ishvaaag
Structural
- Aug 17, 2001
- 3,665
Under the corner of a 1.1 m thick 1976 mat foundation washing from an irrigation ditch has caused a 10x10 m in plan, 8 m deep hole. The street level plus 4 livable levels building above is for now standing there in cantilever with some minor cracks above, quite likely with people within, sustained by the rigidity of the mat plus their connected belt walls (or foundatin box with the street level floor, there is 1 underground level), all reinforced concrete about fck=175 kgf/cm2, the walls 0.30 m or so thick.
The understood cause, washing by water has been removed, the irrigation ditch having been deviated it seems reasonably far away from the building now (the building hopefully out of the underground line of flow, yet who knows). The general setup of the soils in the area is a quaternary lake bed with silts for around 7 m, then gravels or whatever to 18 m, and then that I remember a hard "competent" layer (the nature of which I don't remember exactly, but might be either gypsum marls or gypsum rock), all this by the description of my ex partner, that did the project in the seventies'. So it seems it is the silts that have washed one way or another.
There was a precedent in the town (around 30000 people) quite similar in dimensions, unknown cause to me, but was then adjudicated in the news to losses in the public sewage system, and on worse foundation, isolated footings; the building anyway also survived the brunt of the thing in inversion of moments. Not being at all related to that job, I don't know what repair was made of what decision was then made about the building.
My expartner is considering his (and mine's with him in what would be called here one "marrón", a "brown", you can imagine why) intervention on the repair of the said corner under the mat with the idea of using piles to the competent layer 18 m below, outside the walls that then would catch the loads from the mat and walls. The council -quite surprisingly to me- is surmised to be acquiescent to such kind of solution in the public domain. If neccesary, some bridging of the loads at street level -within the cellar- could be investigated.
Since he wanted to bridge the void with the piles I immediately suggested the need of sheated piles (or well, just steel) but I am not at all happy with letting the void there, with some risk of the slopes still failing to cause further loss of support inwards the mat. So I will likely remain insistent on refilling the void, an 800 m3 job that, logically, will be a significant amount of the cost.
There may be already some geotechnical report but one on just this purpose will be made. For the moment I have not seen the site nor any photo of it.
Irrespective of our engagement to the job, and just for the purpose of my illustration, I am interested in your view on this repair job and how in general terms you would proceed, not only along the external piles of my expartner view, but also alternative solutions from inside the building as well, that by the way, have been already proposed by others, it seems on floating micropiles not reaching the competent level (they will have their geotech info, one must think). No idea if they refill or not. Just what you would do or how you would tackle one job like this.
The understood cause, washing by water has been removed, the irrigation ditch having been deviated it seems reasonably far away from the building now (the building hopefully out of the underground line of flow, yet who knows). The general setup of the soils in the area is a quaternary lake bed with silts for around 7 m, then gravels or whatever to 18 m, and then that I remember a hard "competent" layer (the nature of which I don't remember exactly, but might be either gypsum marls or gypsum rock), all this by the description of my ex partner, that did the project in the seventies'. So it seems it is the silts that have washed one way or another.
There was a precedent in the town (around 30000 people) quite similar in dimensions, unknown cause to me, but was then adjudicated in the news to losses in the public sewage system, and on worse foundation, isolated footings; the building anyway also survived the brunt of the thing in inversion of moments. Not being at all related to that job, I don't know what repair was made of what decision was then made about the building.
My expartner is considering his (and mine's with him in what would be called here one "marrón", a "brown", you can imagine why) intervention on the repair of the said corner under the mat with the idea of using piles to the competent layer 18 m below, outside the walls that then would catch the loads from the mat and walls. The council -quite surprisingly to me- is surmised to be acquiescent to such kind of solution in the public domain. If neccesary, some bridging of the loads at street level -within the cellar- could be investigated.
Since he wanted to bridge the void with the piles I immediately suggested the need of sheated piles (or well, just steel) but I am not at all happy with letting the void there, with some risk of the slopes still failing to cause further loss of support inwards the mat. So I will likely remain insistent on refilling the void, an 800 m3 job that, logically, will be a significant amount of the cost.
There may be already some geotechnical report but one on just this purpose will be made. For the moment I have not seen the site nor any photo of it.
Irrespective of our engagement to the job, and just for the purpose of my illustration, I am interested in your view on this repair job and how in general terms you would proceed, not only along the external piles of my expartner view, but also alternative solutions from inside the building as well, that by the way, have been already proposed by others, it seems on floating micropiles not reaching the competent level (they will have their geotech info, one must think). No idea if they refill or not. Just what you would do or how you would tackle one job like this.
