustusten vahvistamista puristuspaaluilla pidetään yleisesti parhaana menetelmänä historiallisille rakennuksille. Tämän tutkimustyön tekijä suunnitteli erikoiskaluston työtä varten kehitetylle kierrepaalulle. Anastylosis periaatteen mukaisesti käytetyssä tornin vahvistamismenetelmässä säilytettiin rakenteiden autenttisuus. Vanhat kivilatomukset ovat osittain näkyvissä. Niiden välissä oleva tyhjä tila antaa arkeologeille ja insinööreille mahdollisuuden tutustua suoritettuun työhön. Tornin perustukset vahvistettiin vaiheittain paaluilla sekä valetulla betonilaatalla. Torni painaa 5&#160;500 tonnia ja se on neljän pilarin varassa. Jokaisella pilarilla on erillinen kelluva paalutettu laattaperustus. Tässä työssä on osoitettu, että plastisuusteorian ala- ja ylärajalauseiden avulla myötäävän kitkamaan ja myötäävän paalutuksen varaan perustettu pitkänomainen anturaperustus voidaan mitoittaa geo- ja rakenneteknisesti murto- ja käyttörajatilassa samalla menetelmällä. Menetelmä sisältää geoteknisinä vaatimuksina anturan pohjapaineen, kokonaispainuman ja kulmakiertymän (=&#160;epätasaisen painumisen) määrittämisen, rakenteellisina vaatimuksina plastisoituvien kohtien riittävän muodonmuutoskyvyn, kenttä- ja tukimomenttien, epätasaisen painumisen aiheuttamien pakkomomenttien sekä halkeamatarkastelun määrittämisen. Spiraaliporapaalujen toiminnallisuus varmistettiin koepaaluilla. Maanlujittumista varten jokainen spiraaliporapaalu koestettiin kahdella esikuormituksella ja loppupuristuksilla.