In highway and railway structures Leca® Lightweight Expanded Clay Aggregate is commonly used as a light fill material to reduce subgrade settlement and to improve stability of structures and areas of weak and unstable ground. It serves the similar targets when used in pedestrian and bicycle ways, railway yards and different platform and embankment structures.
WITH RESPECT TO THE PROJECT SPECIAL FEATURES, THE Leca® Lightweight Expanded Clay Aggregate LAYER CAN BE DESIGNED TO FULFILL SEVERAL OBJECTIVES AT ONE TIME: TO PROVIDE FROST INSULATION, TO BLOCK CAPILLARY WATER RISE AND TO FUNCTION AS A DRAINAGE LAYER.
In the reconstruction of highways and railways Leca® Lightweight Expanded Clay Aggregate can be applied to repair settlement defects, to increase levelling and to improve bearing capacity. In addition, with the help of Leca® Lightweight Expanded Clay Aggregate road and rail embankments that require widening can be constructed with minimal effect due to increased loading to the existing structure.
With respect to the project special features, the Leca® Lightweight Expanded Clay Aggregate layer can be designed to fulfill several objectives at one time: to provide frost insulation, to block capillary water rise and to function as a drainage layer.
THE ABILITY TO REDUCE SETTLEMENT OF AN EMBANKMENT WHEN INCORPORATING Leca® Lightweight Expanded Clay Aggregate CAN OFFER HUGE BENEFITS; REDUCING TIMESCALES FROM YEARS TO A FEW MONTHS 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. 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 durability of 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® Lightweight Expanded Clay Aggregate, subsoil strengthening and lengthy settlement can be reduced or even avoided altogether. Using Leca® Lightweight Expanded Clay Aggregate 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® Lightweight Expanded Clay Aggregate 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® Lightweight Expanded Clay Aggregate with no specialist techniques necessary.
Loads produced by fill structures may reduce stability of subgrade soil. Insufficient stability may result in the subgrade breaking and collapse of the structure. Greater-than-allowed displacement of the structure or its surroundings is also possible.
Leca® Lightweight Expanded Clay Aggregate provides an excellent solution to stability issues.
As a rule, stability issues are typical for subgrade soil with low strength index. This is of particular importance in areas with crossfall relief or, for example, in a vicinity of a river bed.
Leca® Lightweight Expanded Clay Aggregate improves the stability of the soft soil subgrade by reducing the load impact.
When Leca® Lightweight Expanded Clay Aggregate is applied to improve stability; the following design aspects shall be taken into account:
- Properties of underlying subgrade and its loading history
- Pore water pressure
- Groundwater and/or perched water level and possible open water level
- Inclination of ground surface or soil layers and possible river bed located beside the structure
- Required safety factor of structure against collapse
- Dead and live loads
- Adjacent buildings and foundations.
Principles of subgrade stability improvement byLeca® Lightweight Expanded Clay Aggregate are shown in Figures 1.1 and 1.2. Sliding surfaces emerged in a road embankment and stresses of a subgrade produced by rock fill and Leca® Lightweight Expanded Clay Aggregate fill are presented in different colors. Red lines indicate the sliding surface and subgrade stress created by conventional rock. Green lines show the sliding surface of the fill structure implemented with Leca® Lightweight Expanded Clay Aggregate and the additional stress impacting the subgrade.
Highway Embankment Widening
Ground supported embankment widening by means of heavy rock aggregate may cause settlements of the existing structure and/or its extension, especially in the event of a soft soil subgrade. When Leca® Lightweight Expanded Clay Aggregate is applied as a fill material for construction of the road widening, harmful settlements of the widening can be decreased or completely eliminated.
A proper design is required to prevent detrimental differential settlements in the connection of the existing structure and new fill, and pavement cracking produced by tensile stress. The road embankment widening principle is presented in Figure 5.3. Same principle can be applied in other applications, for example at connection of interchanges and bus stops to existing road and street structures.
We have a team of representatives in the UK with extensive experience and knowledge on utilising Leca® Lightweight Expanded Clay Aggregate on a variety of Geotechnical Civil Engineering projects.
For a free consultation on Leca® Lightweight Expanded Clay Aggregate please contact Leca® UK: