Underpinning

AGM’s proven Underpinning Technology in many projects

The current underpinning technology to construct 100- 150mm bored micropile requires tenants to be evacuated as it involves massive breaking of walls and digging up of foundations. A process that is both messy and cumbersome. On top of that, the underpinned pile must be structurally attached to the existing foundations which inadvertently involve enormous architectural and M&E repairs.

However, with the advent of AGM’s proven track record using the patented “Pin-Hole Reverse Underpinning Technology” for the past 11 years, over 1300 units of cracked houses located in ex-mining lands, deep fills, soft alluvial coastal areas and peaty estates has been restored without recurring settlement.

AGM underpinning hydraulic machines can drive piles at a minimum of 50mm from the wall/column’s face. This enables high load transfer through the pile head by taking advantage of enhanced concrete shear stresses in the foundation pile cap or ground beam. We have a range of pile injection machines small enough to pass through a 2ft wide door and yet able to drive a length of 2.4m-3.0m pile which is just slightly shorter than the clear floor to ceiling height!

 

What should you expect

Economical rectification of building settlement Corrective uplift of tilted building
Noise and vibration free No messy Work
Immediate pre-loading of underpinning pile Pre-loading can be securely welded-off at pile head
All underpinning pile is 100% pre-tested New innovative underpinning for pile foundations
Rapid completion between a week to 2 months Environmental friendly

Before and After.
Completed underpinning with 60% jacked to original tilt.

 

Settlement monitoring during the lift up of the buildings at certain critical points

 

Why use patented “Pin-Hole Reverse Underpinning Technology”

  • Accessible in confined spaces without demolishing walls
  • Pin hole coring or minor floor hacking is involved
  • Noise and vibration free
  • Can be carried out safely even without tenants evacuation
  • Piles can be driven from 50mm away the wall’s face
  • Underpinned pile can be pre-tested and preloaded
  • Sinking and tilted buildings can be lifted up
  • High capacity piles can be injected from 20t-350t
  • Economical concrete, timber or pipe piles can be used
  • Fast and early project completion targets
  • Cost saving in architectural repairs after underpinning

 

Overview Of Technologies

Our latest method of underpinning that is fast and cost-effective: Pin-Hole Reverse Underpinning Technology, not normally require any further structural strengthening as the underpinning pile is connected to the existing pile cap.

 

Figure 1 Compact and mobile 50-100t underpinning machines

a. Figure 1 shows the pile injection driven in limited headroom and confined space. It is vibration free and the pile is injected up to a maximum of 80 tons per pile.

 

Figure 2 Underpinning point 125 x 125 load test at 40 tons at 7 days

b. Load test for a working load of 40tons (see Figure 2) .We have capability to to inject up to 400t per pile .

 

Figure 3 Pouring non-shrink grade 60 cement grout into the pile heade. Figure 5 shows a sample of the completed pin hole underpinning process.

c. The underpinning pile can be preloaded and welded off to the specially adapted pile head. The final step involves cement grouting to the pilecap to firmly to form a rigid fixity with the pile cap as shown in Figure 3.

 

Figure 4 Left shows the completed injected pile and the right after preloading and grouting

d. More importantly, the pile head is specially designed to engaged with the pile cap at a very close distance (about 100mm from edge of pile to wall) to the column, reducing the risk of shear failure as shown in Figure 4.

 

Figure 5 Completed underpinning process where this section has settled

f. Sometimes it will be necessary to correct the tilt or settlement of the building by lifting portion of the building which will require synchronised jacking of the underpinning piles.

 

Why is there a need for foundation underpinning

A building structure must be founded on some kind of foundation that can transfer the building loads onto competent soil layers below it. Low rise housing raft foundation is founded directly on the compacted top layer, but piles may be required to transfer the column loads deeper into the ground. When the building structure experiences distress, more often than not it will be caused by foundation failures rather than inadequate structural design.

Building foundation failures leads to settlement of building and hence cracks formation on the walls and structural frame. As distinguished from the shrinkage cracks due to moisture, these cracks usually increases in width and seriousness over a long period of time leading to the large diagonal cracks formations. These settlement cracks in the building normally occur;

  • progressively over a period of time as a result soil consolidation in soft clayey soils,
  • or suddenly after a heavy downpour especially associated with poorly compacted back-filled,
  • during the occurrence of an extended drought for raft foundations supported on expansive soils,
  • during a slope failure or deep excavations adjacent to the building, and
  • lowering of ground water table.

To repair the building cracks, underpinning by compensating piles may be required partially or completely to support and stabilise the foundations. Underpinning is a generic term to describe the process of strengthening an existing foundation by adding support to transfer the building loads to more competent soil layers. This can be done by various means, such as piering (installing steel piers), concrete caissons or piles. Each have their own advantages and disadvantages. There is a dilemma in selective underpinning at certain portions of the buildings because the non-underpinned areas may settle further relative to the underpinned areas causing differential settlements. Detailed soil investigations and site monitoring to determine the cause of the foundation failure is often needed in order to select the appropriate underpinning method in lieu of the local experiences.

 

Current methods in underpinning

Due the myriads of foundation failures and movements, it will be necessary to carry out underpinning at the vulnerable positions where the foundation is particularly weak. If the footing is observed to have settled around at the peripheral of the building, underpinning from the outside of the building may be helpful. However if there are internal columns that are settling, then underpinning must be carried inside the building.

There are many proprietary methods for underpinning inside and outside the buildings;

  1. Underpinning carried out outside the peripheral building may be non-invasive and least disturbing to residents such as
    • Peripheral pile injection/ piering using helical screws etc., which is usually done with the aid of reaction brackets attached to the exterior side ground beams.
    • Peripheral pile injections using the reaction of the underside of the ground beam unfortunately allows only small short pile sections usually about 0.6m in length to be driven one at a time.
    • Cantilever pile and beam method of installation where the piles are installed outside the building walls.
  2. Underpinning inside the building is invasive and hazardous and normally requiring the evacuation of residents;
    • Piled raft system is used if the damage is extensive and it usually requires existing floors removed in order to construct the mini-piles.
    • Micro-pile system involving drilling and grouting mini piles through the foundation footing to enable structural connection to the building.
    • Grout injection system under pressure of a liquid below the slab or foundation to improve the bearing capacity of the soil underneath it, however this can only be applied for soils of high permeability and cost effective for shallow depths of soil improvements only.

With the exception for low capacity underpinning piles installations, existing methods require heavy machineries to push/inject the mini piles with extensive structural works to transfer the building column loads on to the newly installed piles. To construct new foundation mini piles inside the confines of the building, the contingency cost of reinstating the interior architectural finishes and fittings of the house due to the invasive underpinning works may be expensive. Further, in some case where the building is distorted, it would be useful to preload the pile and structurally lift up the building.

 

Why use “Pin-Hole Pile Injection Underpinning Technology”

In view of the current difficulties faced in underpinning, Advanced Geomechanics Sdn Bhd (AGM) has innovated and patented the “Pin-Hole Pile Injection Underpinning Technology”. From our continuous research and improvement over the last decade, the cost of foundation repairs has been tremendously reduced by the use of portable and compact hydraulic injection machines to engage with a specially adapted pile head and inject a high capacity pile through a 100mm to 250mm sized hole cored through the footing/foundation slab/raft. This patented pilehead is devoid of small delicate components and therefore robust and easy to fabricate with basic welding tools. This high load transfer through the pile head is reliably achieved solely by bearing mechanism.

The unique features of Pin-Hole Pile Injection Underpinning Technology enables it to:

  • inject pile at very high load provided the foundation slab thickness is adequate,
  • portable and manuverable hydraulic machine in confined works spaces,
  • drive long pile lengths up to the clear floor to the ceiling height,
  • use only a small tiny cored hole of diameter of 100mm to 250mm for pile installation,
  • drive a pile vertically within 150mm to the wall’s face to take advantage of the enhanced concrete shearing capacity in proximity to the column’s face,
  • use any pile shape or material such as concrete, timber, used rail etc.,
  • easily preload the pile by welding the pile head,
  • transfer load of the pile through the patented pile head by bearing against the footing,
  • adjust pile preload through the hydraulic jack especially with selective underpinning,
  • structurally lift the building through a synchronised hydraulic jacks system,
  • enable idot and fail proof pile head connector, and
  • easily customise and fabricate the pilehead to site requirements.

Another main advantage of this system is that the pile capacity can be easily and reliably tested, therefore AGM’s underpinning technology can provide a 100% guarantee in our specified minimum working load of the injected pile. Most design codes, recommends that a pile should be injected to 250% of the pile working load. By using a pair of settlement gauges, a calibrated hydraulic jack and a thrust frame, the safe pile working load capacity of the driven pile can be proved by preloading at the pilehead to twice the pile working load over an extended period of time such that the pile’s settlement ceases completely with no appreciable pile settlements occurs or is less than 0.05mm/day. Normally, the short term pile capacity test is conducted in two peak cycles over a 36 hour period, but in lieu of this critical underpinning works, we recommend that the pile load tests be conducted at twice the working load for 4-7days such that no appreciable pile settlements occurs or is less than 0.05mm/day to prove the long term stability of the pile. Should the pile settles further, the recommended pile working load should be correspondingly reduced to satisfy this criteria and retested.

Conventional method of underpinning controls the existing settling foundation by gradually transferring the building load in due time to the new installed underpinning piles. One of the main drawbacks of this method is that in the process of transferring the building load to the newly installed underpinning piles, it will cause further potential settlement cracks in the building until all the building load distribution has been stabilized. Whereas AGM’s underpinning technology will prevent future cracks from developing in the building from the onset of pre-loading underpinning piles. Synchronised jacking of the underpinning piles to lift the portions of the buildings to correct the tilt can also be easily carried out as well.

AGM’s underpinning technology has advantage over other systems because the 75tons pile driving machine weights only 750kg and is mounted on a transportable hand push carriage which is small enough to pass through a door measuring 600mm wide x 1600mm high!.

AGM’s hydraulic pile installation is vibration free with low noise emission and safe. Using the “Pin-Hole Pile Injection Underpinning Technology” to inject a pile through a 100-250 mm hole in the footing/foundation slab/raft is neat as there is no messy excavations and invasive destruction of the interior of the building. Therefore, it is also possible to carry out underpinning inside the building in isolated areas that can be cordoned off so that residents does not necessarily have to vacate the building. If the foundation slab is too thin, alternative support load transfer system to engage with the building using I-beams is used.

More importantly, considerable cost savings in material and construction time is possible without guaranteed quality by using AGM’s underpinning technology.