Backfill construction management method

Abstract

To provide a construction management method of back-filled portion constructed by rolling and compacting powdery improved soil.SOLUTION: A construction management method of back-filled portion of a ground includes: a step of erecting a casing in the ground; a step S5 of removing soil or an object to be removed in the erected casing down to a prescribed depth; a step S6 of mixing and stirring the removed soil or prepared soil with cement-based solidification material by a blending ratio set based on target strength of the back-filled portion on a ground to produce powdery improved soil; a step S7 of throwing the produced powdery improved soil into the casing to backfill the casing with the powdery improved soil up to a prescribed height; a step S9 of rolling and compacting the thrown powdery improved soil by a rolling / compacting load set based on the target strength; and a step S8 of pulling the casing up to a degree not exceeding a height of the powdery improved soil.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a construction management method for backfilling using powder-improved soil. [Background technology]

[0002] In conventional redevelopment projects, when the framework or piles of an existing structure are not reused in a new structure, it is common to remove a portion of the existing structure that interferes with the new structure in advance and then backfill the area (hereinafter referred to as the backfill area or backfill hole). Fluidized treated soil or lean-mix cement milk is often used as backfill material in existing pile removal and backfill work. However, when the backfill area is long, there have been reported cases where material separation due to bleeding or other factors occurs in the shallow part of the fluidized treated soil, resulting in unstable strength (see, for example, Non-Patent Document 1). Cases of strength problems in existing pile removal and backfill work have also been reported with lean-mix cement milk (see, for example, Non-Patent Document 2). Therefore, a construction management method that can consistently ensure the quality of the backfill area throughout the entire depth is required.

[0003] When liquefied treated soil is used as backfill material, not only does material cost increase depending on the number of existing piles to be removed and the length of the backfill holes, but coordination with other construction work (such as setup changes) may also be necessary, raising concerns about process delays. Therefore, the present patent applicant has proposed a construction management method as shown in Patent Document 1. To reduce material costs, this construction management method involves mixing on-site generated soil and cement-based solidification material in powder form on-site to produce powder-improved soil, pouring this powder-improved soil into the backfill holes, and then further agitating the backfill holes using a soil improvement machine or the like to build soil improvement columns in a slurry state.

[0004] On the other hand, a conventional ground improvement method is known in which the soil to be improved is excavated and a solidification material is filled into the excavated soil (see, for example, Patent Document 2). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] "Quality Investigation of Liquefied Stabilized Soil Backfilled in Excavated Holes after Removal of Existing Piles", Hirofumi Sakihama, Hironori Horii, Hikaru Yaegashi, Proceedings of the 2014 Annual Meeting of the Architectural Institute of Japan, pp.435-436, 2014 [Non-patent document 2] "Research on the removal of existing piles interfering with new piles (Part 3) Properties of backfill soil after removal of existing piles," Yasushi Furukawa et al., Proceedings of the 55th Geotechnical Engineering Research Conference, 21-9-1-07, 2020 [Patent documents]

[0006] [Patent Document 1] Patent Application No. 2020-201809 (currently unpublished) [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-152515 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the conventional method of Patent Document 1 assumes that groundwater exists (flows into) the backfill hole and that mixing and stirring in a slurry state is possible. However, depending on the hydraulic conditions in the backfill hole (for example, when groundwater does not appear in the backfill hole after the existing pile is removed), application may be difficult. If this method is not applicable, it is necessary to separately prepare improved soil in a slurry state above ground. Furthermore, even if the construction conditions are met and the method is applicable, it is necessary to separately prepare a ground improvement machine that is not normally used in existing pile removal and backfilling work.

[0008] In order to pour improved soil in powder form into the backfill hole without there being any groundwater in it and build a backfill area of over 10 meters, construction management is required to compact and compact the powder improved soil at a specified load and meet the target strength throughout the entire depth, but there are no standardized methods for calculating the compaction load or for managing construction.In addition, to carry out the above construction, a separate compactor specifically for the backfill area must be prepared.

[0009] The present invention has been made in view of the above, and aims to provide a construction management method for a backfill area constructed by compacting powder-improved soil. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems and achieve the objectives, the construction management method for backfilling sections of the present invention is a method for construction management of backfilling sections of the ground, characterized by having the steps of erecting a casing in the ground, removing the soil or object to be removed inside the erected casing to a predetermined depth, mixing and stirring the removed soil or previously prepared soil with a cement-based solidification material on the ground in a ratio set based on the target strength of the backfilling section to prepare powder-improved soil, pouring the prepared powder-improved soil into the casing and backfilling the casing with the powder-improved soil to a predetermined height, compacting the poured powder-improved soil with a compaction load set based on the target strength, and raising the casing to a level not exceeding the height of the powder-improved soil.

[0011] In addition, another backfill construction management method according to the present invention is characterized in that, in the above-mentioned invention, the same multi-function excavator is used to remove the soil or object to be removed from the casing to a predetermined depth, and to compact the added powder-improved soil with a compaction load set based on the target strength.

[0012] In addition, another backfilling construction management method according to the present invention is characterized in that, in the above-mentioned invention, it further includes a step of conducting an in-situ test to confirm the strength of the backfilling after backfilling is completed, and determining whether the backfilling satisfies the target strength over the entire depth.

[0013] Another backfill construction management method according to the present invention is characterized in that, in the above-mentioned invention, the ground is made up of soil containing foreign matter, the removed soil is separated above ground into foreign matter and in-situ excavated soil, the in-situ excavated soil is obtained, and the obtained in-situ excavated soil is mixed and stirred with a cement-based solidification material to produce powder-improved soil. [Effects of the Invention]

[0014] According to the method for managing the construction of backfilled areas of the present invention, the method for managing the construction of backfilled areas in the ground includes the steps of erecting a casing in the ground, removing the soil or object to be removed from the erected casing to a predetermined depth, mixing and stirring the removed soil or previously prepared soil with a cement-based solidification material on the ground in a ratio set based on the target strength of the backfilled area to prepare powder-improved soil, pouring the prepared powder-improved soil into the casing and backfilling the casing with the powder-improved soil to a predetermined height, compacting the poured powder-improved soil with a compaction load set based on the target strength, and raising the casing to a level not exceeding the height of the powder-improved soil, thereby achieving the effect of compacting the powder-improved soil to construct a backfilled area that meets the target strength.

[0015] In addition, according to another backfill section construction management method of the present invention, the same multi-function excavator is used to carry out the steps of removing the soil or object to be removed from within the casing to a predetermined depth and compacting the added powder-improved soil with a compaction load set based on the target strength, thereby achieving the effect of easily and appropriately constructing the backfill section using the multi-function excavator used to remove the soil or object to be removed from within the casing.

[0016] In addition, according to another backfilling section construction management method of the present invention, after backfilling is completed, an in-situ test is conducted to confirm the strength of the backfilling section, and a step is further included in which it is determined whether the backfilling section satisfies the target strength over the entire depth, thereby achieving the effect of being able to confirm the construction quality of the backfilling section.

[0017] In addition, according to another construction management method for backfilled areas of the present invention, the ground is made up of soil containing foreign matter, and the removed soil is separated above ground into foreign matter and in-situ excavated soil, the in-situ excavated soil is obtained, and the obtained in-situ excavated soil is mixed and stirred with cement-based solidification material to produce powder-improved soil.This makes it possible to inexpensively avoid the mixing of foreign matter into the backfilled areas, and has the effect of contributing to the ease of construction and stability of the construction of new structures to be constructed later. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic flow diagram showing an embodiment of a backfilling construction management method according to the present invention. [Figure 2] Figure 2(1) is a photograph showing an example of a rolling plate attached to the lower end of a drilling tool, and (2) is a horizontal cross-sectional view of the casing and rolling plate. [Figure 3] FIG. 3 is a photograph showing an example of adjusting the load of the drilling machine in the example. [Figure 4] FIG. 4 is a diagram showing an example of the relationship between the unconfined compressive strength and depth of the backfilled portion in the example. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the backfilling construction management method according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to this embodiment.

[0020] In order to uniformly compact and consolidate the backfill area in the depth direction using powder-improved soil in a powder state, it is important to have a method for calculating the compaction load that satisfies the target strength. In an embodiment of the present invention, the compaction load is calculated based on the target strength, and by equipping a boring machine (multifunctional excavator) with a compaction mechanism, it is possible to construct the backfill area using powder-improved soil, which is inexpensive and ensures the quality of the backfill area throughout the entire depth. Note that this embodiment is intended for application to the multifunctional large-diameter boring method that is often used in existing pile removal work.

[0021] As shown in FIG. 1, the backfilling construction management method according to this embodiment is carried out by the following steps S1 to S13.

[0022] First, in step S1, the soil and cement-based solidification material that will make up the powder-improved soil are selected, and the amount of cement to be added (mixture) that will satisfy the target strength of the backfill area is determined through a pre-mix test (similar to conventional mix planning). In the pre-mix test, it is desirable to prepare the test specimen with a density equivalent to that of the local ground. It is desirable to use soil generated on-site (in-situ generated soil), but if foreign matter is mixed in or the soil is contaminated, it is sufficient to prepare high-quality soil separately.

[0023] In the next step S2, the rolling pressure that satisfies the target strength is calculated from the ultimate bearing capacity. This calculation method is a conservative evaluation because it does not take into account the effect of cement solidification.

[0024] In the next step S3, the rolling load is calculated using the cross-sectional area of the rolling plate (e.g., steel plate) attached to the tip of the drilling tool of the drilling machine and the rolling force calculated in step S2 above. Figure 2(1) is a photograph showing an example of a rolling plate attached to the bottom end of the drilling tool, and (2) is a horizontal cross-sectional view showing the relative positions of the casing and rolling plate during rolling. As shown in this figure, the casing 1 is made of a cylindrical steel pipe, and inside it is a small-diameter, disk-shaped rolling plate 2 arranged coaxially with the casing 1. The outer diameter d of the rolling plate 2 is set slightly smaller than the inner diameter D of the casing 1. The rolling plate 2 is movable horizontally and vertically within the casing 1.

[0025] In the next step S4, a rolling plate is attached to the lower end of the drilling tool, and the load of the drilling machine is adjusted to satisfy the rolling load determined in step S3 above, and the rolling mechanism is adjusted. For example, the load may be adjusted by attaching a casing to the drilling machine.

[0026] In the next step, S5, work begins to remove the existing piles, improved piles, and underground obstacles. A casing is erected in the ground surrounding the object to be removed to protect the drilling wall, and the above-mentioned drilling machine is used to remove the soil inside the casing and the object to be removed to the specified depth (similar to conventional removal work).

[0027] In the next step S6, the soil generated on site and the cement-based solidification material determined in step S1 above are stirred and mixed in powder form on the ground using a backhoe or the like to produce powder-improved soil.

[0028] In the next step S7, the powder improved soil prepared in step S6 is poured into the casing using a backhoe or the like. Note that the rolling force in step S9 described below is only transmitted to the lower part of the rolling section to the extent of the outer diameter of the rolling plate, so it is desirable to adjust the amount of powder improved soil poured in as appropriate.

[0029] In the next step S8, the casing is raised to a height that does not exceed the height of the powder-improved soil before compaction begins. The overlap width between the powder-improved soil formed by adding the powder-improved soil and the casing is preferably about 0.5 m to 1 m. The casing may also be raised after compaction.

[0030] In the next step S9, the drilling tools with the rolling plates attached are inserted into the casing and placed on the top surface of the powder conditioner, and static rolling of the powder conditioner begins. The number of times of rolling is preferably about 1 to 3 times.

[0031] In the next step S10, it is determined whether a predetermined backfilling height has been reached, and steps S7 to S9 are repeated until backfilling is complete. If the predetermined backfilling height has been reached, it is determined that backfilling is complete (Yes in step S10), and soil is piled up on top of the powder improved material to address subsidence of the ground surface (step S11).

[0032] In the next step S12, a sounding test (for example, an in-situ test such as a screw weight penetration test or an automatic ram sounding test) is carried out on the backfilled portion.

[0033] In the next step S13, it is confirmed whether the target strength is met across the entire depth based on the test results. If it is met, it is judged as passed (Yes in step S13) and construction management is terminated. On the other hand, if it is not met, it is judged as failed (No in step S13) and the process returns to step S5 above.

[0034] According to the above construction management method, powder-improved soil that is not in a slurry state can be used to compact and compress uniformly in the depth direction, and backfilling that meets the target strength throughout the entire depth can be easily and appropriately constructed. Furthermore, since the backfilling is constructed using a boring machine equipped with a compaction mechanism, there is no need to prepare special mixing equipment or compaction equipment to mix the material inside the casing, which is inexpensive. Furthermore, the construction quality of the backfilling can be confirmed by in-situ testing after backfilling is completed.

[0035] Furthermore, according to this embodiment, the rolling pressure required for backfilling work using powder-improved soil can be calculated from the ultimate bearing capacity α × c (= 1 / 2 of the target strength) × Nc, with a safety factor of 1.0. This makes it possible to build a column of powder-improved soil underground while backfilling the removal hole in the depth direction with dry powder-improved soil.

[0036] Furthermore, according to this embodiment, compared to the general backfilling method using liquefied treated soil, there is no need for labor (delivery, pouring using tremie pipes) or setup changes during construction. Compared to backfilling materials such as liquefied treated soil, which causes material separation, or lean blended cement milk, which is easily affected by muddy water, the quality of the backfilled area can be stably ensured in the depth direction, thereby avoiding problems such as poor strength development.

[0037] In the above embodiment, the ground is composed of soil containing foreign matter, and the removed soil may be separated above ground into the foreign matter and the in-situ excavated soil, which may then be mixed and stirred with a cement-based solidification material to produce powder-improved soil. This can inexpensively prevent foreign matter from being mixed into the backfilled area, and contribute to the ease and stability of construction of new structures to be constructed later.

[0038] <Example> Next, an embodiment of the present invention will be described. The total length of the backfill constructed in this example is 8.6 m, and the casing for the multi-function large-diameter drilling method is 10,000 mm in total length (2,000 mm x 5), with an inner diameter of 1,390 mm and an outer diameter of 1,500 mm. The backfill is constructed in silty fine sand ground.

[0039] The target strength of the backfilled area is 40 kPa or more in unconfined compressive strength. To meet this, the amount of cement added was set at 100 kg / m based on a preliminary mix test. 3 The specimen density was set at 1.39 g / cm in wet density. 3 The wet density of the local ground is 1.41 g / cm 3 The pressure was set as close as possible to the value indicated by the formula. In addition to cement-based solidification materials, on-site generated soil was also used for the powder improved soil. The rolling pressure during compaction was calculated as 1.2 x 20 x 5.1 = 122.4 ≒ 123 kPa, based on the ultimate bearing capacity α x c x Nc (where α is the correction coefficient for the foundation shape (= 1.2), c is the cohesion (= 20), and Nc is the bearing capacity coefficient (= 5.1)). The outer diameter of the compaction plate attached to the drilling tools was set to 1250 mm, taking into account the inner diameter of the casing. The cross-sectional area of the compaction plate was 1.23 m 2 Therefore, the required rolling load is 123kPa x 1.23m 2 = 151.3kN ≒ 15 tons or more. Next, the load of the drilling machine was adjusted to 16 tons to satisfy the rolling load. Figure 3 shows the state after adjusting the load of the drilling machine.

[0040] Using the multi-functional large-diameter drilling method, excavation was carried out to the specified depth, and powder-improved soil consisting of locally generated soil and cement-based solidification material that had been mixed above ground was poured into the casing with a backhoe. The amount poured into the first backfill layer was equivalent to a backfill height of 3m, and static compaction was carried out three times with a compaction plate attached to the drilling tools. The removed casing was then pulled up 2m. The overlap width of the powder-improved soil and the casing was 1m. The amount poured into the second and subsequent backfill layers was equivalent to a backfill height of 2m, and the procedure thereafter was the same as for the first backfill layer.

[0041] The results of the screw weight penetration test and automatic ram sounding test (each conducted twice) conducted after the backfill section was constructed are shown in Figure 4. From these results, it can be seen that the backfill section met the target strength of 40 kPa or more.

[0042] As described above, the backfill construction management method of the present invention is a method for managing the construction of a backfill section in the ground, and includes the steps of erecting a casing in the ground, removing the soil or object to be removed from the erected casing to a predetermined depth, mixing and stirring the removed soil or previously prepared soil with a cement-based solidification material on the ground in a ratio set based on the target strength of the backfill section to prepare powder-improved soil, pouring the prepared powder-improved soil into the casing and backfilling the casing with the powder-improved soil to a predetermined height, compacting the poured powder-improved soil with a compaction load set based on the target strength, and raising the casing to a level not exceeding the height of the powder-improved soil, thereby making it possible to compact the powder-improved soil and construct a backfill section that meets the target strength.

[0043] In addition, according to another construction management method for backfilling sections of the present invention, the same multi-function excavator is used to carry out the steps of removing the soil or objects to be removed from within the casing to a predetermined depth and compacting the added powder-improved soil with a compaction load set based on the target strength, so that the backfilling section can be easily and appropriately constructed using the multi-function excavator used to remove the soil or objects to be removed from within the casing.

[0044] In addition, according to another backfilling construction management method of the present invention, after backfilling is completed, an in-situ test is conducted to confirm the strength of the backfilling section, and a step is further included in which it is determined whether the backfilling section satisfies the target strength over the entire depth, thereby making it possible to confirm the construction quality of the backfilling section.

[0045] In addition, according to another construction management method for backfilled areas of the present invention, the ground is made up of soil containing foreign matter, and the removed soil is separated above ground into foreign matter and in-situ excavated soil, the in-situ excavated soil is obtained, and the obtained in-situ excavated soil is mixed and stirred with cement-based solidification material to produce powder-improved soil.This makes it possible to inexpensively avoid the mixing of foreign matter into the backfilled areas, and contributes to the ease and stability of construction of new structures to be constructed later. [Industrial Applicability]

[0046] As described above, the construction management method for backfilling sections according to the present invention is useful for the construction management of backfilling sections constructed before constructing new structures on site ground contaminated with foreign matter, and is particularly suitable for the construction management of backfilling sections constructed using powder-improved soil. [Explanation of symbols]

[0047] 1 casing 2 Rolling board

Claims

1. A method for managing construction of a backfilled portion of ground, comprising: a step of mixing and stirring the removed soil or previously prepared soil with a cement-based solidification material on the ground in a ratio set based on the target strength of the backfill area to prepare powder-improved soil; a step of pouring the prepared powder-improved soil into the casing and backfilling the casing with the powder-improved soil to a predetermined height; a step of calculating a rolling force that satisfies the target strength of the backfill area from the product of the adhesion (c) of the ground and the bearing capacity coefficient (Nc), and setting a rolling load based on the calculated rolling force; a step of compacting the poured powder-improved soil with the set rolling load; and a step of raising the casing to a level where the lower end of the casing does not exceed the height of the powder-improved soil.

2. A construction management method for a backfilled section as described in claim 1, characterized in that after backfilling is completed, an in-situ test is conducted to confirm the strength of the backfilled section, and a step is further included in which it is determined whether the backfilled section satisfies the target strength over the entire depth.

3. A construction management method for backfilling sections as described in claim 1 or 2, characterized in that the same multi-function excavator is used to carry out the steps of removing the soil or object to be removed from the casing to a predetermined depth and compacting the added powder-improved soil with a predetermined compaction load.

4. The ground is made up of soil containing foreign matter. A construction management method for backfilling areas described in any one of claims 1 to 3, characterized in that the removed soil is separated on the ground into foreign matter and in-situ excavated soil, the in-situ excavated soil is obtained, and the obtained in-situ excavated soil is mixed and stirred with a cement-based solidification material to produce powder-improved soil.

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