Introduction In June 2008 there was a leakage in a diaphragm wall of Vijzelgracht station. This leakage caused a sand-water mixture to pass through the wall, resulting in significant (up to 0.15 m) settlement of a block of 4 adjacent buildings. It was noted that the piled foundations under 2 of these buil- dings had not only settled because of the sand that disappeared, but also that the bearing capacity was significantly reduced because the remaining soil around the pile tips now had a much lower relative density than it had before the incident. The brickwork walls of the buildings were braced with timber beams immediately after the incident in order to avoid progressive collapse of the buildings. The leakage was attributed to a steel stop end not being removed at this location and failure of the repair measures consisting of High Density Injection. On September, 10 2008 a further episode of severe leakage resulted in substantial settlement of buildings Vijzelgracht 4 to 10. More details about this incident can be found in [Korff et al, 2009]. The houses adjacent to the wall were monumental buildings from around 1670. A foundation consis- ting of 52 timber piles per house extends to the first sand layer. Before construction of the North South Line these buildings were equipped with monitoring instruments (figure 1). Deformations and damage As shown in figure 2, the block of houses Vijzel- gracht (VZG) 20-26 settled a maximum of 150 mm due to the incident in June 2008. The buil- ding tilted towards the corner of VZG 26 and towards the location of the leakage. A slight sagging was found between VZG 26 and VZG 24 and hogging towards VZG 22. Significant cracks of up to 20 mm were reported. The location and direction of the cracks indicate a shear deformation and horizontal extension in the plane of the wall. The largest crack width was found at VZG 24, just as the differential settle- ments indicate. A twist movement of the block was also found. The actual damage derived from the observations for these buildings (26, 24) would be category 5, very severe (Burland et al 1977). A significant tilt of the buildings was observed, with severely sloping floors and separation of the rear façade from the house. The front façade experienced a maximum tilt of 1:78 perpendicular to the façade and 1:184 parallel to the façade at the corner of Vijzelgracht 26. Both relative rotation and deflection ratio have been calculated for the front façade as 0.62% and 0.47% respectively, leading with a horizontal strain of 0.04% to damage category 5. The damage categories matched well with the actual damage. Damage to the buildings is especially severe in terms of serviceability due to the overall rotation of the building perpen- dicular to the facades. It appears that tilt, in extreme circumstances, can cause severe problems of serviceability and stability to buildings. In this case this proved more problematic than the cur- vature and resulting cracking of the building. Tilt usually does not receive very much attention. The corrective grouting project After the incident, it was decided to use corrective grouting to increase the bearing capacity of the sand and consequently lift the buildings up to an agreed maximum of 10 mm to prove it was possible to restore the pile capacity and stability of the building. The layout of the site is shown in figure 3, with the diaphragm wall on the right. The corrective grouting area is coloured grey, the lines are the TAMs and the thick, grey lines show foundations of the settled buildings. The liquid Figure 2 Deformations after incident June 2008 (measurements dated July, 31st 2008). Vijzelgracht 26 Vijzelgracht 24 Vijzelgracht 22 -200 -150 -100 -50 0 50 100 150 0 5000 10000 15000 20000 25000 Distance from corner (m) z top x top y top z mid x mid y mid 26-24-22 All in mm Building damage and corrective grouting research at North South line project in Amsterdam In Amsterdam, the North South subway line provides opportunities for researchers in several geotechnical fields. As partner in the Centre for Underground Construction (COB), The authors perform their PhD research while the project is continuing. An incident of leakage strongly influenced the North South Line project in 2008. Building damage and correc- tive grouting were studied at a building with a piled foundation that was partly disturbed due to ground loss. This paper shows results for compensation grouting and increased understanding of the influence of the foun- dation on building deformations. Lessons can be incorporated in future projects, which closes the circle of innovation in these fields. Summary Figure 1 Weaverbuilding Vijzelgracht 26 with prism locations (Photo Projectbureau NoordZuidlijn). Adam Bezuijen Deltares/Delft University of Technology, Delft, The Netherlands Mandy Korff Deltares/Cambridge University 8 GEOtechniek – Special 17th ICSMGE – Alexandria – Egypt 8 GEOtechniek – Special 17th ICSMGE – Alexandria – Egypt
Transcript
IntroductionIn June 2008 there was a leakage in a diaphragmwall of Vijzelgracht station. This leakage causeda sand-water mixture to pass through the wall,resulting in significant (up to 0.15 m) settlementof a block of 4 adjacent buildings. It was notedthat the piled foundations under 2 of these buil-dings had not only settled because of the sandthat disappeared, but also that the bearingcapacity was significantly reduced because theremaining soil around the pile tips now had amuch lower relative density than it had beforethe incident. The brickwork walls of the buildingswere braced with timber beams immediatelyafter the incident in order to avoid progressivecollapse of the buildings. The leakage wasattributed to a steel stop end not being removedat this location and failure of the repair measuresconsisting of High Density Injection. On September,10 2008 a further episode of severe leakageresulted in substantial settlement of buildingsVijzelgracht 4 to 10. More details about thisincident can be found in [Korff et al, 2009].
The houses adjacent to the wall were monumentalbuildings from around 1670. A foundation consis-ting of 52 timber piles per house extends to thefirst sand layer. Before construction of the NorthSouth Line these buildings were equipped withmonitoring instruments (figure 1).
Deformations and damageAs shown in figure 2, the block of houses Vijzel-gracht (VZG) 20-26 settled a maximum of 150mm due to the incident in June 2008. The buil-ding tilted towards the corner of VZG 26 andtowards the location of the leakage. A slightsagging was found between VZG 26 and VZG24 and hogging towards VZG 22. Significantcracks of up to 20 mm were reported.
The location and direction of the cracks indicatea shear deformation and horizontal extension inthe plane of the wall. The largest crack width wasfound at VZG 24, just as the differential settle-ments indicate. A twist movement of the blockwas also found. The actual damage derived fromthe observations for these buildings (26, 24)would be category 5, very severe (Burland et al1977). A significant tilt of the buildings wasobserved, with severely sloping floors andseparation of the rear façade from the house.The front façade experienced a maximum tiltof 1:78 perpendicular to the façade and 1:184parallel to the façade at the corner of Vijzelgracht26. Both relative rotation and deflection ratiohave been calculated for the front façade as0.62% and 0.47% respectively, leading with ahorizontal strain of 0.04% to damage category 5.The damage categories matched well with theactual damage. Damage to the buildings isespecially severe in terms of serviceability due
to the overall rotation of the building perpen-dicular to the facades. It appears that tilt, inextreme circumstances, can cause severe problemsof serviceability and stability to buildings. In thiscase this proved more problematic than the cur-vature and resulting cracking of the building. Tiltusually does not receive very much attention.
The corrective grouting projectAfter the incident, it was decided to use correctivegrouting to increase the bearing capacity of thesand and consequently lift the buildings up to anagreed maximum of 10 mm to prove it was possibleto restore the pile capacity and stability of thebuilding. The layout of the site is shown in figure3, with the diaphragm wall on the right. Thecorrective grouting area is coloured grey, thelines are the TAMs and the thick, grey lines showfoundations of the settled buildings. The liquid
Building damage andcorrective groutingresearch at North Southline project in Amsterdam
In Amsterdam, the North South subway lineprovides opportunities for researchers inseveral geotechnical fields. As partner in theCentre for Underground Construction (COB),The authors perform their PhD research whilethe project is continuing. An incident of leakagestrongly influenced the North South Lineproject in 2008. Building damage and correc-tive grouting were studied at a building witha piled foundation that was partly disturbeddue to ground loss. This paper shows resultsfor compensation grouting and increasedunderstanding of the influence of the foun-dation on building deformations. Lessonscan be incorporated in future projects, whichcloses the circle of innovation in these fields.
Summary
Figure 1 Weaverbuilding Vijzelgracht 26 with prism locations (Photo ProjectbureauNoordZuidlijn).
Adam Bezuijen Deltares/Delft University of Technology, Delft, The NetherlandsMandy Korff Deltares/Cambridge University
8 GEOtechniek – Special 17th ICSMGE – Alexandria – Egypt8 GEOtechniek – Special 17th ICSMGE – Alexandria – Egypt
leveling instruments (LL1 through LL14) attachedto basement walls that were used for the displace-ment monitoring and the position in the diaphragmwall where the leakage occurred (between panels89 and 90) are shown.
A cross-section is shown in figure 4. The TAM'swere placed at an angle of 16 degrees. HorizontalTAM layout was not possible because it wasnot allowed to excavate the box further beforestabilizing the buildings. Grouting was perfor-med using a Biltzdämmer a hydraulically-settingpremixed dry mortar (Heidelberg, 2009). Three different mixtures were used. The groutwas injected using different TAMs at the sametime in the injection periods.
Analysis of injection and building heaveFigure 5 shows the heave and settlement measuredjust before, during and after the correctivegrouting campaign. The vertical lines in the figure indicate the period in which grout wasinjected. The heave hx (with x a number) refers to instrument LLx.
Although the grout injections started at 10-08-2008, it first only increased the settlement rate,probably due to the TAM installation and firstinjections. Most settlement was recorded atsome distance from the leakage (LL3 and LL4).The first injections were needed to strengthenthe soil and to reduce the progress of ongoingsettlements. Grouting in September and thebeginning of October of 2008 led to heave of thebuildings. Settlements continued between thegrout injections. The corrective grouting has ledto significant increase of the CPT values of thelayers injected. Although the buildings are success-fully lifted and stabilized, it was found that the
efficiency of the corrective grouting (measuredon the foundation) was very low, 1.7% or less.Furthermore, ongoing settlements lead to afurther decrease of the efficiency. A possibleexplanation is that during the incident the weightof the building is partly taken by the frictionbetween the piles and the soft soil layers abovethe first sand layer. When the grouting stops,the soft soil layers will consolidate (these layerswere disturbed by the leakage and the grouting)and will develop a negative skin friction on thepiles. The pile foundation is still loaded on ultimatebearing capacity and therefore the developmentof negative friction will lead to extra settlement.This settlement will continue until the consolida-tion of the soft layers is finished and the frictionpiles become end bearing piles again. Apart from the loose sand due to the leakage andthe ongoing settlement there is an additionalreason for the low efficiency and that is the useof the Blitzdämmer as injection material. The per-meability of Blitzdämmer cake is 10 times higherthan the permeability of a bentonite cementcake. Research from Bezuijen & Van Tol (2008)and Sanders (2007) has shown that this willprevent the formation of fractures and will leadto compaction grouting with a lower efficiency.Furthermore, all liquid will be pressed out ofthe Blitzdämmer in the permeable soil beforethe hardening starts. The consolidation of theBlitzdämmer decreases the maximum possibleefficiency to 25% depending on the type ofmixture used. For sandy soil conditions it is probably better to use a grout with givesa grout cake with a lower permeability.
ConclusionsBuilding damage and corrective grouting werestudied at a building with a piled foundation that
was partly disturbed due to ground loss througha nearby diaphragm wall construction. The resultshave been used to validate research results forcompensation grouting conducted at Deltaresand to increase the understanding of buildingsinfluenced by ground displacements dependingon the type of foundation.
The authors would like to thank the Project-bureauNoord-Zuidlijn and Saturn X v.o.f. for the authori-zation to use and publish the monitoring data.
References– Bezuijen, A., Kaalberg,F.J. , Kleinlugtenbelt, R.and Roggeveld, R.P. (2009) Corrective groutingin sand to restore pile foundations Vijzelgracht,Amsterdam Int. Conference of Soil Mechanicsand Geotechnical Engineering, Alexandrie, Egypt.– Bezuijen, A. & Tol, A.F.van, 2008. Mechanismsthat determine between fracute grouting andcompaction grouting in sand Proc. 6st Int.Symposium on Geotch. Aspects of UndergroundConstruction in Soft Ground, Shanghai.– Burland, J.B., Broms, B.B. De Mello, V.F.B. (1977). Behaviour of Foundations andStructures Ninth International Conference on Soil Mechanics and Foundation Engineering, Tokyo, Japan.; 495-546.– Heidelberg, 2009. http://www.heidel-bergcement.com/de/en/geotechnik/produkte/Blitzdaemmer.htm (March 2009).– Korff M., Mair R.J., Tol A.F. van and KaalbergF.J., 2009. Building damage examples due toleakage at deep excavations in AmsterdamInt. Conference of Soil Mechanics andGeotechnical Engineering, Alexandria, Egypt.– Sanders M.P.M. 2007, Hydraulic fracturegrouting, Laboratory experiments in sand Msc thesis, Delft University of Technology. �
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GEOtechniek – Special 17th ICSMGE – Alexandria – Egypt 9GEOtechniek – Special 17th ICSMGE – Alexandria – Egypt 9
