Building response due to deep excavations in Delft: Criteria vs. performance

Building response due to deep excavations in Delft: Criteria vs. performance

Oikonomidis, P.

Van Tol, A.F. (mentor)
Everts, H.J. (mentor)
Bakker, K.J. (mentor)
Mortier, H. (mentor)

Civil Engineering and Geosciences

Geoscience & Engineering

Geo-engineering

2015-04-30

This thesis is focusing on the building damage parameters monitoring techniques and the validation of the current damage prediction methodology on building response next to deep excavations. Settlement risk assessments were done in Delft tunnel project to define and control the risk of damaging the adjacent buildings to the tunnel by following the LTSM methodology steps. Deformations were predicted for every building according to the allowable building damage category and limits were set for every execution phase. Prisms were installed on the buildings facades and these were targeted by robotic total stations hourly, so the horizontal and vertical deformations of the buildings facades were monitored during the execution. Limits were set then on horizontal/vertical displacements per execution phase by assuming that the building actual performance would be similar to the predicted one in the deformation models so the damage criteria of horizontal strain-angular distortion were transformed into horizontal-vertical displacements of a façade prism. The actual damage parameters calculation of horizontal strain/angular distortion per execution phase through a spreadsheet showed that the façade prism cannot be representative for the whole facade as the actual façade status in Boscardin and Cording (1989) graph was in different position than it should be. Moreover, the side walls are more susceptible to damage than the façade as it was seen in the Westvest 5a building. A total station should be used to monitor building deformations but with monitoring points (prisms) installed at all visible building walls and measured during the execution works so the damage parameters to be properly calculated. Thus the actual building status (performance) can be accurately presented and directly compared with the predefined deformations limits (criteria) at every execution phase. For the calculation of façade’s horizontal strain, backside prisms should be used or the one at the most distance to the façade of the side walls. Plus, a bed joint measurement at major execution phases would indicate the critical hogging/sagging areas of the side walls. In case of excessive deformations, a flexible/weak building will tend to follow the greenfield deformations and there will be possible damages on the walls due to differential settlements but the stiff/strong building will rotate and move as a rigid body so no damages expected to be seen. Attention should be given on the free standing buildings, the ones with no buildings next to them as it seems that these are free to move parallel to the building pit and this movement can lead to greater values on the critical damage parameters. Limiting Tensile Strain Method is a practical tool to predict building deformations, conservative most of the times but quite reliable. In cases where special execution techniques are applied or there are critical buildings adjacent to deep excavations then special calculations methods should be used where all available data (building-soil conditions-execution) are imported into sophisticated finite element models (2D-3D) for accurate deformations prediction. At the last step of LTSM, the building is categorized in a damage class and allowable deformations limits are set in Boscardin and Cording (1989) graph (criteria). The actual building status then can be controlled during execution when the damage parameters of horizontal strain and angular distortion are monitored and consequently presented on the graph (performance). In general the damage criterion of Boscardin and Cording (1989) is relatively precise but in cases of excessive deformations it will probably over- / under- estimate the actual damage.

deep excavations
building
damage criteria
deformations
monitoring

http://resolver.tudelft.nl/uuid:ec41d827-96bc-4e1b-87b4-78f59eb53806

Student theses

master thesis

(c) 2015 Oikonomidis, P.