GB2138057A

GB2138057A - Method of building strengthened, embanked foundation

Info

Publication number: GB2138057A
Application number: GB08409638A
Authority: GB
Inventors: Kazuo Horimatsu
Original assignee: Tekken Construction Co Ltd; Tekken Corp
Current assignee: Tekken Construction Co Ltd; Tekken Corp
Priority date: 1984-04-11
Filing date: 1984-04-11
Publication date: 1984-10-17
Also published as: AU587376B2; GB2138057B; ES542114A0; ES8609742A1; AU4099585A

Abstract

A method of building strengthened, embanked foundation capable of forming therein a tunnel comprises the steps of burying, during embanking work of the lower part of the foundation, a plurality of nets (11) which are vertically spaced in embanking material for the foundation at least in its internal zone including side wall portions (12) of the tunnel later formed so as to substantially horizontally intersect imaginary sliding surfaces (SL) occurring in the portions upon excavation of the tunnel, forming a crushed-stone arch layer (19) overlying from both upper side portions to the upper central portion of the later formed tunnel during further course of the embanking, providing a hanging support to the ceiling wall portion of the later formed tunnel by coupling said ceiling wall portion to the arch layer (19) by hanging rods (20) during formation of said arch layer and, after completion of the embanking, excavating a zone defined by the side and ceiling wall portions in the embanked foundation to form the tunnel therein. <IMAGE>

Description

SPECIFICATION Method of building strenghthened, embanked foundation This invention relates to a method of building a strengthened, embanked foundation of roadbed and the like.

In constructing such a new road as a high way intersecting existing old roads, waterways or the like, there has been generally employed a method of building an embankment at least over the existing road or the like in a manner of two level crossing. In this case, it is necessary to build a hollow structure transversing the embankment to secure a space for retaining the existing road or the like. Such hollow structure should be a concrete-made tunnel, substructure of bridge, box structure or the like, and the peripheral portions of this structure must be sufficiently stabilized for preventing its side and ceiling walls from being broken or collapsed.

The two level crossing according to the known method has been practiced in a manner as shown in FIG. 1, wherein a buried hollow structure SB such as a tunnel is built with concrete or the like material over each of, for example, an old road OR and a water-way WR prior to the construction of a new road NR, and thereafter an embankment is built over these structures SB for the new road construction but, in order to transport embanking materials to intended site of the new road, it is necessary to provide preparatory construction roads PR leading to respective parts of the site between the old road OR and the water-way WR and beyond the former.

According to this method, however, the embanking for the new road construction must be performed after sufficient hardening of such material as concrete of the structure SB because, at each time when the new road crosses the old road or the like, thc structure SB must be built prior to the new road construction, and it has been impossible to continuously construct the new road but only intermittently, so that the construction period could be easily prolonged.Yet, the provision of the preparatory construction roads PR has been generally necessary for avoiding any additional prolongation of the construction period caused inherently when the intermittently constructed new road is utilized for the transport of embanking material, whereby a considerably larger amount of costs has been required and it has been occasionally impossible to provide the construction road for geographic reasons.

A primary object of the present invention is, therefore, to provide a method of building a strengthened, embanked foundation which allows a continuous construction of a new road or the like without requiring any interruption for having the new road constructed across existing roads, water-ways and the like.

Another object of the present invention is to provide a method of building a strengthened, embanked foundation of a new road which allows to effectively utilize the new road just constructed for continuing the embanking with respect to crossing zone of the new road with existing roads and the like, and thus to liberate the new road construction from any provision of the preparatory construction road.

Still another object of the present invention is to provide a method of building a strengthened, embanked foundation of a new road, which is contributive to a remarkable reduction of required construction period for the new road by allowing the just constructed new road itself utilizable for continuous embanking, and is thus high in the economy.

Other objects and advantages of the present invention shall be made clear in the following explanation of the invention detailed with reference to an embodiment shown in accompanying drawings. In the drawings: FIGURE 1 is a schematic diagram for explaining a conventional method of constructing a new road transversing existing road and the like; FIG. 2 is a fragmentary section of the strengthened, embanked foundation being built for a new road construction according to an embodiment of the present invention, for explaining a state in which side wall portions and adjacent pillar-shaped crushed-stone layers of a tunnel later formed in the foundation are being built; FIG. 3 is a fragmentary section of the foundation completed following the state of FIG. 2; and FIG. 4 is a fragmentary section of the foundation similar to FIG. 3 but in a state in which the tunnel is formed in the foundation.

It should be appreciated that the present invention is not to be limited only to the particular embodiment shown but is to rather include all alterations, modifications and equivalent arrangements possible within the scope of appended claims.

The method of building strengthened, embanked foundation according to the present invention shall be detailed with reference to FIGS.2 through 4.

Referring first to FIG. 2, in the present method, a buried net 11 is initially placed on a ground surface 10 preferably over the entire area of the site where the embanking is performed for building the foundation. For the buried net 11, it is preferable to employ one which consists of a synthetic resin thread of polyethylene series having a tensile elastic modulus of 7.0 Kg/cm2, a plurality of which are meshed to provide a grid of 2.5 to 3.0 cm and to have an allowable tensile-resisting stress of about 1,000 Kg/m.

In order to form two opposing side wall portions of a tunnel of a rectangular section to be excavated in the foundation, while performing the embanking, a pair of soil cement layers 1 2 forming each cemented side wail of the tunnel and a slope soil layer 1 3 forming each slope wall adjacent and outside the layer 1 2 are built up on the buried net 11 as spaced horizontally and erected vertically, with a plurality of slope nets 14 embedded in these layers 1 2 and 1 3 as vertically spaced at intervals of about 10 to 15 cm. These slope nets 14 are preferably of polyethylene series threads of a smaller size in diameter and meshed grid than that of the buried net 11 so as to have an allowable tensile-resisting stress ofabout 500 Kg/m.The width of the slope nets 14 is selected to be enough for extending from the inner face of the coil cement layer 12 through the layers 12 and 1 3 sufficiently into embanked material outside the layers 13.

Further outside the respective side wall portions including the layers 12 and 13, also during the embanking performed, a air of pillar-shaped crushed-stone layers 15 are formed respectively as spaced by a predetermined distance from each slope soil layer 13, so as to be an erected pillar-like structure as a whole, while the embanking is performed with respect to spaces between the opposing side wall portions, between each side wall portion and each crushed-stone layer 1 5 and remaining portions outside both layers 15, over the length of the tunnel to be formed, that is, the width of the foundation to be built.During such embanking, a plurality of further buried nets are placed on every layer preferably of 40--60 cm height of embanked material, concurrently with the formation of the respective side wall portions 12, 1 3 and crushedstone layers 15, these further buried nets 11 having a width enough for being spread over an area across both pillar-shaped crushedstone layers 1 5 and reaching further outside these layers 1 5. In this case, it should be readily understood by any skilled in the art that these further buried nets may be substantially of the same size as the initially buried net immediately on the ground surface, or vice versa.

In the present instance shown, therefore, the lower part of the foundation including the side wall portions of the tunnel to be formed later is built with three of the slope nets 14 buried between respective buried nets 11 as spaced vertically from and parallelly to each other, while the embanking is repetitively performed with a sufficient rolling compaction also repeated simultaneously with such steps as described above of forming the respective layers 12, 13 and 15.

As the embanking has advanced to a predetermined height of the tunnel's side wall portions and erected crushed-stone layers 1 5, a foundation layer 1 6 of crushed-stone is formed on each of the erected layers 1 5 together with a plurality of relatively narrower buried nets 11 a also mutually spaced vertically and spread beyond the width of the layer 16 which is relatively larger than the height and aligned at the center with the layer 1 5.

Referring next to FIG. 3, it will be seen that a further upper part of the foundation is embanked above the crushed-stone foundation layers 16, repeating the steps of forming the soil cement layers 12 and slope soil layers 1 3 and, when the layers 12 and 13 of the tunnel's side wall portions reach a required height for the tunnel, the embanked layers are flatened as sufficiently subjected to the roll compaction to the level of the height. Thereafter, a sheet member 1 7 is placed across the upper ends of the opposing side wall portions, and a ceiling wall layer 18 is formed with soil cement all over the sheet member 17.In forming the ceiling wall layer 18, preferably, more than two of the buried nets 11 are horizontally placed to be embedded in this layer 18 in vertically closer spaced relation to each other so that the layer 18 will be thereby reinforced. For the sheet member 17, a plastic made sheet material may be effectively employed, or any of such rigid member as a rustproof steel plate, concrete plate and the like may even be used alternatively.

Referring further to FIG. 3, it will be also seen that, during the foregoing embanking of the further upper part and subsequent embanking of still further upper part or top part of the foundation being built, a crushed-stone arch layer 19 substantially of semi-cylindrical dome-shaped structure is formed across both crushed-stone foundation layers 16 so as to enclose the upper part of the tunnel's side wall portions and ceiling wall portion.During the formation of the arch layer 19, further, a plurality of hanging rods 20 interlocked at their lower end through any known means such as a washer to either one or both of the sheet member 1 7 and the buried net 11 in the ceiling wall layer 18 are provided as disposed at many positions both in the width and longitudinal directions of the tunnel to be formed (oniy two of which rods are shown in the drawing). In this case, preferably, stringers 21 extending in the tunnel's longitudinal direction are provided against the lower surface of the sheet member 1 7 so that the lower ends of the hanging rods 20 may be coupled to these stringers 21 and thereby a supportive hanging force of the rods to the ceiling wall layer 18 may be increased. The upper ends of these hanging rods 20 are extended above the top part of the crushedstone arch layer 19 and are secured to stringers 22 provided on the top part in the longitudinal direction of the tunnel to be formed, so that the rods 20 will be effectively coupled to the arch layer 19 to achieve the supportive hanging force to the ceiling wall layer 18. The subsequent embanking for the further and top parts of the foundation is thereafter continued up to a predetermined height with repetition of the provision of any further buried nets 11 and of the roll compaction, so as to complete the embanking for the strengthened foundation.

After the completion of the embanking, as shown in FIG. 4, the embanked material in the region surrounded by the opposing side wall portions comprising the soil cement layers 12 and slope soil layers 13, as well as the ceiling wall layer 18 and ground surface 10 is excavated and removed with the buried nets 11 lying within the region also cut and removed, and a tunnel 23 is formed in the strengthened foundation.During this tunnel excavation, it is likely that the elm banked material tends to slide along the imaginary sliding surfaces such as shown by chain lines SL in the drawing and normally occurring diagonally through both side wall portions of the excavated tunnel, from the base parts pf the crushed-stone arch layer 19 and its foundation layers 16 through the embanked material inside the pillar-shaped crushed-stone layers 1 5 to the respective base parts of the soil cement and slope soil layers 12 and 1 3 in the present instance, which generally entailing in a collapse of the wall portions.According to the present invention, however, the side wall portions of the tunnel 23 are sufficiently strengthened for not causing such sliding nor the collapse as above, by means of interlocking action of the respective buried nets 11 and slope nets 14 with the soil cement, slope soil and crushed stone forming the respective layers 12, 13, 16 and 19 as well as the embanked material of the side wall portions.

More in detail, a tensile force due to a sliding force caused along the sliding surfaces SL is imparted to the respective buried and slope nets 11 and 14 lying horizontally through the sliding surfaces SL and, once such tensile force is imparted, the respective materials compacted within respective net meshes to form in microscopic view a pillar-shaped body in each mesh are caused to receive a shearing force of the net-forming threads but this shearing force transmitted to the respective pillar-shaped bodies in the net meshes act to cancel the tensile force, whereby the entire materials outside the sliding surfaces SL can be stably retained.In other words, so long as the total strength of the respective nets and pillar-shaped bodies of the materials forming the side wall portions is larger than the sliding force, the nets and pillar-shaped bodies will not behave themselves independently of each other but as integralized with each other and even with the materials inside the sliding surfaces, so as to stabilize the side wall portions remarkably reliably with respect to the sliding surfaces. In addition, the respective buried nets in the crushed-stone layers 16 and 1 9 will act to prevent these layers from being horizontally displaced while increasing the horizontal shearing force of the nets and, in this respect, too, the stabilization of the side wall portions can be also effectively achieved.The foregoing interlocking feature is also applicable to the relationship between the buried nets 11 and the embanked material in any other portion of the embanked foundation.

During the excavation of the tunnel 23, on the other hand, the ceiling wall portion of the tunnel is also apt to fall and collapse, but the vertical and horizontal ground pressures likely to occur are born by the crushed-stone arch layer 1 9 and foundation layers 1 6 and eventually by the pillar-shaped crushed-stone layers 1 5 and any collapse of the ceiling wall portion can be effectively prevented from occurring. In interposed layers of the embanked material between the arch layer 1 9 and the ceiling wall layer 18, a relatively smaller vertical ground pressure is still present to cause the layer 1 8 to settle.However, this vertical ground pressure is born specifically by the supportive hanging force of the hanging rods 20 and stringers 21 and 22 coupled to the rods and any settling of the ceiling wall layer 1 8 can be effectively prevented from occurring.

As a result, all peripheral portions of the tunnel 23 can be stabilized substantially completely even after the excavation of the tunnel.

Exposed tunnel wall surface may be subjected to a cement casting or the like. Further, the soil cement layers 1 2 may be replaced by a concrete structure. The number of the buried and slope nets 11, 1 Ia and 14 and of the combination of the hanging rods 20 and stringers 21 and 22 may properly be selected depending on the scale of the embanked foundation to be built.Further, while a plurality of pairs of the pillar-shaped crushed-stone layers 1 5 are provided along the length of the tunnel and these layers 1 5 may be formed in the form of continuous wall body if occasion demands, they can even be omitted so long as the embanking material compacted between the ground surface 10 and the respective crushed-stone foundation layers 16 for the arch layer 1 9 provides a sufficient support for the layer 18, without imparing the bearing function of the crushed-stone foundation and arch layers 16 and 19.

According to the method of the present invention as has been disclosed, the embanked layers even right above the excavated tunnel in the strengthened, embanked foundation can sufficiently endure the load of running vehicles during the continuous construction of the foundation for the new road or the like, trucks for transporting the embanking material and so on can be allowed to run immediately on the just embanked new road having the excavated tunnel and thus it is made unnecessary to provide any construction road for the new road construction. Since it is unnecessary to wait for completion of the hollow structure as in the past, the new road can be extended even before excavation of the tunnel, so that the construction period can be remarkably shortened and the construction can be well economized.

Claims

1. A method of building a strengthened, embanked foundation of roadbed including a tunnel at a position corresponding to an existing road, water-way or the like for constructing a new road as embanked intersecting said existing road or the like, the method comprising the steps of forming a soil cement layer and slope soil layer erected to form each of opposing side walls of said tunnel later formed with a plurality of buried nets mutually vertically spaced and substantially intersecting an imaginary sliding surface occurring upon excavation of the tunnel between said side walls and with at least a slope net embedded between respective said buried nets and extending across said soil cement and slope soil layers, performing an embanking for building said foundation including peripheral portions of the side walls, forming in the foundation being embanked a crushed-stone foundation layer at a position laterally outwardly spaced from the upper part of each of the side walls of the tunnel later formed, forming in the foundation being embanked a ceiling wall layer of a soil cement with at least one of the buried nets, forming in the foundation being embanked an arch-shaped crushed-stone layer across said crushed-stone foundation layers and over the upper portion of the tunnel later formed, providing to said ceiling wall layer a hanging force with said arch-shaped crushedstone layer as a supporting means, continuing said embanking on already achieved embankment to complete the embanking, and excavating a zone below the ceiling wall layer and between the side walls to form the tunnel while cutting and removing said buried nets lying within said zone.

2. A method according to claim 1 which further comprises a step of forming in said foundation being embanked a pillar-shaped crushed-stone layer between each of said crushed-stone foundation layers and the ground surface.

3. A method according to claim 1 wherein said step of providing said hanging force comprises a step of coupling a hanging rod means secured at an end to a stringer means provided against a lower surface of said ceiling wall layer to another stringer means provided on the top part of said arch-shaped crushed-stone layer at the other end.

4. A method of building a strengthened, embanked foundation of roadbed including a tunnel, said method being-substantially as described herein with reference to the drawings.