2. Description of the prior art In U. S. Patent No. 5,522, 676 in the name of one of the applicants, there, is disclosed an undercut excavation method in which posts are inserted into holes drilled in the ground so that their top ends are flush with the ground, and a concrete floor is poured on said ground and on top of the posts; then the ground is excavated under the concrete floor which also serves as a concrete roof for the excavation. In case of a multi-level excavation, new posts are inserted into the ground of the first excavation and the procedure repeated at the lower level. In order to solidify the installation, additional posts are stood-up on top of the new posts in the excavated area, usually besides the originally inserted posts, to produce a double-post supporting arrangement. This is called"double-post excavation"or"double-post mining"when the system is used for mining purposes.

In a further improvement of the above system disclosed in U. S. patent No.

5,944, 453, a method is disclosed in which resilient elements are provided at the bottom of the lowermost posts for absorbing shock energy or excessive loads due to

ground movement and thereby protect the installation against seismic events or excessive ground movement.

However, in a number of instances, such as excavation of underground parking areas or garages or some mining applications, it would be sufficient to use a single post support arrangement and it is, therefore, desirable to adapt the undercut excavation method to such installations.

OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a method of undercut excavation using posts that are superimposed on top of each other and interconnected to form a single post arrangement for supporting floors of multi-level underground installations.

A further object is to provide such installations with protection against seismic events or excessive ground movement.

Other objects and advantages of the invention will be apparent from the following description thereof.

In essence, the method of the present invention comprises: (a) drilling holes of predetermined size and length in the ground, suitable for a multi-level undercut excavation; (b) inserting a plurality of posts into each of said holes, said posts being superimposed one on top of the other, and providing spacers between said posts into which concrete can penetrate so as to interconnect the ends of said posts with one another ; (c) positioning said posts so that uppermost posts have their top ends essentially flush with the ground and are capable of supporting a solid

layer of concrete; (d) pouring a layer of concrete onto the ground and on the top ends of the uppermost posts and allowing said concrete to solidify; (e) excavating beneath the layer of concrete now serving as a concrete roof for the excavation, to a level of next superimposed posts separated by the spacers from posts above; (f) pouring a new layer of concrete at this level so that said concrete penetrates within the spacers and ties the ends of the superimposed posts, while forming a floor supported by the ground at this level and posts below ; and (g) continuing the undercut excavation in this manner until a desired number of levels has been excavated.

In the event protection against seismic events or excessive ground movement is desired, resilient elements capable of absorbing chock energy or excessive loads due to ground movement may be placed under the lowermost posts.

When reference is made herein to posts, these include both concrete and metal posts, such as steel posts, of any shape that would be capable of supporting a layer of concrete that forms a floor or roof at the various levels of excavation. The preferred posts are made of concrete, including reinforced concrete, and are of round configuration. Also, when reference is made to the pouring of a layer of concrete onto the ground or at different levels of excavation, this includes the pouring or casting of a concrete floor/roof which is reinforced, for example, with rebar or similar reinforcing elements within the concrete. It should be noted that the spacers between the posts representing different levels of excavation are such as to permit insertion of

rebars or similar reinforcing elements within their structure and thereby allow formation of the reinforced concrete layer that joins the ends of the superimposed posts at the various levels of excavation, while being supported by the posts below.

There are presently drills available, e. g. Foremost's dual rotary drills built in Calgary, Canada, which can drill holes 6 to 40 inches (15 cm to 1 m) in diameter to a depth of 1500 ft (450 m) or more. However, it would be practically impossible to make single posts of such great lengths and insert them in such holes. The present invention overcomes this problem by providing a plurality of such posts and inserting them in a superimposed fashion one after the other while providing suitable spacers between them where concrete floors/roofs would be poured after excavation to that level has been carried out. Thus, posts 18 inches (45 cm) in diameter and 10 feet (3 m) long would be very suitable for such purposes, although other sizes, shapes and lengths may, of course, also be used if desired. Also, by providing spacers between such posts, anchoring of the concrete floors/roofs at the various levels is greatly facilitated.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of a non-limitative example, with reference to the accompanying drawings in which: Fig. 1 is a side view of superimposed posts arrangement for an excavation in accordance with the present invention of levels A, B, C and D; Fig. 2 is a side view similar to that of Fig. 1, but in addition having a resilient element under the lowermost post for absorbing shock energy; Fig. 3 is a perspective view showing a spacer arrangement between two superimposed posts;

Fig. 4 is a section view along line A-B of Fig. 3 showing one possible disposal of spacer rods; Fig. 5 is a side view of a spacer arrangement between two posts and of a concrete floor/roof poured within the spacer; Fig. 6 is a side view of another type of spacer arrangement between two superimposed posts ; and Fig. 7 is a perspective view of two level excavation in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 illustrates the arrangement of superimposed posts in accordance with the present invention. A hole 12 is drilled in the ground from the surface 10 to the bottom 14, representing a distance X. Posts 16,18, 20,22 and 24 are inserted into the hole 12 one after the other and spacers 15 are provided between these posts.

Depending on the type of spacer used, such spacers 15 can be positioned on the top end of each post or can be attached to the bottom of each post that is superimposed on a lower post or provided in any other suitable manner. When a number of such holes 23 have been drilled and posts disposed in them as shown in Fig. 1, a layer of concrete 26 is poured onto the ground 10 and on top of the uppermost posts 24 and this concrete is allowed to solidify. Then, excavation is carried out within level A under the layer of concrete 26 which serves as a roof for such excavation. This roof rests on the top ends of posts 24 and is supported by the column of posts 24,22, 20, 18,16 interposed by spacers 15. The excavation proceeds to the level defined by the spacers 15 between posts 24 and 22 where another layer of concrete 28 is poured to form a floor for the level A above and a roof for level B which is excavated next. The

floor/roof 28 is cast so that concrete penetrates between posts 22 and 24 through the spacer 15 and connects posts 22 and 24 to each other. Then, excavation of level B is carried out in the same manner, with concrete layer 28 serving as the roof for this excavation and being supported by the posts 22. In the similar manner excavations at levels C and D are carried out with floor/roof layers 30 and 32 being cast sequentially after each excavation and the bottom floor 34 being poured last under level D if no further levels are desired.

Fig. 2 illustrates an undercut excavation arrangement similar to that of Fig. 1, however, in order to provide protection against seismic events or excessive ground movement, depth Y of the hole 12 is slightly greater than depth X in Fig. 1 and a resilient element 36 is placed at the bottom of the hole 12 on which the lowermost post 16 rests. Such resilient element may be a spring or a plastic block or other element that has the ability to absorb shock loads.

Fig. 3 illustrates one possible design of the spacer 15 used between two superimposed posts, in this case posts 22 and 24. It can be made, for example, of steel plates 38 and 40 disposed parallel to each other and held apart by a plurality of short steel rods 42. On the opposite sides of the plates 38, 40, there may be provided cylindrical enclosures 44,46 adapted to receive the ends of posts 22 and 24 respectively. Rods 42 may be disposed in any suitable manner, for example as shown in Fig. 4, and they should be strong enough to support the posts inserted above them in the hole 12. The length of the rods 42 will essentially correspond to the thickness of the concrete floor/roof that will be cast at the level where the spacers are provided; for example, a suitable length would be 8 inches (20 cm). The diameter of the rods 42 could, for example, be about 2 inches (5 cm) and the thickness of the plates 38, 40 to

which the rods are welded by their ends could be about 1 inch (2.5 cm). The height of the enclosures 44,46 projecting on each side of the plates 38, 40 could, for instance be about 6 inches (15 cm) and the diameter of the cylindrical enclosures 44,46 should be slightly greater than that of the posts whose ends penetrate into these enclosures. These are, of course, only examples of suitable dimensions which will normally depend on the size of the holes drilled, post loading and the number and size of posts used for the excavation.

Fig. 5 is a side view of the spacer arrangement shown in Fig. 3, but in addition it shows the concrete floor/roof 48 cast in that area. The concrete penetrates between the plates 38 and 40 of the spacers and is supported by the post 22. The floor/roof is reinforced by rebars 50 forming a rebar pattern which also penetrates between the plates 38, 40 and between rods 42 that connect these plates with one another.

In Fig. 6, another arrangement of the spacer 15 is shown, which is similar to those shown in Fig. 3 and Fig. 5, but in which plate 40 is bolted to the bottom of the post 24 by means of bolts 52 cast into the end portion of the concrete post. This solidifies the spacer 15 and facilitates its positioning when the post 24 is lowered on top of the post 22 with the spacer 15 being bolted to the bottom end of the post 24.

Also, rather than bolting spacer 15 to the bottom end of post 24, it could be bolted in a similar to the top end of the post 22. Moreover, in lieu of bolting, the spacer could be attached to an end of a post by any other suitable means, such as wedge type pins or rods cast into the concrete posts.

Fig. 7 illustrates in perspective a two level excavation in accordance with the present invention that could serve, for example, as an underground garage. As the first step of the excavation, holes 12 are drilled from the surface 10 to a total depth X.

In this case, six such holes are drilled. Posts 20,22 and 24 are then inserted into said holes so as to provide levels A, B and C. The excavation in this case is rectangular and the holes are disposed at a distance L in the longitudinal direction with two such distances being used in this example, and at a distance W in width. The disposition is such that when a layer of concrete 26 is poured onto the ground 10 and on the top ends of the posts 24, upon solidification it will rest on the top ends of posts 24, thus forming a roof for the excavation of level A under this roof.

It should be noted that according to this invention, when posts 20,22 and 24 are inserted in holes 12 on top of each other, there are provided spacers 15 between these posts, such as illustrated in Fig. 3, Fig. 5 and Fig. 6. In this Fig. 7 they are not clearly shown because they are imbedded in the concrete floors/roofs. These spacers 15 are provided at each level where a floor/roof is to be cast. Thus, after excavation of level A in Fig. 7, a new concrete layer 28 is poured to form the floor for level A and the roof for level B. This concrete layer is supported by posts 22 when the excavation of level B is undertaken. Once the excavation of level B in completed, a new layer of concrete 30 is poured on the ground and it is supported by the ground under it and by the posts 20 which can remain in the ground as anchors if only two levels of the excavation are desired. However, the excavation could also proceed under the concrete layer 30 and another concrete layer could be poured on the ground at the bottom end of posts 20, linking said posts and solidifying them so that they would be solid enough to support the entire structure.

The novel method of the present invention has several advantages over the methods of U. S. Patents Nos. 5,522, 676 and 5,944, 453, particularly when used for undercut excavation in normal ground, such as for underground garages. It is simpler

to drill a few long holes in the ground than to drill shorter holes from each level of the ground, which would require bringing heavy drilling equipment from one level to another and then taking it up after the excavation is complete. It is also easier to insert several posts into such holes on top of one another than to insert such posts from each level of the excavation, because again one does not need to transport the posts from one level to another. Also, using single columns of posts rather than a double post system produces a saving in the number of posts used in the installation.

It should be noted that the invention is not limited to the above described preferred embodiments, but that various modifications obvious to those skilled in the art can be made without departing from the invention and the scope of the following claims.