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Weber - Saint-Gobain

Civil Engineering

Reducing Settlement

Leca®’s ability to reduce settlement can offer massive benefits, reducing timescales from years to a few months for new or extended carriageways or for embankments and even, in some instances, eliminate settlement periods altogether.

Construction of embankments over weak and compressible soil deposits, where the loading of the embankment causes soil consolidation and settlement, is common.

A120 Stansted

The ability to reduce settlement of an embankment when incorporating Leca® LWA can offer huge benefits; reducing timescales from years from years to a few months abd even, in some instances, eliminate settlement periods altogether.  Construction of embankments over weak and compressible soil deposits, where the loading of the embankment causes soil consolidation and settlement, is common.

Depending on the height of the embankment, the depth of the weak soil deposit and the consolidation properties of the soil strata, total settlements can be very deep and problematic in terms of road evenness, function and durabilityof the road construction.

In the most difficult cases, various combinations of soil strengthening techniques are available, for example, preloading, vertical drainage and deep stabilisation with piles all of which are time consuming and costly to install.
By lightening the embankment with Leca® LWA, subsoil strengthening and lengthy settlement can be reduced or even avoided altogether.

Figures A and B give example of bunded an un-bunded Leca® LWA filled earth embankment constructed above weak and compressible subsoil with marginal settlement expected.

By lightening the embankment with Leca® LWA, subsoil strengthening and lengthy settlement can be reduced or even avoided altogether.

Figure A (click image to enlarge)
Figure B (click image to enlarge)

Case Study

A120 Stansted

West Coast mainland embankment widening, Shap

Using Leca® LWA on large scale cut and fill operations and construction on soft soils or bad ground can overcome stability problems, reducing the risk of landslide and deformation. Used in road embankments, Leca® LWA exerts much lower horizontal earth pressures compared with other backfill materials, helps improve stability and reduce the need for counterfill.
When widening existing carriageway or rail embankment, the weight of the newly constructed fills can often result in the new surface settling lower than the original surface and could pull the existing surface out of level.

Leca® LWA has an installed bulk density of approximately 20% of that of general fill materials and will considerably reduce settlement of the road or rail carriageway, both immediately and in the long term. Widening and replacing existing carriageways is also simplified by using Leca® LWA with no specialist techniques necessary.

Cut and fill operations (click image to enlarge)

General Fill Load Compensation

Efficient drainage of the structural layers of the road build up can prevent loss of load bearing properties caused by water and ensure a good load bearing capacity throughout the road life.

Using free draining Leca® LWA as a structural material within the road build up will intercept the percolating water and water rising by capillary action from the sub-formations and direct the rising water away from the upper construction layers to improve the load bearing capacity.

In areas prone to mining subsidence or where ground conditions contain natural sub-formation voids, drainage, culvert or tunnels and there is a danger of collapse, expensive techniques such as load transfer are often considered.  However, using Leca® LWA can eliminate these costs and consierably lighten the load to provide similar benefits to those when used in weak soil areas.

Figures C and D give examples of minimized and equalized load embankments constucted with Leca® LWA using the load compensation method

Figure C click figure (click to enlarge)
Figure D click figure (click to enlarge)

Weak Undergound Voids

When constructing over weak underground voids or soils with low bearing capacity, the load compensation method may be considered using Leca® LWA.

By extracting a volume of existing soil from beneath the new construction, the equivalent volume of Leca® LWA replacing that soil will reduce the load on the sub-formation by four times.  By using Leca® LWA extraction can be kept to a minimum in rder to achieve nil settlement as demonstrated by the example below.

Cut and fill operations (click to enlarge)

General Fill Slope Stability

Leca® LWA is a lightweight material with open voids even when compacted.

This characteristic provides high drainage capacity and together with a very low density will greatly assist in reducing the risk of bearing capacity failure and increase the stability of the side slopes.

Leca® LWA is extremely lightweight making it very cost effective to transport.

Slope Stability (click to enlarge)

Efficient Drainage

Efficient drainage of the structural layers of the road build up can prevent loss of load bearing properties caused by water and ensure a good load bearing capacity throughout the road life.

Using free draining Leca® LWA as a structural material within the road build up will intercept the percolating water and water rising by capillary action from the sub-formations and direct the rising water away from the upper construction layers to improve the load bearing capacity.

Providing Efficient Drainage

Carriageways in cuts that extend below the natural level of the groundwater, frost damage and loss of load bearing capacity can also be reduced by forming drain trenches filled with Leca® LWA at both sides of the road, along which the water is led away. Used within the carriageway drainage, Leca® LWA will help filter and increase microbiological breakdown of pollutant run off from fields and highways.
Maintaining levels within any foul or surface water drainage system can be difficult when the drain runs across a soft soil site. Leca® LWA can be used as a light weight pipe surround to reduce the pressure to the underlying soils and minimize the likelihood of irregular settlement.

 

 

(click to enlarge)

Structural Earth Pressure (structural fill)

When used against retaining walls, Leca® LWA will reduce the weight acting on the rear of the structure by at least 75%, in comparison to traditional fill materials.

In figure 1 the ‘comparing pressure distribution diagram’ indicates that backfilling with Leca® LWA (A) rather than conventional sand or gravel (B) reduces the earth pressure on a 5m high wall by 75%.

This reduction in weight can avoid potential sliding, overturning, slip and tilting or bearing failures and enables savings by increasing spacing between buttressing walls and reducting structural dimensions.  The bulk weight of the wall can also be reduced and more cost efficient, attractive materials can be used in place of costly, unattractive structural concrete.

Using Leca® LWA will minimise the differential settlement between piled bridge abutments and the embankment fill.  As it is a free draining materia, Leca® LWA has the added advantage of eliminating the need to rear wall block drainage.

The 'pull out' resistance of Leca® LWA makes it an ideal solution for reinforced soil retaining walls.  Particularly when constructed over weak sub-soils or voids, this method has been proven to cut overall construction costs considerably.

Leca® LWA is used extensively to reduce vertical loading.  Structures such as underground parking, tunnels or roof garden benefit greatly from the reduction in pressure and avoid additional costs of strengthening.

Being light weight and round in nature, Leca® LWA can be transported and placed more easily than that of traditional fill in these difficult to access areas.

(click to enlarge)

Structural Earth Pressure (adjacent water)

When constructing quays, the soft ground conditions often call for the use of lighter fills to guard against slides or deformation that can damage structures and a number of solid berth structures have been built in recent years using Leca® LWA.

It can be used to an advantage in many quay designs such as sheet pile, sheet pile cell and caisson structures and is also used as fill replacement in solid berth structures when quayside waters are dredged to greater depths.

0-4mm Leca® LWA not only has a very low unit weight, it also has minimal buoyancy, making it particularly suitable for filling directly into water.

Quay Construction

By depositing the aggregate directly into place from a boat equipped with its own offloading gear, exceptionally fast progress can be made with 250-300 cubic metres per hour quite achievable.

1. The light weight of Leca® LWA can ensure the stability of a quay even when ground conditions under the sea floor are poor.

2. Leca® LWA has been used to water depths of 12 metres during quay construction.

Cross Section

(click to enlarge)

Environmentally Friendly

With deep compaction layers and speed of installation when using Leca® LWA de-watering is kept to a minimum and the void filled in a faction of the time compared to using traditional fills.  By depositing the aggregate directly into place from a boat equipped with its own offloading gear, exceptionally fast progress can be made with 250-300 cubic metres per hour quite achievable.

The additional advantage on this location is one of an environmental nature. Leca® LWA is a completely natual product, is an inert and stable material with no risk of leachate seepage in to the surrounding waterway.

Protecting Services

Surrounding utilities and drainage carried within bridge beams with Leca® LWA is a lightweight, simple to install alternative to that of sand traditionally used to support and insulate these services. The added benefit of using the lightweight round granules of Leca® LWA as a pipe surround is that there is little danger of any damage to pipelines during backfilling and the likelihood of damage from settlement or over-loading is reduced.

Leca® LWA can be used as a lightweight pipe surround, reducing the pressure to the underlying soils and minimising the likelihood of irregular settlement.

Surrounding utilities and drainage carried within bridge beams either side of the carriageway with Leca® LWA is a lightweight, simple to install alternative to that of sand traditionally used to support and insulate these services.

The added benefit of using the lightweight round granules of Leca® LWA as a pipe surround is that there is little danger of any damage to pipelines during backfilling and the likelihood of damage from settlement is also reduced.

Westwood Link Road Wigan