Prediction of damage to cement-based structures subject to tunnelling-induced settlements

Cirillo, Gerardo (2003-12)

Thesis (MScEng)--University of Stellenbosch, 2003.

Thesis

ENGLISH ABSTRACT: Tunneling in busy urban areas is becoming a common practice, caused by the everincreasing number of commuters. This causes a decline in the service level that the surface transportation systems provide in cities. Tunneling induces movement of the soil directly surrounding the tunnel. These movements are translated into surface movements, which are translated into structural displacements of the surrounding surface infrastructure. These displacements, for which the infrastructure may not have been designed, put a question mark on the infrastructure aesthetics, serviceability, as well as structural stability. Burland and Wroth (1974) proposed a simple analytical damage assessment approach (Limiting tensile strain method (LTS)) to aid in the design of tunnels with respect to the structural integrity of the affected surface infrastructure. This study is concerned with the accuracy of this approach applied to the damage assessment of laterally unconfined, solid masonry walls, subject to a sagging mode of settlement deformation with no soil to wall friction. It is also concerned with the proposal of modifications to the approach, where deemed necessary. Finite element models of solid masonry walls are built and analysed in order to determine the accuracy of the simple analytical damage assessment approach with regard to the prediction of strains in solid masonry walls subject to tunneling-induced displacements. The predictions are found to be accurate for walls ofL/H ratio equal to 2 and larger. For walls of L/H ratio smaller than 2, the predictions are found to be underestimates. The simple analytical damage assessment approach is unable to account for the stiffness of the soil directly under the foundation of the wall. The stiffness of the soil plays a major role in the stress and strain distributions in the wall. It is therefore deemed necessary to modify the simple analytical damage assessment approach by accounting for the soil to wall interaction and the effect it has on the settlement damage to solid masonry walls. The soil to wall interaction is found to reduce the number of mitigating measures originally recommended for the walls, by the simple analytical damage assessment approach, as it accounts for the bedding of the wall into the soil previously unaccounted for. This study has reached the point where it is able to accurately predict whether a laterally unconfined, solid masonry wall, subject to a sagging mode of settlement deformation with no soil to wall friction will experience magnitudes of strain surpassing the yielding strain of the material. This was fundamentally achieved by developing a better representation of the strains in solid masonry walls as well as accounting for the inherent soil to wall interaction This study is intended to pioneer the proliferation of similar studies for various other structures. A methodology, applicable for similar investigations envisaged for other structures, is hereby developed.

AFRIKAANSE OPSOMMING: Tonnels in besige stedelike gebiede is besig om 'n allerdaagse verskynsel te raak a.g.v. die skerp toename in pendelaars. Die rede hiervoor is die afname in die kwaliteit van bogrondse vervoerdienste. Tonnels veroorsaak beweging van grond direk in aanraking met die tonnel. Hierdie bewegings versprei na die oppervlak wat strukturele verplasings veroorsaak. Vir n' struktuur wat nie vir hierdie verplasings ontwerp is nie, ontstaan vrae oor die estetika, diensbaarheid asook die stabiliteit van die struktuur. Burland en Wroth (1974) het 'n eenvoudige analitiese skade-assesseringsmetode voorgestel (Limiting tensile strain method (LTS)) vir die ontwerp van tonnels m.b.t. die strukturele integriteit van die geaffekteerde oppervlak se infrastruktuur. Hierdie studie handeloor die akkuraatheid van dié benadering, toegepas op die assessering van skade op lateraalonbeperkte, soliede messelwerkmure, onderhewig aan die deurbuigings mode van versakkingsdeformasie, met geen grond tot muur wrywing. Eindige element modelle van messelwerkmure is gebou en geanaliseer om die akkuraatheid van die eenvoudige analitiese skade-assesseringsmetode te bepaal, m.b.t. die voorspelling van die vervormings in messelwerkmure onderhewig aan grondverplasings veroorsaak deur tonnels. Die voorspellings is akkuraat in mure met lengte tot hoogte (L/H) verhoudings van 2 en hoër. Vir mure met LIH verhoudings van minder as 2, word daar gevind dat die voorspellings onkonserwatief is. By die eenvoudige analitiese skade-assesseringsmetode word die styfheid van grond direk onder die fondasies van die muur nie in ag geneem nie. Die grondstyfheid speel 'n kardinale rol by die spannings- en vervormingsverdelings in die muur. Dit is daarvoor nodig om die eenvoudige analitiese skade-assesseringsmetode aan te pas om die grond tot muur interaksie in ag te neem. Die interaksie tussen die grond en die muur veroorsaak 'dat a minder of geen skade voorkomende maatreëls getref hoef te word as wat oorspronklik deur die envoudige analitiese skade-assesseringsmetode voorgestel sou word. Dit neem die inbedding van die muur in die grond in ag, wat voorheen geïgnoreer is. Die studie het 'n punt bereik waar dit akkuraat kan voorspelof 'n lateraalonbeperkte, soliede messelwerkmuur, onderhewig aan die deurbuiging mode van versakkingsdeformasie en met geen grond tot muur wrywing, vervormings hoër as die swigvervorming van die material salondervind. Dit is bereik deur 'n beter voorstelling van die vervormings in soliede messelwerkmure asook die in agneming van inhirente grond tot muur interaksie. Die studie is veronderstel om die voorganger te wees vir soortgelyke studies toegepas op verskeie ander struktuurklasse. Die sistematiese metode wat hier ontwikkel is kan toegepas word op die ander struktuurklasse.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/53556
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