Please note that no new specifications have been added, only minor changes to improve the clarity of the ideas presented herein.
The standard method of constructing Cast In Drill Hole (CIDH) piles is as follows: Drill a hole in the ground based upon the projected load and the soil/rock capacity to support the load. If caving of the hole occurs, then install temporary casing or fill the hole with a heavier than water drilling fluid. Next lower into the hole a steel rebar or bars tied together to form a cage. Finally fill the hole with concrete and remove the temporary casing or allow for drilling fluid to be displaced by the placement of the heaver concrete.
The above method has several inherent weak points that are typically covered by making conservative design requirements. Caving of the surrounding soil/rock when the hole is open. The odds of this happening increases dramatically when the diameter is increased. There is also the disturbed zone around the perimeter of the hole. This is from the drilling action against the existing soil. This almost always results in a loss of strength at the critical interface between the soil and the concrete. The hole must be sufficiently larger than the rebar cage to ensure that the rebar will have a minimum cover of concrete to protect it from corrosion. There are also issues with the timing of the concrete placement. The inspection, casing removal, and concrete pour are all performed by different groups all working at the same time. Therefore, scheduling of each pile pour is critical. Once the concrete is mixed there is a definite time limit on its usefulness. In summery one pile requires the timing and close scheduling of several groups. Then if load testing is desired it must wait for the concrete to cure. Due to the high possibility of problems and the high cost of remedial repair these piles are typically constructed with a level of overdesign in the plans to ensure a minimum capacity pile.
Many of the above problems can be eliminated or minimized if the rebar is first covered with a minimum protective cover of concrete that has an undulating shape. The advantage to the undulating shape is that covered rebar will perform well when transferring load to or from lower strength material.
The attached figures listed here show how this will work:
The claim of this patent is if the order of the CIDH pile construction is changed the above listed problems can be eliminated or minimized. The basic idea is to cover the steel rebar with an undulating coating of concrete prior as shown in
The ground improvement and grouting industry have developed a large number of grouting materials. This includes what is known as “granddaddy grout”. That is a simple mixture of water and Portland cement and possibly fly ash to help it flow. The choice of grout and/or granular fill is not a subject of this patent application. The system proposed herein will work with a wide verity of grout and granular fill material. The choice of those materials for any given project would depend upon many factors such as desired load capacity, cost, and availability of materials.
It is helpful to look at the basic aspects of how a CIDH pile functions. The Youngs modulus of the steel is so large compared to the concrete, or the modulus of the soil that it carries all of the load initially. Moving down the pile the load is transferred to the concrete which ultimately transfers it to the soil. This compressive load transfer inside the concrete is primarily through the gravel portion of the concrete mix. This is why densification of wet concrete is so important. The individual gravels must be in contact with the adjacent gravel. Then at the foundation soil/concrete interface the load must be transferred from the outer surface of the concrete to the soil which has been disturbed by the drilling process.
Examination of the load transfer finds that the high strength of the concrete is only utilized at the steel rebar/concrete interface. As the load moves out away from the rebar it becomes spread out over a larger and larger area. Thus, the same load is carried by a larger volume of concrete. This results in lower and lower levels of stress per unit of concrete. The end result is that the majority of the concrete is underutilized, and its primary function is to be filler material.
For concrete the primary purpose of the sand and cement is to hold the gravel size rock in-place. Therefore, a similar product can be produced by first installing dense sand and gravel and then injecting a cementing or grouting agent under pressure. The primary limitation to this “out of order process” is the stress level at the rebar to concrete interface where load transfer 14 occures. The ribs on the rebar are intended to work with wet concrete forming around them. This can be overcome by pouring concrete around the rebar and allowing it to harden prior to installing the rebar in the pile hole. At this point in the process the key to successful load transfer is provided by the shape of the concrete. Tests to date indicate that if the concrete is molded in an undulating shape there is very good load transfer between the concrete and the dense sand and gravel material used to finish filling the hole.
It has become obvious that the majority of the concrete in a CIDH pile is underutilized. Once the load has been transferred from the steel to the concrete then a lower strength filler material such as dense sand and gravel that is grouted in place will suffice. Therefore, the grouting process results in a superior overall product because it improves the pile to soil contact. Given the variable nature of natural soil formations it is essential that all casing be removed prior to grouting. This is to ensure that the grout will encounter and improve all weak layers along the pile/soil interface.
Given the tendency for grout to travel out into the soil beyond the limit of the drilled hole the end result is a pile that functions like it is larger than the initial drill size of the hole. Thus, a small diameter pile could have the same capacity as a larger pile.
For a permanent stabilization project
Another use for the modified rebar 1 with its undulating concrete cover 2 is presented on
For the purpose of making a load transfer system it is not necessary to use concrete nodes on the rebar. Where the corrosion of the rebar is not a concern then the nodes could be fashioned by making spiral shaped rebar around the central load bearing steel.
This figure shows the basic design and operation of the modified rebar. This shows the undulating concrete molded 2 around two adjacent rebar 1. It should be noted that the modification claimed herein is not limited to concrete. Other variations are covered later in this submittal. What is claimed as that it is necessary for the covering to have an undulating shape. As shown, where more than one rebar 1 is required the undulating shapes 2 can be aligned out of phase to improve the connectivity. This configuration is also a way for two rebar 1 to be spliced together. The load 3 is delivered to the system through the rebar 1. Said load is then transferred from the rebar 1 to the molded concrete 2 by friction 14 along the ribs of the rebar 1. Load is then transferred out of the molded concrete 2 primarily across the sloping face 5 of the undulation. The sloping face 5 will transfer the load to the adjacent material. The adjacent material may be another concrete mold 2, gravel 6, sand 7, or solid grout 8. The load passes through several mediums to reach the edge of the boring 9. At that point like with all other cast in drill hole piles the load is transferred to the surrounding soil 10. Following the principal of physics, that the stiffest element carries the vast majority of the load. In this case that would be the densified gravel 6. The primary purpose of the sand 7 and solid grout 8 are to hold the gravel 6 in place. This is why the order of construction is important. First the saturated sand 7 and gravel 6 are vibrated into a dense configuration. Then the liquid grout 13 is injected to lock the dense sand 7 and gravel 6 into place. This is done by first injecting water into the filled boring through the pipe 11 and vibrating the sand 7 and gravel 6 into a dense configuration. This can be accomplished using a typical concrete vibrator 12. As the wet mix of sand 7 and gravel 6 become dense then the vibrator 12 is withdrawn. Depending upon site conditions pipe 11 could be used to withdraw, excess water from the boring. Once the sand 7 and gravel 6 are in a dense configuration the liquid grout 13 can be injected primarily to lock the sand 7 and gravel 6 into place. Because the boring is not lined or cased the grout 13 will seep out beyond the edge of the boring 9. This will improve the contact and load transfer at the interface between the edge of boring 9 and the surrounding soil 10. Once the liquid grout 13 has flowed to its limit it will solidify into solid grout 8. This completes the load transfer process from load 3 to the surrounding soil 10. As will be shown in additional figures it is possible to reverse this load transfer process from surrounding soil 10 that needs support. The weight of soil 10 can be transferred to rebar 1 which will carry it as load 3 to a depth where it can be transferred back to a soil 10 layer that can provide support.
This figure shows a completed pile that is subject to an external load 3. The grout pipes 11 are left behind after the piles has been completed. As shown the load is transferred from the rebar 1 to the node 2 along the ribs of the rebar 1. From there it passes through the material of the node 2 to the dense sand 7 and gravel 6, that is locked in place by the solid grout 8. This is shown by the arrows 4 where the sloping face 5 is placing a compression load of the dense sand 7 and gravel 6. The load then is delivered to the surrounding soil 10 which has been improved by the solid grout 8. Because the hole is unlined at the time that the liquid grout 13 is injected into the system it is free to flow into the weakest zones of the surrounding soil 10. This action of improving the weakest zones causes the overall strength of the surrounding soil 10 to be improved. As discussed above the weakest interface between a pile 17 and the supporting medium is at the edge of the pile 9. Leaving the pile unlined provides the greatest possibility that this interface will be improved.
This figure shows how these piles could be used to support a temporary excavation. By tying the piles together, a moment frame can be constructed. Unlike the pile presented in
This is a close up showing a moment frame 23 that ties two piles 17 together. The rebar 1 shown are threaded which also can function as bolts to help attach the moment frame 23 to the piles 17. The drawing also shows a cut away view of the pile 17. It should be noted that the piles 17 as shown are not complete or ready for service as the grouting is not complete.
This shows another use for this pile 17 system. Using multiple rows of piles 17 can result in the formation of a gravity retaining wall. At the present time gravity walls are built from the bottom of a temporary excavation using select compacted fill with horizontal ties. That method uses the solid mass of the reinforced fill to hold the remaining soil in-place. The method proposed herein claims that by using numerous small piles 17 that provide vertical support to the existing soil 10 the soil closest to a proposed cut or retaining wall will function the same as a gravity wall. Thus, the soil 10 closest to the cut or wall that typically requires support is now self-supporting. The piles 17 have turned the problem into the solution. Given that these piles are not large enough to be soldier piles they do need to be tied together to function as a unit. Given that the entire rebar 1 does not need to be covered with nodes 2 makes it possible to use the upper part of the rebar 1 to tie the piles 17 together. This system of tying the piles 17 together could be either a concrete slab or grade beams 24. The same slab or grade beam system 24 could also be used to help support the wall face 25 by tying the wall rebar 1 to the pile 17 rebar 1. With the soil 10 self-supporting the wall 25 only needs to provide erosion control. Also, the wall 25 needs to support the sand 7 fill above the back drain 26.
This shows an idealized section of a gravity wall created by installing piles 17 in close formation as discussed in
This shows the typical excavation and reinforced fill soil 29 for the construction of a gravity wall. The excavation removes the soil 10 to the back cut limit 28, which is very similar to the gravity wall boundary line 26 in
Given that the rebar 1 is modified by shaping nodes 2 around the rebar prior to its use allows for other uses.
This figure shows a continuous level soil 10 surface where a proposed excavation 34 is planned. To improve the stability of the proposed excavation 34 trenches 31 have been excavated perpendicular to the alignment of line 34. It should be noted that the alignment of the trenches 31 does not require them to be perpendicular to the proposed excavation 34. This depiction of the modified rebar 1, and the fill is in the process of backfill trenches 31. It should be noted that the modified rebar 1 can be laid in the partially filled trench 31 at an angle, if a horizontal alignment is not desired. Where needed piles 17 can be added to improve the stability of the backcut soil 10 that will remain after the excavation 34 is mad along the dashed line.
This figure shows the completed excavation supported by filled and grouted trenches 31 reinforced by rebar 1 covered by nodes 2. The soil 10 along the cut face line 34 is supported horizontally by the filled trenches 31 and vertically by the piles 17. For analyses purposes, the stability of a typical cut is a two-dimensional analysis. The advantage of this condition is the stability analysis is now a three-dimensional analysis with filled trenches 31 providing additional stability to the overall cut slope. For localized stability piles 17 can be added along the cut 34 between the trenches 31.
This presents a different method of creating a node 2 along a rebar 1. As shown the center rebar has been replaced with an injection pipe 11. Two or more small rebar 36 are bent to form a spiral around the center pipe 11. These smaller rebar 36 are attached to the pipe 11 by welding 37. In this embodiment the grout pipe 11 serves two purposes. First, it is the method of providing water or grout and with multiple injection holes 38 that can be closed off using a method known as a tube-a manchette system. Second the pipe 11 is sufficient to support axel load 3. The load 3 is transferred to the small bent rebar 36 through the weld 37. The spiral shape is filled with gravel 6 which extends beyond the spiral bent rebar 36. The gravel 6 is densified and locked into place by the solid grout 8 that was originally injected into pile 17 through the injection hole 38. Again, the slope of the bends in the small rebar 36 impart a portion of the original load 3 to the gravel 6 in the form of a compression load 4. The grouted 8 gravel 6 transmits the compression load 4 through the gravel 6 to the surrounding soil 10. The interface along edge of the drilled hole 9 is improved by the gravel 6 being densified and pushed into the surrounding soil 10. What is clamed herein is that all of the load transfer systems described in
This figure shows two rebars. On is a strait rebar 1 and the second is a smaller bent rebar 36. The purpose of this figure is to show how a node 2 can be made using standard rebars. The node 2 requires several of these bent rebars 36 attached to the strait rebar 1. If the attachment is done by welding then the strength of the strait rebar 1 may be reduced. However, analyses should be performed to determine how much load an individual node 2 would be transferred from rebar 1 to the soil 10.
This figure shows a group of small bent rebar 36 form a node 2 around the primary rebar 1. This system would have a node 2 filled with gravel 6 which are held in place by a screen. Similar to the previous node 2 systems described in
The rebar 36 transfers the load to both the gravel 6 inside the node 2 and the pile 17 gravel 6 fill. The load is disseminated through the gravel 6 to the soil 10. The load transfer is improved by the densified gravel 6 pressed into the soil 10 and possible grout 8 intrusion into the soil 10. What is clamed herein is that all of the load transfer systems described in
This Application claims the benefit of U.S. Provisional Application 63/204,672 Filed on Oct. 19, 2020 and U.S. Provisional Application 63/234,687 Filed on Aug. 18, 2021 which are hereby incorporated into this Patent Application.
Number | Date | Country | |
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63204672 | Oct 2020 | US |