Underpinning:

Underpinning is a type of remedial work employed to eliminate ongoing movement in a structure. Generally underpinning is required when either the foundations of a building are inadequate or the subsoil on which the foundations are bearing has weakened, or a combination of both. As such the underpinning work may include either strengthening of the subsoil, generally done by pressure grouting, or by improving the foundations themselves with piles and ground beams, or a combination of both pressure grouting and piling.

Underpinning Methods:

The slideshow below shows the sequence of events for one particular method of underpinning that is sometimes appropriate. The relevant structure is supported off newly installed helical piles and proprietary brackets. This method of piling is known screwpiling. For more information on screwpiling go to Screwpile Ireland Ltd.

 

Below Are Three Alternative Possible Solutions Which May Also Be Employed Depending On Loading And Ground Conditions.

 

1. Pressure Grouting:

 

Pressure Grouting is a commonly used method of soil stabilization where neat cement colloidal grout is injected under pressure through the foundations of a building into the subsoil, to a depth of approximately eight feet. The grout permeates from the grout hole through the adjacent soil to produce a bulb of grout in the subsoil under the foundation. This gives rise to an increase in the stability of the soil and is intended to stabilize the soil sufficiently to arrest any ongoing movement.

 

To establish whether or not pressure grouting is a suitable solution it will be necessary for our engineer to examine the type of soil present beneath the foundations, as some types of soils, mainly clays, are not suitable for grouting.

 

 

 

 

2. Pile & Beam Combination:

(Two Compression Piles plus one needle beam.)

 

This arrangement is used when either the sub-soil is not suitable for grouting, or the sub-soil is so weak that grouting will not increase its strength to a sufficient level.

 

Two compression piles are bored through the weak strata to a suitable load bearing stratum, possibly rock. Once these are bored, a needle beamed is formed beneath the foundation and spanning from one pile to the other. The load of the structure is passed from the foundation onto the needle beam, through the piles and into the suitable load bearing stratum.

 

This solution is used where there is reasonable access to both sides of the foundation, for piling.

 

 

 

 

3. Pile & Beam Combination:

(Tension & Compression Piles plus one cantilever needle beam.)

 

This solution is again used where either the sub-soil is not suitable for grouting, or the sub-soil is so weak that grouting will not increase its strength to a sufficient level, and there is not reasonable access to both sides of the foundation for piling.

 

A tension pile and a compression pile are bored through the weak strata to suitable strata, again possibly rock. Once these are bored, a cantilever needle beamed is formed spanning from the tension pile over the compression pile and running beneath the foundation. The load of the structure is passed from the foundation onto the cantilever needle beam, through the compression pile and into the suitable load bearing stratum. The tension pile restricts any up lift at it’s end of the needle beam.

 

If you are concerned that your house or other structure has been affected by failure at foundation level and believe that some underpinning may be required, feel free to contact our office for some expert advice from a fully qualified Engineer with over ten years experience in the area.

You can request for us to call you back by clicking here and filling out the form. Alternatively our contact details can be found by following this link: Contact Us. We will do our very best to answer all of your questions.

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