US3807182A

US3807182A - Method of installing support tendons

Info

Publication number: US3807182A
Application number: US00249779A
Authority: US
Inventors: H Schnabel
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-05-03
Filing date: 1972-05-03
Publication date: 1974-04-30
Anticipated expiration: 1991-04-30

Abstract

A method of installing support tendons in clay soil by thermally hardening a mass of clay soil and by anchoring the tendons in the hardened mass.

Description

United States Patent [1 1 Schnabel, Jr.

[111 3,807,182 [4 1 Apr. 30, 1974 METHOD OF INSTALLING SUPPORT TENDONS [76] Inventor: Harry Schnabel, Jr., 7010 Longwqod Dr., Bethesda, Md. 20034 [22] Filed: May 3, 1972 [21] Appl. No.1 249,779

[52 us. CI. 61/35, 61/36 A, 6l/53.54, (Sl /53.62 [51] Int. Cl 1302:! 5/74 [58] Field of Search 61/36 A, 35, 39, 53.54,

[56] References Cited UNITED STATES PATENTS 3,436,923 4/1969 Lagerstrom 61/39 I/ Q, 1 I. /1. I 11-0044 1. lulu L! 3/1941 Ackley 61/36 2,235,695 2,514,509 7/1950 O'NeaL. 61/36 A l/l966 White FOREIGN PATENTS OR APPLICATIONS 609,386 9/1960 Italy 61/36 A Primary Examiner.la cob Shapiro Attorney, Agent, or F irmSchuyler, Birch, Swindler, MqK sz lec q t 57 ABSTRACT A method of installing support tendons in clay soil by thermally hardening a mass of clay soil and by anchoring the tendons in the hardened mass. I

19 Claims, 8 Drawing Figures PATENTEDAPRIBO m4 3L80'IL182 SHEET 1 BF 5,

PATENTEUAPR 30 um SHEEI 2 BF 5 mommmmmiou mmmmao m4 3.807.182

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. 1 METHOD OF INSTALLING SUPPORT TENDONS BACKGROUND OF THE INVENTION The instant invention relates to a method of installing and anchoring tendons for supporting structures. The

invention is particularly applicable to the support of sheeting walls used in building excavations and will therefore be shown and described in connection with such an excavation. However, the invention is not limited to sheeting walls and can be employed in connection with various other applications including, but not limited to, anchoring guy wires and cable ends of suspension structures and tendons for supporting foundation structures in tension. The invention is limited,

, sired, and then inserting the tendon with an anchor plate at its innermost end into the hole and grouting about the tendon and anchor plate to fill the hole and bond the tendon to thesurr ounding soil. However, in

cohesive soils, generally those comprising substantial proportions of clay or loess, the use of such-tendon installations has found limited success due to the low compressive and shear strength of such soils. The problem resides in thelow shear strength of such soils,

whereby the anchored tendon tends to pull out of its installed position.

In another field of art, that of constructing building foundations capable of supporting the compression loads exerted on the earth by large structures, a technique has been developed to harden unstable loess soils. This technique is described in papers by I. M. Litvinov, both in Highway Research Board Special Report 60, Soil and Foundation Engineering in the Union of Soviet Socialist Republics, National Academy of Sciences- National Research Council, 1960; and in Volume 96, Number SM 1, Journal of the Soil Mechanics and Foundations Division, American Society of Civil Engineers, 1970. Briefly, this hardening technique reduces the tendency for loess soils to settle when wetted under load, and comprises the steps of boring spaced holes vertically into the earth, inserting a heating means into each bore and then heating the surrounding earth while the heating means is being withdrawn from the bore. By this technique a column of hardened earth is prepared which extends, necessarily for foundation construction purposes, from the lowest point of treatment to the surface whereon the foundation is to be built. This technique'has been developed to provide a load-bearing surface of greater compressive strength, wherein theoretically a structure may be placed on top of such surface with less danger of deported by the method of'this invention. In the descrip-. tion the earthen face 1 is discussed as resulting from the structive settling. However, settling still occurs because the clay soil between the-hardened spaced areas retains its weak characteristics, and it is not practical to harden a sufficient area tobear the substantial compressive loads of typical buildings.

method of installing support tendons, wherein the advantages found in the useof such tendons in favorable soil conditions may be obtained in clay bearing soils.

An important object of the invention is to provide a method for supporting a wall reinforcing an upright earthen face of an excavation or land-fill, which method finds wide application and reduces the cost of such an excavation or land-fill.

Briefly, the invention'contemplates a method of improving the tendon anchoring characteristics of a mass of clay soil and emplacing a support tendon extending from said mass to a structure which requires tensile support. Heat is applied to a location in the soil, spaced from the structure to be reinforced at a temperature andfor sufficient time to harden a mass of the soil around the location of heating. A support tendon is then anchored to this hardened mass of soil and to the structure thus providing a tensile support for the struc- .ture. Preferably the heating is achieved by the local ap- BRIEF DESCRIPTION OF THE DRAWINGS The invention having been generally described, a specific embodiment will be discussed in detail with reference to the accompanying drawings in which:

FIG. 1 is a side sectional view of a sheeting wall supporting an earthenface into which a casing is being driven.

. FIG. 2 is'a fragmentary top sectional view showing the apparatus for providing pressurized fuel and air to the burners, the casing and burner extracting mechanism, and illustrating one embodiment of the subject method.

FIG; 3 is a detail of the burner unit within the casing of FIG; 2.

FIG. 4 is a fragmentary top sectional view showing the insertion of a tie-back support tendon through the casing.

FIG. 5 is a fragmentary top sectional view showing the support tendon grouted in place in the hardened soil mass.

FIG. 6 is a side sectional view showing two rows of the. support tendons completely installed. r

FIG. 7 is a side sectional view showing the method of this invention applied to stabilize and support the foun dation of a radio or television tower or similar structure. Y

FIG. 8 is a side sectional view showing the method of DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS As shown in FIG. 1, an earthen face 1 is reinforced by a conventional sheeting wall 2 which is to be supexcavation of the earth 3 on one side of the wall leaving undisturbed earth on the other side of the wall. l-Iowever, the invention is also applicable to an earthen face resulting from a-partial or complete earth filling on the earth face side of the wall. While only a single tie-back support tendon installation willbe described, manifestly a plurality of such installations may, and likely would, be used in a typical sheeting wall nstallation. The term clay soil is used to indicate soil consisting of or containing a substantial proportion of clay or loess or any similar substance having the characteristics of clay and hardenable by heat.

Essentially, the earthen face 1 is reinforced by a plu rality of side-by-side, horizontally spaced, upright soldier piles 4 which may take the form of l-l-beams. The piles are: conventional and include flanges 5 to which areaffixed studs 6 for attaching wooden lagging members 7. Alternatively, the members 7 may be short sections of suitable length for'fitting behind the flanges 5 of adjacent piles 4 in the well known manner. This wooden lagging 7 supported by the piles 4 present a sheeting wall 2 which prevents slippage of the earth from the face 1 into the excavation -3.

' Without reinforcement, the earth 9 behind the face 1 would tend to shear along some inclined plane of slip- I page and fall into the excavation 3. Although the piles 4 and the lagging members 7 present a sheeting wall 2 which bears against the face 1, this wall alone does not provide adequate support against the horizontal forces produced by the adjacent soil. Therefore the sheeting wall must be further supported against such forces.

The piles 4 are preferably interconnected by one or moreelongated wales 10 which extend horizontally of face 1 outside of piles 4. The wales are constructed of steel or the like andare attached to piles 4 by welding or other conventional means such as bolts or rivets.

At suitable, horizontally spaced positions along the wale 10 holes 11 are provided through both the wale l0 and the lagging members 7 behind the wale. These holes 11 are of suitable diameter to permit the passage therethrough of boring casing 12 and its related boring point 13. This casing and its related boring tip 13 are rotatably inserted into the earth 9 by means of boring drive unit 14 carried by a suitable conventional mounting and transporting means 15.

When the casing 12, which, for example, may be a three-inch diameter pipe, has been inserted to a suitable depth, the boring tip 13 is disengaged by conventional techniques, and the casing 12 is withdrawn a short distance by a conventional casing puller 16 (FIG. 2). A heating unit 17 is then inserted into the exposed outer open end of the casing 12. One configuration of this heating unit-l7 comprises a burner 17A (FIG. 3) with associated fuel tank 18 and air compressor 19 positioned outside the exposed upper end 20 of the casing 12. The fuel from the tank 18 is pressured by fuel compressor 21 and is distributed to the various treatment locations from manifold 22. The pressurized fuel-air mixture preferably is supplied to the burner unit 17A for burning at a location adjacent to the innermost end 23 of the casing 12, but alternatively may be burned in a unit at the outer exposed end 20 of the casing 12 with the hot gases of combustion 24 being conducted by the burner unit 17A tothe innermost end 23 of the casing 12, where they may contact the surrounding earth. The space between the casing 12 and the burner unit 17 is sealed, such that the pressurized products of combustion 24 cannot readily escape up the casing 12 but instead tend to be forced into thesurrounding earth. Compressed air, preferably in excess of the requirements for combustion of the fuel and at a pressure above atmospheric pressure, may be supplied to assist in forcing these hot gasesinto the soil. A suitable popoff valve or other safety device may be installed at the top of the casing to bleed off'excess pressure. Moreover, additional stabilizing chemicals may also be supplied to the area of soil heating to further treat this area, making it more susceptible to thermal hardening.

The effect of these hot gases on the clay soil is to hardenand substantially increase the compressive and shear strength of a surrounding mass 25 of such soil. The strengthened area extends radially outward from the location at which the heat is applied, and the extent of this strengthened mass is dependent upon the temperature of the gases supplied and the time duration of the heat treatment. Manifestly, the degree of strengthening will vary, depending upon the characteristics of the soil, and will decrease radially outward from the location of the application of the heat, such that the outer portions of the strengthened mass will blend into the surrounding unaffected soil. Thus there may be no clearly defined boundary between the strengthened mass 25 and'the surrounding soil 26.

While the heatingand strengthening process is in progress, the casing 12 and, heating unit 17 may be slowly withdrawn together from the original fully inserted position. The rate'of suchwithdrawal and the temperature of the gases 24 are .regulated thus to produce an extended mass 25 of treated soil, extending radially outward from the point of application of the heat and axially with the withdrawal of the heating unit 17 and casing 12. This mass will be terminated at a point spaced well behind the face 1.

When the desired mass has been sufficiently treated by this heating process, the heating unit 17 is then removed and the casing 12 is againinserted substantially to its original emplaced depth. A tendon 27, with its associated earth anchoring means "28, .is then inserted through the casing 12 to a position within the strengthened mass (FIG. 4). The tendon 27 may be a steel rod, cable, or any other well known structure. The casing 12 may then be withdrawn by any conventional means. As the casing 12 is withdrawn, grout 29 may be inserted through the casing 12 around the tendon27 to fill the space between the-tendon 27 and the wall 30 of the bore. By grouting as the casing 12 is withdrawn, collapse of the wall 30 of the bore is prevented, and this grouting firmly anchors the tie-back tendon to the strengthened mass 25 of earth (FIG. 5). This strengthened'mass-of earth, .withits substantially improved compressive and shear strengths, thus supplies the necessary support for the tensile stresses to be placed upon the tendon 27.

At such time as the grout 29 has hardened and thus firmly anchored tendon 27 into the earth, the outer end 27A of the tendon 27, which protrudes through both the sheeting wall 2 and the support wale 10, may be secured to the wale .10 by any well' known anchoring means 31 (FIG. 6), withor without pre-stressing of the tendon. Thus the tendon 27, in tension, provides the lateral support necessary for the sheeting wall 2.

' Whereas a tendon conventionally installed in such a wires or cable ends for a suspension structure anchored according to the invention. 7

It is to be understood that the embodiment shown is illustrative of the present invention and is not to be a limitation thereof, as other embodiments and variations will occur to those skilled in the art. Such variations may include but are not limited to: use of electrical resistance heating, application of heat to the soil through the walls or through perforations in the walls of the casing, and insertion of the tendon without use of the casing and then heating the surrounding soil through the surfaces of this tendon. The foregoing and other variations and substitutions may be made to the specific embodiments disclosed herein without departing from the principles of this invention. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.

What is claimed is:

1,. A method of installing support tendons in clay soil comprising the steps of:

.forming an opening in said clay soil,

applying heat to a location adjacent said opening in said clay soil spaced from the surface of said soil at a temperature and for a time sufficient to harden a mass of said soil around said location,

emplacing a support tendon extending from said surface to said mass and anchoring said tendon to said mass and to a structure spaced from said location.

2. The method of installing supporttendons in clay soil according to claim 1 wherein said heat is applied by contacting said soil with hot gases at said location.

3. The method of installing support tendons in clay soil according to claim 2 wherein said hot gases are produced by burning a combustible mixture at said location.

4. The method of installing support tendons in clay soil according to claim 2 wherein said hot gases are.

produced by burning a combustible mixture at a position removed from said location and conducting the products of combustion to said location.

5. The method of installing support tendons in clay soil according to claim 1 further comprising emplacing a casing in said soil, the innermostiend'of said casing extending at least to the depth of said'location of soil to be treated, said applying heat to said soil being from said casing, and said tendon being emplaced through said casing.

6. The method of installing support tendons in clay soil according to claim 5 wherein said heat is applied to said soil by contacting said soil with hot gases emanating from said casing.

7. The method of installing support tendons in clay soil according to claim 6 wherein said hot gases are produced by burning a combustible mixture within said casing.

8. The method of installing support tendons in clay soil according to claim 6 wherein said hot gases are produced by burning a combustible mixture adjacent the inner end of said casing.

9. The method of installing support tendons in clay soil according to claim 6 wherein said hot gases are produced by burning a combustible mixture at a position' removed from the interior of said casing and are then conducted through said casing to said soil.

10. The method of installing support tendons in clay soil according to claim 5 wherein said heat is applied to said soil while said casing is being partially with drawn.

11. The method of installing support tendons in clay soil according to claim 10 wherein said heat is applied to said soil by contacting said soil with hot gases emanating from said casing while said casing is being partially withdrawn.

l2. The-method of installing support tendons in clay soil according to claim 1 wherein the emplacement of said tendons comprises the steps of:

inserting said tendon into said hardened mass, and

grouting between said tendon and said mass.

13. The method of installing support tendons in clay soil according to claim 12 further comprising the steps:

emplacing a casing into said hardened mass, said inserting of said tendon being through said casingto the innermost end thereof, and

withdrawing said casing from said' soil.

14. A method of installing support tendons in clay soil located behind a wall which reinforces an upright earthen face, and method comprising the steps of:

forming an opening in said clay soil,

applying heat to a location-adjacent said opening in said clay soil spaced behind said wall at a temperature and for a time sufficient to harden a mass of said 'soil around said location,

emplacing a support tendon extending from said wall 1 to saidmass and anchoring said tendon to said mass and to said wallf 15. The method of installing support tendons in clay soil according to claim 14 wherein said heat is applied by contacting said soil with hot gases at said location.

16. The method of installing support tendons in clay soil according to claim 14 further comprising emplacing a casing in said soil from said wall, the innermost end of said casing extending at least to the depth of said location of soil to be treated, said applying of heat to said soil being from said casing.

17. The method of installing support tendons in clay soil according to claim 16 wherein said heat is applied to said soil while said casing is being partially withdrawn.

18. The method of installing support tendons in clay soil according to claim 14 wherein the emplacement of said tendons comprises the steps of: v

inserting said tendon into said hardened mass, and

grouting between said tendon and saidmass.

19. The method of installing support tendons in clay soil according to claim 18 further comprising the steps emplacing a easing into said hardened mass, said inserting of said tendonbeing through said casing to the innermost end thereof and withdrawing said casing from said soil.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 807, 182 Dated April 30, 1974 lnvent0r(s) Harry Schnabel, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, claim 14, line 3 thereof, change "and" to -said-.

Signed and sealed this 10th day of September 1974.

(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM M34050 USCOMM-DC 6O376-P69 a U. 5. GOVERNMENT PRINTING OFFICE 2 I", 0-366-334.

Claims

1. A method of installing support tendons in clay soil comprising the steps of: forming an opening in said clay soil, applying heat to a location adjacent said opening in said clay soil spaced from the surface of said soil at a temperature and for a time sufficient to harden a mass of said soil around said location, emplacing a support tendon extending from said surface to said mass and anchoring said tendon to said mass and to a structure spaced from said location.

2. The method of installing support tendons in clay soil according to claim 1 wherein said heat is applied by contacting said soil with hot gases at said location.

4. The method of installing support tendons in clay soil according to claim 2 wherein said hot gases are produced by burning a combustible mixture at a position removed from said location and conducting the products of combustion to said location.

5. The method of installing support tendons in clay soil according to claim 1 further comprising emplacing a casing in said soil, the innermost end of said casing extending at least to the depth of said location of soil to be treated, said applying heat to said soil being from said casing, and said tendon being emplaced through said casing.

9. The method of installing support tendons in clay soil according to claim 6 wherein said hot gases are produced by burning a combustible mixture at a position removed from the interior of said casing and are then conducted through said casing to said soil.

10. The method of installing support tendons in clay soil according to claim 5 wherein said heat is applied to said soil while said casing is being partially withdrawn.

12. The method of installing support tendons in clay soil according to claim 1 wherein the emplacement of said tendons comprises the steps of: inserting said tendon into said hardened mass, and grouting between said tendon and said mass.

13. The method of installing support tendons in clay soil according to claim 12 further comprising the steps: emplacing a casing into said hardened mass, said inserting of said tendon being through said casing to the innermost end thereof, and withdrawing said casing from said soil.

14. A method of installing support tendons in clay soil located behind a wall which reinforces an upright earthen face, and method comprising the steps of: forming an opening in said clay soil, applying heat to a location adjacent said opening in said clay soil spaced behind said wall at a temperature and for a time sufficient to harden a mass of said soil around said location, emplacing a support tendon extending from said wall to said mass and anchoring said tendon to said mass and to said wall.

15. The method of installing support tendons in clay soil according to claim 14 wherein said heat is applied by contacting said soil with hot gases at said location.

18. The method of installing support tendons in clay soil according to claim 14 wherein the emplacement of said tendons comprises the steps of: inserting said tendon into said hardened mass, and grouting between said tendon and said mass.

19. The method of installing support tendons in clay soil according to claim 18 further comprising the steps of: emplacing a casing into said hardened mass, said inserting of said tendon being through said casing to the innermost end thereof and withdrawing sAid casing from said soil.