A cast-in-place pile and the process for manufacturing of the same

Abstract

 A method for forming non-cylindrical drilled concrete piles, the cast-in-place concrete piles having non-cylindrical cross section as well as in the production of conventional piles but with better economic results.

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relate to a cast-in-place pile and the construction process for manufacturing of the cast-in-place pile.

TECHNICAL BACKGROUND

[0002] In the field of foundation engineering practice, a construction work where concrete piling is required it is the conventional practice to drill holes on the ground to the proper depth with earth auger so the cylindrical cast-in-place concrete piles can be produced. For friction piles and friction-end-bearing piles with the frictional force as the main bearing force, it is necessary to enhance the bearing capacity of a single pile by lengthening the length of the pile and/or by enlarging the pile diameter. The length of the pile is determined by the depth of sustaining layer of the ground. As the pile diameter being enlarged, the periphery surface will increase in linear relation with respect to diameter, while the volume will increase in square relationship accordingly. It is evident that to enlarge the pile diameter to increase the skin-frictional force of the pile at the cost of more concrete material would be irrational.

OBJECTIVES OF THE INVENTION

[0003] One of the objectives of the invention is to provide the new type of cast-in-place piles which will efficiently increase the bearing capacity of a single pile without increasing materials to obtain better economic results.

[0004] Another objective of the invention is to provide a new type of cast-in-place pile group which is formed by the rigid connection of the cast-in-place piles of the invention with pre-embedded parts to form the diaphragm wall.

[0005] The third objective of the invention is to provide a construction process for manufacturing the above mentioned cast-in-place piles.

SUMMARY OF THE INVENTION

[0006] This invention provides a new type of cast-in-place concrete pile constructed by grouting concrete into the borehole, the cross section profile of said borehole being composed of two or more connected arcs.

[0007] This invention also provides a construction method for the cast-in-place pile comprising the following process:

1)Drilling, to drill a borehole with its cross section profile composed of more than two connected arcs, to the designed depth;

2)Grouting concrete and lifting auger upward until the surface of the filling concrete reaches the cave-in position or above the underground water level;

3)Lowing the reinforcing cage;

4)Pouring aggregate and supplementary concrete;

5)Recharging cement mortar followed by vibro-tamping, and recharging as required to compensate the shrinkage of the pile.

[0008] The drilling rig is also a rotary drilling type, but the borehole has a noncylindrical profile composed of circular curves . Each section of the curves is circular due to rotary drilling, however the borehole possesses non-cyclindrical profile, which is formed by intersection of two or more circular holes. The following shapes of borehole are ideal ones:

[0009] Borehole of flower shape, which is formed by a central hole intersected by three or four outer smaller holes;

[0010] Boreholes arranged in a row, which is formed by two or more circular holes side by side along a straight line and the said holes are intersected with the neighbor.

[0011] Filled with concrete in above-said holes, the flower-shape-piles or the row-piles may be formed. The rigid connection of row-piles with pre-embedded parts will form rowed pile group into a diaphragm wall.

DESCRIPTION OF THE DRAWINGS

[0012] The description refers to the accompanying drawing in which like reference characters refer to like parts throughout the several views and in which:

FIG. 1 shows schematically the cast-in-place flower-shape-pile;

FIG. 2 shows schematically cast-in-place row-pile;

FIG. 3 shows schematically a conventional continuous underground wall/diaphragm wall;

FIG. 4 shows schematically the conventional soldier pile/bulkhead pile;

FIG. 5 shows schematically the diaphragm wall comprising the row-piles with rigid connection;

FIG. 6 shows a plan view in a deep foundation pit supported by the cast-in-place row-piles connected together;

FIG. 7 shows a side view of the row-pile support similar to that in FIG. 6;

FIG. 8 is the schematic drawing showing the pile formation process.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] Referring to the drawings, FIG. 1 and FIG. 2 show the flower-shape-pile and row-pile respectively. For simplicity, we adopt the logo S.P. and express their dimensions in the form as S.P.Dc-nxDs/L, where D_c and D_s represent the diameters ( in mm) of the central hole and the side/outer holes respectively, L is the length of the pile ( in m ), n is the number of the side/outer holes to distinguish the type of the non-cylindrical cast-in-place piles, for row-pile n = 2; for flower-shape-pile n = 3 ( basic ) or n = 4 ( optional ).

[0014] With minor modification on the drill rack, the conventional multi-shaft long auger drilling rig can be used for drilling non-cylindrical boreholes. For the flower-shape borehole, the rig has four augers, four shafts, and the central ones are greater than outers.

[0015] Typical procedure to form cast-in-place concrete pile is illustrated in FIG. 8, where: 17 shows the drilling process; 18 shows the grouting process after stopping of drilling footage, 23 is grouted concrete/cement, 24 is the belled pier formed by diffusion under high grouting pressure, like 4 in FIG. 1 as well; 19 shows the process of lowering the reinforcing cage 25 into the borehole, to lower the cage either by vibrating it or by loading a drive-in force on it depending on concrete conditions; 20 shows the process of pouring aggregate 26 after the reinforcing cage being set well, or pouring supplementary concrete as required; 21 shows the recharging process, cement mortar passing through the refilling tube 27 to compensate the shrinkage of the pile; 22 illustrates the vibro-tamping process with a vibrator 28, and refilling should be repeated.

[0016] For short reinforcing cage , say, about 10 meters concrete can be pumped into the borehole during the grouting process then the cage being set by vibration. As the length of cage increasing, the concrete should be finer to reduce the difficulty to lower down the cage, the concrete composes fine gravels instead of coarse aggregate. The longer the cage employed, the finer the concrete preferred, for cage longer than 20 meters, cement mortar would be the choice, and aggregate pouring process then followed.

[0017] The industrial application of this invention is possible because the related equipment and techniques have been proved to be applicable. Being a new approach in foundation engineering this invention is suitable for industrial and residential construction in areas with complicated or special geological conditions. It has many advantages: rapidity, high efficiency, good quality, safety and lower cost in operation, and in favor of the environment protection as well. For instance, the flower-shape-pile, with the same bearing capacity, can decrease the material consumption by more than 50%, compared with that in the cylindrical or rectangular piles. Moreover, when they are constructed as pile groups, the group-pile effect of the piles of this invention is lesser than that of the piles with simple cylindrical profile. Whether it is used as a foundation pile ( carrying the vertical load, resisting to lifting, or carrying the alternating load ) or as a diaphragm wall pile, it would not be inferior to other types. The rigid structure of well-connected row-piles can be designed as a substitute for the expensive and time-consuming continuous underground wall/diaphragm wall with same effectiveness in resisting soil pressure and barring water. When the row-piles are employed as a support for deep foundation pit, the construction of temporary support bodies can be obsolete, it would remarkably save both materials and working time by combining the piles and wall together as one integrated structure. The process of hole-boring and concrete grouting are carrying out consecutively without intermission, the successive processes as lowering the reinforcing cage, pouring aggregate, recharging cement followed up, so the whole procedure would be completed as in one operation. Besides, all types of the non-cylindrical cast-in-place piles are constructed in dry working environment without any alkaline mud or other pollutants left.

[0018] Comparing with the current technology, the cast-in-place pile of this invention has the following advantages:
1. Comparison between the flower-shape-pile of this invention and the cylindrical pile
Take an ordinary cylindrical pile with diameter 800 mm to compare with a flower-shape-pile with nearly same lateral surface area, the S.P. 400-3x300 of the same length. Referring to FIG. 1, 1 shows the cross section of the flower-shape-pile, 2 shows the referring cross section of a cylindrical pile with 800 mm diameter

Pile Type	Specific Lateral Area (sq. m )	Specific Volume (cu. m )	Area Ratio	Volume Ratio
Cylindrical, 800	2.513	0.503	0.89	2.13
S.P. 400-3x300	2.827	0.236	1.00	1.00

Above comparison shows that with the same length, when the periphery frictional area of a cylindrical pile is only 89 % of that of the flower-shape-pile, but its volume ( concrete consumption ) is 2.13 times of that of the flower-shape-pile. It means that the bearing capacity can be improved about 10 % while the material consumption can be dropped drastically.
2. Comparison between the row-pile of this invention and the conventional diaphragm wall
In foundation engineering practice, before construction of an underground diaphragm wall of a deep pit, temporary support must be set up to resist the horizontal pressure from the back soil and water. A huge amount of construction work and complicated technique are required. Referring to the drawings . FIG. 3 illustrates a conventional continuous underground wall body 8 with its pilot wall 9 ; FIG. 4 illustrates a temporary support consisted of conventional soldier pile of lined up bulkhead piles 10 and water-tight plain concrete piles 11. Apparently, the construction speed is low and cost high. By using the method of this invention to construct diaphragm wall with row-piles, the serious problem can be easily solved, referring to FIG. 5, FIG. 6, and FIG. 7. A typical procedure of the construction of the diaphragm wall may be briefed as:

1 ) Drilling the boreholes of the row-piles, one by one along the center line of diaphragm wall, then grouting concrete, lowering the reinforcing cage with the built-in pre-embedded parts 7 ( FIG. 2 ) into the borehole, and proceeding other processes as FIG. 8 shows, the complete set of row-piles then is built up;

2 ) Drilling and pouring concrete to form the water-tight plain concrete piles 11;

3 ) As the concrete cured for several days, excavating the soil in the pit layer by layer from the ground surface until the first row of the pre-embedded parts has been fully exposed, then welding the rigid connection parts 12 ( FIG. 5 );

4 ) Like steps going on, until all rigid connections are made;

5 ) On the rim of the pit making the locking beam 13 and the ground anchors 14 (FIG. 6 ) as required ( only on the rim of the pit, at the middle span ).

[0019] The adoption of the row-piles provided by this invention does not need any temporary structure, neither bracings nor web-beams, simplified the technique, effectively reduced the labor , time, and cost. In addition, the safety in construction can be better guaranteed. In its specific aspects the diaphragm wall developed from the row-pile, the pile-and-wall integrate design in foundation engineering, an advanced concept, can be realized with tremendous economic gains. Another implicit superiority to the conventional cylindrical pile is making fully use of steel materials. In a cylindrical pile, the main reinforcements should be evenly distributed along the circumference to prevent steel cage from twisting, a large amount of the steel bars close to the neutral zone of the pile for bending resistance, failing to play their role. While the row-piles are not circular in cross section, the steel cage could not twist in the borehole, so the main reinforcements can be reasonably distributed in the force-bearing surfaces and be fully used. Almost about one-third of steel could be saved ( compared with cylindrical piles ).

Claims

1. A cast-in-place pile constructed by grouting concrete into the borehole, the cross section profile of said borehole being composed of two or more connected arcs.

2. A cast-in-place pile as described in claim 1 with the feature that the arcs forming the cross section profile of said borehole are circular arcs.

3. The cast-in-place pile as described in claim 2 with the feature that the said borehole is formed by the intersection of two or more circular boreholes.

4. The cast-in-place pile as described in claim 3 with the feature that the said borehole therein is composed of a central borehole intersected by other three or more holes.

5. The cast-in-place pile as described in claim 3 with the feature that the said borehole therein is composed of two or more cylindrical boreholes arranged side by side with their centers on one straight line and the adjacent two boreholes intersected with each other.

6. The cast-in-place pile as described in claim 5 with the feature that the piles are connected with pre-embedded steel parts and rigid connectors.

7. A construction method for the cast-in-place pile comprising the following process:

1 ) Drilling, to drill a borehole with its cross section profile composed of more than two connected arcs, to the designed depth;

2 ) Grouting concrete and lifting auger upward until the surface of the filling concrete reaches the cave-in position or above the underground water level ;

3 ) Lowing the reinforcing cage ;

4 ) Pouring aggregate and supplementary concrete;

5 ) Recharging cement mortar followed by vibro-tamping, and recharging as required to compensate the shrinkage of the pile .

8. The construction method for the cast-in-place piles as described in claim 7 with the feature that the arcs forming the above said cross section profile of the boreholes are circular arcs.

9. The construction method for the cast-in-place piles as described in claim 8 with the feature that the borehole therein is composed of two or more intersected cylindrical boreholes.

10. The construction method for the cast-in-place piles as described in claim 8 with the feature that the above mentioned borehole is composed of a central borehole intersected by two or more other boreholes.

11. The construction method for the cast-in-place piles as described in claim 8 featured in that the above mentioned borehole is composed of two or more cylindrical boreholes arranged side by side with the centers of the boreholes on one straight line and the adjacent two boreholes intersected with each other .

Drawing