Page 245 - 360.revista de Alta Velocidad - Nº 5

Soil stabilization in new railway construction

As you can see, 30 cm thick sub‐ballast layer is replaced by a 25 cm thick treated material with
a hydraulic binder layer. It allows the use of a soil of the working zone that does not require
as stringent conditions as the one of sub‐ballast features (for instance, many quarries don't
meet the Los Angeles index in Northwest Spain). Also the thickness of the formation layer is
considerably reduced (from 40 to 20 cm) when it is stabilized with cement and the required soil
characteristics are much more permissive.
The soil may be the same used in the construction of any suitable layer (the formation layer for
instance) or other which comply with some minimum requirements. The hydraulic binder could
be medium resistant category cement or hydraulic lime. A 3‐4% by weight of aggregates in case
of cement and 1,5 – 2,5 % for lime jobs is usually used. The dosage depends on the nature of
the soil to be treated, that is way previous tests with different provisions must be carried out.

The minimum requirements to the soil must be:

UPPER LAYERS FORMATION LAYER

< 80 mm Pass 2 mm 20 – 55 %
Sieve size < 80 mm
Pass 0,063 mm 2‐20 %
Plasticity LL < 30, IP < 10 LL ≤ 40, IP ≤15
Organic material < 1 % < 1%
SO3 < 0,5 %
Salt water soluble < 0,2 %
Minimum binder content by 3 % cement 3 % cement or2 % Quick lime
mass
Compression resistance 7 2,5 MPa 1,5 MPa
days specimens

As for the permeability of this layer, check that its value is less than 10 ‐ 6 cm/s, which should
be achieved easily.

Having one or some layers stabilized with hydraulic binder increases the degree and speed of
consolidation of the structural package, which improves the lateral resistance of track.

In order to assess the behaviour of vertical stresses the structure of project and the different
alternatives, a comparative analysis has been done. The program makes a multilayer analysis,
commonly used for the assessment of different packages in different surfaces.
To use this program there are the following assumptions:

• Layers are horizontally infinite and finite vertically, except the bottom layer which is
considered as a bottomless.
• Layers consist of homogeneous, isotropic and elastic materials and they are characterized
by its modulus of elasticity E and its coefficient of Poisson.
Boundary conditions considered were as follows:

(a) On the surface:
• Tangential stresses are null, except in the case that horizontal loads are applied.

(b) At finite depth:
• In case of adhesion between two layers: stresses and deformations are equal on both

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