US3526096A

US3526096A - Method of making rockfill foundations

Info

Publication number: US3526096A
Application number: US783016A
Authority: US
Inventors: Joseph P Frein; Arthur Casagrande
Original assignee: Morrison Knudsen Co Inc
Current assignee: Morrison Knudsen Co Inc
Priority date: 1968-12-11
Filing date: 1968-12-11
Publication date: 1970-09-01
Anticipated expiration: 1987-09-01

Description

p 1970. J. P. FRIEIN ET R 3,526,096

METHOD OF MAKING ROCKFILL FOUNDATIONS 7 Filed Dec. 11, 1968 3 Sheetsfsheet 1 mvgmoas JOSEPH P. FREIN ARTHUR CASAGRANDE i BY v N I v. H ATTORNEYS Sept. 1, 1970 FRElN ET AL I 3,526,096

METHOD OF MAKING ROCKFILL FOUNDATIONS Filed D60. 11, 1968 2 Sheets-Sheet 3 INVENTORS JOSEPH P. FREIN ARTHUR CASAGRANDE ATTORNEYS United States Patent 3,526,096 METHOD OF MAKING ROCKFILL FOUNDATIONS Joseph P. Frein, Boise, Idaho, and Arthur Casagrande,

Belmont, Mass., assignors to Morrison-Knudsen Company, Inc., a corporation of Delaware Filed Dec. 11, 1968, Ser. No. 783,016 Int. Cl. E02d 27/04, 27/52 US. Cl. 6146 16 Claims ABSTRACT OF THE DISCLOSURE Rockfill foundation for support of a bridge pier, or the like, in which the lower portion of the foundation is made from large size, hard durable rock without any particular treatment. The upper portion of the foundation is formed from individually compacted rock layers raising to within a desired range of water surface. A surcharge of rock approximately equal to the expected load is added to the compacted layer. Surcharged rock is then used to form a breakwater around the work area for construction of a weight distributor block on the upper surface of the compacted layers.

The present invention is concerned with rockfill foundations and their construction methods.

In deep water work, for example at depths in excess of 300 feet, use of the air-floated caisson method for construction of bridge tower piers, and the like, presents insurmountable air pressure, caisson stability, and anchorage problems which, in the past, have precluded the operational range of this method for over-water construction.

Conventional methods of dumping rockfill have not been able to supplement the operational range of the airfloated caisson method or other known over-water con struction methods for deep water work. In particular, conventional methods of dumping rockfill do not eliminate the possibility of sudden and substantial settlement or consolidation due to earth tremors or under load. In waters subjected to tidal currents, and the like, it is not feasible to solidify rockfill with treme concrete or grout, or to drill large diameter holes through rockfill for addition of weight supporting concrete.

The present invention considerably extends the range of operations in deep and hazardous waters for bridge pier construction, and the like, while eliminating the possibility of foundation settlement or consolidation under load or the likelihood of settlement under severe and prolonged earthquake vibrations.

These and other objects of the invention will be evident from a description of specific uses of its teachings. The accompanying drawings will be referred to for this description. In these drawings:

FIGS. 1 through 6 illustrate stages in forming a rockfill island for a bridge tower, or the like, in accordance with the teachings of the invention,

FIG. 7 is a cross-sectional view illustrating use of the invention for bent and cable anchorage foundation,

FIG. 8 is a cross-sectional view illustrating use of the invention for bent and cable anchorage foundation, and

FIG. 9 is a schematic cross-sectional view showing use of the invention at various foundation locations in construction of a suspension bridge.

Prior to start of actual construction of a rockfill, boring logs of subsurface and subterranean profiles should be obtained in the general area of the rock foundation. These will determine depth and nature of overburden and the nature and placement of subterranean support. Preferably, the subterranean support should lend itself to establishing a substantially horizontal base within a practicable area of rockfill. If overburden is subject to compression, subsidence, or erosion, the overburden should be excavated from the area of the lower foundttion.

Also, a source of hard, sound, durable rock capable of producing large stones with a minimum of fines should be established. Igneous rock, preferably granitic rock, is representative of satisfactory rockfill foundation material for purposes of this invention.

Quarried rock, in relatively large stone sizes, is dumped in approximately horizontal layers, without any particular treatment, covering the general embankment area. This lower foundation should be dumped to within a prescribed range of water surface depending on end use of the foundation.

Individual horizontal layers of rock, of prescribed maximum depth, are laid centrally of thefoundation, with each layer being individually compacted before addition of another layer forming a compacted zone with a substantially horizontal upper surface.

A surcharge of rock is added by stockpiling rock centrally on the upper surface of the compacted zone. The surcharge of rock should be approximately equal to or greater than the expected load for the foundation. An ad vantage of this method, in addition to the safety factors involved, is that the foundation, if settlement or consolidation is tooccur, will occur as the surcharge is added so that practically no time lapse is required for settlement or consolidation. 7

The surcharge is then leveled or moved, with excess surcharge being spread laterally over the side of the foundation to establish a placement for constructing a Weight distribution block on the upper surface of the compacted zone.

Referring, in sequence, to FIGS. 1 through 6 which illustrate use of the teachings of the invention in forming a rock island in deep water for a bridge pier, and the like, a lower foundation 10 of large size stone is laid on subterranean support 12. The area of this foundation extends over a predetermined outline on the subterranean support determined in part by the outline of superstructure to be built on the foundation and angle of repose of the rock. Lower foundation 10 extends upwardly to approximately feet below water surface in this embodiment.

FIG. 2 illustrates a subsurface vibrator 14 supported by

barges

16 and 18 compating individual layers 20 added to lower foundation 10. These individual layers of rock do not ordinarily exceed 20-foot in depth and are compacted individually before the addition of other layers. The depth of individual layers to be compacted will be determined in part by the vibration equipment available and the depth at which the first layer can be compacted will be determined in part by the effectiveness of available vibration equipment at such depth. In the embodiment shown, five compacted layers are added to lower foundation 10 raising the rock island to within approximately fifty feet of water surface.

As shown partially in dotted lines at 24 in FIG. 3, rock is stockpiled centrally of the foundation to create a surcharge equal to or greater than the expected load for the foundation. In the embodiment shown, this surcharge extends substantially above water surface. Upon completion of the stockpiling, the surcharge is leveled to within approximately 15 feet above water surface. The surcharged rock is spread laterally as shown in FIG. 4, providing a broader 'base for excavation equipment.

As shown in FIG. 5, the centrally located portion of the surcharged rock pile is excavated and rock is placed outwardly of the excavation. This rock, in combination with the rock from leveling the surcharge forms dike 35 which acts as a breakwater for protection of the work area. Excavation extends downwardly to the upper surface of the compacted layers and covers an area sufiiciently large for work equipment to build a weight distribution block and pier structure. In the embodiment shown, excavation extends to approximately 50 feet below Water surface.

A distribution block or bridge pier is built on the upper surface of the compacted layers centrally of the foundation utilizing an open caisson or other means suitable for the shallow water conditions. After construction of pier 40, the lower edge of the pier, at the juncture between the pier and the compacted layer, is sealed with grouting compound 44.

Breakwater 35 can be maintained in location or can be moved over the side establishing sidewall layer 48 as shown in FIG. 6. Sidewall layer 48 adds to the sidewall strength of the foundation and removal of breakwater 355 permits navigation closer to pier 40.

The method described provides a presettlement and preconsolidation of the foundation. Spreading of the surcharge laterally achieves a wider island than needed with side sloping at the angle of repose of the rock. This provides added protection for the foundation compensating for any tendency of the slopes to become flatter as a result of wave action and earthquakes. If wave action reduces the diameter, the minimum diameter can be maintained by armoring the upper portions of the slopes. At such stage wave action should have established an underwater berm which would form a satisfactory base for founding armor stone.

The teachings of the invention are also applicable to establishing weight carrying rock embankments for shoreline construction as shown in FIGS. 7 and 8.

Referring to FIG. 7, lower foundation rock 50 extends from the shoreline out to an offshore position a sufiicient distance to provide lateral support and a horizontal area for compaction. Compacted zone 52 for cable anchorage 54 starts at the shoreline and extends offshore. Because of a leverage action of cable anchorage 54, a large portion of the load is directed downwardly on compacted zone 52. During formation of this foundation, surcharge or rock equal to or greater than the load is added to the compacted zone 54 and then moved laterally over the side of the compacted zone.

Compacted zone 56 provides support for bent 58. Weight distribution block 60 is cast on the upper surface of compacted zone 56 at about sea level. Compacted zone 56 is also surcharged before building the distribution block 60 and surcharge rock is moved laterally offshore to widen the embankment.

From the cross-sectional views of compacted zones 52 and 56 in FIG. 7, it will be seen that the area of compacted zone need not extend across the full surface of a foundation. In practice the cross-sectional areas and depths of the compacted zones are determined in large part by the configuration of the structure to be supported and its load. Compacted zones 52 and 56 are formed from individually compacted layers and the weight distributor means are sealed at the upper surface of the compacted zones as described earlier.

The height of compacted layers formed directly on subterranean support is determined largely by topography with remaining portions of the foundation providing lateral support. As shown in FIG. 8, compacted zone 62 for bent 64 and compacted zones 66 and 68 for cable anchorage 70 are compacted directly on subterranean support 72. Portions 74 and 76 of the rock foundation are laid without any particular treatment and provide lateral support and protection against wave action. Surcharging of compacted zones is applied as described earlier with surplus stone being used to widen the foundation.

FIG. 9 shows the profiles or rock foundations formed in accordance with the present invention.

Rock islands

80 and 82 support bridge towers 84 and 86 respectively. Rock foundation 88 supports cable anchorage 90 and bent 92. Rock formation 94 supports cable anchorage 96 and bent 98.

Various modifications in the specific embodiments described will be available to those skilled in the art in the light of this disclosure therefore, the scope of the present invention is to be determined from the appended claims.

What is claimed is:

1. Method for constructing a rockfill island for support of a bridge tower, or the like, comprising the steps of:

dumping hard durable rock in approximately horizontal layers over a predetermined lower foundation area and extending upwardly to Within a predetermined distance of water surface,

establishing a zone of compaction having an upper surface and of predetermined height and cross-sectional area by compacting a plurality of individual, limited-height substantially horizontal rock layers, with each individual rock layer being compacted before adding an additional layer,

dumping a surcharge of rock on the upper surface of the compacted zone, such surcharge of rock adding a weight to the foundation approximately equal to or greater than expected load to be carried by the foundation, and

removing at least a portion of the surcharged rock to establish a placement for weight distributor means on the upper surface of the compacted zone.

2. The method of claim 1 in which the compacted layers of rock are added to the lower foundation of hard durable rock raising the overall height of the foundation.

3. The method of claim 1 in which surcharged rock is removed by excavating centrally of the foundation to the upper surface of the compacted zone.

4. The method of claim 1 including the following steps carried out prior to dumping the hard durable rock over the predetermined lower foundation area,

making subsurface borings to determine subterranean support profile, and

excavating undesirable overburden from the foundation area.

5. The method of claim 3 in which the surcharge of rocks extends above water surface including a step prior to excavating centrally of the sugrcharge of:

leveling surcharge to within a prescribed distance of water surface with surplus surcharge being moved laterally.

6. The method of claim 3 including the step of:

placing excavate-d rocks contiguous to the excavation to form a rock dike which acts as a breakwater surrounding the excavation.

7. The method of claim 3 in which the excavation step is carried out through at least a portion of the surcharge rock to the upper surface of the compacted layers.

8. The method of claim 1 including the step of:

casting weight distributor means on the upper surface of the compacted layer.

9. The method of claim 8 in which the periphery of the weight distributor means at the upper surface of the compacted zone is sealed with a grouting compound.

10. The method of claim 6 in which the breakwater dike about the excavation area is removed to a predetermined depth below water surface but not below the upper surface of the compacted zone, such breakwater rock being moved laterally over the side of the foundation to increase the lateral area at the foundation in the horizontal plane of the upper surface of the compacted zone.

11. The method of claim 1 in which the lower foundation of hard durable rock is dumped to a height approximately feet below water surface.

12. The method of claim 11 in which a plurality of rock layers of approximately 20-foot depth each are compacted on the lower hard durable rock foundation with the height of the compacted layers extending to a height approximately 50 feet below water surface.

13. The method of claim 3 in which the centrally located excavation through surcharge rock extends approximately 50 feet below water surface.

14. Method of constructing a rockfill embankment for founding footings for bridge piers, bents, anchorages, and the like, comprising the steps of dumping hard durable rock over a predetermined lower foundation area,

establishing a zone of compaction having an upper surface and predetermined height and cross-sectional area by compacting a plurality of individual, limitedheight, substantially horizontal rock layers, with each individual rock layer being compacted before adding an additional rock layer,

dumping a surcharge of rock on the upper surface of the compacted zone, such surcharge of rock adding a load to the foundation approximately equal to or greater than the load to be carried by the foundation, and

15. Method of claim 1 in which peripheral portions of the weight distributor means at the upper surface of the compacted zone are sealed with a grouting compound.

16. The method of claim 1 in which the rock embankment extends offshore from a shoreline with the compacted zone extending from subterranean support to water surface and the remainder of the dumped level rock providing lateral support for the compacted zone.

References Cited UNITED STATES PATENTS 1,489,428 4/1924 Cushing 6l4 2,382,763 8/1945 Young 6146 2,939,290 6/1960 Crake 6146.5

JACOB SHAPI'RO, Primary Examiner US. Cl. X.R. 61--4, 50, 52