Existing structure excessive distortion - Consolidation Issue Back Analysis

[LFR]

Hi All,

I have question/curiosity with regards to consolidation of an exisiting strucure founded at this point presumably on clay soils. The structure shows some excessive distortion in somce areas and the underlying clay soil are likely to blame. The structure has prob 20 yrs and not sure if they did a site specific geotech investigation for it.

My question/curiosity is, if there is any way to do a back analysis to understand if consolidation (primary and secondary) is complete? I pressume some boreholes and some testing (consolidation, etc) of a nearby location maybe necessary to determine soil properties and consolidation parameters.........and to somewhat understand what the stratigraphy was prior to building the structure (do bh's around the structure and within and interpoolate to understand approx. thicknesses and changes in these within the footprint?).

This said, assuming no historic data available I wont know what the initial thickness of the compressible stratum was before the strucutre (if my interpolation excersise is not practical) and therefore in my mind making it hard to establish if consolidation is fully complete or not.

Maybe I am overthinking it but curious to see what the geotech world has to say.

Thanks in advance
Cheers
Luis

 

[GeoPaveTraffic]

It could be done. Will require a fair number of borings and considerable laboratory testing. Will also require a good geologist and geotechnical engineer with local experience. Could easily top $30k in exploration and analysis costs in the mid-west US. So the first question is "What are trying to gain by doing this?"

Mike Lambert

 

[LFR]

Thanks for your input Mike....figured lots of investigation and testing would be required and local knowledge for sure.

It is for a soccer stadium that is having excessive cracking in areas due to settlement issues apparently (havent seen the strucutre myself, yet). So figure understanding where we are in the consolidation process would benefit into addressing a repair procedure/program, since this maybe complete by now (dont know). Investigation will likely be necessary even to develop remedial supports, helicals, piles, etc.

Maybe no need to spend time understanding the stage of consolodation and just go with investigation tailored for "pinning/support" of the structure......or do you have any other suggestions for repairs: grouting, foams, chemical, etc.

Do you have any case studies where a back analysis was conducted?

Thanks a lot
Luis

 

[geotechguy1]

Depending on how urgent the repairs are you could also consider establishing survey monitoring points on the building to see if movement is occurring.

Also, it may be worth investigating if INSAR ground deformation data exists for your location. (

https://www.sixense-group.com/en/of...g-atlas-insar/atlas-insar-historical-studies)

I haven't directly used it myself but apparently their is data available from INSAR with ~5mm accuracy. I don't know how far back the data sets run but the sattelites that collect them have been up since the early 90s I believe. If you can get access to this information for your site this would give you a pretty clear idea of historical settlement.

 

[LFR]

Hi geotechguy1,

It did cross my mind to do some monitoring of the structure with some survey targets.....at this point we just started the subject so hoping to visit the site this coming week to see what is up and understand urgency. it is an active stadium and the main one for the local team so time may be limiting to collect enought relevant data. Not discarded yet.

It is in south america so not sure that INSAR high tech covers these areas lol. Checked it out, looks pretty interesting and amazing we can do that now. I do work in Canada so will def. have it in mind for sites there.

Cheers!
L

 

[geotechguy1]

Worth looking into - alot of mid size and larger geotech companies are getting into using tools like this, at least in NZ / Australia / UK. Didn't seem to be common in Canada when I left a few years ago, although I think Golder has used it quite a bit. Ideally you'd have access to someone on staff who is an expert in ARCGIS and tools like this.

 

[EireChch]

To me this is called a route cause assessment (RCA). 30k US, is a small price for any stadium to pay, not matter what size. This is definitely required as you need to know what the problem is before you start to specify remedial solutions.

 

[GeoPaveTraffic]

Ok, next step (for me at least) would be to get more info on when the problems started to occur, if the problems are continuing, how wide spread the problems are in the structure, and with the project structural engineer, develop a preliminary opinion on who the structure has moved. During the part of the process I would determine where to place monitoring points and get an ongoing monitoring program in place. The key to the monitoring program will be accuracy. The data quality and resolution will both need to be very high to determine if/how the structure is still moving. Lastly I would try and locate existing subsurface and foundation data for the structure.

Based on all of the above, I would start developing an exploration plan to fill the gaps in the historical data. Hard to say at this point how many borings, depths, sample types, etc. will be needed; but expect an extensive program. The $30k number i though out eariler was for a relatively samll structure, for something like a stadium, would probably exeed $75k to get a good start on the work.

As for your initial question, yes it should be possible to "look back in time" to determine how much consolidation has happened and estimate where the soils are relative to primary and secondary consolidation. However, this require that the site be fairly uniform and that the "problem" soils extend beyond the structure.

As for INSAR, I've not heard of this data set; but it sounds interesting. I wonder what the horizontal resolution of the data is like. Would the data be granular enough to see individual areas/columns of the structure?

Mike Lambert

 

[TigerGuy]

Along with your survey targets, install some crack monitors. This way, you will be able to determine the relative movement of both sides of visible cracks. Variations in the soils can lead to differential movement in the structure.

Regards

 

[LFR]

Hi,

GeoPaveTraffic, thanks again for your input. Agreed, I am starting to look into some of the points you indeicated as I type. I am visiting the site tomorrow to fully understand the task at hand. I believe the strucutral engineering team that designed the structure will be present. I am hoping the strucutral team will have some historical info for the project but agreed that the possible scope will be creeping the 100k. But it is the main team in the biggest city here in Ecuador so the should have some funds lol.

As for the survey targets, will see the areas with issues and maybe we the strucutral team see some possible locations of interest for monitoring. Agreed that the quality of the info is key.

With regards to the back analysis, figured it may be dependant on some of the surrounding site conditions and the consistence of this across the site. Have been looking for papers or cases online but with no luck to date since I am curious now for personal reasons even if this possible project goes dead in the water.

The INSAR info def. look very interesting and it is the way of the future really.....no sure as of its qlty. since I have not dug deep into it yet but LIDAR and new drone imaging technoligies, etc are gaining ground in our discipline.

TigerGuy, thanks for the added value. I have seen those in use before and certainly for the complexity of the setup very usefull info. Thnx

Thakns for all the inoput guys!!!

Cheers
Luis