Monday, April 11, 2016

Control of Ground Water

This can take one of two forms which are usually referred to as temporary and permanent exclusion.



Permanent Exclusion: this can be defined as the insertion of an impermeable barrier to stop the flow of water within the ground.

Temporary Exclusion: this can be defined as the lowering of the water table and within the economic depth range of 1500 can be achieved by subsoil drainage methods, for deeper treatment a pump or pumps are usually involved
.
Simple Sump Pumping: suitable for trench work and/or where small volumes of water are involved.

Problems of Water in the Subsoil

1. A high water table could cause flooding during wet periods.

2. Subsoil water can cause problems during excavation works by its natural tendency to flow into the voids created by the excavation activities.

3. It can cause an unacceptable humidity level around finished buildings and structures.

Underpinning Columns

Columns can be underpinned in the some manner as walls using traditional or jack pile methods after the columns have been relieved of their loadings. The beam loads can usually be transferred from the columns by means of dead shores and the actual load of the column can be transferred by means of a pair of beams acting against a collar attached to the base of the column shaft.

Underpinning Columns

Root Pile or Angle Piling

This is a much simpler alternative to traditional underpinning techniques, applying modern concrete drilling equipment to achieve cost benefits through time saving. The process is also considerably less disruptive, as large volumes of excavation are avoided. Where sound bearing strata can be located within a few metres of the surface, wall stability is achieved through lined reinforced concrete piles installed in pairs, at opposing angles. The existing floor, wall and foundation are predrilled with air flushed percussion auger, giving access for a steel lining to be driven through the low grade/clay subsoil until it impacts with firm strata. The lining is cut to terminate at the underside of the foundation and the void steel reinforced prior to concreting.

Root Pile or Angle Piling

In many situations it is impractical to apply angle piling to both sides of a wall. Subject to subsoil conditions being adequate, it may be acceptable to apply remedial treatment from one side only. The piles will need to be relatively close spaced.

Friday, December 11, 2015

'Pynford' Stool Method of Underpinning

This method can be used where the existing foundations are in a poor condition and it enables the wall to be underpinned in a continuous run without the need for needles or shoring. The reinforced concrete beam formed by this method may well be adequate to spread the load of the existing wall or it may be used in conjunction with other forms of underpinning such as traditional and jack pile.

'Pynford' Stool Method of Underpinning

Needle and Pile Underpinning

This method of underpinning can be used where the condition of the existing foundation is unsuitable
for traditional or jack pile underpinning techniques. The brickwork above the existing foundation must be in a sound condition since this method relies on the `arching effect' of the brick bonding to transmit the wall loads onto the needles and ultimately to the piles. The piles used with this method are usually small diameter bored piles.

Needle and Pile Underpinning

Monday, November 30, 2015

Jack Pile Underpinning

This method can be used when the depth of a suitable bearing capacity subsoil is too deep to make traditional underpinning uneconomic. Jack pile underpinning is quiet, vibration free and flexible since the pile depth can be adjusted to suit subsoil conditions encountered. The existing foundations must be in a good condition since they will have to span over the heads of the pile caps which are cast onto the jack pile heads after the hydraulic jacks have been removed.

Jack Pile Underpinning