US20060177279A1

US20060177279A1 - Reinforcing wall in a deep excavation site

Info

Publication number: US20060177279A1
Application number: US11/053,882
Authority: US
Inventors: William Starke
Original assignee: Deep Foundations Contractors Inc
Current assignee: Deep Foundations Contractors Inc
Priority date: 2005-02-10
Filing date: 2005-02-10
Publication date: 2006-08-10

Abstract

A reinforcing wall, for shoring of excavations, in a deep exaction site is made using a reinforcing pile comprising a length of hollow structural steel, and one or more hollow structural steel channels extending across said pipe for receiving tieback anchors so as to permit said pipes to be anchored into ground behind said pipes when installed in an upstanding position in vertical holes in the ground by installing said tieback anchors through said channels. The shoring wall is made by drilling a row of holes along an edge of said deep excavation site, inserting upstanding piles with prefabricated tieback channels, in at least some of said holes, pouring cementitious material into and around said holes around said piles to form upstanding soldier piles, excavating material from said excavation site to expose said upstanding soldier piles on one side thereof, installing (driving drilling etc.) tieback anchors through said channels into ground behind said upstanding soldier piles.

Description

FIELD OF THE INVENTION

The present invention relates to the field of deep excavations, and in particular to the formation of reinforcing walls for such excavations.

BACKGROUND OF THE INVENTION

Construction of a large building, such as an office block, usually begins by making a deep excavation on the building site. Shoring of the sides of deep excavation, which is needed to restrict the movement of soils adjacent to the excavation and to ensure the safe support of neighboring structures and utilities, is commonly carried out by drilling a row of adjacent holes, which are then filled with concrete to form concrete piles that are reinforced longitudinally (ie: vertically). These concrete piles may overlap so that adjacent piles are interlocked, (secant piles), or may be placed in close juxtaposition (tangent piles) to form a caisson wall. The terms “caisson”and “pile” are, in this submission, used interchangeably as in this connection they are created by first drilling a hole in the ground and then filling it with plain or reinforced cementitious material. For the purpose of simplicity, this cementitious material is henceforward referred to as “concrete”, although it can be premixed and poured or placed into the hole, or mixed in place with the existing soil using a cementitious admixture.
It is common practice to use the caisson pile wall as a backform against which a permanent wall can be cast. The piles of the caisson wall are usually reinforced with either a cage comprising vertical reinforcing steel bars connected by steel hoops or a steel spiral, or by steel wide-flange beams. The placing of reinforcing bars is time consuming and requires the use of skilled labor.
Some form of tieback connection usually retains the piles. There are many forms of tieback connections. One example is shown in FIGS. 1 a and 1 b, which show a connection 10 a consisting of a short horizontal steel waler plus steel adapting structures constructed on site. In such a design, the tieback connection is offset from the wide-flange beam's web 12 so that eccentric loads are introduced into the connection 10 a. In this case, extra bracing must be added to compensate for the eccentricity, which further increases the amount of work required to make the wall. As seen in FIG. 2, other connections 10 b may employ a long steel waler beam 14 and I-beam 16, in which case there is considerable interference with the formwork required to create the permanent building wall. Further with on site connections, cutting and welding costs are high, quality assurance is difficult to ensure and the progress of the excavation is retarded.
Other typical connections to be employed can be prefabricated off site, using designs as shown in FIGS. 3 a, 3 b and 3 c. In this case, a wide flange beam 7 is cut and welded to a square pipe 15. This latter type of connection is expensive and time consuming to fabricate and can create alignment problems, as the pile is in effect fabricated from relatively short sections. Further, the wideflange section is flexible and can easily bend across its secondary axis and can twist when placed in a drilled hole.

SUMMARY OF THE INVENTION

Disclosed is a method of making a retaining wall using a caisson (or pile) wall of concrete piles, some of which can be “soldier” piles. Each soldier pile may be reinforced by a large diameter steel pipe (or any hollow structural steel member) which is in turn reinforced with pre-formed channels through which tiebacks can be drilled or otherwise installed into the earth behind. The channels may be in the form of small diameter steel pipes or any hollow structural steel cross section (square, rectangular, etc.) extending at an angle through the piles. The tiebacks are drilled through the piles as excavation proceeds and the surface of each pile is exposed. The piles can be provided with reinforcing sleeves in the vicinity of the tieback channels.
Thus, according to one aspect, the invention provides a method of making a reinforcing wall in a deep excavation site, comprising: drilling a row of holes along an edge of said deep excavation site, inserting upstanding piles in at least some of said holes, said piles having transverse channels for receiving tieback anchors insertable into said channels, pouring cementitious material into said holes around said piles to form upstanding soldier piles, excavating material from said excavation site to expose said upstanding soldier piles on one side thereof, drilling or installing tieback anchors through said channels into ground behind said upstanding soldier piles and forming said reinforcing wall with said exposed upstanding soldier piles.
In another aspect, the invention provides a reinforcing pile for use in making a caisson wall adjacent a deep excavating site, comprising a length of strong pipe, and one or more channels extending across said pipe for receiving tieback anchors so as to permit said pipes to be anchored into ground behind said pipes when installed in an upstanding position in vertical holes in the ground by driving said tieback anchors through said channels.
In yet another aspect, there is provided a use of a reinforcing pile in making a caisson wall adjacent a deep excavation site, the pile comprising a length of strong pipe, and one or more channels extending across said pipe for receiving tieback anchors so as to permit said pipes to be anchored into ground behind said pipes when installed in an upstanding position in vertical holes in the ground by driving said tieback anchors through said channels.
In yet another aspect, there is provided a use of a reinforcing pile in a caisson wall as a column to support vertical loads, the pile comprising a length of strong pipe, and one or more channels extending across said pipe for receiving tieback anchors so as to permit said pipes to be anchored into ground behind said pipes when installed in an upstanding position in vertical holes in the ground by drilling or installing said tieback anchors through said channels.
There are many advantages in using concrete soldier piles made with piles that are reinforced with channels in accordance with the invention. The caisson wall can easily be constructed using components pre-fabricated off site. The piles are rigid and do not bend or twist when placed in a drilled hole. Particularly, the Applicant has discovered that survey results reveal significantly less movement in walls made in accordance with this invention.
Since fabrication of the large steel pile and channels is done off site, quality control is improved. Prefabrication off site is more cost-efficient than on site welding. Finally, eccentric loading on the caisson or pile is reduced since the tieback connection is in alignment with the center of the pile.
Other aspects and advantages of embodiments of the invention will be readily apparent to those ordinarily skilled in the art upon a review of the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described in conjunction with the accompanying drawings, wherein:
FIGS. 1 a and 1 b illustrate a front election view and a side elevation view, respectively, of a typical tieback connection detail at a caisson wall;
FIG. 2 illustrates another typical tieback connection detail at a caisson wall;
FIG. 3 a, 3 b and 3 c illustrate a typical prefabricated tieback sleeve for wide flange beams in a side elevation, plan view and front elevation, respectively;
FIG. 4 is of a retaining wall made in conjunction with the teachings of this invention;
FIGS. 5 to 7 illustrate a method to make the wall of FIG. 4, in accordance with the teachings of this invention;
FIG. 8 illustrates one example of how caisson or pile holes may be positioned to form a caisson or pile wall in accordance with the teachings of this invention;
FIGS. 9 a and 9 b illustrate a prefabricated large diameter steel piles with reinforcings in a side elevation and plan view, respectively, in accordance with the teachings of this invention; and
FIG. 10 illustrates a key section of the prefabricated pipe of FIGS. 9 a and 9 b positioned with a caisson hole of FIG. 5.
This invention will now be described in detail with respect to certain specific representative embodiments thereof, the materials, apparatus and process steps being understood as examples that are intended to be illustrative only. In particular, the invention is not intended to be limited to the methods, materials, conditions, process parameters, apparatus and the like specifically recited herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 4, there is illustrated a retaining or shoring wall 17 in the field made in conjunction with the teachings of this invention. The retaining wall is made from a caisson pile wall comprising filler piles and soldier piles which is restraining the supported soil and rock. The tieback anchors 19 are positioned such as to minimize interference with the formwork required to cast a permanent retaining wall. In this way, the soil load is retained by a composite of steel piles and concrete.
FIGS. 5 to 7 illustrate a method of making the reinforcing wall in a deep excavation site as seen in FIG. 4. First a number of caisson holes (one hole 20 being shown in FIG. 5) are drilled through overburden soils or rock, as seen in FIG. 5. Positioning of the caisson holes varies with each situation; for instance, the holes may be positioned to form tangent piles or secant piles depending on the nature of the soil. As an example only, FIG. 8 illustrates one possible caisson pile wall formed by a series of secant caisson holes. One hole is illustrated as having a large diameter pile 22 placed therein, with its small diameter channel 23 shown in phantom lines, as is described in more detail below. In this way, a caisson pile wall 25 may be formed by drilling a number of holes 20 some or of which receive the reinforced large diameter piles 22.
As seen in FIG. 6, a prefabricated, reinforced large diameter steel circular pile 22 is then placed within the holes. It is not generally necessary to place a pile in each hole. Typically the piles are placed in alternate holes, although they might, for example, be placed in every fourth hole depending on the nature of the soil and the depth of the excavation. Each pile is leveled and aligned.
FIGS. 9 a and 9 b illustrate a prefabricated large diameter pile 22 used in conjunction with the teachings of this invention. The pile has pre-fabricated channels 30 therein for accommodating tiebacks. In one embodiment, the channels 30 constitute holes 32 (see in FIG. 6) drilled through the large diameter pile 22, with small diameter steel channels 23 welded to each hole. The small diameter channel bisects the large diameter pile at a horizontal incline. Each small diameter channel is of a diameter required for drilling or installing the tieback.
Weld locations 34 of each small diameter pipe to a hole may be fitted with a reinforcing sleeve for additional strength. In one embodiment, the circumference of the large diameter pile may be welded, for example, with a 10 mm weld 40 all-around. Prefabrication of the pile results in improved cost-effectiveness and improved quality control. Prefabrication also facilitates the accuracy in placing and alignment of the tiebacks along the length of the pile.
FIG. 10 illustrates a key section of a pipe of FIG. 7 in a hole as drilled in FIG. 5.
As seen in FIG. 6, soldier piles 39 are then formed by pouring concrete around and usually within the large diameter steel pile. Typically, a 1 Mpa to 20 Mpa concrete is used so that during excavation the sides of the piles can be exposed by scraping away the concrete, for example, with a backhoe, to permit insertion of a tieback. Stronger concrete can be used to fill the piles, if desired. For example, if a final wall is a load-bearing wall, or for any other reason requires augmented strength, a stronger concrete may be used.
Use of soldier piles 39 increases the strength of the resulting retaining wall. For the same weight of steel, a hollow structural steel pile filled with high strength concrete provides superior bending moment resistance compared with either steel wide-flange beams or reinforcing steel cages.
As the excavation of the site proceeds, the concrete of the soldier piles becomes exposed. The excess cementitious material facing the excavating is trimmed back with a backhoe to expose the face of each pile and the tieback channels. As each channel is exposed, tieback anchors are drilled or installed through the channels into the earth behind the soldier piles 39. The tiebacks can be installed using equipment as known in the art. Each tieback anchor installed at an angle relative to the large diameter pile. The length of the tieback anchor varies due to the nature of the soil. In this way interference between the tieback anchors and the retaining wall is minimized, enabling the use of thinner permanent walls.
The wall can be completed either by adding formwork and pouring concrete between the soldier piles and the formwork, or if the ground forces are not high it may be sufficient to apply shotcrete to the exposed front of the soldier piles.
It should be noted that although the invention has been described as using a large diameter pile as the pile and a small diameter pipe as channels, any suitable structural member can be used. For example, the piles and channels can also be oval, square, rectangular, triangular, etc., in addition to being cylindrical.
Numerous modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method of making a shoring wall for excavations, comprising:

drilling a row of holes along an edge of said deep excavation site;

inserting upstanding hollow structural piles in at least some of said holes, said piles having integrated tieback connections, the tieback connections for receiving tieback anchors insertable into said connections;

pouring cementitious material into said holes around and into said piles to form upstanding soldier piles; and

drilling or installing tieback anchors through said channels into ground behind said upstanding soldier piles.

2. The method of claim 1, wherein said piles comprise large piles.

3. The method of claim 2, wherein said connections comprise one or more small pipes extending across said upstanding piles.

4. The method of claim 3, wherein said small pipes extend through said upstanding piles at an angle.

5. The method of claim 2, wherein the piles are steel piles.

6. The method of claim 4, wherein said cementitious material has a strength less than about 5 MPa so that it can be scraped away by a backhoe during excavation.

7. The method of claim 1, wherein said upstanding piles are placed in said row of holes with at least one intervening hole being devoid of a said pile.

8. The method of claim 7, wherein said upstanding piles are placed alternately in said holes.

9. The method of claim 1, wherein said shoring wall is formed by adding formwork and pouring concrete between said soldier piles and said formwork.

10. The method of claim 1, wherein said shoring wall is formed by applying concrete to the exposed surface of said soldier piles.

11. The method of claim 10, wherein said applied concrete is shotcrete.

12. The method of claim 1, wherein said soldier piles are arranged in a secant relationship.

13. The method of claim 1, wherein said soldier piles are arranged in a tangent relationship.

14. A reinforcing pile for use in making a shoring wall in a deep excavation site, comprising a length of strong pile and concrete, and one or more channels extending across said pile for receiving tieback anchors so as to permit said pile to be anchored into ground behind said piles when installed in an upstanding position in vertical holes in the ground by drilling or installing said tieback anchors through said channels.

15. Use of a reinforcing pile in making a shoring wall in a deep excavation site, the pile comprising a length of strong pile and concrete, and one or more channels extending across said pile for receiving tieback anchors so as to permit said piles to be anchored into ground behind said piles when installed in an upstanding position in vertical holes in the ground by drilling or installing said tieback anchors through said channels.

16. Use of a reinforcing pile in a shoring wall in a deep excavation site as a column to support vertical loads, the pile comprising a length of strong pile, and one or more channels extending across said pile for receiving tieback anchors so as to permit said piles to be anchored into ground behind said piles when installed in an upstanding position in vertical holes in the ground by driving said tieback anchors through said channels.