AU2011237223A1 - Steel pile driving method involving degasification process - Google Patents

Abstract

Disclosed is a steel pile driving method for driving a steel pile into the ground using a vibratory hammer and a transfer pipe that is disposed along the lengthwise direction of the aforementioned steel pile, wherein the steel pile driving method involves a step for inserting the aforementioned steel pile to a prescribed depth in the aforementioned ground by spraying water from the aforementioned transfer pipe while operating the aforementioned vibratory hammer, a step for forming a base protecting section around the end of the aforementioned steel pile by spraying a solidifying fluid material from the aforementioned transfer pipe while operating the aforementioned vibratory hammer, and a step for degassing the aforementioned solidifying fluid material by operating the aforementioned vibratory hammer for a fixed period of time after the aforementioned steel pile has been positioned at an anchoring depth and the spray of the aforementioned solidifying fluid material has been halted.

Description

SPECIFICATION STEEL PILE DRIVING METHOD INVOLVING DEGASIFICATION PROCESS Technical Field [0001] The present invention relates to a method of driving a steel pile, which employs a flowable solidifying agent such as cement milk, and in particular to a method of driving a steel pile, in which degasification is performed for the flowable solidifying agent at the time of forming a foot protection portion. The present application claims priority based on Japanese Patent Application No. 2010-084868 filed in Japan on April 1, 2010, the disclosures of which are incorporated herein by reference in their entirety. Background Art [0002] In this specification, the term "flowable solidifying agent" means various kinds of flowable kneaded materials, including cement, which become solidified as time goes by after being poured. For example, a flowable solidifying agent includes cement milk having cement kneaded with water (additives or other chemical agents may be contained in the cement milk), soil cement having cement milk kneaded with soil, mortar material having cement milk kneaded with sand, and concrete material having cement milk kneaded with sand (fine aggregate) and gravel (coarse aggregate). Further, in this specification, the term "steel pile" means a steel material driven into the ground such as a steel material for civil engineering or construction, which includes H-shaped steels, steel sheet piles and steel pipes. [0003] The flowable solidifying agent is poured into a mold to form a structure body of a building, or is injected or installed into the ground to form a structure body in the 2 ground. The flowable solidifying agent contains a relatively large number of bubbles because air is confined in a space between the cement and water during the kneading, pressure pumping, and pouring. If the flowable solidifying agent solidifies while containing the bubbles, the solidified agent has a weaker strength than those without containing the bubbles. Thus, it is preferable to perform degasification, more specifically to remove the excess bubbles from the flowable solidifying agent after being poured. In general, the degasification process for the flowable solidifying agent is called "compaction." Compaction is performed by applying an appropriate vibration energy to the flowable solidifying agent. The vibration enables the removal of excess bubbles, so that a tight and high-strengthened solidified body can be obtained. [0004] As a general compaction vibration device, a rod-shaped vibrator, for example, as described in Patent Document 1 is known. The rod-shaped vibrator generates vibration having a frequency in the range of 116.7 Hz to 200 Hz and amplitude in the range of about 0.5 mm to 1.25 mm (in this specification, the "amplitude" means one half of a peak-to-peak vibration wave). Of vibration devices, the rod-shaped vibrator provides relatively high frequency. In the high frequency range, the vibration energy largely attenuates, which makes the vibration less likely to reach a long distance. This means that the degasification effect of the rod-shaped vibrator is limited only in the vicinity of the rod-shaped vibrator. With the rod-shaped vibrator, the degasification is required to be performed by repeatedly inserting the rod-shaped vibrator into the flowable solidifying agent at short intervals (for example, every 50 cm) while applying the vibration energy. Thus, the flowable agent after being solidified is likely to have a nonuniform degasified state, which makes it difficult to obtain a uniform and strong solidified agent. [0005] Further, the rod-shaped vibrator is applicable only to the flowable solidifying agent to be driven in a manner such that the surface thereof is exposed. Thus, the 3 rod-shaped vibrator cannot be used in the flowable solidifying agent to be driven into the ground. Conventionally, there has been no effective manner of degasifying the flowable solidifying agent used for forming an underground structure. [0006] As the structure formed in the ground and employing the flowable solidifying agent, composite steel piles with soil cement have been well known. In a method of driving a steel pile, a vibratory hammer is attached to a base end portion of a steel pile, and vibration energy is applied to the steel pile, thereby driving the steel pile into the ground while loosening the resistance of the ground. For a solid ground, a steel-pile driving construction method employing water jet is known as described in Patent Document 2. [0007] In the construction method described in Patent Document 2, plural transportation piles are attached to the steel pile along the axial direction thereof, and injection nozzles are disposed in the vicinity of the end portion of the steel pile. At the time of driving the steel pile, highly pressurized water is injected from the injection nozzles while applying the vibration with the vibratory hammer to excavate the ground, thereby loosening the resistance of the ground. With the construction method employing the water jet, the ground located below the steel pile is excavated, and hence, it is impossible to obtain a force for supporting the end portion of the steel pile after the steel pile is driven. To address this circumstance, after the steel pile is inserted to a predetermined depth in the supporting layer, the flowable solidifying agent is injected from the injection nozzle to solidify the agent, so that a foot protection portion is formed in the vicinity of the end portion of the steel pile. The foot protection portion is a solidified body of the flowable solidifying agent. With the foot protection portion, it is possible to obtain the force for supporting the end portion of the steel pile. Related Art Documents 4 Patent Documents [0008] Patent Document 1: Japanese Examined Patent Application, Second Publication No. S54-31608 Patent Document 2: Japanese Patent No. 3850802 Disclosure of the Invention Problems to be Solved by the Invention [0009] The flowable solidifying agent used in the steel-pile driving construction method described in Patent Document 2 also contains excess bubbles. Thus, in order to form a much stronger foot protection portion, it is desirable to remove gas from the flowable solidifying agent. However, the general rod-shaped vibrator cannot be applied to the flowable solidifying agent to be poured into the ground. Thus, the idea of removing gas from the flowable solidifying agent to be injected into and solidified in the ground has not been thought of previously. [0010] On the inner and the outer surfaces at the end portion of the steel pile described in Patent Document 2, raised portions or ribs are provided for the purpose of enhancing adhesiveness with the foot protection portion. The raised portions or ribs transfer vibration from the vibratory hammer at the time of injecting the flowable solidifying agent to generate a pressure wave in the vicinity of the raised portions or ribs. This pressure wave has an effect of providing a certain degree of degasification. However, the flowable solidifying agent containing relatively large bubbles is continuously supplied, and hence, the gas cannot be sufficiently removed only with the raised portions or ribs of the steel pile. Further, with the construction method described in Patent Document 2, after the steel pile reaches a designed depth (settled depth) and the driving of the steel pile is stopped, operation of the vibratory hammer is stopped, and the 5 flowable solidifying agent is injected for a predetermined period of time. As a result, the flowable solidifying agent becomes solidified in a state where the flowable solidifying agent contains large-sized bubbles. This means that the strength of the foot protection portion is reduced. [0011] In view of the circumstances described above, an object of the present invention is to provide a method of driving a steel pile capable of removing gas from a flowable solidifying agent in the ground to form a tight and uniform foot protection portion having high strength. Means for Solving the Problems [0012] In order to achieve the above-described object, the present invention employs the following. (1) An aspect of the present invention provides a method of driving a steel pile using a vibratory hammer and a transportation pipe disposed along a longitudinal direction of the steel pile to drive the steel pile into the ground, the method including: injecting water from the transportation pipe while operating the vibratory hammer to insert the steel pile in the ground up to a predetermined depth; injecting a flowable solidifying agent from the transportation pipe while operating the vibratory hammer to form a foot protection portion in the vicinity of an end portion of the steel pile; and operating the vibratory hammer for a predetermined period of time after the steel pile reaches a designed depth and the injection of the flowable solidifying agent is stopped, thereby removing gas from the flowable solidifying agent. (2) In the method of driving a steel pile according to (1) described above, the vibratory hammer may be operated at a first amplitude set for the insertion in the inserting of the steel pile and the forming of the foot protection portion, and the vibratory hammer may be operated at a second amplitude set for removing gas in the removing of 6 gas from the flowable solidifying agent. (3) In the method of driving a steel pile according to (1) or (2) described above, the steel pile may have a line-shaped raised portion provided on an inner surface of the end portion. (4) In the method of driving a steel pile according to (1) or (2) described above, the steel pile may have a planer rib raised portion provided on an outer surface of the end portion. Effects of the Invention [0013] According to the method described in (1) above, it is possible to remove gas from the flowable solidifying agent in the ground, especially in the vicinity of the end portion of the steel pile, so that a stronger structure can be formed in the ground. [0014] According to the method described in (2) above, the amplitude of the vibratory hammer in the step of removing gas from the flowable solidifying agent is set independently of the amplitude of the vibratory hammer in the step of inserting the steel pile and the step of forming the foot protection portion, so that gas can be removed from the flowable solidifying agent in a more favorable manner. [0015] According to the method described in (3) above, the line-shaped raised portion provided on the inner surface of the end portion of the steel pile enables further improvement in the degasification effect. [0016] According to the method described in (4) above, the planer rib raised portion provided on the outer surface of the end portion of the steel pile makes it possible to improve the adhesiveness of the foot protection portion with the steel pile, and to form a foot protection portion having a larger size.

7 Brief Description of the Drawings [0017] FIG. 1 A is a side view illustrating a steel pile used in a method of driving the steel pile according to an embodiment of the present invention. FIG. I B is a plan view illustrating a steel pile used in the method of driving the steel pile. FIG. IC is a partially sectioned perspective view schematically illustrating the vicinity of an end portion of the steel pile. FIG. ID is a partially enlarged view illustrating a planer rib raised portion provided on the outer surface of the end portion of the steel pile. FIG. lE is a sectional view taken along line A-A in FIG. ID. FIG. 2 is a graph illustrating an effect of removing gas from a flowable solidifying agent according to the method of driving the steel pile of the present invention. FIG. 3 is a diagram illustrating a method of selecting a vibratory hammer. FIG. 4 is a diagram schematically illustrating a flow from a process (A) to a process (G) in the method of driving the steel pile. FIG. 5A is a graph illustrating a change in depth of end position of the steel pile with respect to time. FIG. 5B is a table showing how processes are managed for samples I to 4. Embodiments of the Invention [0018] Hereinbelow, a detailed description will be made of a method of driving a steel pile according to an embodiment of the present invention. [0019] 8 The method of driving a steel pile according to this embodiment includes operating a vibratory hammer for a predetermined period of time after completion of driving the steel pile, in other words, after the steel pile is positioned at a designed depth (settled depth) and injection of a flowable solidifying agent is stopped, thereby removing gas from the flowable solidifying agent existing in the vicinity of an end portion of the steel pile in a non-solidified state. Conventionally, vibratory hammers have been used merely to drive the steel pile. No attempt has been made so far to actively utilize vibration energy of the vibratory hammer for the purpose of removing gas from the flowable solidifying agent existing in the ground. (0020] The vibratory hammer is a vibration device having a frequency range and amplitude range totally different from those of the rod-shaped vibrator described above. The frequency of the vibratory hammer is lower, and the amplitude of the vibratory hammer is larger as compared with those of the rod-shaped vibrator. Thus, the settings of the frequency and the amplitude for degasification by the vibratory hammer are totally different from those by the rod-shaped vibrator. The lower frequency makes the vibration energy attenuate more gradually, and is advantageous in that vibration is likely to reach a longer distance. The larger amplitude is advantageous in that larger vibration energy can be obtained. By uniformly transferring the vibration energy to the entire flowable solidifying agent to uniformly remove gas, uniformity in terms of strength can be achieved in the solidified body. [0021] The flowable solidifying agent is compacted by performing degasification. The wording "degasification" or "remove gas" and the wording "compaction" as used in this specification are different only in terms of expression, and represent the same phenomenon. [0022] 9 If predetermined vibration energy is applied to a flowable solidifying agent existing in a non-solidified state, cement particles adhered to each other are separated, losing resistance to shearing force. This causes the flowable solidifying agent to be in a liquid form, increasing the fluidity of the flowable solidifying agent and accelerating degasification of the large bubbles contained between the cement particles, thereby obtaining a compacted flowable solidifying agent. After being compacted, the flowable solidifying agent solidifies to form a strong foot protection portion in the vicinity of the end portion of the steel pile. With the method of driving the steel pile according to this embodiment, the degree of strength of the foot protection portion improves as compared with that formed through the method without performing degasification. [0023] The flowable solidifying agent has a characteristic in which fluidization is more likely to occur as the frequency of movement of cement particles occurring in unit time increases and the relative displacement (amplitude) between the cement particles increases. Thus, in theory, by adjusting either or both of the frequency and the amplitude, it is possible to adjust the degree of fluidization, in other words, the degasification effect. With the general amplitude-variable vibratory hammer, it is true that the frequency can be changed. However, it is the amplitude that can be changed more easily and widely. Thus, it is possible to optimally insert the steel pile and form the foot protection portion by operating the vibratory hammer with a first amplitude set for the insertion at the time of inserting the steel pile, and operating the vibratory hammer with a second amplitude set for the degasification at the time of removing gas from the flowable solidifying agent. [0024] A raised portion provided at an end portion of the steel pile transfers vibration from the vibratory hammer at the time of degasification to generate a pressure wave in the vicinity of the raised portion. This pressure wave also has a degasification effect.

10 Thus, the raised portion has an effect of further enhancing the degasification effect obtained by the vibration from the vibratory hammer. [0025] 1. Basic mode of method of driving steel pile Hereinbelow, a basic mode of the method of driving a steel pile including the degasification step according to this embodiment will be described with reference to FIG. lAto FIG. IE. [0026] FIG. I A is a side view illustrating a steel pile, and FIG. 1 B is a plan view illustrating the steel pile. FIG. IC is a partially sectioned perspective view schematically illustrating the vicinity of the end portion of the steel pile (foot protection portion) after the completion of construction. FIG. ID is a partially enlarged view illustrating a planer rib raised portion provided on an outer surface of the end portion of the steel pile. FIG. I E is a sectional view taken along line A-A in FIG. ID. A steel pile 1 illustrated in FIG. IA is a steel pipe pile. The present invention is directed not only to a steel pipe pile but also, for example, to a steel pipe sheet pile and an H-shaped steel pile. The outer diameter of the steel pile I is in the range, for example, of 600 mm to 1500 mm. [0027] The outer surface of the steel pile I is provided with plural transportation pipes 3 (four transportation pipes in the drawing) along the axial direction (in the longitudinal direction) of the steel pile. The transportation pipe 3 may be attached on the inner surface of the steel pile 1. Within the transportation pipe 3, a pipeline is provided for pressure feeding of water or flowable solidifying agent. The end portion of the transportation pipe 3 is located in the vicinity of the end portion of the steel pile 1. This end portion is provided with an injection port 3a of an injection nozzle (not illustrated) having an appropriate form. The injection port 3a has a diameter in the range, for example, of 3 mm to 8 mm. A base end of the transportation pipe 3 is separated away from the outer surface of the steel pile 1 in the vicinity of the base end of the steel pile 1, and is connected with a device (not illustrated) disposed on or above the ground. This device includes a device for switching water and the flowable solidifying agent, a device for feeding water and the flowable solidifying agent, a tank, and a kneading device. The transportation pipe 3 may be drawn from the steel pile 1 to the ground surface to be removed in the final step of construction. [0028] Plural planer rib raised portions lb protruding radially may be attached on the outer surface in the vicinity of the end portion of the pile body Ia. The planer rib raised portions lb are attached in a manner such that a plate surface of each of the planer rib raised portions l b is parallel to the axial direction of the steel pile. With the planer rib raised portions lb described above, a foot protection portion having a larger diameter can be effectively formed. The planer rib raised portions I b may have a rectangular shape or a corner-cut rectangular shape (having a shape in which one or more corners are cut off in the rectangular shape), for example. The number of the planer rib raised portions I b is, for example, 2 to 5. The planer rib raised portions I b are arranged, for example, in the circumferential direction of the steel pile 1 at equal angles as illustrated in FIG. lB. [00291 As illustrated in FIG. I D and FIG. IE, the planer rib raised portion I b is formed by striped steel plates. On the surface of the striped steel plates, elongated small raised portions I b I are arranged alternately at opposite angles to each other to form a generally-reticular-shaped pattern as a whole. Each of the small raised portions IbI has, for example, a length of 28 mm and a width of 4.5 mm. Note that the arrangement pattern of the large number of small elongated raised portions IbI is not limited to the example illustrated in the drawing. [0030] As illustrated in a sectioned portion of FIG. IC, the inner surface of the end portion of the pile body la may be provided with one or more line-shaped raised portions 12 (slip resistance, slip keeper) Ic. The line-shaped raised portions Ic illustrated in the drawing are formed by plural ring-shaped raised portions arranged horizontally at predetermined intervals. The line-shaped raised portions Ic may be formed by spirally shaped raised portions, rather than the plural ring-shaped raised portions. [0031] A foot protection portion Cl formed in the vicinity of the end portion of the pile body la in FIG. IC is a solidified body of the flowable solidifying agent injected from the transportation pipe 3. The foot protection portion Cl is formed so as to extend from a predetermined depth (maximum depth) D4 to a drawing depth DI with respect to the steel pile 1. In the example illustrated in FIG. IC, the drawing depth Dl is located at almost the same position as the upper end D2 of a supporting layer (interface between an intermediate layer and the supporting layer). A designed depth (settled depth) D3, which is a final position of the steel pile 1, is located above the predetermined depth D4. The foot protection portion CI has a diameter larger than the steel pile I. Part of the flowable solidifying agent enters the inside of the steel pile 1, and solidifies, whereby the foot protection portion Cl is formed integrally with the end portion of the steel pile 1. This makes it possible to obtain a force for supporting the end portion of the steel pile 1. Note that the planer rib raised portion lb and the line-shaped raised portions lc are provided for the purpose of enhancing the adhesiveness between the foot protection portion Cl and the steel pile 1, and improving the degasification effect. [0032] As described later, after the steel pile 1 is positioned at the designed depth (settled depth) D3, supply of the flowable solidifying agent is substantially stopped, and the vibratory hammer is caused to operate, thereby performing the degasification process, in other words, the compaction process. [0033] As the flowable solidifying agent, it may be possible to employ cement milk having cement kneaded with water (additives or other chemical agents may be contained 13 in the cement milk). The ratio of water relative to cement (W/C) falls in the range, for example, of 50% to 150%. [0034] 2. Theory of compaction of flowable solidifying agent with vibratory hammer <Comparison with rod-shaped vibrator in terms of compaction performance> In the case where the flowable solidifying agent is compacted with the rod-shaped vibrator on the ground, a high frequency in the range of about 116.7 Hz to 200 Hz is employed. If the vibration frequency is high, amplitude of the vibration sharply attenuates with distance from the vibration source. Thus, in the case of using the rod-shaped vibrator, compaction is performed on the entire flowable solidifying agent by inserting the rod-shaped vibrator in plural positions (in general, about every 50 cm) of the flowable solidifying agent. However, application of the rod-shaped vibrator to the flowable solidifying agent existing in the ground is structurally impossible. Further, it is difficult to dispose the rod-shaped vibrator at a desired position in the ground. [0035] On the other hand, the vibratory hammer is attached at the upper end of the steel pile, in other words, above the ground. Vibration from the vibratory hammer transfers through the steel pile to the end portion of the steel pile existing in the ground. In this embodiment, in the case where compaction is performed with the vibratory hammer in the ground, low frequency in the range of about 11.7 Hz to 18.3 Hz is employed. If the vibration frequency is low, the vibration is less likely to attenuate, and reaches a long distance from one vibration source. In this respect, it is reasonable to employ the vibratory hammer to perform compaction of the flowable solidifying agent existing in the ground. [00361 Next, in connection with the compaction performance, the rod-shaped vibrator is numerically compared with the vibratory hammer used in the method of driving a steel pile according to this embodiment. The compaction performance for the flowable 14 solidifying agent with the vibration device can be evaluated using vibration acceleration fl and vibration compaction energy Ec. By calculating these values, it is possible to compare both devices in terms of compaction performances. Note that the term "vibration compaction energy" means vibration energy used for the compaction. [0037] Table I shows comparison results in terms of the vibration acceleration fl and the vibration compaction energy Ec between a general rod-shaped vibrator and the vibratory hammers used in the method of driving the steel pile according to this embodiment. Vibratory hammers in examples have motor outputs of 90 kW, 120 kW, 180 kW, and 240 kW. Selection of appropriate vibratory hammers will be described later. The vibration acceleration q and the vibration compaction energy E, were calculated using parameter values and expressions shown in the table. The character g represents acceleration of gravity (9.81 m/s 2

).

15 [0038] [Table 1] G eneral Vibratory ham mer (Ex amples) Parameter Unit rod-shaped vibrator 90 kW 120 kW 180 kW 240 kW 1 167 x 102 Frequency f Hz to 1.830 x 10 1.630 x 10 1.330 x 10 1.170 x 10 2 000 x 102 Angular 7.328 x 102 frequency sec' 1 to 1.149 x 10 2 1.023 x 103 8.352 x 10 7.347 x 10 u [= 2 nf_ 1.256 x 10 3 Amplitude A mm 1.250 5.000 V ibration 6 712 x 10 2 acceleration a m/s 2 to 6.601 x 10 5.233 x 10 3.488 x 10 2.699 x 10 [-Aw 2 x 10-] 1.972 x 103 V ibr ation 6.842 x 10 acceleration G to 6.729 5.334 3.556 2.751 [- a/g] 2.010 x 10 2 Ratio ir of 75:1 vibr ation ac celer action 1 (2.010 x 102/2.751 - 73 1) V ibrating mass kg 5.000 6.000 x 10 3 7.950 x 10 3 1.180 x 101 1.995 x 10' W, V ibr ation load W kN 4.905 x 10-2 5.886 x 10 7.799 x 10 1.158 x 10 2 1.957 x 10 2 [-Wg x 10-3) 1 E center Nm 6 131 x 10-2 2.943 x 102 3.899 x 102 5788 x 102 9.785 x 10 2 V ibr ation gePig kN 3.356 to9.858 3.961 x 102 4.159 x 102 4.116 x 102 5.384 x10 2 force P. [ (K' w'/) x 10 _] Vibration c cm pa cti on 4.256 x 10-' energyE kNm to 2.275 2.469 2.637 3.671 [-A(Wf + P) x 10-3] 1.239 x 10-2 Ratio ECR of Vibration 1:180 compaction (2.275/1.239 x 10-2 = 176.4) energy E [0039] In Table 1, vibrating mass Wv of the vibratory hammer corresponds only to the vibrating mass of the vibratory hammer. For the driving of the steel pile, total vibrating mass obtained by adding the vibrating mass of the vibratory hammer to the vibrating mass of the steel pile is employed as the vibrating mass W,. In this embodiment, only 16 the vibrating mass of the vibratory hammer is employed to compare compaction performances of the vibratory hammer itself as a vibration device with those of the rod-shaped vibrator. [0040] As for vibration acceleration , the rod-shaped vibrator having high frequency has advantageous values as compared with the vibratory hammer. Thus, for the vibration acceleration rl, a vibration acceleration ratio 11r between the rod-shaped vibrator and the vibratory hammer is obtained in a manner such that this ratio is maximum within a target frequency range. The vibration acceleration ratio 11, was about 75:1. More specifically, the vibration acceleration fl of the rod-shaped vibrator is 75 times that of the vibratory hammer at the maximum. [0041] Further, for vibration compaction energy Ec, the vibratory hammer having a large vibrating mass has advantageous values as compared with the rod-shaped vibrator. Thus, for the vibration compaction energy Ec, a vibration compaction energy ratio Ec, between the rod-shaped vibrator and the vibratory hammer is obtained in a manner such that this ratio is minimum within a target frequency range. The vibration compaction energy ratio Ecr was about 1: 180. More specifically, the vibration compaction energy Ee of the vibratory hammer is at least 180 times that of the rod-shaped vibrator. [0042] On the basis of the comparison results with the rod-shaped vibrator, it can be understood that, with the vibratory hammer, the advantage of the vibration compaction energy Ec compensates for the disadvantage of the vibration acceleration ri, and the vibratory hammer can achieve the compaction performances equal to or higher than those obtained by the rod-shaped vibrator. This is because the amplitude A of the vibratory hammer is set to values higher than the "ordinary amplitude." The "ordinary amplitude" of the vibratory hammer means values set for inserting the steel pile. In the example in Table 1, the minimum required amplitude A of the vibratory hammer set for 17 the compaction is 5 mm. Such a large amplitude can be obtained only with low frequency and large eccentric moment. [0043] The method of driving a steel pile according to this embodiment employs the vibratory hammer that can generate vibration with an amplitude capable of dealing with the degasification process and that can change this amplitude from the amplitude suitable for the inserting process to the amplitude suitable for the degasification process. [0044] <Setting of time for vibration-forced degasification> Next, the time for vibration-forced degasification required for the vibration compaction will be discussed. In general, the rod-shaped vibrator is inserted at about 50 cm intervals, and compaction time tB for each insertion is about 15 sec to 20 sec. Degasification time tv with the vibratory hammer can be obtained from the following expression by using compaction time tB concerning the rod-shaped vibrator, a ratio ar of the vibration acceleration and a ratio Eer of the vibration compaction energy shown in Table 1. t= wtB'qr/Ecr tv: time for vibration-forced degasification with vibratory hammer (second) a: coefficient of margin-adding time 1,: vibration acceleration ratio tB. time for vibration-forced degasification with rod-shaped vibrator (second) Ec,: vibration compaction energy ratio [0045] The character a represents a coefficient multiplied for obtaining an additional time for the vibration-forced degasification, and 2 to 3 is sufficient for the coefficient. Table 2 shows calculation results. Values of vibration acceleration ratio q, and vibration compaction energy ratio Eer used in calculation in Table 2 are obtained by taking into account that about 10% loss of vibration acceleration r occurs due to 18 frictional force between the vibratory hammer and soil. The rod-shaped vibrator is inserted directly into the flowable solidifying agent, and hence, the vibration compaction energy is transferred in full. On the other hand, the vibratory hammer is located on the ground and the flowable solidifying agent exists in the ground, which inevitably causes loss due to friction with the soil during transfer of the vibration. Thus, the vibration compaction energy generated by the vibratory hammer is not transferred in full to the flowable solidifying agent, and is transferred with about 10% loss. [0046] On the basis of the results shown in Table 2, the time required for the degasification with the vibratory hammer falls between about 19 seconds and 29 seconds. Thus, about 30 seconds of degasification is considered to be adequate for degasifying with the vibratory hammer at the maximum. [0047] [Table 2] General Vibratory Parameter Unit rod-shaped hammer vibrator (240 kW) Frequency f Hz 2.000 x 102 1.170 x 10 Vibration acceleration 80:1 ratio *l Vibraton compaction 1:165 energy ratin F_ *_ Vibration 19 (a= 2) added see t 20 ty 29(a=3) time tB, t _ *1: Value obtained by taking into account about 10% loss of vibtarotory hammer occurring due to frictional force with soil in the value in Table 1 0048] FIG. 2 is a graph conceptually illustrating the effect of compacting the flowable solidifying agent with vibration generated by the vibratory hammer. The horizontal axis 19 represents the time required for vibration-forced degasification. The vertical axis represents density of the flowable solidifying agent. By applying vibration compaction energy, bubbles are removed from the flowable solidifying agent, and the density of the flowable solidifying agent increases. The density-increasing curve varies to some extent depending on various conditions such as viscosity of the flowable solidifying agent. However, by applying vibration with a predetermined amplitude, the density reaches the upper limit within about 30 seconds at the longest from the start of applying the vibration. In other words, the compaction can be completed. [0049] <Setting of amplitude of vibratory hammer> At least about 3 mm of amplitude is empirically necessary to insert the steel pile with the vibratory hammer, and the amplitude is generally set in the range of 3 mm to 6 mm. On the other hand, in order to enhance the effect of removing gas in the flowable solidifying agent existing in the ground with the vibratory hammer, it is preferable to set the amplitude in the range of 5 mm to 10 mm, at which amplitude is not conventionally set. This is because high vibration compaction energy is required. Thus, in the method of driving the steel pile according to this embodiment, a vibratory hammer capable of changing amplitude in the range of 3 mm to 10 mm is selected. [0050] <Setting of vibration acceleration of vibratory hammer at the time of insertion> lt is assumed that the frictional force of soil is 1 when the vibration acceleration rl is 0. Further, it is also assumed that the soil in this case is clay. Clay is the most difficult soil to reduce the frictional force with vibration. If a water jet is not employed, the frictional force of the soil empirically decreases to 0.2 or less in the case where the vibration acceleration 1 is 5G or more. If a water jet is employed, the frictional force of the soil empirically decreases to 0. 1 or less in the case where the vibration acceleration I is 3.5G or more. The method of driving the steel pile according to this embodiment 20 employs the water jet for inserting the steel pile. Thus, it is sufficient to set the vibration acceleration r of the vibratory hammer necessary to insert the steel pile to 3.5G or more. The upper limit of the vibration acceleration q is set to about 1OG on the basis of the upper limits of the amplitude and the frequency. Thus, the vibration acceleration r at the time of insertion is set in the range of 3.5G to 10G. [0051] <Method of selection of vibratory hammer> The method of driving the steel pile according to this embodiment employs one vibratory hammer, and performs three processes including a process of inserting the steel pile into the ground (first process, inserting process), a process of injecting the flowable solidifying agent (second process, foot protection portion-forming process), and a process of removing gas from the flowable solidifying agent (third process, degasification process). Thus, it is necessary to select a vibratory hammer that satisfies the conditions required for all the processes. [0052] Next, steps of (a) to (e) concerning selection of an appropriate vibratory hammer will be described as an example of a case where a steel pile under a specific standard is driven into the ground having a specific soil characteristic through the method of driving the steel pile according to this embodiment. Note that the standard for the steel pile given as an example includes an outside diameter <p of 1000 mm, a plate thickness of 14 mm, a length of 20 m, and a mass in unit length of 340 kg/m. [00531 (a) Determination of frequency The frequency of the vibratory hammer is determined to be one frequency in the range of 11.7 Hz to 18.3 Hz (specific type is not yet determined at this point in time). [0054] (b) Calculation of mass of steel pile 21 On the basis of the mass in unit length of 340 kg/m and the length of 20 m, the mass W, (kg) of the steel pile is calculated as follow: Mass W, (kg) of the steel pile = 340 x 20 = 6800 [0055] (c) Calculation of resistance value at the time of inserting steel pile The characteristic of the soil located at the steel pile being inserted can be obtained from a soil-boring log indicating depth and N values. On the basis of the soil-boring log, a resistance R against insertion can be calculated at a desired embedded depth of the steel pile (inserted length in the ground) through the following expression: Resistance R against insertion = 300N-A, + (10N N Le + 2Ni-L,)-A, N: Maximum N value AP: Cross-sectional area (M 2 ) of enclosed end portion of steel pile Ni: Average N value of depth of steel pile being inserted Le: Depth (m) of steel pile inserted into clay soil L,: Depth (m) of steel pile inserted into sandy soil A,: Circumferential length (m) of steel pile By substitution of each parameter, which is an example, the resistance R against insertion can be obtained as follow: Resistance R (kN) against insertion = 300 x 50 x 0.79 + (10 x 2 x 11.7 + 10 x 5 x 1.3 + 2 x 22.5 x 2.0) x 3.14= 13071 [0056] (d) Selection of vibratory hammer type FIG. 3 is a known "vibratory hammer selection diagram based on weight." The type of vibratory hammer is selected from FIG. 3 on the basis of the mass W, of steel pile of 6800 kg and the resistance R against insertion of 13071 kN calculated in (b) and (c) above. In this example, the vibratory hammer having a motor output of 180 kW is selected. [0057] 22 (e) Examination of appropriateness of specific vibratory hammer and Decision of amplitude in each process It was examined whether the vibratory hammer with the motor output of 180 kW has specifications applicable to the first process to the third process in the method of driving the steel pile according to this embodiment, and on the basis of the examination result, amplitude A suitable for each of the processes is set. [0058] (e-1) Setting for first process Table 3 shows methods of examining whether the specified type of vibratory hammer is applicable to the method of driving the steel pile according to this embodiment, and in particular to the first process. The upper half of Table 3 shows parameters indicating specifications of the specified type, and mass W, of the steel pile. The lower half of Table 3 shows examination items and examination results. [0059] [Table 3] Specificatons of vibratory hammer (180 kW) and steel pile mass Parameter Umat Frequency f Hz 13.3 Angular frequency c [= 2Tf] sec, 83.5 Eccentric moment K N-m 0 to 1570 Vibrating mass W,, kg 11800 Steel pile mass W, kg 6800 Examination items Value Examination result Maximum amplitude of vibratory hammer satisfies amplitudeA (>5 mm) required for degasification in thirdprocess 8.6 mm OK .= KJ[(W+ W,)-g] x 10' Satisify vibration acceleration-r (>3.5G) for inserting steel pile in first process 3.5 G OK -rl = 3.5 Satisify vibration acceleraton -r (> 3.50) for inserting steel pile in first process, and satisfy amplitude A(> 3mm) 4.9 25 mm OK A= -n x g x 10 3 /h? [0060] 23 In the examination, it is first determined whether the maximum amplitude of the vibratory hammer satisfies the amplitude necessary for degasification in the third step. This is the most important requirement of the method of driving the steel pile according to this embodiment, and hence, is examined first. The maximum amplitude Ama calculated on the basis of the maximum value Km,. of the eccentric moment K is 8.6 mm. This satisfies the amplitude range of 5 mm to 10 mm, which is required for performing degasification in the ground in the method of driving the steel pile according to this embodiment. Next, examination was made to determine whether the amplitude A calculated on the basis of 3.5G of the minimum acceleration required for insertion employing the water jet in the first process falls within the amplitude range of 3 mm to 6 mm set for the insertion. The amplitude A is about 5 mm, and satisfies the amplitude range for the insertion. As described above, it was examined whether this type of vibratory hammer is applicable to the method of driving the steel pile according to this embodiment, and the amplitude A appropriate for the first process is determined. [0061] (e-2) Setting for second process In the second process, the water jet is switched into the flowable solidifying agent, and the flowable solidifying agent is injected. In this second process, the vibratory hammer operates with the same frequency and amplitude as those in the first process. [0062] (e-3) Setting for third process In the third process, the injection of the flowable solidifying agent is basically stopped, and only the vibratory hammer operates to perform degasification. The same frequency is applied. The amplitude A is set to an appropriate value of not less than the minimum amplitude of 5 mm required for the degasification but not more than the 24 maximum amplitude Amax. For example, by setting the eccentric moment K to the maximum eccentric moment Kmax, the amplitude of 8.6 mm is obtained. At this time, the vibration acceleration ri is 6.1G. The degasification period of time is 30 seconds at the maximum. [0063] 3. Embodiment of the method of driving steel pile Next, the method of driving the steel pile, which includes the degasification process, will be described with reference to FIG. 4. Processes (A) to (G) in FIG. 4 schematically illustrate an example of a method of driving a steel pile in accordance with the method of driving the steel pile according to this embodiment. This method includes a first process (process (A) and process (B) in FIG. 4) of injecting water from the transportation pipe 3 while operating the vibratory hammer 2 to insert the steel pile I up to the predetermined depth D4, a second process (process (C) to process (E) in FIG. 4) of injecting the flowable solidifying agent from the transportation pipe 3 while operating the vibratory hammer 2 to form the foot protection portion in the vicinity of the end portion of the steel pile 1, and a third process (process (F) in FIG. 4) of operating the vibratory hammer for a predetermined period of time after the steel pile is positioned at the designed depth (settled depth) D3 and the injection of the flowable solidifying agent is stopped, thereby removing gas from the flowable solidifying agent. [0064] <First process> As illustrated in the process (A) in FIG. 4, the vibratory hammer 2 holds the base end portion (upper end portion in the case where the steel pile is driven in the vertical direction) of the steel pile 1 with a chuck device. For example, two positions of the steel pipe pile on the upper circumferential edge are held. The vibratory hammer 2 generates one-way vibration by transferring a turning force from a motor to paired eccentric weights, and rotating the eccentric weights in opposite directions to each other. This vibration direction is used as the driving direction. A general vibratory hammer 25 for driving the steel pile has specifications, for example, including a motor output in the range of 90 kW to 240 kW, frequency in the range of 11.7 Hz to 18.3 Hz, eccentric moment in the range of 420 N-m to 3600 N-m, and body weight in the range of 7 t to 37 t. The method of driving the steel pile according to this embodiment employs a vibratory hammer in which an amplitude appropriate for degasification can be set in a changeable manner. [00651 In the driving processes illustrated in the process (A) and the process (B) in FIG. 4, in cooperation with the vibratory hammer 2, highly pressurized water (for example, clear water) W is injected from the injection port 3a of the transportation pipe 3 attached to the steel pile I in the insertion direction. The injection pressure is set, for example, in the range of 3 MPa to 15 MPa. The highly pressurized water W serves as a water jet cutter to excavate the ground. In the inserting process, the amplitude of the vibratory hammer 2 is set generally in the range of 3 mm to 6 mm. With the vibration energy and the excavation force from the highly pressurized water, the steel pile 1 is continuously inserted. [0066] After the end portion of the steel pile 1 passes the upper end D2 of the supporting layer and reaches the predetermined depth (maximum depth) D4 illustrated in the process (B) in FIG. 4, the driving is stopped. The distance from the upper end D2 of the supporting layer to the inserted and excavated depth D4 is set, for example, to about three times the outer diameter of the steel pile 1. Then, the injection of the highly pressurized water W is stopped. [0067] <Second process> In the first step of the flowable solidifying agent-injecting process illustrated in the process (C) to the process (E) in FIG. 4, the fluids supplied to the transportation pipe 3 are changed from water to the flowable solidifying agent. Then, the flowable 26 solidifying agent C is injected from the injection port 3a while the vibratory hammer 2 is being operated, and the steel pile 1 is stopped or moved vertically in a predetermined range. The flowable solidifying agent C is injected, for example, at a pressure of about 15 MPa or less. In the flowable solidifying agent-injecting process, the amplitude of the vibratory hammer 2 is set to the first amplitude, which is the same amplitude employed in the first process. In the flowable solidifying agent-injecting process, cement particles in the flowable solidifying agent vibrate with the same vibration energy of the vibratory hammer as that in the first process, enabling degasification to some extent. However, a large amount of flowable solidifying agent is supplied, and hence, sufficient degasification cannot be performed in the flowable solidifying agent-injecting process. [0068] For example, as illustrated in the process (D) in FIG. 4, the steel pile 1 is drawn until the end portion of the steel pile I reaches the drawing depth DI located at almost the same position as the upper end (interface between the intermediate layer and the supporting layer) D2 of the supporting layer. [00691 Next, as illustrated in the process (E) in FIG. 4, the steel pile 1 is driven from the drawing depth Dl to the designed depth (settled depth) D3 while the flowable solidifying agent C is being injected. [0070] The flowable solidifying agent-injecting process illustrated in the process (C) to the process (E) in FIG. 4 may be performed only one time, or may be performed plural times depending on the situations such as hardness of the ground. In the case where the ground is hard, this process is preferably repeated an appropriate number of times in order to mix the solidifying agent. This makes it possible to reliably form the foot protection portion in the vicinity of the end portion of the steel pile. [0071] <Third process> 27 In the first step of the degasification process illustrated in the process (F) in FIG. 4, the supply of the flowable solidifying agent is stopped at the position of the designed depth (settled depth) D3 after the steel pile reaches the designed depth (settled depth) D3 and the driving is stopped. The minimum amount of the flowable solidifying agent may be supplied as a minimum required pressure, rather than completely stopping the supply. This is to prevent the clogging of the injection nozzle. The supply of the minimum amount of the flowable solidifying agent for the purpose of preventing clogging described above is considered to be a state where the supply of the flowable solidifying agent is substantially stopped. This is because this minimum supply is not the supply for the purpose of forming the foot protection portion. Then, the amplitude of the vibratory hammer 2 is set to the second amplitude suitable for the degasification, and the vibratory hammer 2 is caused to operate for a certain period of time, for example, for about 30 seconds. In the degasification process, the amplitude of the vibratory hammer 2 is set in the range of 5 mm to 10 mm. [0072] The movement of the solid particles can be more effectively enhanced, by increasing the amplitude of the vibratory hammer with the increase in the size of the cement particles in the flowable solidifying agent. By enhancing the movement of the cement particles, the degasification effect can be enhanced. Further, as the amplitude of the vibratory hammer 2 increases, the flowable solidifying agent can be more likely to be mixed. [0073] In the degasification process, the vibratory hammer applies vibration in the axial direction to the line-shaped raised portion (slip resistance, slip keeper) provided on the inner surface of the end portion of the steel pile. The bearing force caused by the vertical vibration from the line-shaped raised portions generates a pressure wave in the axial direction, and the generated pressure wave is applied to the flowable solidifying agent, thereby further enhancing the degasification effect. Further, the line-shaped 28 raised portions function as slip resistance (slip keeper) that prevents slipping of the contact surface of the steel pile relative to the flowable solidifying agent that has been solidified, whereby vibration can be further effectively transferred. In particular, by attaching the planer rib raised portions protruding radially, the degasification effect can be enhanced. The planer rib raised portions vibrate in both the vertical direction and the horizontal direction. The pressure wave caused by the horizontal vibration of the planer rib raised portions also enhances the degasification effect. By providing another small raised portion on the plate surface by using the striped steel plate or the like, the degasification effect can be further enhanced. [0074] Gas removed from the flowable solidifying agent is forcibly discharged upward with the vibration of the steel pile. Upon completion of the degasification process, the vibratory hammer 2 is terminated. [0075] It should be noted that the first amplitude of the vibratory hammer set in the first process and the second process, and the second amplitude set in the third process are not always different from each other, and may be set to an equal value. [0076] <Final process> Finally, a process of drawing the transportation pipe 3 illustrated in the process (G) in FIG. 4 is performed. The vibratory hammer 2 is first detached from the steel pile 1. Then, the transportation pipe 3, together with the injection nozzle provided at the end portion thereof, is detached from the steel pile I (forcibly pulling up the transportation pipe 3). The transportation pipe 3 is drawn while the upper end portion of the transportation pipe 3 is being hung, for example, by a crane (not illustrated). At this time, the transportation pipe 3 is drawn while the flowable solidifying agent C is being injected from the injection port 3a. This makes it possible to form, at the outer side of the steel pile 1, a circumferential surface solidified portion C2, which is a solidified body 29 of the flowable solidifying agent. The circumferential surface solidified portion C2 increases a frictional force on the circumferential surface of the steel pile 1. The injection is stopped when the injection port 3a reaches the vicinity of the ground surface. [0077] 4. Construction example FIG. 5A and FIG. 5B are diagrams each illustrating process management of construction examples I to 4 using the method of driving the steel pile according to this embodiment. FIG. 5A is a graph illustrating how depths of the end position of the steel pile change with time. FIG. 5B is a table showing process management in terms of time. Although not illustrated, the flow rate of water or flowable solidifying agent is also managed for each process. The process management is performed with a timer, pressure gauge, flowmeter or other unit. [0078] Sections [1] and [2] in FIG. 5A represent the inserting process (first process), in which water is injected while the vibratory hammer is caused to vibrate with the first amplitude. Sections [3] to [7] represent the flowable solidifying agent-injecting process (second process), in which the flowable solidifying agent is injected while the vibratory hammer is caused to vibrate with the first amplitude. The section [3] represents a process of switching from water to the flowable solidifying agent. Section [8] represents the degasification process (third process), in which the supply of the flowable solidifying agent is stopped and the vibratory hammer is caused to vibrate with the second amplitude. Industrial Applicability [0079] According to the present invention, gas in the flowable solidifying agent can be removed in the ground, in particular in the supporting layer where the end portion of the steel pile is located, which makes it possible to obtain a further strong underground 30 structure. Reference Signs List [0080] 1 steel pile I a pile body I b planer rib raised portion Ic line-shaped raised portion (slip resistance, slip keeper) 2 vibratory hammer 3 transportation pipe 3a injection port 4 distance meter W highly pressurized water C flowable solidifying agent C 1 foot protection portion C2 circumferential surface solidified portion

Claims (3)

1. 2. The method of driving a steel pile according to Claim 1, wherein in the inserting of the steel pile and the forming of the foot protection portion, the vibratory hammer is operated at a first amplitude set for the insertion, and in the removing of gas from the flowable solidifying agent, the vibratory hammer is operated at a second amplitude set for removing gas.
2. 3. The method of driving a steel pile according to Claim I or 2, wherein the steel pile has a line-shaped raised portion provided on an inner surface of the end portion.
3. 4. The method of driving a steel pile according to Claim 1 or 2, wherein the steel pile has a planer rib raised portion provided on an outer surface of the end portion.