Methods for improving the soil quality of pile sludge

Abstract

This invention provides a method for improving the soil properties of pile sludge generated during pile construction, so as to meet both acceptance standards and treated soil utilization standards, without using cement-based or lime-based solidification materials. [Solution] In pile construction, crushed and dried bamboo chips with a moisture content of 30% or less are added to the pile sludge at a dry weight ratio of 9-15%, so that the organic matter content of the pile sludge does not exceed 15%. Preferably, the total length of the bamboo chips is 5 mm or more and 20 mm or less, the thickness of the bamboo chips is 1 mm or more and 3.5 mm or less, and the moisture content of the bamboo chips is 28% or less. The moisture content of the pile sludge is preferably 27% or more and 41% or less. The pile sludge is a coarse-grained soil containing 50% or more coarse particles, preferably a sandy soil where the sand content is greater than or equal to the gravel content. Preferably, the pile sludge has a liquid limit W L The water content is between 20% and 40%. Preferably, the pile sludge is a soil type in which the water content exceeds the liquid limit.

Description

Technical Field

[0001] The present invention relates to a method for improving the soil quality of pile sludge, which can improve the soft pile sludge so that it can be transported without using a cement-based or lime-based solidifying agent.

Background Art

[0002] Sludges such as dredged soil and pond bottom mud are soft soil materials, so it is difficult to load and transport them as they are on a truck or the like. Therefore, in order to transport them by a dump truck or the like, usually, a stabilization treatment (soil quality improvement) of mixing and stirring a cement-based or lime-based solidifying agent into the sludge is performed.

[0003] However, when mixing a cement-based solidifying agent into sludge, the cost of the solidifying agent is high, and the pH change of the soil due to the use of cement becomes a problem as an influence on the soil environment. Therefore, the inventors of the present invention have previously filed Patent Document 1 in order to solve this problem.

[0004] The "method for improving soil materials" of Patent Document 1 is to mix crushed bamboo materials at 270 kg / m , ,

[0006] or more into soil materials containing moisture at a water content ratio above the liquid limit.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Since the amount of carbon dioxide emissions during cement production is large, using a cement-based solidifying agent for improving the soil quality of pile sludge will result in an enormous amount of carbon dioxide emissions due to its use. Therefore, in order to prevent global warming, a strong reduction in carbon dioxide emissions is desired (for example, the Kyoto Protocol, etc.).

[0007] Furthermore, intermediate treatment plants that accept sludge generated during pile construction (pile sludge) are required to have an "organic matter content of 15% or less" as an acceptance standard. The 15% organic matter content requirement for this intermediate processing plant is calculated as the weight of organic matter relative to the dry weight of the soil. Hereafter, the "acceptance criteria for pile sludge at the intermediate treatment plant" will simply be referred to as the "acceptance criteria."

[0008] Furthermore, the "Standards for the Use of Treated Soil," issued on June 12, 2006, for projects under the jurisdiction of the Ministry of Land, Infrastructure, Transport and Tourism, defines "a muddy state corresponding to construction sludge" as follows: This refers to a condition where a standard dump truck cannot load the soil to a certain height, and where it is impossible for a person to walk on top of it. In terms of soil strength indicators, this condition corresponds to the cone index q. c The general range is approximately 200 kN / m 2 The following or a uniaxial compressive strength of approximately 50 kN / m 2 It is as follows: Hereafter, the above-mentioned "Standards for the Use of Treated Soil" will simply be referred to as the "Standards for the Use of Treated Soil."

[0009] Therefore, the pile sludge generated during pile construction needs to be improved to meet both the "acceptance standards" and the "treated soil utilization standards." However, applying the method described in Patent Document 1 for this purpose presents the following problems.

[0010] (1) Differences in target soil types The soil material covered by Patent Document 1 is "bottom sediment collected from a reservoir" in the example, and is soft clay. In one example, this soil has a liquid limit W L The initial water content is approximately 73% and 97%. On the other hand, in the pile sludge generated during pile construction, the fine particle content (less than 0.075 mm in particle size) is 30% or less in the examples described later, with coarse particles (fine or larger) making up the majority, and in one example, the liquid limit W L The initial water content is approximately 27% and the initial water content W is approximately 41%. Therefore, although the target soil types differ, the initial water content W is equal to the liquid limit W.L They are common in points exceeding

[0011] (2) Acceptance criteria (Acceptance criteria for bamboo sludge in intermediate treatment plants) In Patent Document 1, as the "crushed bamboo materials", three types, namely large bamboo chips, small bamboo chips, and bamboo flakes obtained by crushing "fresh bamboo materials", are used. However, the usage amount that satisfies "cone index > 200 kN / m 2 >" based on the "treatment soil usage criteria" is about 300 kg / m 3 or more in the case of bamboo flakes in the examples of Patent Document 1. Also, this usage amount is about 550 kg / m 3 or more in the case of small bamboo chips, and about 780 kg / m 3 or more in the case of large bamboo chips. Therefore, assuming the specific gravity of soft clay is about 1.5, the organic matter content is about 20% (= 300 / 1500) in the case of bamboo flakes. Similarly, the organic matter content is about 37% in the case of small bamboo chips and about 52% in the case of large bamboo chips.

[0012] Also, as described above, the organic matter content of 15% which is the acceptance criteria for the intermediate treatment plant is the weight of organic matter relative to the dry weight of the soil. For the soil material targeted by Patent Document 1, in one example, the initial water content ratio W is about 97% and the water content ratio of bamboo chips is about 55%. Therefore, in the case of Patent Document 1, the weight of organic matter relative to the dry weight of the soil is about 25% (≈ 20 × 1.97 / 1.55) even in the case of bamboo flakes with the least usage amount, and it is impossible to satisfy the above-mentioned acceptance criteria (15% or less).

[0013] (3) Forms of crushed bamboo materials The "crushed bamboo materials" used in Patent Document 1 are three types: large bamboo chips, small bamboo chips, and bamboo flakes. Among them, only bamboo flakes are promising. This is because, as described above, it is impossible to satisfy the acceptance criteria (15% or less) for small bamboo chips and large bamboo chips. However, bamboo flakes are "mostly fine material and their dimensions cannot be confirmed with the naked eye," and measurements taken using a microscope indicate that they are 0.333 to 10.5 mm in length and 0.013 to 0.8 mm in thickness. These bamboo flakes, compared to the larger and smaller bamboo chips that can be seen with the naked eye, require grinding into a mince-like consistency, resulting in excessively high manufacturing costs.

[0014] This invention was devised to solve the problems described above. In other words, the object of this invention is to provide a means for improving the soil properties of pile sludge generated during pile construction so that it satisfies both acceptance standards and treated soil utilization standards, without using cement-based or lime-based solidification materials. [Means for solving the problem]

[0015] According to the present invention, a method for improving the soil quality of pile sludge is provided, which involves mixing crushed and dried bamboo chips with a water content of 30% or less with the pile sludge at a dry weight of 9 to 15%, so that the organic matter content of the pile sludge does not exceed 15%. [Effects of the Invention]

[0016] According to the method of the present invention, bamboo chips are added to the pile sludge at a dry weight ratio of 9 to 15%, so that the organic matter content of the pile sludge does not exceed 15%, thereby reliably meeting the above-mentioned acceptance criteria (organic matter content of 15% or less).

[0017] Furthermore, Patent Document 1 uses "crushed fresh bamboo material," and the moisture content (by weight) of the bamboo material in the examples is approximately 103% for large bamboo chips, approximately 70% for small bamboo chips, and approximately 55% for bamboo flakes.

[0018] In contrast, the method of the present invention uses "bamboo chips with a moisture content of 30% or less that have been crushed and dried." Crushed and dried bamboo chips with a moisture content of 30% or less absorb moisture from the pile sludge while simultaneously clinging to and binding the sludge together. As a result, when the pile sludge does not contain organic matter, the cone index after mixing is 200 kN / m³ when bamboo chips are present in a dry weight ratio of 9% to 15% relative to the pile sludge. 2 The following examples confirmed that the above-mentioned criteria for the use of treated soil were met, exceeding the stated limits. [Brief explanation of the drawing]

[0019] [Figure 1] This is a photograph of the prepared bamboo chips. [Figure 2] This is the particle size distribution curve of the pile sludge used in the experiment. [Figure 3] This figure shows the relationship between the bamboo chip addition rate and the corn index in indoor experiments. [Figure 4] This is a photograph of the appearance of pile sludge after bamboo chips were added and mixed during a field experiment. [Modes for carrying out the invention]

[0020] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0021] (definition) "Water content" refers to the weight ratio obtained by dividing the weight x of water contained in an object by the weight y of the object when dry. In other words, water content (weight %) = x / y × 100 ... (1) The moisture content of bamboo chips is measured by drying the sample in a drying oven at around 60°C and measuring the weight change. The moisture content is then determined from the weight y at the point where the weight change stops and the weight (x+y) before drying. Since bamboo chips can burn at high temperatures, the dry state is defined as a constant weight of 60°C where there is no risk of ignition or combustion, and the test is conducted accordingly.

[0022] On the other hand, for soil, the moisture content is defined by JIS standards at 105±5℃ dry, and the process is carried out in accordance with these standards (JIS A 1203:2020). Therefore, the definition of the value of y differs between soil and bamboo chips.

[0023] As mentioned above, the 15% organic matter content requirement for acceptance at the intermediate processing plant is the weight of organic matter relative to the dry weight of the soil. In other words, the organic matter content in the acceptance criteria can be calculated as follows: Content (weight %) = a / b × 100 ... (2) where a is the weight of organic matter and b is the dry weight of the soil. Furthermore, the fine-grained content is the dry weight of soil with a particle size of 75 μm or less relative to the total dry weight of the soil.

[0024] Furthermore, the addition rate of bamboo chips based on the wet weight standard is determined by the wet weight of the bamboo chips and the wet weight of the soil. In other words, the addition rate of bamboo chips based on wet weight refers to the weight ratio obtained by dividing the wet weight c of the bamboo chips by the wet weight d of the soil. That is, the addition rate of bamboo chips based on wet weight (%WB) = c / d × 100 ... (3)

[0025] On the other hand, the dry-based addition rate of bamboo chips is based on the dry weight of the bamboo chips and the dry weight of the soil. If the moisture content ratio of the soil and bamboo chips is known, the dry weights of the soil and bamboo chips can be determined, and from this, the dry-weight-based addition rate of bamboo chips (%DB) can be calculated. In other words, the dry weight basis addition rate of bamboo chips (%DB) can be calculated as follows: Dry weight of bamboo chips / Dry weight of soil × 100 ... (4). Hereafter, the dry-weight-based addition rate of bamboo chips will simply be referred to as the "dry-base addition rate of bamboo chips."

[0026] Note that the water content ratio, content, content rate, and addition rate are all expressed as weight ratios, and unless otherwise specified below, they all refer to weight percentages.

[0027] The "corn index" is a type of indicator that represents the strength of the ground. Corn index q cThe measurement is performed by continuously pushing a cone-shaped penetrometer into the ground (or sludge) at a predetermined penetration velocity, and then dividing the average value of the penetration resistance force acting on the bottom surface of the cone by the bottom area of ​​the cone at the penetration tip. This measurement method is specified in JIS A 1228.

[0028] (Bamboo chips) Bamboo chips are made by crushing felled bamboo into thin flakes using a crushing machine, and then cutting them to a predetermined length using a cutter.

[0029] The bamboo chips used in the following examples have maximum lengths of 5 mm, 8 mm, and 20 mm. Note that the 5 mm bamboo chips contain some chips shorter than 5 mm. Similarly, the 8 mm and 20 mm bamboo chips also contain chips shorter than the maximum length. The bamboo chips prepared were all of the same thickness, ranging from 1 mm to 3.5 mm.

[0030] Hereafter, the maximum length of a bamboo chip will simply be referred to as "the length of the bamboo chip." Additionally, bamboo chips with a maximum length of 5mm are simply called "5mm chips." Similarly, bamboo chips with a maximum length of 8mm and 20mm are simply called "8mm chips" and "20mm chips," respectively.

[0031] (Moisture content of bamboo chips) The prepared bamboo chips were not used as is, but were dried beforehand in the sun or in a drying oven. In the examples described later, the moisture content of the dried bamboo chips was 30% or less.

[0032] (Properties of bamboo chips) Figure 1 shows photographs of the prepared bamboo chips, where (A) is a 5mm chip, (B) is an 8mm chip, and (C) is a 20mm chip. The bamboo chips in (A), (B), and (C) are of a size that can be seen with the naked eye in terms of length and thickness. Furthermore, they feel dry and smooth to the touch, and hardly stick to the hands. Also, clumps of tangled bamboo chips could be easily separated by hand.

[0033] (Particle size distribution of pile sludge) Figure 2 shows the particle size distribution curve of the pile sludge used in the experiment. In this diagram, (A) represents the pile sludge during the laboratory experiment, (B) and (C) represent the pile sludge during the field experiment, and (D) represents the pile sludge collected only. Hereafter, the pile sludges (A), (B), (C), and (D) will be referred to as pile sludge A, B, C, and D, respectively.

[0034] The Japanese Geotechnical Society has established classifications and names for the particle size of ground materials. Ground with a particle size of less than 0.075 mm (75 μm) is called "fine-grained," ground with a particle size of 0.075 mm (75 μm) or more but less than 75 mm is called "coarse-grained," and ground with a particle size of 75 mm or more is called "stone-grained." Based on this classification, pile sludges A, B, C, and D all contain 50% or more coarse particles and have a maximum particle size of less than 20 mm, and can be described as "coarse-grained" ground. Hereafter, ground containing "coarse grains" will be referred to as "coarse-grained soil."

[0035] In the broad classification of the Japanese Geotechnical Society, "coarse-grained soil" is divided into "sand" (particle size less than 2 mm) and "gravel" (particle size 2 mm or larger). Soil with more sand than gravel is called "sandy soil," and soil with more gravel than sand is called "gravelly soil." Based on this classification, pile sludges A, B, C, and D all have a sand content greater than or equal to gravel content, and can be described as "sandy soil."

[0036] Furthermore, pile sludge A and B are classified as "fine-grained sand" in the medium classification because they contain 15% or more "fine-grained material," and as "fine-grained sand" in the minor classification because they contain less than 5% "gravel." On the other hand, pile sludge C is classified as "sand" in the medium classification because "fine-grained" and "gravel" components make up less than 15%, and as "fine-grained sand mixed with gravel" in the minor classification because "fine-grained" and "gravel" components make up 5% or more. Furthermore, pile sludge D corresponds to "gravelly sand" in the medium classification, with "fine-grained" content being less than 15% and "gravelly" content being 15% or more, and to "gravelly sand mixed with fine-grained" in the minor classification, with "fine-grained" content being 5% or more.

[0037] The organic matter content of each pile sludge was A: 3.1%, B: 3.5%, and C: 2.0%.

[0038] (Example 1) In an indoor experiment, 5mm chips, 8mm chips, and 20mm chips were mixed separately into pile sludge A, and the cone index q was determined. c The following measurements were taken. The bamboo chips were added at weight ratios of 8%, 10%, and 12%. The moisture content of the bamboo chips was also measured.

[0039] Table 1 shows the physical properties of pile sludge A used in Example 1.

[0040] [Table 1]

[0041] As shown in Figure 2(A), pile sludge A is mostly "fine-grained particulate sand" consisting of fine and medium-grained sand with particle sizes of 0.075 mm to 0.85 mm. Also, the liquid limit W L The liquid limit W is 27% and the water content of pile sludge A is approximately 41%, and the water content of pile sludge A is 27%. L It far exceeds that limit. Therefore, pile sludge A can be described as sludge that "cannot be piled up in a dump truck, and people cannot walk on top of it."

[0042] Table 2 shows the results of the indoor experiment.

[0043] [Table 2]

[0044] In Table 2, the addition rate of bamboo chips is expressed as a weight ratio to the water-containing pile sludge A in the wet-base case, and as a weight ratio to the dry weight of pile sludge A in the dry-base case. The addition rate in the dry-base case is calculated based on the water content of pile sludge A (40.8%) and the water content of the bamboo chips.

[0045] Table 2 shows that the moisture content of the bamboo chips ranged from 12.4% to 19.3%. Furthermore, when the length of the bamboo chips is 5, 8, or 20 mm, and the dry base addition rate of the bamboo chips is in the range of 9.4 to 15.0%, the corn index q c The power is 217-5285 kN / m 2 It fell within the range. Therefore, under all conditions of the laboratory experiment, the cone index q c The target value is 200 kN / m 2 It exceeded expectations.

[0046] Figure 3 shows the bamboo chip addition rate and corn index q from laboratory experiments. c This diagram shows the relationship. In this figure, the horizontal axis represents the percentage of bamboo chips added (by weight) to the wet base and dry base, and the vertical axis represents the corn index q. c (kN / m 2 ). The broken lines in the figure show the results when the bamboo chip lengths were 5, 8, and 20 mm.

[0047] From this diagram, we can see that the cone index q of the 20mm tip c The cone index q is largest for 8mm tips and 5mm tips in that order. c It's getting smaller. Table 2 shows that the moisture content of 8mm chips and 20mm chips is 12.4% and 12.8%, respectively. Since the difference is small, the influence of bamboo chip length is greater than that of moisture content, and longer bamboo chips result in a higher corn index q. c There is a tendency for it to increase. Furthermore, as can be seen from Table 2 and Figure 3, even when the dry base addition rate for 5mm tips is the minimum of 9.4%, the cone index q c The target value is 200 kN / m 2 This has been achieved. Therefore, if the moisture content of the bamboo chips is 20% or less, the dry base addition rate of the bamboo chips can be reduced to 9.4%.

[0048] (Example 2) In field experiments for pile construction, 8mm chips were mixed into pile sludge B, and 5mm chips and 20mm chips were mixed into pile sludge C, respectively, and the cone index q of each was determined. c We measured it.

[0049] Table 3 shows the physical properties of pile sludge B and C used in Example 2.

[0050] [Table 3]

[0051] As is clear from Figures 2(A) and (B), pile sludge B has almost the same particle size distribution as pile sludge A, and is mostly "fine-grained particulate sand" consisting of fine and medium-grained sand with particle sizes of 0.075 mm to 0.85 mm. Also, the liquid limit W L The water content of pile sludge B is 36.5%, and the water content of pile sludge B is approximately 37.5%, and the water content of pile sludge is at the liquid limit W L It slightly exceeds this limit. Therefore, pile sludge B can be described as sludge that "cannot be piled up in a dump truck, and people cannot walk on it." On the other hand, as mentioned above, pile sludge C differs from pile sludges A and B in its particle size distribution, with less than 10% being fine particles with a particle size of less than 0.075 mm, approximately 30% being coarse particles with a particle size of more than 0.85 mm, and the remainder being fine sand and medium sand, making it "fine-grained gravel mixed sand".

[0052] Table 4 shows the results of the field experiment.

[0053] [Table 4]

[0054] In Table 4, the addition rate of bamboo chips is expressed as a weight ratio to the water-containing pile sludge B and C in the wet base, and as a weight ratio to the dry weight of pile sludge B and C in the dry base. The addition rate in the dry base is calculated based on the water content of pile sludge B and C (37.5% and 27.6%).

[0055] In Table 4, for 5mm chips, the moisture content of the bamboo chips was 19.6%, which is similar to the 19.3% in Example 1. Furthermore, the dry base addition rate for the bamboo chips was 11.5%, and the cone index q c It is 230 kN / m 2 In Example 1, the dry base addition rate of the bamboo chips was 11.8%, and the cone index was 315 kN / m². 2 It is lower than, but the Corn index q c The target value is 200 kN / m 2 It has achieved the ultimate.

[0056] Furthermore, in Table 4, the moisture content of the bamboo chips was 27.3% for 8mm chips, which was more than twice the 12.4% in Example 1. In this example, the dry base addition rate for the bamboo chips was 10.8%, and the cone index q c It is 680 kN / m 2 In Example 1, the bamboo chip dry base additive rate was 12.5%, and the cone index was 756 kN / m². 2 Corn index q of a similar magnitude c This was obtained.

[0057] On the other hand, in Table 4, the moisture content of the bamboo chips was 26.8% for 20mm chips, which was more than twice the 12.8% in Example 1. Also, in this example, the dry base addition rate for the bamboo chips was 10.8%, and the cone index q c It is 180 kN / m 2 And the cone index q c The target value is 200 kN / m 2 It fell below that. This is likely because the ignition loss of pile sludge after bamboo chip addition was 5.9%, indicating that the amount of bamboo chips added was less than expected.

[0058] Furthermore, Figure 3 shows that the length of the bamboo chips has a greater influence than the moisture content, and that longer bamboo chips result in a higher corn index q. c Since the value will increase, if the dry base addition rate of the 20mm tip is 9% or more, the cone index q c The target value is 200 kN / m 2 It can be said that it definitely surpasses that.

[0059] From the above-described examples 1 and 2, it became clear that by satisfying the following conditions, pile sludge generated during pile construction can be improved to meet the "acceptance criteria" and "treated soil utilization criteria" without using cement-based or lime-based solidification materials.

[0060] (1) A method for improving the soil quality of pile sludge generated during pile construction, which involves mixing crushed and dried bamboo chips with a moisture content of 30% or less with the pile sludge at a dry weight ratio of 9-15%, so that the organic matter content of the pile sludge does not exceed 15%.

[0061] If the pile sludge generated during pile construction does not contain organic matter, the bamboo chip content will be between 9% and 15% by weight relative to the dry weight of the pile sludge, thus reliably meeting the acceptance standard (15% or less). If the pile sludge generated during pile construction contains organic matter, and the organic matter content in the pile sludge is less than 6%, then the bamboo chips will be 9% or more, and the total organic matter including the bamboo chips will be 15% or less. Thus, it can similarly meet the acceptance criteria (15% or less).

[0062] Furthermore, by using crushed and dried bamboo chips with a moisture content of 30% or less, the corn index q c The target value is 200 kN / m 2 It can consistently exceed the standard and meet the standards for the use of treated soil.

[0063] The basis for the "moisture content of 30% or less" is that the moisture content of the 8mm tip in Example 2 was 27.3%. In Example 2, an 8mm chip with a water content of 27.3% was used, generating 680kN / m 2 Corn index q c This has been obtained, and even with a moisture content of 30%, the corn index q c The target value is 200 kN / m 2 It exceeds the standard and can be judged to meet the criteria for the use of treated soil.

[0064] Furthermore, if the standard values ​​cannot be met with bamboo chips alone, a solidifying agent may be added. In other words, the effect of CO2 sequestration by bamboo chips is greater than the reduction in cement usage, so it's acceptable to use a small amount of bamboo chips to achieve carbon neutrality.

[0065] In addition to condition (1), it is preferable that the following conditions be met.

[0066] (2) The process must include a step for inspecting the organic matter content and water content of the pile sludge. This process ensures that the acceptance standard (15% or less) is reliably met by calculating the amount of bamboo chips to account for organic matter in the pile sludge if it contains organic matter. Furthermore, the amount of bamboo chips required for pile sludge containing moisture generated during pile construction can be calculated from the water content of the pile sludge.

[0067] (3) The total length of the bamboo chips must be between 5 mm and 20 mm. The embodiments of the present invention are carried out within this range. However, the present invention is not limited to this range and may be less than 5 mm or more than 20 mm.

[0068] (4) The thickness of the bamboo chips must be between 1 mm and 3.5 mm. In the embodiments of the present invention, this range was observed. However, the present invention is not limited to this range, and may be less than 1 mm or greater than 3.5 mm.

[0069] (5) The moisture content of the bamboo chips must be 28% or less. In the embodiments of the present invention, the corn index q was set at moisture content of 19.3% and 19.6% for 5mm chips, 12.4% and 27.3% for 8mm chips, and 12.8% for 20mm chips. c The target value is 200 kN / m 2 It far exceeds that. Furthermore, the dry base addition rate of bamboo chips in the examples ranged from 9.4% to 15.0%.

[0070] Since crushed and dried bamboo chips are thought to absorb moisture from the pile sludge and bind it together, the lower the moisture content of the bamboo chips, the better the cone index q. c It has a high effect in enhancing [something]. Therefore, the lower the moisture content of the bamboo chips, the better, and it may be 12% or less.

[0071] (6) The water content of the pile sludge shall be between 27% and 41%. In the embodiments of the present invention, the water content of pile sludge A was approximately 40.8%, the water content of pile sludge B was approximately 37.5%, and the water content of pile sludge C was approximately 27.6%, and in all cases the effects of the present invention were obtained. However, the present invention is not limited to this scope, and the water content of the pile sludge may be less than 27% or more than 41%.

[0072] (7) The pile sludge is preferably coarse-grained soil containing 50% or more of coarse particles with a particle size of 0.075 mm or larger, and more preferably sandy soil in which the sand content is equal to or greater than the gravel content. In the examples, pile sludges A and B were "fine-grained fragmented sand" containing 60% or more particles with a particle size of 0.075 mm or larger, while pile sludges C and D were "fine-grained fragmented sand" containing 80% or more particles with a particle size of 0.075 mm or larger. Furthermore, the effects of the present invention were confirmed in pile sludge A, B, and C. However, the pile sludge targeted by this invention may be coarse-grained soil containing 50% or more coarse particles, as long as it is sludge that "cannot be piled up in a dump truck and cannot be walked on by a person."

[0073] (8) The pile sludge is at the liquid limit W L The percentage must be between 27% and 40%. Liquid limit W L In the example of Patent Document 1, the figure was approximately 73%, while in the examples of the present invention, it was approximately 27% and approximately 36.5%, and measurement was not possible for pile sludge C and D. The reason for this is that the target soil types are different; the target sludge in Patent Document 1 is "soft clayey," while the pile sludge in the embodiment of the present invention is "fine-grained particulate sand" or "fine-grained gravel-mixed sand." Furthermore, the liquid limit W of pile sludge according to the present invention L This is not limited to the scope described above.

[0074] (9) The water content of pile sludge is the liquid limit W L To exceed. This is similar to Patent Document 1 in that "the water content of the sludge exceeds the liquid limit." However, liquid limit W L Although measurement was not possible with pile sludge C and D, they were similar to pile sludge A and B in that they were "too heavy to be piled up in a dump truck, and too heavy for a person to walk on." Therefore, the pile sludge targeted by this invention has a water content that is at the liquid limit W. L It is not limited to soil types exceeding this level.

[0075] Figure 4 shows photographs of the pile sludge after bamboo chips were added and mixed in a field experiment. (A) shows the sludge after 5mm chips were added, (B) after 8mm chips were added, and (C) after 20mm chips were added and mixed.

[0076] The chip-containing pile sludge with 20mm chips added, as shown in Figure 4(C), is difficult to sell as recycled soil because the bamboo chips are conspicuous as foreign matter in the sludge, and its reuse options are likely to be limited. On the other hand, with the chip-infused pile sludge shown in Figure 4(A), dust generation was observed during construction because the bamboo chips were too fine. Therefore, it is considered that bamboo chips smaller than 5 mm pose problems in terms of workability. Based on the results of the field experiments described above, it can be concluded that the usable total length of bamboo chips is between 5mm and 20mm. Furthermore, among the lengths of 5mm, 8mm, and 20mm, 8mm is deemed to be the optimal length.

[0077] (Construction method) At the site of pile construction, the addition of crushed and dried bamboo chips is preferably carried out in the following manner, for example.

[0078] (1) Inspect the organic matter content and water content of the pile sludge generated during pile construction. This process allows for the calculation of the amount of bamboo chips to be used, taking into account any organic matter present in the pile sludge. In this example, however, the pile sludge is assumed to contain no organic matter (organic matter content = 0). (2) The crushed and dried bamboo chips are measured in advance for their total length, thickness, and moisture content, and then stored in a predetermined weight in a flexible container bag, for example, with a capacity of 1 m³. 3 One flexible container bag can hold approximately 300 kg of bamboo chips with a moisture content of 30% by wet weight. (3) At the pile construction site, the generated pile sludge is placed in a container of known weight, and the weight of the pile sludge is measured by lifting the container with a crane or the like, and the dry weight of the pile sludge is calculated using the water content of the pile sludge. (4) For example, to pile sludge weighing and converted using the method described above, the contents of one flexible container bag containing 300 kg of bamboo chips with a moisture content of 30% (wet weight) are added on-site and mixed.

[0079] This construction method allows for the mixing of crushed and dried bamboo chips, at a weight ratio of approximately 9.2% relative to the dry weight of the pile sludge, with the pile sludge generated during the pile construction work, right at the construction site.

[0080] According to the embodiments of the present invention described above, bamboo chips are added to the pile sludge at a dry weight ratio of 9-15%, so that the organic matter content of the pile sludge does not exceed 15%, thereby reliably meeting the acceptance criteria (organic matter content of 15% or less) described above.

[0081] Furthermore, Patent Document 1 uses "crushed fresh bamboo material," and the moisture content (by weight) of the bamboo material in the examples is approximately 103% for large bamboo chips, approximately 70% for small bamboo chips, and approximately 55% for bamboo flakes.

[0082] In contrast, the method of the present invention uses "bamboo chips with a moisture content of 30% or less that have been crushed and dried." Crushed and dried bamboo chips with a moisture content of 30% or less absorb moisture from the pile sludge while simultaneously clinging to and binding the sludge together. As a result, when the pile sludge does not contain organic matter, the cone index after mixing is 200 kN / m³ when the weight ratio of bamboo chips to the pile sludge is between 9% and 15%. 2 The above-described examples confirmed that the above-described criteria for the use of treated soil can be reliably met.

[0083] Furthermore, the "crushed and dried bamboo chips with a moisture content of 30% or less" in this invention have a total length of 5 mm or more and 20 mm or less, and a thickness of 1 mm or more and 3.5 mm or less. This length and thickness are comparable to the small bamboo chips described in Patent Document 1. Therefore, unlike the bamboo flakes described in Patent Document 1, which "are mostly made of fine material and cannot be visually inspected," this product does not require mincing, and can therefore be manufactured at a low cost.

[0084] Furthermore, using the construction method described above, it is possible to mix the pile sludge generated during pile construction with bamboo chips that have been crushed and dried at the pile construction site in a desired weight ratio relative to the pile sludge. Furthermore, since the use of cement-based or lime-based solidifying agents in conventional pile construction can be replaced with bamboo chips, this invention can significantly contribute to reducing carbon dioxide emissions to prevent global warming.

[0085] The scope of the present invention is not limited to the embodiments described above, but is indicated by the claims, and includes all modifications within the meaning and scope of equivalence to the claims. [Explanation of symbols]

[0086] a. Weight of organic matter, b. Dry weight of soil, c. Wet weight of bamboo chips, d. Wet weight of soil, q. c Corn index, W; Initial moisture content, W L Liquid limit, x: weight of water, y: weight of dry object

Claims

1. A method for improving the soil quality of pile sludge, comprising mixing crushed and dried bamboo chips with a moisture content of 30% or less with the pile sludge, in an addition ratio of 9% to 15% by dry weight, so that the organic matter content of the pile sludge does not exceed 15%.

2. The method for improving the soil properties of pile sludge according to claim 1, further comprising the step of inspecting the organic matter content and water content ratio of the pile sludge.

3. The method for improving the soil quality of pile sludge according to claim 1, wherein the total length of the bamboo chips is 5 mm or more and 20 mm or less.

4. The method for improving the soil quality of pile sludge according to claim 1, wherein the thickness of the bamboo chips is 1 mm or more and 3.5 mm or less.

5. The method for improving the soil quality of pile sludge according to claim 1, wherein the moisture content of the bamboo chips is 28% or less.

6. The method for improving the soil properties of pile sludge according to claim 1, wherein the water content of the pile sludge is 27% or more and 41% or less.

7. The method for improving the soil quality of pile sludge according to claim 1, wherein the pile sludge is coarse-grained soil containing 50% or more of coarse particles with a particle size of 0.075 mm or larger.

8. The method for improving the soil properties of pile sludge according to claim 1, wherein the pile sludge is sandy soil in which the sand content is greater than or equal to the gravel content.

9. The method for improving the soil properties of pile sludge according to claim 1, wherein the liquid limit of the pile sludge is 27% or more and 40% or less.

10. The method for improving the soil properties of pile sludge according to claim 1, wherein the pile sludge is a soil type in which its water content exceeds the liquid limit.

Images