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Fundamentals: Lateral earth pressure on foundations

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  1.  
    • CommentAuthorgyrogear
    • CommentTimeNov 16th 2016 edited
     
    Local authority (France) wants to build a public swimming pool in front of our inner-city residence.
    We have formed an association to appeal the project or at least get some say in the design.
    Public consultation phase now well under way...
    We are in particular interested in getting the building sunk into the ground, in order to limit impacts...

    No geotechnical explorations performed (yet) -- early days -- but the area is known to contain gypsum dissolution pockets...

    We are wondering to what extent we could use this potential soil status to leverage our argument for deeper foundations (thus a lower roof line).

    In particular, how far can we go in "claiming" the advantages of a deep foundation (? diaphragm wall etc.) and earth thrust etc. (or other effects) to offset the (potentially) poor soil conditions?

    As you will have gathered, we are none of us civil engineers, so a few links to sites would be of great help, since one day soon we might have to be defending our cause...

    Many thanks,

    gg
  2.  
    Deeper foundations do not mean a lower roof line, it just means deeper foundations.

    Lateral pressure from foundations is taken to be 45deg down and to the side of the base of the foundations. (as a standard)

    Unless it is a big project deep level soil surveys are unlikely. Usually industry standard foundations will be specified with the caveat that adjustments may be needed if unexpected soil conditions are encountered. A bit like when you do a build the BCO will want to see the foundation trench once dug and may require a variation (deeper or wider) depending upon his opinion about what he sees.

    Generally speaking 'public good' trumps private interest. Rather than attacking a technical aspect, for which there will be a solution (at a cost) you may be better to challenge the need, the unacceptable change to a residential area, noise, the ability of the local infrastructure to cope (local roads etc.) and any other reason that you can show that the location is inappropriate.
    •  
      CommentAuthordjh
    • CommentTimeNov 16th 2016
     
    Posted By: gyrogearAs you will have gathered, we are none of us civil engineers, so a few links to sites would be of great help, since one day soon we might have to be defending our cause...

    I'd suggest your cause would benefit greatly by getting a proper [certified] engineer's opinion. It should be very difficult for planners and politicians to ignore that.
    • CommentAuthorgyrogear
    • CommentTimeNov 16th 2016 edited
     
    Many thanks to PIH and DJH - much appreciated indeed.

    It is a rather large project, in effect : 2 pools (beginners and 25-meter) and very high (17 meters...).
    With a solarium on the roof.
    They can build right up to our property line, so our 4th-floor flat will have a terrace roof right in front of us, in our West at 7 meters distance, with umbrellas and people drinking beer and staring into our lounge and bedroom... (goodbye romantic sunsets...)

    And we are not worst off by a long chalk (our ground-floor neighbours will likely be totally deprived of light !

    Not to mention the primary and infant schools to the NORTH - the 17-meter structure will in effect blank out all sunlight to the yards...

    The assessor's report (receive y'day...) tamely asks "for more enlightenment" on this shading aspect.

    So fearing we will get bonked, we are trying to get forewarned and fore-armed - many thanks for the recommendation to get a certified engineer's opinion, will do, even if we have to crowd-fund for it !

    Cheers again,

    gg
  5.  
    An engineer will be engaged automatically to make an assessment of soil conditions based on soil tests made on the building site long before construction begins, this is obligatory. Even if extraordinary soil conditions are found a solution will be put forward by the engineer. Hiring your own engineer would be a waste of money.

    Normally an environmental impact assessment will be carried out , the conclusions of which will be presented to the public . Part of this assessment should include any issues with over shading. My advice would be to focus your attention on this report. Write letters and make appointments to talk to local councillors to make sure your concerns have been heard. Try to find out which local councillors are opposed to the current placement of the project or would be sympathetic to your concerns and develop an on going relationship with them so that your concerns have representation when meetings take place.

    Find examples of similar projects in the region that have had negative impacts on shading, use them as examples in your arguments.

    Find local associations that are interested in environmental causes and see if you can engage their help in your cause.

    There might be a group of "green" architects in your area that you can talk to and see if they will look at the proposed project and make an assessment that can be presented to local councillors.
  6.  
    Posted By: gyrogearLocal authority (France) wants to build a public swimming pool in front of our inner-city residence. No geotechnical explorations performed (yet) -- early days -- but the area is known to contain gypsum dissolution pockets... We are wondering to what extent we could use this potential soil status to leverage our argument for deeper foundations (thus a lower roof line). In particular, how far can we go in "claiming" the advantages of a deep foundation (? diaphragm wall etc.) and earth thrust etc. (or other effects) to offset the (potentially) poor soil conditions? gg
    Hi Gg, if your area is known to contain gypsum dissolution pockets then its similar to building on limestone rock in Galway and Clare. The west has had some cases where a section of ground beneath a house fell down into a sink hole because the limestone got dissolved. Most foundations in that neck of the woods are raft foundations so any sink holes that may develop beneath a house are bridged over by the raft foundation. The depth you go down with the raft has little bearing on the proposed risk. Most rafts in Galway/Clare are built at ground level because there's not much topsoil to dig away, you'd need a rock-breaker to go deeper.
    • CommentAuthorgyrogear
    • CommentTimeNov 16th 2016 edited
     
    <blockquote><cite>Posted By: bot de paille</cite>
    Hiring your own engineer would be a waste of money.

    talk to local councillors to make sure your concerns have been heard.
    Find examples of similar projects in the region
    Find local associations that are interested in environmental causes
    There might be a group of "green" architects in your area</blockquote>

    All good stuff, thanks for that ! will pass on to our action committee.


    <blockquote><cite>Posted By: Viking House</cite>The west has had 1/2 cases where a section of ground beneath a house fell down into a sink hole because the limestone got dissolved.</blockquote>

    Excellent news ! thanks VH.

    UPD - More seriously it indicates that the developers will not be willing to drop the level of the slab any more than the strict minimum required for their technical purposes, since this not only will not reduce the risk, but will also turn out expensive...
    (it is therefore up to our pressure group to persuade the developer that it *IS* in his interests to drop the roof line for other motives, namely, Preventing Civil Unrest...) :devil:

    That the once-finished swimming pool might fall down a sink hole, sounds too good to be true !

    gg

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