GB2149441A - Method of constructing a roadway and elements for use in the construction - Google Patents

Abstract

A method of constructing a roadway consists of casting in situ a plurality of upstanding concrete elements 11 to form a plurality of areas bounded by the elements 11, placing between the elements 11 in each of the areas a pre-fabricated concrete standard element 10 having an upper side and downwardly extending side walls and re-inforcing ribs 14, inserting pre-fabricated interlocking elements 12 between the elements 10 and 11 and filling the spaces beneath each element through holes in the element with sand 13 which is compacted. <IMAGE>

Description

SPECIFICATION Method of constructing a roadway and elements for use in the construction This invention relates to a method of constructing a roadway over which vehicles can travel. The term "roadway" used throughoutthe specification and claims is intended to cover roads, highways, aircraft runways and aprons. The invention also relates to a roadway when constructed by the method according to the invention and to elements for use in constructing the roadway.

High quality roadways nowadays are being construted by using high technology.

However,theknown methods of construction still produce roadways having imperfections, caused by the utilisation ofthe roadway and also duetotheir maintenance.

The commencement of deterioration of a roadway usuallyoriginatesfrom the subgrade, upon which compacted layers ofthe roadway are constructed.

These symptoms are often observed in soils having unstable conditions as a result of having expansion and contraction coefficients of some importance.

Owing to changes in these subgrades affected by loads, degradations, erosions or expansion and contraction coefficients, the deterioration is distributed slowly but surelyto the surfacing ofthe roadway.

It should be understood that the term slowly is realtive, because it can take ten years in relatively good soil conditions and abouttwo tofouryears only in labile soil conditions to show deterioration, such as undulation, in the surfacing course ofthe roadway. In about six minths to one year roadways constructed on bad soil conditions are subject to rapid deterioration so that much repairwork has to be carried out at high costs. From the foregoing, it is obvious that deterioration of the surface, which forms the most expensive part of the roadway construction, is largely caused by a weakening process of the subgrade which representsthe less expensive part ofthe total construction of the roadway.

It often happens that portions ofthe finished roadway have to be broken up and restored afterwardsforthe installation of water, oil and gas pipes, electricity and telephone cables etc. It should be noted that these relatively small portions are not susceptible to be replaced with the use of heavy road making equipment and the broken up ortions cannot be restored satisfactorily to the original condition and often cause a beginning of deterioration ofthe road bed.

The above mentioned two crucial points, usually neglected by constructors or designers, are considered to be of considerable importance. Therefore, we have made an attemptto providearoadwayconstruc- tion which should meet the technical requirements of roadway construction, in general, and in addition satisfy the following conditions.

That is, the new method of roadway construction should: 1. meet all thetechnical requirementsofthe roadway construction in general such as: rigidity; the ease in which to construct: the speed of construction; the economic costs; 2. make possible the repairing ofthe subgrade (supporting sand layer, i.e. the most inexpensive part) at minimum costs, atanytimes if need be; 3. make it easy to take up part of the roadway and to replace it, the replacement having a rigidity the same as that of the original part in a relativelyshort time.

According to the present invention in one aspect there is provided a method of constructing a roadway comprising the steps of casting in situ a plurality of upstanding elements to form areas bounded by the upstanding elements, placing between the upstanding elements in each area a prefabricated element having an upper side and side walls which extend downwardlyto define beneath the pre-fabricated element a space, inserting interlocking elements between the upstanding elements and the prefabricated elements and then filling said space with sand and compacting the sand.

According to the present invention in another aspect there is provided elements for use in carrying out the method comprising a flexible element formed of concrete cast in situ, a pre-fabricated element formed of concrete having an upper side and downwardly extending side walls, and pre-fabricated interlocking elements.

An embodiment ofthe invention will now be described, by way of an example, with reference to the accompanying drawings, in which: Figure 1 shows a plan view ofthe standard and the flexible elements used in a roadway constructed according to the present invention; Figure 2 is a cross-section through the roadway; Figure 3 is a plan view of a standard element used in the roadway construction; Figure 4 is a side elevation of the element shown in Figure 3; Figure 5 is a front elevation ofthe element shown in Figure 3; Figure 6 is a plan view of a flexible element and standard element interconnected by an interconnecting member; Figure 7 is a side elevation ofthe elements shown in Figure 6; Figure 8 is a front elevation of the elements shown in Figure 6;; Figure 9 is a plan view of an interconnecting element; Figure 10 is a side view ofthe element shown in Figure 9; and Figure 11 is a frontview of the element shown in Figure 9.

The new method of roadway construction utilises two pre-fabricated re-inforced concrete elements and a third element of concrete cast.

These elements interlock in such a way that they can resistany deformationthrough vertical and horizontal pressure and can be easily removed and replaced and restored if need be.

Soil improvement is carried out afterthe elements have been laid and is done bythe injection of sand.

This soil compaction by injection is repeated periodically untii maximum compaction is attained.

The three elements consist of: A standard element 10, covering the largest part of the surface of the roadway, which is of standard dimensions and is made of high quality pre-fabricated re-inforced concrete.

Aflexible connecting part 11 which functions as the interlocking element. It is cast in situ so that it will comply with the geological requirements ofthe roadway under construction (e.g. the existing curve, intersection, slope etc of the ground).

A locking element 12 which is made of high quality pre-fabricated concrete and has a standard size.

Soil stabilisation by sand-filling 13 takes place after all standard elements 10 have been laid. Sand-filling 13 is done byflashing in sand and water until complete compaction is attained.

The sand layer 13 becomes compacted also through vibrations caused by vehicles travelling over the roadway and all spaces between the standard elements 10 arefilled again by sand injection.

Re-fillings havetotake place periodically and the intervals, as shown by our experiences with roadways constructed with the present method, become greater with the passing of time.

The pre-fabricated concrete standard elements 10 cover 93 to 95% of the roadway surface.

The requirements ofthe geological shape ofthe roadway construction can be easily met by the use of pre-fabricated concrete, because ofthe in situ cast elements 11 whose shape and size can be adapted to the surfacing.

The use of exclusively pre-fabricated concrete to coverthe whole area ofthe surface will impair precision and necessitate locking elements of all shapes and sizes to fit in.

Casting in situ of the whole area of the surface will meet witch difficulties owing to the structure and system of construction.

The interlocking elements 12 interlockthe standard elements 10 and are easy to replace if need be. The standard elements 10 can be pre-fabricated in a factory and are cost-saving while high quality can be guaranteed. Transportation and installation are also made easy.

The system with interlocking elements 12 is carried on in a way that they will make an integral part ofthe total surfacing, i.e. that any pressure on it is passed on to the surrounding elements so that equal pressure distribution is assured.

The existing holes on the upper part ofthe elements afterthe installation are filled byflashing sand and water. Sand flashes can be usedforthis purpose.

Consolidation ofthe sand 13 will take place through vibrations caused by on going traffic and new hollow spaces will appear so that refilling will become necessary.This phenomenon will recurand re-filiing has therefore to be done at intervals which with time will become longer each time. Refilling has to be determined according to the results of tests.

The standard elements 10 have the shape of an inverted box. The element 10 is, at is underside, re-inforced bytwo ribs 14which extend substantially diagonally as shown in Figure 3.

The undersideofthe upperside partisslightly arch-shaped. Each standard element 10 is provided with four holes 15 each having a diameter of 1 to 20 cm lined with fibreglass (to be cast simultaneously with the flexible elements) and four other holes 16 with a diameter of 1 to 4 cm for pressure release in the middle.

Attheendofthediagonallyconstructed ribs 14 are grooves 17 for receiving the interlocking elements 12 which are placed in a slanting position relative to the diagonal ribs 13. These elements 12serveto lockthe standard elements 10 with the adjacentflexible elements 11.

The flexible elements 11 generallyhaveatrapezoid- al shape and are symmetrical orassymmetrical.

The locking elements 12 are of a parallelogram shape and placed in a slanting position vis-a-vis the standard and flexible elements 10 and 11.

The advantages of the present method with regard to the conventional method are as follows: (a) the use of less material but having a greater rigidity; (b) no expansion joints are required in the construction; (c) the edge of the elements represents the most rigid part of the surface course; (d) soil improvement by sand injection afterall elements are laid out facilitates construction and makes later improvements ofthe base course easy to perform; (e) the relatively higher positioned surface and the interlocking of elements exclude any undulation ofthe surface course; (f) easy to take up partofthe roadway and to restore it; (g) restoration can be carried out without causing any deformative impression as to the original replaced element and in a relatively short time; (h) no "pumping" process because of the pressure releasing holes; ; (i) it can be carried out quickly as replacing elements can be fabricated simultaneously with the land "cut and fill" process; (j) more economical; (k) very low maintenance costs.

In constructing a roadway the elements 11 are cast in situ, the elements 10 arethen placed in position and interlocked withthe elements 11 by means ofthe elements 12 and sand is flashed through the holes 15 to be compacted beneath the elements 10.

Claims (9)

1. Amethod of constructing a roadwaycomprising the steps of casting in situ a plurality of upstanding elements to form areas bounded by the upstanding elements, placing between the upstanding elements in each area a pre-fabricated element having an upper side and side walls which extend downwardly to define beneath the pre-fabricated element a space, inserting interlocking elements between the upstanding elements and the pre-fabricated elements and then filling said space with sand and compacting the sand.

2. A method as claimed in claim 1, in which holes are provided in the upper side of each pre-fabricated elementthrough which the sand isflashed.

3. Elements for use in carrying out the method claimed in claim 1 or claim 2, comprising a flexible element formed of concrete cast in situ, a prefabricated element formed of concrete having an upper side and downwardly extending side walls, and pre-fabricated interlocking elements.

4. Elements as claimed in claim 3, in which the pre-fabricated element is re-inforced on its underside by substantially diagonal ribs and grooves provided at the ends ofthe ribs for receiving the interlocking elements.

5. Elements as claimed in claim 3 or claim 4, in which the upper side ofthe pre-fabricated element is provided with holes through which sand can be flashed and with vent holes for pressure release.

6. A method of constructing a roadway substantially as hereinbefore described with reference to the accompanying drawings.

7. Elementsfor use in the construction of a roadway substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

8. A roadway when constructed in accordance with the method claimed in claim 1 or claim 2 or claim 6.

9. A roadway constructed of elements as claimed in any one of claims 3 to 5 and 7.