METHOD OF HYBRID FOUNDATION USING THE SAME

FIELD OF INVENTION

The present invention relates to a hybrid foundation forming device, more specifically, the present invention relates to the hybrid foundation forming device to form the hybrid found by combining a friction pile with a foundation base simultaneously and integrally. Furthermore, the present invention relates to a construction mefood of hybrid foundation using this hybrid foundation forming device to form the hybrid foundation quickly while saving materials and construction time compared to the arts.

BACKGROUND ART

Foundation is a very important part of constructions. In fact, there are many methods of foundation reinforcement for civil constructions or even high-rise buildings. However, designers will give different methods of foundation reinforcement depending on the geology of each area to be built, the number of floors and the purpose of use of such construction.

For high-rise buildings or very large loads, it is required to use pile foundations such as concrete pile foundation, bored pile foundation, barrette pile foundation. However, it takes a long time and high costs to construct the piles, and moreover such construction causes many negative impacts on the environment and daily life of residents near the such construction. In addition, this mefood will give very poor performance on thick soft ground because the length of foe piles must increase even though the buildings are not high. In addition, the proportion of high-rise buildings or very large loads in Vietnam is not much. The current popular construction works in Vietnam as well as in Southeast Asian countries are civil constructions with the number of floors from 5 floors or less. For such constructions, a shallow foundation or additional bamboo piles, melaleuca piles, concrete piles, etc. are mainly used, which is sufficient to safe bearing capacity for the construction.

For a long time, it has been customary and practical to cast the shallow foundation in a good ground or reinforced ground at a depth of 1.5-2m. With such construction method, the volume of excavated soil is very large, the deep foundation pit is easy to landslides, so it is required for construction methods with high costs to protect walls of the foundation pit. After, clean the bottom of the foundation pit, install formwork, and arrangement reinforcement steels girder according to the design, cast the shallow foundation concrete at the bottom of the foundation pit so that the shallow foundation rises to the foundation base and up to the ground, let it dry and hard before removing the formwork. Then, backfill the soil and compact to avoid subsequent subsidence of the foundation, which is costly in labor and cost Until now, most of the shallow foundations of constructions are carried out according to this construction method and this is considered normal.

For civil constructions with more than 5 floors, it is common to choose the option of using strip foundation or raft foundation. However, the strip foundations and the raft foundations often have a relatively large self-weight of the foundation structure, so they cause a significantly loss of the bearing capacity of the entire shallow foundation, moreover, the horizontal slip resistance of this shallow foundation is not good.

Currently, there are many methods of reinforcing soft ground by using concrete funnel (top base) installed on soft ground to limit the depth and amount of excavated soil of the foundation pit.

Vietnamese patent for utility model No. 2-0000761 disclosed a method to reinforce the soft ground by casting concrete top bases at the soft ground to be reinforced by using the funnel-shaped casting molds made of recycled plastic. However, the casted concrete top bases by tins funnel-shaped casting mold has a limitation in that the length of pile part is limited, and this method is only applicable when the load is not much larger than the bearing capacity of the ground. Therefore, this method cannot be used in foundation for buildings with large loads or in thick soft ground.

Vietnamese patent for utility model No. 2-0002033 of the same Applicant disclosed a precast pot shaped concrete top base with a oast cylindrical core that can be separated from a conical part of the top base to form a pile part of the concrete top base. The concrete top base of this patent for utility solution includes the conical part with a rim and a reverse truncated cone, recesses symmetrically arranged on the cone surface of the conical part, and a cylindrical core with tapered lower end is arranged at the center axis of the conical part so that it can be pressed to slide along the axis of the conical part during the forming process of the pile part of the top base. The concrete top base has a flat bottom surface, can be easily transported, stands balanced on the ground without holding, the cylinder core is pressed down to form the pile part, and the interstice of the pressed cylinder core in the conical part will form wedges to fix the concrete top bases together when concreting to lock the surface without using steel hooks as prior arts. However, the concrete top base according to tins patent also has limitations in that it is difficult to transport and install, uncertain and unsafe for workers because the crane hook can only be hooked into the recess on the conical surface of foe conical part, in addition, the length of the pile part is limited because it is created only by foe cylindrical core inside the conical part In addition, because foe cylindrical core is created inside the conical part of the concrete top base, the ability to guide, locate and fix the cylinder core in the conical part is limited.

Vietnamese patent for invention No. 1-0028583 of the same Applicant disclosed a pot shaped concrete top base to reinforcing the soft ground; a cylindrical hole with two guide grooves are connected with the top surface with the bottom surface of the concrete top base. The conical end is formed at the lower end of the cylindrical hole, the precast concrete rod is driven through the cylindrical hole of the concrete top base to increase the load carrying capacity of the foundation. This concrete top base according to this patent can be easily transported, stands balanced on the ground, the length of the pile part can be adjusted by driving the precast concrete posts through the cylindrical hole of the concrete top base, helping increase the load carrying capacity of the foundation. The concrete top base of this patent has two guide grooves to guide, locate and fix the concrete rod to the concrete top base.

Although foundation base/concrete top base structures combined with friction piles have proven their effectiveness in working together to reinforce the soft ground in the mentioned above arts. However, the combination of foundation base and friction pile in the above arts are made from precast concrete top base and friction pile structures at the factory, and reinforced and connected at the construction site. This causes waste of time and labor costs, leading to an increase in construction costs.

SUMMARY OF INVENTION

Deriving from the existing problems of the above arts, the object of the present invention provides a hybrid foundation forming device to form the hybrid foundation by combining a friction pile with a foundation base simultaneously and integrally, to quickly and easily form hybrid foundation in place.

Another object of the present invention provides a construction method of hybrid foundation using the above hybrid foundation forming device to form hybrid foundation which combines the friction pile with the foundation base simultaneously and quickly while saving materials and construction time.

To achieve the above objects, the first aspect of the present invention provides the hybrid foundation forming device in the shape of a stepped cylinder, inchiding: a pile forming pillar is a long cylinder with small diameter; a foundation base pillar is a short cylinder with large diameter arranged at the upper end and concentric with the pile forming pillar, stiffener webs are radially arranged on the outer circumference surfece of the pile forming pillar to be fixed to the inner circumferential surface of the foundation base pillar; a stopper is loosely fitted and blocks the lower end of the pile forming pillar; and a connecting plate is fixed with stiffener webs to connect with the operating mechanism of the vibro-hammer, the press piling machine or the rotary drilling machine.

According to the present invention, the pile fanning pillar has a diameter of 20 cm or more, and a length of 1-20 m; the foundation base forming pillar has a diameter of 1-3 m and a length of 30-150 cm.

According to the present invention, the pile forming pillar including pipe portions which are threaded connected together.

According to the present invention, the stopper is made of concrete or metal material.

According to one embodiment of the present invention, the hybrid foundation forming device further includes a flaring conical hopper expanding from the outer circumferential surfece of the pile forming pillar to the circumference at the lower end of the foundation base forming pillar, with an inclination angle of the flaring conical hopper from 35-50°, in which there are holes with a diameter of more than 5 cm evenly distributed on the surfece of the flaring conical hopper, and the holes are radially arranged on the circumference of the pile forming pillar just below the flaring conical hopper.

According to the present invention, the holes formed on the surfece of the flaring conical hopper have an ascending diameter according to the inclination direction of the flaring conical hopper.

According to another embodiment of the present invention, the foundation base forming pillar of the hybrid foundation forming device further includes a bottom seal plate having an annulus shape with an inner diameter slightly larger than the outer diameter of the pile forming pillar, and an outside diameter slightly less than the inner diameter of the foundation base forming pillar so that the bottom seal plate is fitted in the interior of the foundation base forming pilar below tiie stiffener webs, in which the bottom seal plate is formed from at least two pieces.

According to the present invention, the bottom seal plate is cast by concrete or metal material and has a thickness of 5-10 cm.

According to the present invention, the stiffener webs are indented compared to the bottom surface of the foundation base forming pillar at a distance equal to the thickness of the bottom seal plate.

According to the presort invention, the foundation base forming pillar further including a stiffener ring formed on the inner circumferential surface at the lower end of the stiffener webs, In addition, connecting bars are arranged at the lower end of the stiffener webs to fix two adjacent stiffener webs to against the top of the bottom seal plate.

The second aspect of the present invention provides the construction method of hybrid foundation using the above hybrid foundation forming device to form the hybrid foundation which combines friction piles with foundation base integrally, the method comprises the following steps: step 1: pressing the hybrid foundation forming device to the designed position in ground by pressing and vibrating, or pressing, vibrating and rotating, so that the pile forming pillar is completely submerged, then stop; step 2 pouring concrete or filling material into the inside of the pile forming pillar and the foundation base forming pillar; step 3: continuously pressing the hybrid foundation forming device by pressing and vibrating, or pressing, vibrating and rotating to bring the entire pile forming pillar and the foundation base forming pillar submerged to the designed height; step 4: slowly pulling the hybrid foundation forming device by vibrating and rotating it so that the concrete or filling material flows out from the lower end of the pile forming pillar and the bottom surface of the foundation base forming pillar to fill up the formed foundation pit; and step 5: installing reinforcement steel for the foundation to connect with the pile structure, foundation base, upper strutting beams by driving each steel bar into the uncured concrete of the hybrid foundation.

According to the present invention, the construction method further including the step of wrapping geotextile fabric or polymer film around the flaring conical hopper, or placing a bottom seal plate on the lower end of the foundation base forming pillar before proceeding to step 2.

ADVANTAGEOUS EFFECTS

The hybrid foundation made by using a hybrid foundation forming device according to the present invention fully customizable in diameter and depth/height for both pile and foundation base, 100% mechanized construction.

The construction method is fast, the quality is stable and there is little disturbance to the surrounding environment because it's not required to excavate and transport soil in/out. In addition, because the excavation is not applied but press, vibrate and rotate the hybrid foundation forming device, so the soil part of the hybrid foundation that drifts around compacts the soil, thereby increasing the load capacity of the ground.

In addition, the hybrid foundation formed by the hybrid foundation forming device and process of the present invention can apply the calculation formulas for conventional shallow foundation with the following three advantages: (1) the soil is compacted, its mechanical properties are better than the original; (2) the weight of the foundation soil mass is not deducted from the bearing capacity of the foundation; and (3) there is no need to calculate the puncture for the foundation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully through a detailed description with reference to the following drawings wherein:

Fig. 1 is a perspective view of the hybrid foundation forming device according to the first embodiment of the present invention;

Fig. 2 is an exploded perspective view of the hybrid foundation forming device in Fig. 1;

Fig. 3 is a sectional view of the hybrid foundation forming device in Fig.2;

Fig. 4 is an exploded perspective view of a hybrid foundation forming device according to the second embodiment of the present invention;

Fig. 5 is the top view of the hybrid foundation forming device in Fig.4; and

Fig. 6 is a sectional view of the hybrid foundation forming device in Fig.4 in the assembled state.

DETAILED DESCRIPTION

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. This detailed description is intended only to demonstrate the general principles according to the present invention without limiting the protection scope of the present Invention.

According to the present invention, the inventor defines “hybrid foundation” as a single shallow foundation (isolated footing) that is reversed 180° to form a mushroom-shaped structure, so that the column of the isolated footing is downward feeing to form a friction pile, and the widely flared footing is right next to the ground.

The structure of the hybrid foundation according to the present invention has excellent performance over the traditional shallow foundation in terms of construction method and load capacity. Specifically, thanks to the mushroom- shaped structure of the hybrid foundation, the excavation volume is small (basically, it’s not required to excavate and transport the soil in/out but make the soil of the hybrid foundation drift around, compact the soil to increase the bearing capacity of the ground when using the hybrid foundation forming device according to the present invention), the existing foundation soil is taken advantage, the ground is compacted due to additionally filling the reinforced concrete volume of the friction pile and the foundation base, it’s not required to have means to keep the wall of the foundation pit in which there are often difficulties when it is raining or the groundwater appears, it takes time to fill the foundation pit and compact it like conventional shallow foundation, thereby the construction time of the hybrid foundation according to the convention is only 30%, and the cost is reduced by 50% compared to conventional shallow foundation. Moreover, the bearing capacity and moment of the hybrid foundation is increased by 1.5-2 times compared to the conventional shallow foundation due to taking advantage of the effects of the above widely flared footing and the friction of the below friction pile. With the hybrid foundation structure according to the present invention, it’s not requited to check the puncture for the foundation when designing.

Referring to Figs. 1 to 3, the hybrid foundation forming device according to the first embodiment of the present invention has the shape of a stepped cylinder, including: the pile forming pillar 10; the foundation base farming pillar 20 that is arranged at the upper end and concentric with the pile forming pillar 10 and connected together through the stiffener webs 40 that arranged radially; the stopper 30 is loosely fitted and blocks the lower end of the pile forming pillar 10; and connecting bar 50 is fixed with the stiffener webs 40 for connection to the operating mechanism of the vibro-hammer, the press piling machine or the rotary drilling machine.

The pile forming pillar 10 of the hybrid foundation forming device is a steel cylinder with a minimum thickness of 5 mm, a minimum diameter of 20 cm, and a length of 1-20 m, preferably, the diameter of 20 cm, 25 cm, 30 cm, 40 cm, 50 cm, the length of 3-8 m, most preferably, the diameter of 25 cm, 30 cm, 40 cm and the length of 5-15 m.

According to the preferred embodiment of the present invention, the pile forming pillar 10 including pipe portions that are installed in series and threaded connected together. Specifically, at the two ends of each pipe portion is formed a male thread (outer thread) and female thread (internal thread), respectively, so that these pipe portions are threaded together to form a pile forming pillar 10, thus its length can be customized according to the designed height of the work to be constructed.

The foundation base forming pillar 20 is a steel cylinder with a diameter of 1-3 m and a length of 30-150 cm, preferably, the diameter of 2 m and the length of 50 cm. As shown in Figs. 1 to 3, the foundation base forming pillar 20 further includes a flaring conical hopper 21 connects the outer circumference surface of the pile forming pillar 10 to the circumference at the lower end of the foundation base faming pillar 20 to form the bottom surface of the foundation base forming pillar 20. According to the present invention, the height of the flaring conical hopper of 0.5- 1.5 m, according to the preferred embodiment of the present invention, a inclination angle of the flaring conical hopper from 35-50°, preferably the inclination angle of 45°, there are holes 22 with a diameter greater than 5 cm, which are radially uniformly distributed on the surface of the flaring conical hopper to distribute the concrete and filling material in the interior of the foundation base forming pillar 20 into the created foundation pit by a hybrid foundation forming device of the present invention when the device is pulled up slowly from the ground. As shown in Figs. 1 and 2, according to the preferred embodiment of the present invention, the holes 22 have an ascending diameter according to the inclination direction of flaring conical hopper 21 from the pile forming pillar 10 to the rim of the foundation base forming pillar 20. This helps the concrete and the filling material inside the foundation base forming pillar 20 be distributed more evenly, In addition, the pile forming pillar 10 further includes the holes 11 which are radially arranged on the circumference just below the flaring conical hopper 21 to ensure that the concrete and the filling material inside the pile forming pillar 10 flow out so that the concrete fills up the connection gap between the foundation base and the friction pile of the hybrid foundation that formed by the device according to the present invention.

As shown in Figs. 2 and 3, according to the preferred embodiment of the present invention, eight stiffener webs 40 are radially interval arranged on the outer circumferential surface of the pile forming pillar 10 connects to the inner circumference surface of the foundation base forming pillar 20 and to fix and keep the foundation base forming pillar 20 concentric with the pile forming pillar 10 at its upper end. According to the present invention, the stiffener webs are made of steel with a thickness of 10-50 mm to ensure the rigidity of the device. On the two stiffener webs 40 opposition with each other, the holes 41 are formed to fix to the connecting bar 50 by bolts or weld.

The rectangular-shaped connecting bar 50 is cut with the notch 52 having a width greater than the diameter of the pile forming pillar 10, and the holes 51 are formed on two sides near notch 52 corresponding to the positions of the holes 41 on the stiffener webs 40, bolts (not shown in the figures) are mounted throughout to fix the connecting bar 50 to the stiffener webs 40. The connecting bar 50 will be clamped by the operating mechanism of the vibro-hammer, the press piling machine or the rotary drilling machine during construction

The stoppar 30 is made of concrete in shape of a stepped cylinder, with a sphere frustum or conical lower end, and a cylindrical upper aid having a diameter smaller than the inner diameter of the pile forming pillar 10 for loosely mounting and blocking the lower end of the pile fonning pillar 10 so that the stopper 30 will keep at the botto of the foundation pit when the hybrid foundation forming device is pulled up. According to another embodiment of the present invention, the stepper can be a flat plate or a cylindrical such that it is loosely fitted to the lower end of the pile forming pillar 10. However, the present invention is not limited to shape and material of the stopper 30, the stopper 30 can be made of steel, etc.

Referring to Figs. 4 to 6, the hybrid foundation fonning device according to the second embodiment of the present invention has the shape of a stepped cylinder similar to the one according to the first embodiment of the present invention except that it does not have the flaring conical hopper, therefore similar details will not be repeatedly described here in order to avoid obfuscation of the present invention.

The hybrid foundation forming device according to the second embodiment of the present invention including: the pile forming pillar 10; the foundation base forming pillar 20 is arranged at the upper end and concentric with the pile forming pillar 10 and connected together through the stiffener webs 40 that radially arranged; the stopper 30 is loosely fitted and blocks the lower end of the pile forming pillar 10; and the connecting bar 50 is fixed to the stiffener webs 40 for connection to the operating mechanism of the vibro-hammer, the press piling machine or the rotary drilling machine.

As shown in Fig. 4, the hybrid foundation fonning device further includes the bottom seal plate 60 having an annulus shape with an inner diameter slightly larger than the outer diameter of the pile forming pillar 10, and the outer diameter is slightly smaller than the inner diameter of the foundation base forming pillar 20 so that the bottom seal plate 60 can be easily disassembled from the interior of the foundation base forming pillar 20 and retained at the foundation pit when the device is gradually pulled up. The bottom seal plate 60 is installed inside the foundation base forming pillar 20 below the stiffener webs 40 to prevent concrete and the filling material inside the foundation base forming pillar 20 from flowing out and prevent the soil below the foundation base forming pillar from entering into the inside of the foundation base forming pillar 20 while the device is pressed into the ground to form the foundation pit. As a result, the soil below the foundation base farming pillar will be pressed down.

According to foe embodiment of the present invention, the bottom seal plate 60 is cast of concrete with a thickness of 5-10 cm, and assembled from four pieces to reduce weight during transportation and to be easily fixed with the bottom of the foundation base forming pillar 20 when operating the device. However, the present invention is not limited to the material and number of pieces forming the bottom seal plate, thereby the bottom seal plate 60 may be made of steel and may be made from 2, 3, 4, or 6 pieces.

To facilitate the positioning and support of the bottom seal plate 60 when mounted inside the foundation base forming pillar 20, as shown in Figs. 5 and 6, the stiffener webs 40 are indented compared to the bottom surface of the foundation base forming pillar 20 with a distance equal to the thickness of the bottom seal plate 60, so that the upper surface of the bottom seal plate 60 against on the lower edge of the stiffener webs 40. In addition, the inner circumferential surface at the bottom of the foundation base forming pillar 20 is provided with the stiffening ring 42 having the lower surface located on the same plane as the lower edge of the stiffener webs 40. The connecting bars 43 fix two adjacent stiffener webs 40 to the stiffening ring 42 to against on the upper surface of the bottom seal plate 60.

The present invention also provides a construction method of hybrid foundation using the above-mentioned hybrid foundation forming device, the method comprising the following steps: step 1: pressing the hybrid foundation fonning device to the designed position in ground by pressing and vibrating, or pressing, vibrating and rotating, so that the pile forming pillar 10 is completely submerged, then stop; step 2: pouring concrete or filling material into the interior of the pile forming pillar 10 and the foundation base forming pillar 20; step 3: continuously pressing foe hybrid foundation forming device by pressing and vibrating, or pressing, vibrating and rotating to bring the entire pile forming pillar 10 and the foundation base forming pillar 20 submerged to the designed height; step 4: slowly pulling the hybrid foundation forming device by vibrating and rotating it so that the concrete or filling material flows out from the lower end of the pile forming pillar 10 and the bottom surface of the foundation base forming pillar 20 to fill up the formed foundation pit; and step 5: installing reinforcement steel for the foundation to connect with the pile structure, the foundation base, the upper strutting beams by driving each steel bar into the uncured concrete of the hybrid foundation.

According to the present invention, when using a hybrid foundation forming devi ce in accordance with the first embodiment of the present invention, the construction method further includes a step of wrapping the geotextile or polymer film around the flaring conical hopper 21 and the end of the pile forming pillar 10 before performing step 2. This is to ensure that the holes 11 of the pile forming pillar 10 and the holes 22 of the flaring conical hopper 21 are sealed to prevent soil from blocking these holes during the process when the device is pressed down into the ground.

According to the present invention, when using a hybrid foundation forming device in accordance with the second embodiment of the present invention, the construction method further includes fitting foe bottom seal plate 60 on the lower end of the foundation base forming pillar 20 before performing step 2 to prevent soil from entering into the interior of the foundation base forming pillar while the device is pressed into the ground.

According to the present invention, in the process of pressing the hybrid foundation forming device by vibrating and pressing, or vibrating, pressing and rotating to bring the entire pile forming pillar 10 and the foundation base forming pillar 20 submerged to the designed height, concrete or filling material inside the foundation base pillar 20 will press in a way to prevent the soil below the bottom of the foundation base forming pillar 20 from tearing the geotextile/polymer film or breaking the bottom seal plate 60 to enter into the interior of the foundation base forming pillar 20, This helps foundation base 20 to press down the soil below its bottom surface, increase the consolidation and compaction of the underlying ground.

According to the present invention, when gradually pulling up the hybrid foundation forming device by both vibrating and rotating, under the pressure of concrete or filing material inside the pile forming pillar 10 and the foundation base forming pillar 20, the stopper 30, the bottom seal plate 60 or the geotextile/polymer film will be retained at the bottom of the formed foundation pit by the device, st the same time the concrete or filling material flows out from the lower end of the pile forming pillar 10 and from the bottom surface of the foundation base forming pillar 20 or flows through the holes 11 and 22 to fill up the foundation pit and gradually formahybrid foundation according to the upward movement of the device. According to the present invention, when the concrete block of the hybrid foundation formed by the device still uncured, the steel bars are driven into the friction pile and foundation base of this hybrid foundation to strengthen the connection between the Motion pile and the foundation base, and form reinforcement steel for the foundation to connect with the pile structure, the foundation base and the strutting beams above the foundation base.

According to another preferred embodiment of the present invention, firstly wrapping the geotextile or plastic film around the flaring conical hopper 21 and the top of the pile forming pillar 10; then pouring concrete or filling material into the inside of the pile forming pillar pile 10 and the foundation base forming pillar 20; next pressing the hybrid foundation forming device in place by pressing and vibrating, or pressing, vibrating and rotating to the designed height; then slowly pulling the hybrid foundation forming device by vibrating and rotating it so that the concrete or filling material flows out from the lower end of the pile forming pillar 10 and the bottom surface of the foundation base forming pillar 20 to fill up the formed foundation pit the foundation pit has just been created; and finally installing reinforcement steel for the foundation to connect with the foundation base, the upper strutting beams by driving each steel bar into the uncured concrete of the hybrid foundation.

Although the present invention has been disclosed through the preferred embodiment and accompanying drawings, the present invention is not limited therein, A person skilled in the art must understand that many modifications and combinations can be made without departing from the scope of the present invention. Therefore, modifications, equivalents and other embodiments that may be included within the spirit and scope of the present invention as defined by the appended claims.