AU2001284159A1 - Method of stabilizing particulates - Google Patents

Description

METHOD OF STABILIZING PARTICULATES

This invention relates to a method of stabilizing particulates

It is known from a number of prior proposals to attempt to modify the

properties of particulate engineering structures, such as railway ballast, for

example to improve stability, by effectively 'holding' the stones together.

Examples are EP-A- 0, 502, 920, EP-A-0, 641 , 407 and DE-A-394142

wherein multi-component systems, (MCS) such as epoxy or polyurethane

resins are used to bind the particulates together.

The engineering behaviour of particulate supported structures is

modified when MCS are applied. In particular, the engineering strength and

stiffness characteristics are increased. Addition of MCS also modifies the

dynamic characteristics, modifying properties such as the damping ratiq and

the speed of the stress shock waves (for example, compressive, shear and

surface waves).

When applying a multi-component system to particulates it is

desirable to ensure that the reinforced and stabilised structure performs to

an acceptable level during its life cycle. The MCS is preferably applied in the

correct spatial position and down to the correct depth to ensure that the

desired engineering behavioural improvements are obtained. The MCS is

also preferably designed chemically to ensure that its desired properties are

correct for the particular application under consideration, for example

stiffness, strength, viscosity, fatigue limits, acoustic damping, temperature range, biocidal and hydroscopic properties and curing time. Each particular

application of the MCS is likely to be different, since each site application

will be different with respect to geometry, surface/subsurface structural

conditions and engineering characteristics. Additional additives for the MCS

may be required to achieve the desired behaviour and predictability, for

example, cement or asphalt based fillers.

Incorrect application of MCS may lead to premature failure of the

modified structure. In very severe cases, this may lead to unplanned

responses and/or catastrophic failure.

It is an object of the invention to provide a method for the treatment

of particulate based structures which enables these desirable objectives to

be attained.

According to the invention therefore, there is provided a method of

stabilising particulates comprising the steps of:-

a) surveying the surface and substructure of a site using sensing

apparatus and combining with any available existing site data;

b) analysing the results so obtained to determine;

I) where a multi-component system (MCS) is to be applied;

ii) the quantities of MCS to be used;

iii) properties of the MCS; and

c) carrying out selective application of MCS to the structure as determined by the analysis.

Additionally, the method preferably also includes the steps of:-

- analysing the load characteristics required, and

- analysing the structure of in-situ particulates.

The invention also provides a Stabilised ballast structure in a railway

track made by this method.

The method may include the additional step of selecting or

formulating a suitable, for example polyurethane based, MCS coating

material. The method makes possible the adaption of offsite and/or modular

creation of components to achieve stabiliblisation of particulates and

surrounding structures.

MCS may preferably be used to increase the vertical and/or lateral

structural stability (eg. stiffness and strength) and needs to be carefully

controlled to ensure that the stresses and forces dynamically, transiently or

statically are within the fatigue or strength limits of the MCS reinforced

structure with a given factor of safety for the desired life cycles under

consideration. Using an inappropriate MCS may lead to premature and/or

unpredictable failure or undesirable performance deterioration of the

reinforced structure.

Addition of MCS modifies the static and dynamic behaviour of the

particulate structure and therefore the whole or partial structural response. The change in the static and dynamic behaviour is related to the particular

variant of MCS being applied and to the spatial location and properties of

the structure (eg in a railway track application, the rails, sleepers, cutting,

embankment, or in a roadway, the pavement, sidewalk, drainage, road

surface and subsurface), ballast, subballast, subgrade etc.). This change

needs to be assessed to ensure that it is not detrimental with respect to the

static and dynamic behaviour of the applied static and transient loads.

The development of an MCS membrane or barrier, through inappropriate

MCS application, may prevent dissipation of surface and substructure

excess pore pressures leading to failure or undesirable performance of the

structure. Therefore further design considerations need to be taken into

account before MCS is applied, particularly if a desired design objective is

the creation of an impermeable interlayer to ensure the desired properties

of performance (eg. drainage etc.) are achieved.

Using MCS to stabilise and reinforce the 'wet-spot' areas (ie. areas prone

to mud-pumping under load) also needs to be carefully controlled. Addition

of MCS creates a change in the static and dynamic interaction behaviour

and may create further problems and therefore needs to be assessed.

Using MCS as a tailored 'lead-in' to dynamically differently performing

natural or manmade structures such as geological features or bridge decks

needs to be assessed to ensure that the modified dynamic characteristics

are appropriate. This is to prevent for example additional vibrations being induced, leading to 'load-bounce' or return Shockwaves.

Particulates Reinforced and Stabilised by the Treatment Method of the

Invention may be used for:-

Short/long term stabilisation of overstressed structures (eg. mud-

pumping and 'wet-spots' in railway track);

Vertical, lateral and longitudinal stabilisation (in railway track for

example, of transition curves, super-elevations, junctions/points/crossings

and main lines, including high speed lines) for example, to reduce

maintenance.

Stabilisation of particulate structures in tunnels;

Stabilisation of retaining walls, inclines, taxiways and landing areas;

Reinforcement of bridge decks including increasing particulate stiffness

before and after bridges to prevent loads bouncing.

Reinforcement and stabilisation to ensure tight tolerances are maintained

eg. (in rail systems for normal, double-decker and high speed tilting trains

and other types of trains.

Reduce subgrade stresses through increased MCS stiffness and strength

properties.

Reduce subgrade stresses by increasing particulate stiffness to help

prevent local pocketing of subgrades.

Reduce induced particulates plastic strains and attrition, particulate segregation, (eg. through chipping), by reducing particulate movement,

reducing the incidence of fouled particulates. Application of MCS

membrane (for example at interfaces of different structural materials) to

prevent subballast/subgrade infiltration.

Help prevent hydraulic erosion of the surface and substructures.

Allow for increases in applied loads and speed of transient loads without

significantly increasing structural maintenance, and for reducing structurally

induced damage due to applied loads.

Prevent surface movement of the particulates through transient wind forces and through surface waves due to imposed loading.

Reduction of ambient noise generation and transmission. Allow power

washing of the reinforced structures to retain cleanliness at reduced cost.

Improve the static and dynamic performance of the structure.

Some examples of procedures for stabilising ballast, and of the resulting

stabilised ballast structures in accordance with the invention will now be

described by way of example with reference to the accompanying drawings,

wherein:-

Figure 1 is a diagram of a track assembly including

ballast and subgrade, to illustrate the terms and

general track features used in the following

description; Figures 2 and 2b are respectively transverse and longitudinal (in

the running direction) and cross sectional views

of a first embodiment of track structure

according to the invention;

Figures 3a and 3b to Figures 10a and 10b are similar respective

transverse and longitudinal cross-sectional

views of further embodiments of track

structures according to the invention;

Figure 1 1 is a view showing applications of ballast with

MCS to a rail bed, Figure 12 is a longitudinal

section of a bridge deck installation; and

Figure 13 is a flow diagram of the evaluation method

used in particular case.

A diagram of a simplified track structure as shown in Figure 1. This

comprises spaced apart rails 10 extending parallel in the running direction

of the track, supported on sleepers 11 which rest on a ballast layer 12.

This in turn is carried by a layer 13 of sub ballast which rests upon

subgrade 14. Subgrade 14 may comprise any natural or engineered terrain

such as an embankment, the floor of a cutting, or a bridge or viaduct deck.

In the following figures, sections are taken transversely across the track

structure on the line X-X of Figure 1 and longitudinally in the running

directions on the line Y-Y of Figure 1. Figures 2a and 2b relate to stabilisation of points, crossing and other

similar types of structures which are often subjected to lateral loading due

to train inertia forces. Conventional stabilisation methods include the

addition of plates at the end of the sleeper and/or the formation of a running

beam adjacent to the sleepers. Both of these methods rely on increases in

passive resistance, but often do not perform satisfactory due to progressive

plastic movement of the shoulder ballast. The technique used to overcome

this problem (in this design example) is the Crib Tie-back Method (CTbM).

In this technique, a polymer ballast composite beam (15) is constructed

adjacent to the sleepers to help prevent the sleepers 1 1 from moving

laterally as before. However, the beam (15) is now tied-back into the cribs

using the polymer ballast composite anchors (16) which extend across the

track generally between and below sleepers (1 1 ). The force required to

restrain the crib anchors (16) is provided by the weight of the train.

Therefore the technique makes use of the train's own weight to restrain the

beam (15) against permanent lateral movement (in addition to the frictional

resistance under the sleepers). The width of the anchors may or may-not

cover the full width and/or depth of the crib area depending on the level of

anchoring force required.

The composition of the polymer is selected based on the required

stiffness and strength properties required of the composite. In particular,

the tensile strength and shear strength properties of the polymer are determined as part of the design process.

Figures 3a and 3b show a structure to stabilise the vertical movement

of sleepers to problems involving poor formations, or in switch areas prone

to high vertical rail forces, a conventional 'ladder type' of design is used.

In this design only the ballast below the sleeper bottom is stabilised as

shown in Figures 3a and 3b. The ladder comprises a beam 17, 18

extending along the sides of the ballast, and a plurality of cross-beams 19

extending across the track between the beams 17, 18, and between the

sleepers 11. All the beams 17, 18 and cross-beams 19 are below the level

of the sleepers and utilize the full depth of the ballast layer, and are formed

of polymer stabilised the ladder design (Type 1 stabilisation) can only be

used when the depth of the ballast 12 is sufficient to allow frictional locking

of the unstabilised ballast under the sleeper (i.e. the frictional properties of

the unstabilised ballast are used to 'lock' the unstabilised ballast into the

adjacent crib stabilised/reinforced ballast). In poor formation areas the

polymer properties (for example polymer stiffness) are designed to ensure

that an efficient 'pad' type of ballast stabilised foundation is constructed

over the weak area. If the polymer stiffness is high enough, then a more

even distribution of stress at the subgrade interface is produced. For high

maintenance switches the polymer properties are selected to ensure that the

large vertical forces are more efficiently distributed under the switch, but

still retaining good composite damping properties. Figures 4a and 4b show a type 2 design for poor formations and high

maintenance switches wherein the ballast depth is not sufficient to ensure

that the unstabilised ballast under the sleeper is locked into the stabilised

crib ballast (or vertical track forces are too large). Movement and

penetration of the ballast under the sleeper into the formation is therefore

possible. Lifting of the sleeper to stabilise the ballast directly under the

sleeper is possible (this would require a separate design), but often

undesired as it has a detrimental affect on the track alignment. In this

design holes 20 are drilled into the sleepers 1 1 at various locations to allow

polymer to be poured/injected into the underlying ballast and fully/partially

stabilise it as shown in Figure 4a and 4b producing in addition to the

adder' construction of Figures 3a, 3b comprising parallel side beams 17,

18 and cross beams 19 below and between the sleepers 1 1 , a plurality of

anchoring pillars 21 below the sleepers.

In the design of Figures 5a and 5b for wet-spot stabilisation it is

assumed that the ballast 13 is heavily fouled due to subgrade infiltration

(mud-pumping) and must be replaced prior to polymer treatment. The

replaced ballast 12 is then stabilised using the polymer producing a

stabilised layer 22. The polymer is also designed to enable it to 'pool' at

the ballast/subballast interface forming an integral polymer membrane 23.

The membrane stops subgrade infiltration, but should only be applied if

confidence in the capability of the drainage layer is high. The depth of stabilised ballast (from the ballast/subballast interface) may extend up to the

base of the sleeper if considered appropriate but is shown with a layer of

unstabilised ballast 12.

Figures 6a and 6b show a design wherein the polymer is used to ensure

that track lateral tolerances are within specified limits. For example, this

design would be used to ensure that track clearances in tunnels and at track

platforms are within the correct limits. The depth of polymer application is

generally set from the surface of the sleeper top level to below the sleeper

bottom, as shown in Figure 6a and 6b. It is generally not necessary to

stabilise all of the crib areas, however this depends upon the level of loading

and longevity required. The polymer stiffness is usually set high to ensure

that the composite stiffness remains high (ensuring low composite

displacements). As shown, this produces side beams 24 of stabilised

ballast up to the upper surface of the sleepers and cross beams 25 between

alternate pairs of sleepers 1 1.

As shown in Figures 7a and 7b, polymer is used to provide a continuous

stabilised blanket 26 on the ballast surface around the sleepers 1 1 as

shown in Figure 7. The purpose of this blanket 26 is to stabilise the ballast

surface only (although the blanket depth may extend below the sleepers if

a high degree of stabilisation is required).

The blanket 26 is used to provide ballast stability against train generated

wind forces, loss of compaction due to ballast vibration and other detrimental problems like vandalism. For the vibration problems, the

polymer stiffness is generally set low to increase the damping properties of

the polymer. The vibration may originate from many sources including

ground waves generated by high-speed trains (these can become high on

embankment structures or railway track over weak foundations) or by

excessive vibration of other track structures, such as bridge decks vibrating

at their characteristic frequencies.

Figures 8a and 8b show an embodiment for stabilisation of cyclic-top.

Cyclic-top problems generally originate from track misalignment problems

or from dynamic motion of the locomotive and/or carriages. For example,

a wet-spot site may generate oscillations in the train suspension system

causing a sinusoidal type of motion, giving rise to changes in the dynamic

forces on the rail with track length. This sinusoidal motion gives rise to

permanent movement of the ballast at given wavelengths. Cyclic top can

also originate from problems like an uneven subgrade. The design for this

type of problem is based on the formation of two polymer/ballast composite

'running beams' 27, 28 that encompass the area of concern. The beams

can be continuous (as shown in Figure 8) or may make use of the ballast

locking mechanism comprising cross beams 29 under the sleepers as

described in Examples 2 & 3 above. On straight track lateral movement

may not be significant and hence stabilising the crib ballast is only

necessary at certain crib locations (for example, every third of fourth crib). The purpose of these crib stabilisations is to ensure that the beams 27,

28 remain laterally connected. Since this type of stabilisation is generally

for long track lengths, the polymer properties are selected based on the

varying formation properties. For example, a uniform track modulus value

may be selected as the design criteria in the determination of polymer

stiffness.

Finally Figures 9a and 9b show an arrangement of stabilised ballast for

stabilisation of curves on embankments. The design proposed in Figures 2a

and 2b for increasing the lateral stability of railway track may not be

sufficient (generally the shoulder passive resistance is lower than for track

not situated on embankments), in these situations a 'ballast key' 30 may

be required to increase the lateral stability. This ballast key 30 (or keys)

extends beyond the normal depth of stabilisation and is used to increase the

passive resistance of the stabilised track as shown in Figures 9a and 9b.

The ballast keys maybe formed from stabilised ballast as shown in Figure

9a. and 9b, or they maybe formed from another type of material that can be

used to provide an additional anchor force (such as steel soil nails). The

polymer properties are selected based on the criteria discussed in Example

1. The entire upper part of the ballast 31 defining the camber of the curve

is stabilised by adding polymer. The ballast keys 30 extend longitudinally

of the track below the rails.

Stabilised beams 31 may be applied at both sides of the sleepers 1 1 to resist trains that are both faster and slower than the design track curve

speed. Complete embankment stabilisation can be achieved (perhaps for

'weak embankments') by using a soil nailing technique to increase

embankment strength and stiffness in combination with the polymer

stabilisation technique to increase lateral (and vertical if necessary) track

stability.

Figures 10a and 10b show an arrangement for mainline ballast

maintenance reductivity. It is generally accepted that when constructing

new railway track the maintenance of the track can be reduced by ensuring

that the subgrade surface is shaped so that it is parallel to the rail. This

helps to prevent problems like ballast memory, in which the ballast surface

(ie. at sleeper level) takes the same shape as the uneven subgrade surface.

When constructing the new line, at the point of ballast placement on the

track, the polymer can be applied to ensure that a given ballast layer 32

remains parallel to the rail. This ballast layer 32 is applied at a specified

level and extent within the ballast, depending on the design and longevity

required as shown in Figures 10a and 10b. This type of approach helps to

prevent ballast pocketing and hence reduces the likelihood of track

irregularities.

When upgrading existin track the same technique can also be applied

to increase upgraded track longevity for uneven/even subgrades. During

the ballast cleaning/renewal process the polymer can be applied in a similar way to that described for the new track. The polymer is again used to form

a lower composite ballast layer that is parallel to the rail. The design would

be based on (for example) stabilising the ballast from its mid-point down to

the uneven subballast/subgrade interface. Not stabilising the upper ballast

layer allows for normal tamping operations. As with the new track design,

the polymer properties and loading would be matched to the subgrade and

to the level of loading required, through design based criterion like the track

modulus value. Figure 1 1 shows a typical application of the polymer to

form a composite lower surface ballast layer 32 during a ballast cleaning

operation with an uneven subballast and/or subgrade layer. Since this

technique would be applied to long lengths of track the polymer properties

would need to change to match the changing track properties. It is

therefore likely that techniques such as ground penetrating radar would be

required to examine the subsurface profile along the track. A divided chute

ballast placer 33 is used to place a first layer of ballast in front of an

application nozzle 34, and then a further layer of untreated ballast 12 above

the stabilised ballast layer 32.

The designed polymer stabilisation technique can be used to form

transition zones to allow a more uniform change in track modulus at sudden

changes in track stiffness. For example, the polymer/ballast composite

maybe used to form a transition zone from a relatively weak embankment

structure to a stiff concrete bridge deck. The design would encompass the spatial location of the polymer, for example a tailored lower level

stabilisation leading up to the bridge, in combination with desired changes

in polymer properties. By varying the overall stabilised ballast properties

changes in ballast shear wave and track velocities can be achieved to

modify track dynamics. The purpose of the transition zone is to help reduce

problems like 'train-bounce', which arise from sudden changes in track

stiffness. The complex interference patterns generated when train approach

solid structures, due to track ground waves, can increase ballast

maintenance. A designed based ballast stabilisation treatment can reduce

maintenance requirements in these areas. An example of a tailored lead-in

and lead-off ballast stabilised concrete bridge deck is shown in Figure 12.

In this design example the polymer stiffness and spatial location increase as

the railway track approaches the bridge deck (and vise versa off the bridge)

to allow a smoother transition from the embankment to the bridge. On the

bridge deck the polymer stiffness is reduced and its damping properties

increased to reduce vibration problems (and ballast attrition). In these

designs it maybe desirable to introduce rubber pads, or other types of

energy absorbing systems, below the sleeper to allow a more flexible

sleeper foundation base if considered appropriate. The bridge deck 35 is

covered by a full depth layer of stabilised ballast 36, which is sloped at each

side of the deck, whilst a partial layer of stabilised ballast 37 is provided to

either side of the bridge leading to and from the sloped end of layers 36. The transition zones maybe formed by either increasing the slope of

stabilised ballast, as in Figure 12, or by using a stepped arrangement.

An example of the application of the method illustrated by the flowchart of

Figure 10 is the stabilisation of a set of points over which axle loads of 25T

at 1 10mph regularly pass. This section of the line is rated at 35 Million

Gross Tonnes (MGT) and the points are used to divert freight trains onto a

turn-out to a marshalling yard. Lateral movement of the rail at the points

(situated on ballasted track), measured by on-line train instrumentation, is

in the order of 15-25mm depending on the actual axle weight and speed at

the instant of loading. Maintenance of the points is usually performed at 6-

8 monthly intervals (often the points are re-aligned). Site investigations

reveal that the ballast is of a dolerite basalt type with a type D₅₀ of 28mm.

The ballast depth is between 3Q0-400mm, with a subballast layer between

120-150mm overlying a silty-clay subgrade, within a slight depression. CBR

readings and cone-penetrometer readings of the subgrade indicate stiffness

values of 100-120MPa. Poisson's ratio for this type of material is 0.4 with

shear strength coefficients of c' = 4kPa and = 29°. In situ density

readings indicated bulk unit weights around 18kN/m³. The surface

subsurface layering is known and so ground penetrating radar is not

considered necessary.

The subgrade shear-wave velocity is calculated to be around 150m/s.

At 1 10mph the maximum train speed is 49m/s. The development of a transeismic state is therefore not expected at current train speeds (the train

speed is less than 60% of the ground shearwave velocity). Track critical

velocities are also outside current train speed limits. Therefore, this

example primarily concentrates on the static analysis of the track.

The ballast and subballast stiffness values are around 200MPa and

120MPa, with purely frictional strengths of + 46° and f 38° respectively.

The void ratio of the ballast is around 0.72 with a unit weight of 16kN/m³).

The rail (E = 210 Gpa, p = 7850kg/m³) and rail pads (E = 200 MN/m) are

standard UK main line with bolt plate fasteners onto wooden sleepers of

2.6m in length, 0.14m in depth and 0.26m in width. The average distance

between the sleepers is 0.38M. No signs of mud-pumping is evident, wet-

spot formation at this particular site is not considered to be significant. This

is confirmed by observed well maintenance track drainage. Ballast

contamination, due to overstressed ballast, is evident. This has resulted

from the development of large lateral forces as freight trains are diverted

onto the turn-out. Calculation of the expected vertical and lateral train

forces (using standard procedures, for example the procedures laid out in

UK and American Railway Engineering Association (AREA) guidelines)

suggest dynamic amplification factors of 1.5-2x the static axle loads

vertically at 100-1 10mph and 1.2x the static axle loads horizontally at the

turn-out at 15mph. These values are used in combination with the site

investigation material parameters as input to a static mathematical, model, based on the finite element method.

The static mathematical model used is the DIANA finite element

program, which is generally available and represents the current state of the

art in terms of commercially available and represents the current state of the

art in terms of commercially available finite element programs. The 3-

dimensional finite element mesh used comprises 2100 elements of the

following types, 3-noded Class III Beam elements and 20-noded

isoparameteric brick element. A full integration scheme is used and

boundary conditions are smooth in the appropriate vertical directions and

fixed at the base. The mesh is spilt into several layers to simulate the

different ballast, subballast and subgrade depths. Modifying the ballast

material properties as appropriate to their spatial location simulates

variations in the ballast densities. The rails, fasteners and sleepers are

assumed to behave elastically. The ballast, suballast and subgrade are

assumed to behave non-linearly and are modelled using an elasto-plastics

Mohr-Coulomb constitutive soil model using a non associative plastic flow

rule. Material dilation for the ballast and subballast are assumed, based on

the critical state friction angles for the two materials.

Locomotive configurations for the determination of train loading cases

include, CLASS 87 (for example, wheel diameter = 1.150m, wheel to wheel

centres 3.28m, bogie distance = 9.97m, axle weight-202T+ 2T unsprung),

CLASS 86/4 and CLASS 253/254 HST. Freight loading cases include 100 tonne GLW Tank Wagon Class B (for example, wheel diameter =0.95m,

wheel to wheel centres = 2.0m, bogie distance = 13m, axle weight = 25T).

An additional multiplication factor of 1.5 is used to simulate increases in the

dynamic load factor for wheel flats.

The mathematical model is first used to verify the current lateral

displacement values (between 10-25mm lateral deflection depending on

applied lateral force). Once the measured displacement values are simulated

the finite element model is considered calibrated and various designs are

investigated and analysed to determine the optimum design for the added

polymer composite. To determine properties of the required designed

polymer an iterative process is used in combination with the new engineered

track design. The required performance is set at 5mm lateral deflection

under lateral train loading.

The actual design used for this site stabilisation is a tie back design

(several designs are investigated and their performance assessed with

respect to the performance assessed with respect to the performance target

set) . In this particular case, a composite edge beam is tied-back into the

cribs using the polymer composite (the tie-backs are below the sleeper

base). The polymer stiffness used was E = 500MPa and the ballast loading

was 10% by ballast mass. This design shows that a significant increase in

lateral stability is achieved, when compared to an ordinary edge beam type

stabilisation. The simulated modelling shows increases in lateral stability, for this case particular case, of approximately 6 times greater than the

ordinary unstabilised ballast and 4 times greater than edge beam only type

of stabilisation under train loading conditions imposed. The results of the

mathematical model are closely studied in terms of stresses, strains,

displacements etc. to ensure that these quantities are within the acceptable

fatigue limits for the composite/polymer chosen. The mathematical model

is also used to investigate areas of possible plastic deformation, giving raise

to permanent plastic movement, and to enable the design to be modified if

necessary and factors of safety calculated.

To obtain the optimum polymer loading for the designed stiffness and

cyclic properties of the composite laboratory tests were performed. The

results of these laboratory tests are used to estimate the designed life span

of the treated site by applying a similar deviatoric stress state as computed

by the mathematical model. The tests include, direct shear box testing,

triaxial compression testing (monotonic and cyclic) and cyclic boundary

value tests, ie. three-dimensional box tests. The results of the direct-shear

testing (dimensions of 300mm x 300mm) indicated that the unreinforced

(unstablished) ballast for particular case of polymer loading has shear

strength coefficients of c³ =okPa and =46°. Addition of the polymer at

10% loading (by ballast mass) to the ballast increases the shear strength

coefficients to c³ =okPa and ^<r^' = 46°, showing a considerable increase in

strength. These values were confirmed by the unconfirmed triaxial compression tests. The cyclic properties of the reinforced ballast were also

tested. In the first of these tests a reinforced unconfirmed cyclic triaxial

compression test at the simulated peak computer simulated deviatoric stress

state was tested. The results showed an accumulated plastic strain of

0.4% at a peak cyclic deviatoric stress state of 384KPa (as computed by

the mathematical program) after 20,000 load cycles. A second sample was

cycled at a peak load of 768kPa (factor of safety of 2x on internal stress-

state). Again around 0.4% accumulated plastic strains were recorded.

In a simulated boundary value test (traditional three dimensional box-type

of test for railway ballast) 2.66 million load cycles at design loading

conditions were applied to the surface of stabilised ballast (through loading

cap) to obtain the required MGT value for 10 years loading on the WCML.

The stabilised ballast experienced around 1.0mm plastic deformation.

Typical results for unreinforced cyclic ballast tests atthis level of loading are

generally available in the literature and indicate values of accumulated

displacement between 30-40mm. The behaviour of the designed reinforced

ballast is therefore far superior to the unreinforced ballast in both strength

and cyclic properties. No evidence of ballast attrition was observed.

Based on the results of the laboratory tests and the mathematical

modelling a modification to the design is made to reduce stress

concentrations at the sleeper ends. The design is therefore an iterative

process, taking into account the results of the of the mathematical modelling and laboratory tests, in combination with the expected loading

conditions and required performance criteria, to arrive at an optimum design

for this set of points to ensure all the design criteria (displacements, strains

and stresses etc.)are within tolerable limits. The final composite design

therefore satisfies the overall designed life-span performance criteria for

lateral displacements limit of 5mm for 10 years on the West Coast Main

Line. This process therefore gives a complete design procedure and

predictive capability for modified polymer stabilised railway track. To date,

post-treatment performance monitoring by the local maintenance contractor

has shown that the treated site has performed as per the design.

In this example a complete dynamic analysis is not necessary as

subgrade and track critical velocities are significantly higher than the current

train speeds. However, if the subgrade stiffness is lower (or any other

special track circumstances/conditions are observed, for example significant

track irregularities leading to large dynamic track forces) an additional

design step to the above example is necessary. To enable a full dynamic

design and analysis of railway track, and subsequently treated polymer

railway track, a three-dimensional dynamic finite element program is used.

The program allows the user to examine the change in the track behaviour

with polymer application and represents a sophisticated design tool for track

engineers. Examples of suitable MCS compositions are set out below. The

exact proportions of ingredients, and even the diisocyanates and polyols in polyurethane used may be varied along with the physical properties such as

viscosity, as determined by the results of the analysis process set out

above.

Example 1 - [Application to Railway Track]

A ballast layer comprises an aggregate of crushed limestone of mean

dimension 40mm, and this is bound to a depth of 300mm between the

sleepers and rails of the track.

The MCS comprises for example a polyurethane having the following

composition mixed using a Graco Hyrocat (Trade Mark) based machine, and

is poured onto the ballast which is pre-laid to a depth of 300mm. The

foundation for this 300mm layer of ballast is a sand carpet. The design may

require an excess of polymer seeping through the ballast to create a barrier

against upward movement of the sand or subgrade layer.

The polyurethane comprises the following two components, which are

maintained separate prior to pouring, then mixed and poured together.

Component A (Polyol)

Castor oil 49.25% parts by weight

Sorbitol based polyether 28% parts by weight

Polyether Diol 4% parts by weight

Methyl Naphthalene (VYCEL U (TM) 12% parts by weight

Tris (2-Chloropropyl) phosphate 5% parts by weight Sodium Aluminum silicate

(Zeolith (TM) powder) 1 % parts by weight

Phenyl mercuric fatty acid ester

(Thorcat 535 (TM)) 0.5% parts by weight

Dialkyl tin mercaptide

(Fomrez UL22 (TM)) 0.3% parts by weight

^■i

Component B (isocyanate)

Polymeric dimethγlene diphenyl

diisocyanate (MDI) 100% parts by weight

The mix ratio of the two components is:-

Component A - 100 parts

Component B - 56 parts

The composition, including ballast at 5% level gives the following

mechanical properties:-

Bulk density - 1.55 y/cc

Compressive modulus :- 100 - 800

Example 2 [Application to a Railway Track]

A 10%, loaded rail ballast is prepared using a polyurethane/bitumen

composition. The isocyanate terminated pre-polymer is added to a cationic

bitumen in the following preparations:- Polyether based FR emulsifiable pre-polymer 20ppw

60% Cationic bitumen emulsion 100ppw

The pre-polymer is based on the following:-

PPG diol 2000 m.w. 1 OOppw

EID 9086 35ppw

Amgard TMCP (TM) 10ppw

Vycel-U 5ppw

The pre-polymer/bitumen composition is sprayed onto the ballast at a

rate to ensure 10% loading.

The composition cures in two hours, and provides an elastic solid whose

compressive strength at 10% yield is 50MPa at 15°C.

Other curing systems for polyurethane prepolymer include the use of

alkaline agents such as sodium silicate solution, calcium hydroxide and

magnesium hydroxide and magnesium hydroxide and magnesium hydroxide

slurries as well as other organic polymer emulsions. These mixtures can be

used similarly to bind a particulate material such as ballast to produce a

strong supporting composite. The pressure, composition and amount and

location to be sprayed or otherwise applied to the ballast layer is determined

by mathematical modelling of the stress effects from different trains speeds

and loading to determine the polymer/ballast composite required to yield a

predicted lifetime of acceptable performance. Clearly, traffic comprising a high incidence of heavy locomotives with loaded mineral trains will exert

different stresses to relatively light but fast HST units, or infrequent slower

and lighter multiple passenger units.

The polymer formulation enables the ballast to be wetted out and

subsequently allowed to set a tough composite in place on the track bed,

which provides long term load and vibration management of the track.

Claims (11)

1. A method of stabilising particulates comprising the steps of:-

a) surveying the site conditions including surface and substructure

of a site using sensing apparatus;

b) analysing the results so obtained to determine;

I) where a multi-component system (MCS) composition is to be

applied;

ii) the quantities of MCS to be used;

iii) properties of the MCS required; and

c) carrying out selective applications of MCS to the particulates at

the site as determined in step (b) above.

2. A method according to claim 1 comprising the further steps of:-

- analysing the load characteristics required and

- analysing the structure of particulates at the site.

3. A method according to claim 2 comprising the further step of selecting

or formulating a suitable MCS coating material.

4. A method according to any preceding claim wherein the MCS is

selectively applied to ballast in a railway installation, to provide a

structure of stabilised ballast wherein parts of the ballast are stabilised,

and other parts are left untreated by the MCS.

5. A method according to claim 4 wherein the MCS comprises polyurethane based resin system which is used to bond and thereby stabilise stones

comprising a bed of railway ballast.

6. A structure comprising a ballast bed in a railway track wherein the

ballast is selectively treated with MCS to stabilise parts of the ballast and

leave other parts untreated, so that the stabilised parts of the ballast

constitute reinforcing elements for the ballast bed.

7. A structure according to claim 7 wherein said stabilised parts of the

ballast comprise elements extending longitudinally of the track, outside

of the sleepers, and further elements extending transversely of the track,

below and between the sleepers.

8. A structure according to either of claims 6 to 7 wherein the MCS

comprises a single component organic polymer or polymer precursor

which can be poured onto the ballast and cure by reaction with

atmosphere moisture or oxygen, by evaporation, by post application of

a curing agent treatment with irradiation, or application as a provider and

melting onto the ballast.

9. A structure to any either of claims 6 to 7 wherein the MCS comprises

two or more components which are pre-blended prior to pouring into the

ballast.

10. A structure according to any one of the claims 6 to 9 wherein the

polymer is mixed with ballast before placing on the ballast bid and

curing of the polymer.

1. A structure according to any of claims 6 to 10 wherein the structure is

provided by a method according to any one of claims 1 to 5.