JP5658988B2 - Soil cement steel pipe composite pile and its construction method - Google Patents

Description

  The present invention relates to a construction method of a soil cement steel pipe composite pile and a construction method thereof. More specifically, the present invention relates to an improvement in a technique for constructing a composite pile by burying the pile in a soil cement column built in a drilling hole.

  Conventionally, a method of embedding a steel pipe or the like as a reinforcing member in a column (column body) in the ground constructed by ground improvement to make a pile body (composite pile) has been used. For this method, for example, the ground and solidified material such as cement milk are agitated to form soil cement to a predetermined depth in the excavation hole, and before the soil cement solidifies, a pile with spiral blades (extended blades) is rotated. Techniques for constructing soil cement composite piles (synthetic piles) by burying them while making them have been proposed (see, for example, Patent Documents 1 and 2).

JP 2001-317050 A JP 2001-140251 A

  However, in the conventional method as described above, since the ground and solidified material such as cement milk are agitated, depending on the properties of the excavated ground, the excavation performance is significantly lowered, so that the high quality necessary for developing a large bearing capacity is required. The support layer cannot be sufficiently embedded, and the support performance of the pile body cannot be fully expressed.

  Then, an object of this invention is to provide the soil cement steel pipe composite pile which can improve the support performance of the pile body in excavation ground, and its construction method.

  In order to solve this problem, the present inventor has made various studies. In the conventional soil cement method, if the ground can be improved by excavating a relatively hard layer (solid layer), the support performance of the pile body is expected to be improved. However, conventional ground improvement is generally performed by excavating and stirring with a construction jig having a co-rotation prevention blade, and there is a possibility that sufficient stirring cannot be performed in a hard ground.

  Conventionally, the resistance at the time of excavation is a shape characteristic of the excavation jig (for example, a characteristic that a plurality of stirring blades necessary for sufficiently stirring the solid and solidified material such as cement milk are attached) Therefore, it is generally large. For this reason, even if a relatively hard formation is excavated by the conventional construction method, there is a problem that the correlation between the rotational torque and the strength of the ground is low and the variation is large, so that it cannot be handled as a construction management index. In other words, if the hardness of the ground exceeds a certain level, it becomes difficult to distinguish the layer and it can not be used as a management index for the tip support layer, so it is possible to stop drilling before reaching the hard ground, or conversely Even if the ground reaching the predetermined strength is reached, it may not be grasped and excavation may continue.

  Furthermore, when embedding bladed steel pipe piles in a solid formation, the relationship between the rotation speed of steel pipe piles and the penetration speed (burial speed) may change. There is also a problem that the column is disturbed, the surrounding ground is involved, and a space is created.

  Based on these points, the present inventor, who has made further studies focusing on the problems of conventional construction methods, has obtained new knowledge that leads to the solution of such problems. The present invention is based on such knowledge, excavating the ground to be constructed of the composite pile with a drilling rod, injecting cement milk into the drilling hole to build a soil cement column, pulling the drilling rod from the drilling hole, A steel pipe pile with a pressure receiving part that increases the resistance force of the pile at least at the tip of the pile and an adhesion enhancing part for increasing the frictional resistance force with the surroundings is buried in the soil cement column. Then, the pressure receiving portion at the tip of the pile is penetrated from the bottom of the soil cement column, and at least the pressure receiving portion is embedded in a deeper and more solid formation than the formation in which the excavation hole is excavated.

  In such a construction method, a deeper and harder stratum than the stratum to be excavated can function as a support layer that supports the tip of the steel pipe pile via the pressure receiving portion. In addition, as in the conventional construction method, the soil cement and the steel pipe pile can be integrated to achieve a large frictional force. Therefore, the support performance of the pile body (soil cement steel pipe composite pile) in the excavated ground can be improved.

  Moreover, this construction method does not improve the ground of a solid stratum. For this reason, it is unrelated to the problem that sufficient agitation cannot be performed in a solid formation, and since it is not necessary to improve the solid formation in this way, construction is easy and efficient.

  Also, in this construction method, soil cement columns are not constructed in a hard formation, and therefore steel pipe piles are not buried in excavation holes formed in the solid formation. It is possible to handle a high correlation with strength as a construction management index. In other words, the soil cement column is built only in the stratum above the solid strata, and the steel pipe piles are buried only in the hard ground (solid stratum), so the rotational torque and the strength of the ground (including the drilling holes) are buried. Since it is possible to maintain a high correlation with the ground, it is possible to determine a hard ground by using a torque change at the time of embedding (penetration). According to this, it can grasp | ascertain quickly that the front-end | tip of the steel pipe pile penetrated reached | attained the hard ground (solid formation) used as a support layer.

  In such a construction method, as the excavating rod, the discharge port for discharging the ground improvement material such as cement milk is below the lowermost stirring blade, and at least below the lowermost stirring blade, the steel pipe pile It is preferable to use one having a portion larger than the cylindrical diameter. When the excavation rod is pulled out from the excavation hole, a cement columnar part having a diameter larger than that of the steel pipe pile is formed, and the steel pipe pile can be rotationally embedded in the cement columnar part.

  Moreover, in this construction method, when extracting a drilling rod from a drilling hole, it is preferable to pull out while discharging cement milk from a drilling rod. By forming a cement pillar with a diameter larger than that of the steel pipe pile in the excavation hole and embedding the steel pipe pile in the cement pillar, the cement not mixed with the soil part is brought into contact with the surface of the steel pipe pile and solidified. It is possible to construct soil cement steel pipe composite piles that are more firmly integrated.

  Furthermore, it is preferable to embed the steel pipe pile while keeping the rotation speed and the penetration speed constant. When rotating and embedding steel pipe piles, if the rotation speed and penetration speed are not constant, the soil cement may be stirred and rolled up by the adhesion enhancing part such as spiral blades. According to the present invention in which construction is performed while maintaining the speed to be constant, it is possible to avoid the soil cement from being stirred and wound up.

  In addition, the soil cement steel pipe composite pile according to the present invention is a soil cement that is injected and built in a drilling hole excavated in the ground to be constructed of the composite pile, and embedded in the soil cement, and the resistance of the pile tip The pressure receiving part that increases the penetration of the soil cement penetrates the soil cement, and in the soil cement there is an adhesion strengthening part around the pile shaft that enhances the adhesion with the soil cement. It is composed of steel pipe piles in which at least the pressure receiving part is embedded in the formation.

  ADVANTAGE OF THE INVENTION According to this invention, the support performance of the pile body in excavation ground can be improved.

It shows the procedure of construction method of composite piles. (A) Pile core alignment by pile driver, (B) Soil cement column construction by mixing and mixing cement milk and ground, (C) Construction completion of soil cement column , (D) Steel pipe pile erection, (E) Steel pipe pile pile alignment, verticality confirmation, (F) Steel pipe pile rotary embedding in soil cement column, (G) Steel pipe pile pile head level It is a figure showing each process of confirmation. 1 shows one embodiment of the present invention, (A) excavation by excavation rod, (B) extraction of excavation rod while discharging cement milk, (C) erection of steel pipe pile, (D) to solid formation It is a figure showing each process of embedding the steel pipe pile tip with an example of the ground including a solid layer in the deep layer.

  Hereinafter, the configuration of the present invention will be described in detail based on an example of an embodiment shown in the drawings.

  1 and 2 show an embodiment of a soil cement steel pipe composite pile and its construction method according to the present invention. Below, the general construction method of a soil cement steel pipe composite pile (SC pile (steel pipe concrete composite pile)) is demonstrated first (refer FIG. 1), and the characteristic part of this invention is demonstrated after that (refer FIG. 2). .

  The pile driving machine 10 has a leader 12, an auger 13, a steady rest device 14, and the like, excavates the ground G, and rotates and embeds a pile (for example, a steel pipe pile 5) while standing in the excavation hole 4. (See FIG. 1).

  The auger (pile rotating device) 13 is provided so as to be movable along the leader 12 standing upright in the vertical direction, and moves up and down along the longitudinal direction of the leader 12 (see FIG. 1). The steel pipe pile 5 is connected to the auger 13 directly or via a yatco (not shown), and the steel pipe pile 5 is also rotated and penetrated into the ground G when the auger 13 is driven to rotate. In this embodiment, the steel pipe pile 5 in which the spiral blade 5b for penetration is provided at least at the tip is used. By rotating the steel pipe pile 5 in this way, the steel blade pile 5b is generated into the ground. The steel pipe pile 5 is penetrated into the excavation hole 4 using a propulsive force. When the steel pipe pile 10 penetrates the ground G, the auger 3 also descends along the leader 2.

  Moreover, in FIG. 1, the code | symbol 3 is an excavation rod for excavating the excavation hole 4 which is rotationally driven by the auger 13 and in which the steel pipe pile 5 is embed | buried. The excavation rod 3 has a hollow structure and also serves as a pipe for passing a liquid or the like. Further, a nozzle (not shown) that ejects cement milk (an example of a ground improvement material) when the excavation rod 3 performs prior excavation is provided at the distal end portion 3a of the excavation rod 3. Further, a drilling bit 3b for drilling the ground G and stirring and mixing the cement milk and the ground is provided on the base end side of the distal end portion 3a of the drilling rod 3. As will be described in detail later, in the present embodiment, the excavation rod 3 having at least a tip portion 3 a larger than the cylinder diameter of the steel pipe pile 5 is used.

  Here, a series of operations until the ground G is excavated using the excavation rod 3 and the steel pipe pile 5 is buried in the excavation hole 4 will be described in order (see FIG. 1).

  First, when the pile core position of the pile driving machine 10 is aligned with a predetermined position of the ground G to be constructed (see FIG. 1A), the ground G is excavated by the excavating rod 3, and the soil (soil) of cement milk and ground G The soil cement column 30 is built (see FIG. 1 (B)). When the construction is completed, the excavation rod 3 is pulled out from the excavation hole 4 (see FIG. 1C), and the steel pipe pile 5 is installed.

  In order to build the steel pipe pile 5, first the base end (pile head) of the steel pipe pile 5 is lifted by the pile driving machine 10 (see FIG. 1 (D)), and the vertical alignment of the steel pipe pile 5 is confirmed. (See FIG. 1E). Thereafter, the steel pipe pile 5 is rotated and embedded in the soil cement column 30 (see FIG. 1 (F)), and once buried, the pile head level (vertical position of the pile head) of the steel pipe pile 5 is confirmed (FIG. 1 ( G)).

  The above is an example of a general construction method from the construction of the soil cement column 30 in the excavation hole 4 to the embedding of the steel pipe pile 5, but in this embodiment, the following method is carried out to implement the composite soil cement steel pipe. A pile (indicated by reference numeral 1 in FIG. 2) is constructed. That is, in the present embodiment, when there is a more rigid formation (indicated by reference numeral G2 in FIG. 2) in the deep layer of the excavation target formation (indicated by reference numeral G1 in FIG. 2), the solid formation is directly above the solid formation G2. After excavating the soil cement column 30 so as not to reach the geological formation G2, the steel pipe pile 5 is buried so that the tip penetrates the soil cement column 30 and is buried in the deep solid formation G2. Details are as follows (see FIG. 2).

  First, the excavation rod 3 is rotated and excavated to excavate the ground G (see FIG. 2A). When excavating, for example, cement milk is supplied to a pipe provided inside the excavating rod 3 from a plant (not shown) or the like installed on the ground, and discharged from a nozzle located at the tip of the pipe. The discharged cement milk is agitated by the excavating bit 3b, mixed with the ground G, and slurried to build the soil cement column 30. In addition, when excavating with the excavation rod 3, it does not excavate to the hard formation G2, and even if it excavates, the upper part (front part) of the hard formation G2 is made the deepest part of the excavation hole 4 (FIG. 2 ( B)).

  Next, the excavation rod 3 is pulled out from the excavation hole 4. Here, as described above, in the present embodiment, the excavation rod 3 having at least the tip portion 3a larger than the tube diameter of the steel pipe pile 5 is used, so that the excavation rod 3 is pulled out while discharging cement milk. Then, a cement columnar portion (indicated by reference numeral 31 in FIG. 2) having a diameter larger than that of the steel pipe pile 5 can be formed in the excavation hole 4 (see FIG. 2 (B) and the like).

  Subsequently, the steel pipe pile 5 is built in the excavation hole 4. In the present embodiment, the steel pipe pile 5 having a spiral blade 5a around the periphery of the steel pipe pile 5 that enhances the adhesion of the steel pipe pile 5 to the soil cement 30 is embedded in the soil cement column 30 in the excavation hole 4 ( (See FIG. 2C). At this time, the main body part (the shaft part excluding the spiral blade 5a) of the steel pipe pile 5 and a part of the spiral blade 5a pass through the cement columnar part 31 having a higher cement content than the surrounding soil cement, and the outer peripheral surface. Cement milk comes into contact with According to this, as a result of the cement milk solidifying in contact with these outer peripheral surfaces, the soil cement column 30 and the steel pipe pile 5 can be integrated more firmly. In addition, the soil cement and the steel pipe pile 5 can be integrated to realize a large frictional force as in the conventional case. From the above, according to the present embodiment, the supporting performance of the soil cement steel pipe composite pile 1 in the excavated ground can be improved. At the same time, according to the construction method, since the soil cement column 30 and the steel pipe pile 5 are firmly integrated, the area of the spiral blade 5a for increasing the adhesion between the soil cement column 30 and the steel pipe pile 5 is reduced. It is possible to reduce the number of installations.

  By the way, when the bladed steel pipe pile 5 is embedded in the solid formation G2, the relationship between the rotation speed of the steel pipe pile 5 and the penetration speed (embedding speed) may change, and if the rotation becomes excessive, the spiral The soil cement column 30 may be disturbed by the blades 5a, and the surrounding ground may be involved, which may affect the verticality (how much the steel pipe pile 5 is constructed vertically) and frictional resistance. In particular, at the time of embedding, this is likely to occur when the tip of the steel pipe pile 5 comes into contact with a firmer ground. In this respect, in the present embodiment, since the cement columnar portion 31 is formed by discharging cement milk also in the drawing process as described above, when the steel pipe pile 5 is rotationally embedded, the periphery of the spiral blade 5a is It is possible to prevent the strength of the soil cement column 30 from being lowered due to disturbance during construction.

  Furthermore, in this embodiment, the spiral blade 5b at the tip of the steel pipe pile 5 is penetrated from the bottom of the soil cement column 30, and at least the tip of the pile is formed in the solid formation G2 deeper than the formation G1 in which the excavation hole 4 is excavated. Are embedded (see FIG. 2D). In general, if even a part of the steel pipe pile 5 protrudes from the excavation hole 4, it is considered that the bottom surface is not uniform and the support strength of the composite pile deteriorates. It is normal to adjust and install so that a part of 5 does not protrude. On the other hand, in the present embodiment, the tip of the steel pipe pile 5 is intentionally penetrated from the excavation hole 4 (the soil cement column 30), and further embedded in the hard formation G2, so that the solid formation G2 is formed in the steel pipe pile 5. It functions as a support layer that supports the tip, and even improves the support performance of the pile body (soil cement steel pipe composite pile 1) in the ground G. Moreover, since the solid formation G2 is not improved in the construction method according to the present embodiment, the solid formation G2 has nothing to do with the problem that sufficient agitation is difficult in the first place, and such a solid formation. Since it is not necessary to improve G2, construction is easy and efficient.

  Moreover, in the construction method of this embodiment, since the solid formation G2 is not excavated, a high correlation between the rotational torque and the strength of the ground G can be handled as a construction management index. That is, in the present embodiment, only the formation G1 that is higher than the solid formation G2 is targeted for excavation, and the correlation between the rotational torque of the excavation rod 3 and the ground strength during excavation can be kept high, so It is possible to determine the hard ground G2 using the torque change. According to this, it is possible to quickly grasp that the excavation rod 3 has reached the solid formation G2.

  The same can be said when the steel pipe pile 5 is buried. That is, in the construction method of the present embodiment, the steel pipe pile 5 is rotationally embedded after the cement columnar portion 31 is formed. Therefore, the strength of the soil cement column 30 and the cement columnar portion 31 is high with respect to the rotational torque of the steel pipe pile 5. Correlation can be handled as a construction management index. Therefore, using the torque change at the time of rotary embedding, it is understood that the tip of the steel pipe pile 5 has penetrated the bottom of the soil cement column 30 and has reached the hard ground G2 that is the target of the support layer. It is possible to perform torque management that can determine the penetration length of the.

  Moreover, in the construction method which can perform torque management as mentioned above, it is also possible to embed the steel pipe pile 5 while keeping the rotation speed and penetration speed of the steel pipe pile 5 constant. When the steel pipe pile 5 is rotationally embedded, if the rotational speed and the penetration speed are not constant, the soil cement may be stirred and wound up by the spiral blade 5a, but the rotational speed and the penetration speed are thus constant. It is possible to avoid the soil cement being agitated and wound up if it is constructed while being managed. As a specific example for keeping the rotational speed and the penetration speed constant, adjusting the rotational speed of the steel pipe pile 5 by the auger 13 according to the change in torque may be mentioned.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, in the above-described embodiment, the steel pipe pile 5 provided with the continuous spiral blade 5a is shown (see FIG. 2), but this is only an example, and the spiral blade 5a is discontinuous. The soil cement steel pipe composite pile 1 can also be constructed using the provided steel pipe pile 5. Or the soil cement steel pipe composite pile 1 can also be constructed using the steel pipe pile 5 provided with things other than a spiral blade | wing, such as a recessed part and a rib-shaped convex part. In short, at least the tip of the pile penetrates from the soil cement column 30 and is embedded in the solid formation G2, and the resistance of the pile tip ground is increased by the embedded tip, and at the same time the adhesion to the periphery of the pile is enhanced. As long as it can be made, the shape and form of the pressure receiving portion that increases the resistance force of the tip ground in the steel pipe pile 5 and the adhesion force increasing portion that can increase the adhesion force between the soil cement column 30 and the steel pipe pile 5 are particularly limited. Never happen. Although not explained in detail, if a suitable example of the adhesion enhancing portion other than the spiral blade 5b is given, the one that increases the contact area with the formation G2, such as the above-mentioned concave portion or rib-like convex portion, There are sharp protrusions that function like wedges, continuous parts thereof, protrusions made of materials that improve the frictional force with the formation G2, and coverings. Moreover, in the above-mentioned embodiment, the part embed | buried in the formation G2 among the spiral blades provided in the circumference | surroundings of the steel pipe pile 5 is shown with the code | symbol 5b as an example of a pressure receiving part, and the remaining part is with the soil cement column 30. Although the reference numeral 5a shows an example of an adhesion enhancing part that enhances the adhesion, the two do not need to be clearly distinguished from the beginning. In short, the portion that is embedded in the formation G2 and increases the resistance is the pressure receiving part. A portion that can function and enhances the adhesion force with the soil cement column 30 can function as an adhesion enhancement portion, and the range of the pressure receiving portion and the adhesion enhancement portion is individual soil cement steel pipe composite. It may be different in the pile 1.

  Further, in the above-described embodiment, the description has been given while showing the ground G in which a deeper stratum G2 is present in the deep layer of a certain excavation target stratum G1, but the term “solid” here refers to the excavation target ground G1 as a reference. However, there is no numerical value (N value) that strictly separates the excavation target formation G1 and the solid formation G2. The point is not to simply bury the steel pipe pile 5 by providing the excavation hole 4 (and the soil cement column 30) in a certain formation (including the case where the ground strength is changed in the middle), but a deeper formation. If G2 is present, the tip of the steel pipe pile 5 is intentionally penetrated from the excavation hole 4 and is buried in the solid formation G2 which has not been related to the pile body supporting force in the past, so that the soil cement steel pipe composite pile 1 The purpose of the present application is to improve the supporting force, and the division between the two may be appropriately performed according to the actual situation. The ground hardness index shown in FIG. 2 is based on the number of hits (that is, the N value) required to freely drop a hammer having a predetermined weight and drive a standard penetration sampler to a predetermined depth. It does not represent a specific numerical value.

  The present invention is suitable for application in the case of constructing a composite pile by burying the pile in a soil cement column built in the excavation hole.

DESCRIPTION OF SYMBOLS 1 ... Soil cement steel pipe composite pile, 3 ... Excavation rod, 3a ... Tip part, 4 ... Drilling hole, 5 ... Steel pipe pile, 5a ... Spiral blade | wing (adhesive force increase part), 5b ... Spiral blade | wing (pressure receiving part), 30 ... soil cement column, G1 ... formation in which excavation holes are excavated (excavation target formation), G2 ... solid formation

Claims (4)

Use a drilling rod that has a discharge port for discharging ground improvement material such as cement milk below the lowermost stirring blade, and has at least a portion larger than the tube diameter of the steel pipe pile below the lowermost stirring blade Te, to cut excavation and construction subject ground of composite pile,
Injecting ground improvement material such as cement milk into the excavation hole to build a soil cement column,
Pull out the drill rod from the drill hole,
A steel pipe pile that has a pressure receiving part that increases resistance from the ground at least at the tip of the pile, and an adhesion enhancing part that increases the frictional resistance with the surroundings in the pile shaft part rotates into the soil cement column. Buried while letting
A construction method of a soil cement steel pipe composite pile, in which a pressure receiving portion at the tip of the pile is penetrated from a bottom portion of the soil cement column, and at least the pressure receiving portion is embedded in a solid layer deeper than the formation in which the excavation hole is excavated. When withdrawing the drill rod from the drill hole, pull while discharging the cement milk from the drill rod, the construction method of soil cement steel composite pile according to claim 1. The construction method of the soil cement steel pipe composite pile according to claim 1 or 2 , wherein the steel pipe pile is embedded while keeping a rotation speed and a penetration speed constant.   The soil cement steel pipe composite pile constructed by the construction method of the soil cement steel pipe composite pile according to any one of 1 to 3 above.

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