Steel pipe sheet pile foundation construction method

Abstract

To provide a steel pipe sheet pile well foundation construction method which can efficiently and inexpensively prevent a heave of an excavation bottom surface and floating of the whole well, even when an uplift pressure by artesian ground water of the ground is increased.SOLUTION: A steel pipe sheet pile well foundation construction method reinforces bottom plate concrete 21 in a well 10 formed by installing a large number of steel pipe sheet piles 11 into a ground G0 by burying a reinforcement assembly and is supported by a large number of studs extending and fastened to the inside of the concrete and from the steel pipe sheet piles by its whole side face, pumps underground water from the ground by each pump 71 of a plurality of deep wells 34 and lowers an uplift pressure of the ground, automatically controls each of the pumps on the basis of a water level detection result by each water level sensor 72, and automatically adjusts a pumping quantity by each of the pumps from each deep well, from at latest a start timing of an excavation step in the well.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a steel pipe sheet pile well foundation construction method for constructing a foundation for a bridge pier or the like on the ground. [Background technology]

[0002] The steel pipe sheet pile well foundation method has been well-known as a foundation construction method for bridge piers. In this steel pipe sheet pile well foundation method, a number of steel pipe sheet piles are arranged in a well shape and cast into the bottom of the water to form a well. The inside of the well is then excavated to a predetermined depth, and concrete is poured into the bottom to form a base concrete. A top concrete is then formed on top of that, and the pier skeleton is then constructed on top of the top concrete. In this case, when the well foundation is constructed, the bottom of the excavation rises due to uplift pressure from pressurized groundwater in the ground, destroying the water-tight layer in the ground and losing the stability of the steel pipe sheet piles. To prevent this so-called ground swelling, the well is excavated and the base concrete is poured while the well is filled with water.

[0003] As a countermeasure against the above-mentioned swelling, Patent Document 1 discloses a construction method in which an anchoring steel member, which is a long steel plate with multiple reinforcing bars protruding from one surface of one longitudinal end of the plate, is placed between adjacent steel sheet piles in the steel well with the longitudinal reinforcing bars facing the bottom of the steel well and the other surface of the steel plate facing the steel sheet pile, and then concrete is poured into the steel well.Non-Patent Document 1 also discloses a method in which a mesh of reinforcing bars is placed at the bottom of the well and then concrete is poured to create a concrete base reinforced with reinforcing bars. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-42169 [Non-patent literature]

[0005] [Non-Patent Document 1] "Shikoku Expressway Yoshinogawa Bridge Construction" KAJIMA Digest (2021 02) https: / / www.kajima.co.jp / news / digest / feb_2021 / site / index.html Summary of the Invention [Problem to be solved by the invention]

[0006] In some cases, even a concrete base reinforced with rebars may not be sufficient to prevent ground swelling, and the entire well may even rise, due to factors such as the ground consisting of an impermeable layer and a confined aquifer, resulting in high water pressure from the confined groundwater, the friction between the steel pipe sheet pile and the ground being smaller than expected, or the excavation depth inside the well being deep. Furthermore, if the method of placing anchoring steel members with the longitudinal rebars facing the bottom of the well, as in Patent Document 1, is applied to concrete base reinforced with rebars, the anchoring steel members will interfere with the mesh-like rebars, making such application impossible.

[0007] As a countermeasure against the above-mentioned ground swelling, increasing the length of the steel pipe sheet piles must be decided before construction, and may not be possible depending on the supporting layer of the ground. Furthermore, the effectiveness of the groundwater level lowering method may not be known until construction begins, as it may not be effective if the soil conditions differ from those tested. Furthermore, ground improvement or thickening the base concrete requires a review of the steel pipe sheet pile support, which makes the construction method itself very expensive.

[0008] In view of the problems of the prior art as described above, the present invention aims to provide a method for constructing a steel pipe sheet pile shaft foundation that can efficiently and at low cost prevent ground swelling and the entire shaft from floating up when constructing a steel pipe sheet pile shaft foundation, even if the uplift pressure due to pressurized groundwater in the ground increases. [Means for solving the problem]

[0009] A steel pipe sheet pile well foundation construction method for achieving the above object includes the steps of: driving a number of steel pipe sheet piles into the ground to form a well; installing a small-diameter deep well; excavating the inside of the well to a predetermined depth; filling the inside of the well with water and attaching a number of studs by underwater stud welding to the steel pipe sheet piles at a height position corresponding to the side of the base concrete to be constructed in a subsequent step so that they protrude into the inside of the well; installing a reinforcing bar assembly at the bottom of the well; pouring concrete at the bottom of the well to build the base concrete and fix it to the studs; draining water from inside the well; pouring concrete on the base concrete and installing a top concrete; and curing the top concrete for a predetermined period of time. The base concrete is reinforced by embedding the reinforcing bar assembly, and is supported on its entire side by the multiple studs extending from the steel pipe sheet pile into the concrete and fixed thereto, The pipes for installing the plurality of small-diameter deep wells are arranged so as to extend from the inner periphery of the well to the inside of the ground, and small diameter A water level sensor is installed in each deep well to measure the groundwater level, and a pump is installed to pump up the groundwater. A large number of small-diameter deep wells including the plurality of small-diameter deep wells are installed, a pumping test is carried out, and a plurality of small-diameter deep wells are selected from the large number of small-diameter deep wells based on the results of the pumping test so that the groundwater level in the ground is reduced to a predetermined water level drop position or below by pumping from each of the small-diameter deep wells; At the latest, from the start of the excavation process Selected multiple Each pump in the small-diameter deep well pumps groundwater from within the ground to reduce the uplift pressure of the ground, and the pumping amount by each pump is automatically adjusted for each small-diameter deep well by automatically controlling each pump based on the water level detection results from each water level sensor.

[0010] According to this method for constructing a steel pipe sheet pile shaft foundation, while adjusting the ground uplift pressure inside the shaft, the inside of the shaft is filled with water, and then a number of studs are attached to the steel pipe sheet pile by underwater stud welding, a reinforcing bar assembly is installed at the bottom of the shaft, and concrete is poured at the bottom of the shaft to construct a base concrete that is then fixed to the studs.As a result, the base concrete is reinforced against bending stress by the embedded reinforcing bar assembly, and its entire side is supported by a number of studs that extend from the steel pipe sheet pile into the concrete and are fixed in place, thereby resisting shear forces, which prevents swelling at the bottom of the excavation and also contributes to preventing the entire shaft from floating up.

[0011] Furthermore, by installing multiple small-diameter deep wells and equipping each with a water level sensor that measures the groundwater level, and by using pumps to pump groundwater from within the ground through the piping of each small-diameter deep well at the latest from the start of the excavation process, the uplift pressure on the well can be reduced to below the resistance of the well, thereby further preventing swelling at the bottom of the excavation and the entire well from floating up. Furthermore, by automatically controlling each pump based on the water level detection results of each water level sensor, the pumping rate of each pump can be automatically adjusted for each small-diameter deep well, so that the groundwater level is kept below a predetermined target water level drop position, thereby reducing the ground uplift pressure in the well and preventing excess pumping rate from each small-diameter deep well.

[0012] In the above-mentioned steel pipe sheet pile foundation construction method, it is preferable that the base concrete is installed using underwater non-segregating concrete.

[0013] The studs are preferably headed studs.

[0014] The number and installation positions of the studs are preferably set according to the allowable shear force per stud and the load-bearing area.

[0015] By carrying out the process of reducing the uplift pressure of each small-diameter deep well from the start of the excavation process until the completion of the top concrete curing process, it is possible to reliably prevent swelling of the bottom of the excavation and the entire well from floating up.

[0016] It is preferable that the ground has an impermeable layer and a confined aquifer below the impermeable layer, and that each small-diameter deep well is installed extending from within the well to the confined aquifer, and that the water level in each small-diameter deep well is measured.

[0017] When the plurality of small diameter deep wells are selected, Based on the results of the pumping test Before It is preferable to determine the number and planar arrangement positions of the small-diameter deep wells. 。 Pumping test of This is done using multiple small-diameter deep wells installed at the actual construction site, so the pumping effect can be accurately grasped.

[0018] In addition to the plurality of deep wells, it is preferable to install a plurality of observation deep wells to measure the groundwater level in the well, and measure the groundwater level using water level sensors installed in the observation deep wells at the pumping test facility. By using such a plurality of observation deep wells, the distribution of the groundwater level throughout the well can be grasped.

[0019] In addition to the plurality of small-diameter deep wells, a large-diameter deep well having a larger diameter than each of the small-diameter deep wells is preferably installed outside the well shaft to monitor and control the groundwater level in the surrounding ground including the well shaft. In addition, it is preferable to prevent the pumping volume from exceeding the limit by automatically adjusting the pumping volume through automatic control of each pump, thereby preventing failure of each pump due to excessive drop in the water level in each small-diameter deep well and / or clogging due to the drawing of sediment into each small-diameter deep well. [Effects of the Invention]

[0020] According to the steel pipe sheet pile shaft foundation construction method of the present invention, when constructing a steel pipe sheet pile shaft foundation, even if the uplift pressure due to pressurized groundwater in the ground increases, the base concrete is reinforced with a reinforcing bar assembly and its entire side is supported by a large number of studs that extend from the steel pipe sheet pile into the concrete and are fixed thereto, and a small-diameter deep well placed inside the shaft pumps water so that the groundwater well is below a predetermined target water level drop position, so that swelling of the ground at the bottom of the excavation and floating of the entire shaft can be prevented efficiently, at low cost, and reliably. [Brief explanation of the drawings]

[0021] [Figure 1] 1A is a plan view showing a shaft made of a large number of steel pipe sheet piles driven into the ground in a steel pipe sheet pile shaft foundation construction method according to this embodiment, and FIG. 1B is a plan view showing the main parts thereof. [Figure 2] FIG. 2 is a schematic longitudinal cross-sectional view of the well and ground in FIG. 1(a) taken along line II-II. [Figure 3] 3A is a plan view, FIG. 3B is a side view, and FIG. 3C is a front view showing a number of studs arranged on the steel pipe sheet pile of FIG. 1 and FIG. 2. [Figure 4] FIG. 2 is a plan view showing the reinforcing bar assemblies arranged at the bottom of each well in FIG. 1(a). [Figure 5] FIG. 1(b) is a plan view similar to FIG. 1(a), showing the arrangement of multiple small-diameter deep wells and observation deep wells within the well shaft. [Figure 6] 1 is a graph showing the relationship between time and groundwater level in this pumping test. [Figure 7] 1 is a flowchart for explaining steps S01 to S17 of a steel pipe sheet pile well foundation constructing method according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a plan view (a) showing a well consisting of a number of steel pipe sheet piles driven into the ground in a steel pipe sheet pile well foundation construction method according to this embodiment, and Fig. 2 is a schematic longitudinal cross-sectional view of the well and ground in Fig. 1(a) taken along line II-II.

[0023] As shown in Figures 1(a) and 1(b), a large number of steel pipe sheet piles 11 are arranged in an oval shape on a plane and driven into the ground. Joints 11a are formed between each steel pipe sheet pile 11, thereby connecting the steel pipe sheet piles 11 to each other, thereby constructing a shaft well 10. The joints 11a create recesses 11b (Figure 2) between the steel pipe sheet piles 11. The shaft well 10 is oval in plan view, consisting of parallel straight sections 12 and 13 and arc sections 14 and 15 at both ends. The shaft well 10 is divided by two rows of partition walls 16 and 17, each consisting of multiple steel pipe sheet piles 11 driven linearly within it. The shaft well 10 is composed of an end shaft well 10A consisting of the arc section 14 and the partition wall 16, a central shaft well 10B between the partition walls 16 and 17, and an end shaft well 10C consisting of the arc section 15 and the partition wall 17.

[0024] As shown in Figure 2, the ground G0 consists of an alluvial sandy clayey soil layer (A SC ) and alluvial clayey soil layer (A C1 ), an impermeable layer G1 consisting of an alluvial gravel layer (Ag), and a confined aquifer G2 consisting of a diluvial gravel layer (D g1 ), and the diluvial clay layer (D c2 The confined aquifer G2 is a highly permeable ground saturated with groundwater, and a relatively large water pressure (uplift pressure) acts upward from the confined aquifer G2. The steel pipe sheet piles 11 are driven into the impermeable layer G1.

[0025] After the inside of the well 10 is excavated, the base concrete 21 and top concrete 25 are installed by pouring concrete. However, during this process, there is a risk that the pumping pressure from the confined aquifer G2 may cause swelling at the bottom of the excavation or the entire well 10 to float up, so the following measures (1) and (2) are taken.

[0026] (1) The base concrete 21 is formed by embedding multiple layers of reinforcing bar assemblies in a flat manner, and by underwater welding a large number of studs to the steel pipe sheet pile 11 within the well, the base concrete and the studs are integrated. (2) Install multiple small-diameter deep wells within the well shaft, and use pumps to pump groundwater from the ground to reduce the uplift pressure on the well shaft. Water level sensors automatically control each pump, automatically adjusting the amount of water pumped by each pump.

[0027] The base concrete 21 will be described with reference to Figures 3 and 4. Figure 3 is a plan view (a), a side view (b), and a front view (c) showing a number of studs arranged on the steel pipe sheet piles of Figures 1 and 2. Figure 4 is a plan view showing the reinforcing bar assemblies arranged at the bottom of each well in Figure 1(a).

[0028] As shown in Figures 3(a) to 3(c), multiple studs 23 are attached to the outer peripheral surface 11c of the steel pipe sheet pile 11, evenly spaced in the circumferential and longitudinal directions, by underwater stud welding. The studs 23 are headed studs with large head diameters, meeting the JIS B1198 (headed stud) standard. As shown in Figure 3(a), each stud 23 is attached to a position on the outer peripheral surface 11c of the steel pipe sheet pile 11 so as to face in the normal direction. The studs 23 protrude toward the inside of the well 10 as a whole, but are long enough not to interfere with the side surfaces of the reinforcing bar assemblies 22A to 22C (Figure 4), which will be installed in a subsequent process, as indicated by the dashed lines in Figure 3(b). Each stud 23 is attached to the steel pipe sheet pile 11 at a height that corresponds to approximately the vertical center of the side surface of the reinforcing bar assemblies 22A to 22C.

[0029] The number of studs 23 required for the base concrete 21 is calculated to obtain the necessary support reaction force from the allowable shear force per stud, and their installation positions are set according to the load-bearing area. The studs 23 are installed in the wells 10A-10C while the interiors are filled with water. Because the installation is performed using underwater stud welding, the allowable shear force is reduced to 70% based on the "Port Steel Structure Corrosion and Repair Manual" (Coastal Technology Center, 2009). While threaded studs require a long stud length to achieve the required shear resistance, which can hinder the placement of rebar within the well, headed studs provide the required shear resistance even with shorter stud lengths, and are easy to work with during underwater welding.

[0030] As shown in Figure 4, studs 23 are not required for the steel pipe sheet pile 11X located at the intersection of the shafts 10A-10C because the studs have almost no load-bearing area. Instead, studs are attached to each steel pipe sheet pile 11 other than the steel pipe sheet pile 11X. Studs are attached to the steel pipe sheet piles 11 constituting the bulkheads 16 and 17, on opposite sides of the shafts 10A-10C, at 180-degree angles. After the studs 23 are installed, reinforcing bar assemblies 22A-22C, each with a planar shape corresponding to the planar shape of each shaft 10A-10C, are installed within each shaft 10A-10C. Then, concrete is poured to form the base concrete 21. Because the base concrete 21 is poured with numerous studs 23 and reinforcing bar assemblies 22A-22C installed underwater, underwater non-segregating concrete, which has excellent filling properties, is used. The reinforcing bar assemblies 22A-22C are assembled in an onshore factory or yard by arranging and connecting vertical and horizontal reinforcing bars in a mesh pattern at predetermined intervals.

[0031] As described above, the base concrete 21 installed at the bottom of the shafts 10A to 10C is reinforced against bending stress due to uplift pressure by embedding steel bar assemblies 22A to 22C, and is supported on the entire side of the base concrete 21 by a number of studs 23 that extend from the steel pipe sheet piles 11 into the concrete and are fixed to the base concrete 21, as shown in Figure 3(b), thereby resisting shear force and uplift pressure, thereby preventing swelling of the bottom of the shaft and contributing to preventing the entire shaft 10 from floating up.

[0032] Next, the control of the reduction in uplift pressure on the shaft and bottom concrete by small-diameter deep wells will be explained with reference to Figures 2 and 5. Figure 5 is a plan view similar to Figure 1(a), showing the arrangement of multiple small-diameter deep wells and observation deep wells within the shaft.

[0033] As shown by the dashed line in Figure 2, the small-diameter deep well 34 is installed by driving a small-diameter pipe 34a from a recess 11b (see Figure 4) on the inner periphery of the steel pipe sheet pile 11 into the ground G0 to a confined aquifer G2 consisting of an alluvial gravel layer (Ag). The pipe 34a is composed of a perforated pipe 70 near its tip, and a deep well pump 71 is installed near the tip. A water level sensor 72 is also installed to detect the water level in the deep well 34. The deep well 34 is configured to pump groundwater from the confined aquifer G2 using the deep well pump 71. The pipe 34a is installed in the recess 11b on the inner periphery of the steel pipe sheet pile 11 to avoid interference with the reinforcing bars in the top concrete 25 and because the pipe 34a can be installed even after the steel pipe sheet pile 11 has been poured.

[0034] As shown in Figure 5, multiple small-diameter deep wells 31-40 are installed throughout the shaft 10 by installing multiple pipes similar to pipe 34a in Figure 2, and as in Figure 2, each deep well pump pumps groundwater from the confined aquifer G2, and each water level sensor measures the water level in each small-diameter deep well 31-40. The diameter of the small-diameter deep wells 31-40 may be any diameter that fits into the recess 11b of the joint 11a of the steel pipe sheet pile 11. In this embodiment, pipes with a diameter of 125 mm are used, and a deep well submersible pump with a discharge port diameter of 50 mm is used as the deep well pump.

[0035] In addition, a large-diameter deep well 61 for regular use is installed at a position outside the well shaft away from the center of the straight section 12 made up of multiple steel pipe sheet piles 11, and a large-diameter deep well 62 for emergency use is installed at a position outside the well shaft away from the center of the straight section 13 made up of multiple steel pipe sheet piles 11. The large-diameter deep wells 61 and 62 for regular use and emergency use are designed to observe and control the groundwater level in the surrounding ground including the well shaft 10.

[0036] Next, a pumping test will be described, which was carried out using a test facility to confirm that the water level was lowered by pumping water from the confined aquifer G2 using the plurality of small-diameter deep wells 31 to 40 shown in FIG.

[0037] Prior to the pumping test, as shown by the broken line in FIG. 2, a small-diameter pipe 55a was inserted into the ground G0 from the recess 11b (see FIG. 4) on the inner periphery of the steel pipe sheet pile 11. c2 By pouring the pipes so that they reach the stratum, a small-diameter observation deep well 55 is installed. As shown in Figure 5, multiple pipes similar to the pipe 55a in Figure 2 are poured into the recesses 11b at intervals in the circumferential direction throughout the shaft 10, thereby installing multiple small-diameter observation deep wells 51 to 55, and the groundwater level can be automatically measured by each water level sensor.

[0038] A pumping test was conducted using multiple small-diameter deep wells 31-40 in Figure 5, with each deep well pump pumping water from the confined aquifer G2 (Ag layer). The groundwater level was continuously and automatically measured using water level sensors in multiple observation deep wells 51-55, and the pumping volume in the small-diameter deep wells 31-40 was measured. Figure 6 shows the relationship between time and groundwater level, which is the result of the pumping test. Table 1 below shows the average pumping volume (L / min) in each of the small-diameter deep wells 31-40 and the final water level in the deep wells 31-40.

[0039] [Table 1]

[0040] The pumping test results shown in Figure 6 indicate that pumping using multiple small-diameter deep wells 31-40 caused the water levels in observation deep wells 51-53 and 55 to drop below the target water level drop. The amount of water drop in observation deep well 54 was smaller than in the other observation deep wells, suggesting that it was clogged with fine particles. Therefore, manual measurements of the water level in small-diameter deep well 54' adjacent to observation deep well 54 in Figure 5 revealed that the water level had dropped to the target TP (reference elevation) -8.8 m 30.5 hours after the start of pumping, reaching the target water level drop. As described above, the multiple observation deep wells 51-55 allow the distribution of groundwater levels throughout the well 10 to be ascertained.

[0041] Furthermore, among the small-diameter deep wells 31-40, as shown in Table 1, small-diameter deep wells 33 and 35, which have high pumping rates and little water level drop, have high water collection capabilities, while small-diameter deep wells 32 and 38, which have low pumping rates and large water level drop, have poor water collection capabilities. For this reason, valves were attached to the deep well pump drainage pipes during the pumping test observations, and the pumping volume was adjusted by adjusting the valves. Since the pumping volume varied greatly among the small-diameter deep wells 31-40, water level sensors similar to water level sensor 72 in Figure 2 were installed in each of the small-diameter deep wells 31-40 to constantly control the pumping volume. These sensors automatically operated based on the water level in the wells. This was done to prevent pump failure due to excessive water level drop in the wells caused by pumping volume exceeding the capacity of each small-diameter deep well 31-40, and to prevent clogging due to sediment being drawn into the wells.

[0042] Based on the results of the above test work, it was determined that by pumping water from the confined aquifer G2 using multiple small-diameter deep wells 31-40 throughout the entire area of ​​the well shaft 10, it was possible to lower the groundwater level of the confined aquifer G2 to below the target water level drop position and reduce the uplift pressure of the confined aquifer G2. Furthermore, since the water collection capabilities of the multiple small-diameter deep wells 31-40 vary, the pumping volume is adjusted between each small-diameter deep well 31-40. The operation of the deep well pumps in each small-diameter deep well 31-40 is automatically controlled based on the water level detection results of water level sensors installed in each small-diameter deep well 31-40. The above pumping test was performed using multiple small-diameter deep wells 31-40 installed at the actual construction site. Since the conditions of the test work and the actual construction were consistent, the pumping effect could be accurately understood.

[0043] As described above, from the start of the excavation process inside the well 10 to the completion of the curing process of the top concrete 25, groundwater is pumped from the confined aquifer G2 by the deep well pumps of the multiple small-diameter deep wells 31-40, reducing the uplift pressure of the confined aquifer G2 to below the resistance of the well 10, thereby preventing swelling within the well 10 and the entire well 10 from floating up. At this time, the pumps are automatically controlled based on the water level detection results of the water level sensors, automatically adjusting the pumping volume of each pump for each small-diameter deep well 31-40, thereby preventing the pumping volume of each small-diameter deep well 31-40 from exceeding the capacity.

[0044] In Figure 5, a number of pipes similar to pipe 34a in Figure 2 were installed, and a number of small-diameter deep wells for pumping, including small-diameter deep wells 31-40, were installed, and the pumping test described above was carried out. Based on the test results, a number of small-diameter deep wells 31-40 were selected from the many small-diameter deep wells for pumping. The multiple small-diameter deep wells 31-40 are arranged at approximately equal intervals along the many steel pipe sheet piles 11 of the shaft 10, but there are some slight misalignments.

[0045] Next, each step S01 to S17 of the steel pipe sheet pile well foundation constructing method according to this embodiment will be described with reference to the flowchart of FIG.

[0046] First, a temporary bridge is set up in the target area where a steel pipe sheet pile shaft foundation is to be constructed (S01). Next, as shown in Figures 1 and 2, a large number of steel pipe sheet piles 11 are driven into the ground G0 (S02), and joints are made between each steel pipe sheet pile 11, 11 (S03). Each shaft 10A to 10C is constructed, and the overall shaft 10 has an oblong shape in plan view.

[0047] Next, the pipe 34a shown in Figure 2 is installed from the recess 11b of the joint on the inner periphery of the steel pipe sheet pile 11 to the confined aquifer G2 in the ground G0, and a small-diameter deep well 34 is installed, thereby installing multiple small-diameter deep wells 31-40 as shown in Figures 2 and 5 (S04). Each small-diameter deep well 31-40 pumps water from the confined aquifer G2, lowering the groundwater level of the confined aquifer G2 to below the target water level drop position, thereby reducing the uplift pressure of the confined aquifer G2. The pumping rate of each small-diameter deep well 31-40 is automatically adjusted by automatically controlling each deep well pump based on the water level detection results of the water level sensor of each small-diameter deep well 31-40. This control and adjustment of the uplift pressure and pumping rate continues until the curing period has elapsed after the top concrete is poured. The pumping test shown in FIG. 6 and Table 1 is carried out in this step S04, and the number and locations of the plurality of small-diameter deep wells 31 to 40 shown in FIG. 5 are determined.

[0048] Next, the inside of each well 10A-10C is primarily excavated to a predetermined depth (S05), and supports (not shown) are attached to the steel pipe sheet piles 11 (S06). Next, the inside of each well 10A-10C is secondarily excavated to a further predetermined depth (S07). Note that from before the start of the primary excavation step S05 until the completion of the subsequent step of pouring the base concrete 21 (S11), the inside of each well 10A-10C is filled with water to ensure a certain water depth in order to prevent swelling inside the well 10.

[0049] Next, the secondary excavation is performed to pour sand up to a predetermined height onto the excavated bed base to form the sand layer 20 (Fig. 2), and the base surface is leveled (S08). In order to ensure the thickness of the base concrete 21 to be poured in the subsequent process, the height of the sand poured is controlled by poking a red rod from inside the wells 10A to 10C when pouring the sand, and the base surface of the sand layer 20 is also leveled.

[0050] Next, as shown in Figures 3(a) to 3(c), a large number of studs 23 are attached by underwater stud welding to the steel pipe sheet piles 11 at height positions corresponding to the side surfaces of the base concrete 21 (S09). Before attaching the studs, the stud attachment positions of each steel pipe sheet pile 11 are marked.

[0051] Next, the reinforcing bar assemblies 22A to 22C shown in Fig. 4 are suspended by a crane to the underwater reinforcing bar installation positions in the shafts 10A to 10C and installed (S10). The reinforcing bar assemblies 22A to 22C are assembled in a yard near the construction site.

[0052] Next, underwater non-segregating concrete is poured into the water in the shafts 10A to 10C to form the base concrete 21 (S11). The base concrete 21 is poured separately into three locations in the shafts 10A to 10C.

[0053] Next, the wells 10A to 10C are drained and dried up (S12), and then a number of studs are attached by stud welding at height positions of the steel pipe sheet piles 11 corresponding to the sides of the top concrete 25 to be constructed in the next process in order to connect the top concrete 25 and the steel pipe sheet piles 11 (S13). Such stud welding is performed in air.

[0054] Next, after each reinforcing bar assembly is installed in the shafts 10A to 10C, concrete is poured to form top concrete 25 in the shafts 10A to 10C (S14).

[0055] Next, after the top concrete 25 is poured, it is cured for a predetermined period of time until it has a predetermined strength, and then the pumping pressure control and pumping amount adjustment by the small-diameter deep wells 31 to 40 that began in step S05 are stopped, and the small-diameter deep wells 31 to 40 are removed (S15). Next, the support is removed from the steel pipe sheet pile 11 (S16).

[0056] Next, after going through various processes, the pier skeleton is placed on the top concrete 25 (S17), and after processes such as removing the temporary bridge, the process of constructing the steel pipe sheet pile foundation is completed. As described above, the steel pipe sheet pile foundation construction method according to this embodiment can be implemented.

[0057] Although the embodiments for carrying out the present invention have been described above, the present invention is not limited to these, and various modifications are possible within the scope of the technical concept of the present invention. For example, in this embodiment, the groundwater level is measured using a water level sensor provided for each of multiple small-diameter deep wells, but the present invention is not limited to this, and water level sensors for multiple observation deep wells as shown in Figure 5 may also be used, or water level sensors for these observation deep wells may be used in combination.

[0058] Furthermore, although the original ground is shown as being at the bottom of the water in FIG. 2, the present invention is not limited to this and can of course also be applied to land ground.

[0059] 7, between the joint processing step (S03) and the small-diameter deep well installation step (S04), ground improvement below the well shaft may be carried out by a high-pressure jet mixing method using a boring machine to reinforce the tip of the steel pipe sheet pile 11. Such ground improvement is one of the measures to prevent swelling at the bottom of the excavation.

[0060] Furthermore, in this embodiment, the small-diameter deep well uses a small-diameter pipe with a diameter of 125 mm, but the present invention is not limited to this, and any deep well may be used as long as it has a smaller diameter than the pipe (diameter 300 to 400 mm) used for the large-diameter conventional deep well 61 in Figure 5 and has a diameter that can be installed in the recess 11b of the joint 11a of the steel pipe sheet pile 11. [Industrial Applicability]

[0061] According to the present invention, when constructing a steel pipe sheet pile shaft foundation, even if the uplift pressure due to pressurized groundwater in the ground increases, swelling of the excavated bottom surface and lifting of the entire shaft can be prevented efficiently, at low cost, and reliably, thereby enabling the foundations of bridge piers, etc. to be constructed reliably and stably. [Explanation of symbols]

[0062] 10 Izutsu 10A End well 10B Central Izutsu 10C End well 11 Steel pipe sheet pile 11a Joint 11b Recess 11c Outer surface 12,13 Straight section 14,15 Arc section 16,17 Bulkhead 20 Sand layer 21 Base concrete 22 Reinforcement Assembly 22A~22C Reinforced concrete assembly 23 studs 25 Top concrete 31~40 Small diameter deep well 34a Piping 51~55 Observation deep wells 55a Piping 61,62 Large diameter deep well 70 Perforated pipe 71 Deep well pump 72 Water level sensor G0 Underwater ground G1 Impermeable layer G2 Confined aquifer

Claims

1. a process of driving a large number of steel pipe sheet piles into the ground to form a well; installing a small diameter deep well; excavating the interior of the well to a predetermined depth; a step of filling the inside of the shaft with water and attaching a number of studs by underwater stud welding at a height position of the steel pipe sheet pile corresponding to the side of the base concrete to be constructed in a subsequent step so that the studs protrude into the inside of the shaft; placing a rebar assembly at the bottom of the well; a step of constructing the base concrete by pouring concrete into the bottom of the well and fixing the concrete to the studs; Draining water from inside the well; A step of pouring concrete on the base concrete and installing a top concrete; and curing the top concrete for a predetermined period of time. The base concrete is reinforced by embedding the reinforcing bar assembly, and is supported on its entire side by the multiple studs extending from the steel pipe sheet pile into the concrete and fixed thereto, Each pipe for installing the plurality of small-diameter deep wells is arranged so as to extend from the inner periphery of the well to the inside of the ground, and a water level sensor for measuring the groundwater level and a pump for pumping the groundwater are installed for each small-diameter deep well. A large number of small-diameter deep wells including the plurality of small-diameter deep wells are installed, a pumping test is carried out, and a plurality of small-diameter deep wells are selected from the large number of small-diameter deep wells based on the results of the pumping test so that the groundwater level in the ground is reduced to a predetermined water level drop position or below by pumping from each of the small-diameter deep wells; A method for constructing a steel pipe sheet pile shaft foundation, which involves using each pump of the selected plurality of small-diameter deep wells to pump groundwater from within the ground to reduce the uplift pressure of the ground at the latest from the start of the excavation process, and automatically controlling each pump based on the water level detection results of each water level sensor to automatically adjust the amount of water pumped by each pump for each small-diameter deep well.

2. The steel pipe sheet pile foundation construction method according to claim 1, wherein the base concrete is installed using underwater non-segregating concrete.

3. 3. The steel pipe sheet pile foundation construction method according to claim 1, wherein the studs are headed studs.

4. A steel pipe sheet pile foundation construction method according to any one of claims 1 to 3, wherein the number and installation positions of the studs are set according to the allowable shear force per stud and the load area to be borne.

5. A steel pipe sheet pile foundation construction method according to any one of claims 1 to 4, wherein the process of reducing the uplift pressure by each small-diameter deep well is carried out from the start of the excavation process to the completion of the curing process of the top concrete.

6. The ground has an impermeable layer and a confined aquifer below the impermeable layer, Each of the small-diameter deep wells is installed extending from within the well to the confined aquifer; The steel pipe sheet pile foundation construction method according to any one of claims 1 to 5, wherein the water level in each small diameter deep well is measured.

7. A method for constructing a steel pipe sheet pile shaft foundation as described in any of claims 1 to 6, in which when selecting the multiple small-diameter deep wells, the number and planar arrangement positions of the small-diameter deep wells are determined based on the results of the pumping test.

8. A method for constructing a steel pipe sheet pile shaft foundation as described in any one of claims 1 to 7, wherein, in addition to the plurality of small-diameter deep wells, a plurality of observation deep wells are installed to measure the groundwater level in the shaft, and the groundwater level is measured using water level sensors installed in the observation deep wells in the pumping test structure.

9. A steel pipe sheet pile foundation construction method according to any one of claims 1 to 8, wherein a large-diameter deep well having a diameter larger than that of each of the small-diameter deep wells is installed outside the well, separately from the plurality of small-diameter deep wells.

10. A method for constructing a steel pipe sheet pile shaft foundation as described in claim 1, wherein the pumping volume is automatically adjusted by automatically controlling each pump to prevent the pumping volume from exceeding the limit, thereby preventing failure of each pump due to an excessive drop in the water level in each small-diameter deep well and / or clogging due to the drawing of sediment into each small-diameter deep well.

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