Method for dehydrating soil and sand

Abstract

To provide a method for dewatering earth and sand that can quickly and efficiently dewater earth and sand containing a large amount of water using a polymer flocculant.SOLUTION: Relational data between a weight ratio of soil particles in a raw sediment with respect to a weight of a polymer flocculant mixed in the raw sediment and an initial drainage evaluation ratio indicating a degree of improvement in drainage efficiency of treated sediment with respect to a drainage efficiency of raw sediment in an initial stage of drainage is obtained. Then, based on the relational data, an amount of the polymer flocculant to be mixed with the raw sediment to be dewatered is determined, and the treated sediment produced by mixing the raw sediment with the polymer flocculant is dewatered in an initial stage of production.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a method for dewatering earth and sand, and more particularly, to a method for dewatering earth and sand that can efficiently dewater earth and sand containing a large amount of moisture at an early stage using a polymer flocculant.

Background Art

[0002] For earth and sand containing a large amount of moisture such as dredged soil, a polymer flocculant may be mixed as a modifier to reduce fluidity and improve handleability in transportation work. In this way, the polymer flocculant has been used by paying attention to its effect of enhancing the water retention of the original earth and sand.

[0003] A method has also been proposed to improve the drainage efficiency of earth and sand by mixing a polymer flocculant at a predetermined blending ratio to modify the earth and sand (see, for example, Patent Document 1). The treated earth and sand produced by mixing a polymer flocculant at a predetermined blending ratio with the original earth and sand has improved drainage efficiency in the initial drainage stage compared to the original earth and sand before mixing the polymer flocculant during the initial period of production (for example, within 48 hours from the time of production). On the other hand, since the water retention of the treated earth and sand increases due to the polymer flocculant when the period beyond the initial production period is exceeded, the final drainage volume of the treated earth and sand is less than that of the original earth and sand. Therefore, simply obtaining the relationship data between the addition amount of the polymer flocculant to the original earth and sand and the final drainage volume of the treated earth and sand cannot accurately determine the appropriate addition amount of the polymer flocculant to the original earth and sand that is effective for improving the drainage efficiency in the initial drainage stage of the treated earth and sand. Therefore, there is room for improvement in efficiently dewatering earth and sand at an early stage using a polymer flocculant.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention aims to provide a method for dewatering earth and sand that can efficiently dewater earth and sand containing a large amount of water at an early stage using a polymer flocculant.

Means for Solving the Problems

[0006] In order to achieve the above object, the method for dewatering earth and sand of the present invention dehydrates the treated earth and sand produced by mixing a polymer flocculant with raw earth and sand not exceeding 48 hours from the production of the treated earth and sand in a method for dewatering earth and sand that is dehydrated during the initial period of production. In this method, the weight ratio of the soil particles of the raw earth and sand to the weight of the polymer flocculant mixed in the raw earth and sand, and the initial production period the initial drainage evaluation ratio indicating the degree of improvement in the drainage efficiency of the treated earth and sand with respect to the drainage efficiency of the raw earth and sand in the relevant data are used to determine the addition amount of the polymer flocculant to be mixed in the raw earth and sand to be dehydrated. When, for each of the treated earth and sand and the original earth and sand, a test is conducted to measure the amount of drained water discharged from each of the earth and sand while contained in a storage container and set to the same compressive stress, and the final drained water volume of each of the earth and sand is estimated by hyperbolic approximation for the time-dependent change data of the amount of drained water of each of the earth and sand under preset predetermined conditions, and the intermediate drained water volume is divided by the intermediate elapsed time from the start point of drainage to the point in time when the intermediate drained water volume reaches a predetermined ratio of the final drained water volume to calculate the initial drainage gradient of each of the earth and sand, and the ratio of the initial drainage gradient of the treated earth and sand to the initial drainage gradient of the original earth and sand is used as the initial drainage evaluation ratio, and the addition amount of the polymer flocculant is determined so as to be within the allowable range of the weight ratio at which the initial drainage evaluation ratio in the relevant data is equal to or higher than the set threshold value This is the gist of the present invention.

Effects of the Invention

[0007] According to the present invention, by paying attention to the relational data between the weight ratio of the soil particles of the raw earth and sand to the weight of the polymer flocculant mixed in the raw earth and sand, and the initial drainage evaluation ratio indicating the degree of improvement in the drainage efficiency of the treated earth and sand with respect to the drainage efficiency of the raw earth and sand at the initial stage of drainage, it becomes possible to simply and accurately determine the appropriate addition amount of the polymer flocculant to the raw earth and sand, which is effective for increasing the drainage efficiency at the initial stage of drainage. As a result, it is possible to efficiently dewater earth and sand containing a large amount of water at an early stage using a polymer flocculant.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the method for dehydrating earth and sand of the present invention will be described based on the embodiments shown in the drawings.

[0010] The present invention is a method for dehydrating treated earth and sand produced by mixing a polymer flocculant with original earth and sand during the initial period of production.

[0011] Polymer flocculants are generally noted for their effect of enhancing water retention and are used as modifiers for reducing the fluidity of earth and sand containing a large amount of moisture such as dredged soil or as flocculants for water treatment. When a polymer flocculant is mixed with the original earth and sand at a predetermined blending ratio, a large number of flocs are formed in the earth and sand due to the flocculation action of the polymer flocculant. And, a part of the moisture in the soil is retained between the soil particles forming the flocs, and the treated earth and sand with lower fluidity than the original earth and sand is obtained. The remaining moisture in the soil that is not taken in between the soil particles forming the flocs becomes free water (free water) and is in a state where it is easily drained.

[0012] The predetermined blending ratio of the polymer flocculant mixed with the original earth and sand varies depending on the type of the polymer flocculant, etc. For example, for 1 m of the original earth and sand 3It is about 0.1 kg to 20 kg per hit. As the polymer flocculant, for example, organic polymer polymers such as cationic polymers, anionic polymers, nonionic polymers, and amphoteric polymers, and inorganic flocculants such as polyaluminum chloride (PAC) can be used. As the polymer flocculant, those having polyvalent positive ions or metal ions in water, specifically, polyaluminum chloride, band sulfate (aluminum sulfate), ferric polysulfate, alum, etc. can also be used. Alternatively, as the polymer flocculant, a modifier mainly composed of polyacrylate, sodium hexametaphosphate, etc. can also be used.

[0013] Figure 1 shows the time-dependent change data of the drainage volume of the original soil sand without the polymer flocculant and the treated soil sand produced by mixing the polymer flocculant with the original soil sand at a predetermined mixing ratio. The data R shown by the broken line in the figure represents the data of the original soil sand. The initial water content ratio of the original soil sand is set to 1.6 times the liquid limit. The data K shown by the thick solid line in the figure represents the data of the treated soil sand produced by mixing a cationic polymer (Hymolock MX-9134A: manufactured by Hymol Co., Ltd.) and polyaluminum chloride (PAC) with the original soil sand. The addition amount of the cationic polymer to the original soil sand is 10.0 kg / m 3 , and the addition amount of polyaluminum chloride is 2.5 kg / m 3 is set. The polymer flocculant (cationic polymer) used is in a liquid state and contains water and the like in addition to the polymer component.

[0014] Polyaluminum chloride reacts with the alkali component in water to generate positively charged aluminum hydroxide, and has the function of promoting the formation of flocs by neutralizing the negative charge of soil particles. When using a specific polymer flocculant such as a cationic polymer, mixing polyaluminum chloride improves the drainage performance of the treated soil sand. Each of the drainage volume data shown in Figure 1 represents the measurement result of the drainage volume when the loading stress on the soil sand is set to 20 kPa using the drainage test device 1 having the loading mechanism 4 illustrated in Figure 3. The loading stress is calculated by dividing the loading force applied to the soil sand by the loading area.

[0015] As shown in Fig. 1, for both earth sands, the drainage volume per unit time decreases over time, but the final drainage volume of the original earth sand (data R) is the largest. Therefore, it can be seen that the water retention property of the earth sand is enhanced by the polymer flocculant, and the final drainage volume of the treated earth sand (data K) is suppressed. Here, paying attention to the data of the change over time of the drainage volume in the initial period of the elapsed time in Fig. 1, it was as shown in Fig. 2.

[0016] As shown in Fig. 2, in the initial period of manufacturing the treated earth sand, different from the final drainage volume in Fig. 1, when an appropriate amount of polymer flocculant is mixed into the original earth sand, the drainage property of the treated earth sand (data K) is improved compared to the original earth sand (data R). Fig. 2 shows the data from the time when the treated earth sand was manufactured until 3 hours. This initial manufacturing period is, for example, a period not exceeding 48 hours, a period not exceeding 24 hours, or even a period not exceeding 6 hours from the time of manufacture, and this drainage characteristic is remarkable. The present invention was created by paying attention to this point.

[0017] As shown in Fig. 3, the inventors used a drainage test apparatus 1 and various types of earth sands to conduct drainage tests on each original earth sand and the treated earth sand manufactured by mixing a polymer flocculant into each original earth sand. The drainage test apparatus 1 includes a bottomed cylindrical storage container 2 that stores the earth sand S (original earth sand or treated earth sand), upper and lower drain pipes 3 that discharge the water W discharged from the earth sand S to the outside of the storage container 2, a loading mechanism 4 that applies a loading stress to the earth sand S, and a water storage section 5 that stores the water W discharged from the drain pipes 3. Regarding the case where the earth sand S is stored inside the storage container 2 and a loading stress is applied to the earth sand S by the loading mechanism 4, the drainage volume was measured. Then, an analysis was conducted on the relationship between various indexes indicating the consistency of the original earth sand and the drainage characteristics of the treated earth sand.

[0018] As a result, when the data was sorted while paying attention to the activity of the original soil and sand, it was found that there is a high correlation between the activity of the original soil and sand and the degree of improvement in drainage efficiency during the initial period of production by mixing a polymer flocculant with the original soil and sand to produce treated soil and sand. And based on the magnitude of the activity of the original soil and sand, it was found that it is possible to determine whether mixing a polymer flocculant with the original soil and sand is effective in increasing the drainage efficiency during the initial period of production of the treated soil and sand.

[0019] Activity is an index indicating the strength of chemical bonds between soil particles, and is a value obtained by dividing the plasticity index of the original soil and sand by the clay content (%) of particles with a particle size below a predetermined value contained in the original soil and sand. The aforementioned predetermined value is generally defined as 2 μm, and in this embodiment, the predetermined value is 2 μm. The plasticity index is the difference between the liquid limit and the plastic limit, and can be grasped, for example, by conducting the liquid limit and plastic limit tests of soil specified in JIS A 1205. The clay content of particles with a particle size below the predetermined value contained in the original soil and sand can be grasped, for example, by conducting the particle size test method of soil specified in JIS A 1204. If the clay matrix constituting the original soil and sand is of the same type, the activity of the original soil and sand will be approximately the same value. Incidentally, the aforementioned predetermined value may be about 2 μm to 5 μm, and within this range, it can be used as an index of activity in the same way as when the predetermined value is 2 μm.

[0020] Furthermore, the inventors repeatedly analyzed the relationship between the addition amount of the polymer flocculant to the original soil and sand and the drainage efficiency during the initial period of production of the treated soil and sand. As a result, it was found that there is a high correlation between the weight ratio of the soil particles of the original soil and sand to the weight of the polymer flocculant mixed in the original soil and sand (hereinafter referred to as the soil particle polymer ratio) and the initial drainage evaluation ratio indicating the degree of improvement in the drainage efficiency of the treated soil and sand with respect to the drainage efficiency of the original soil and sand at the initial stage of drainage (during the initial period of production of the treated soil and sand).

[0021] Therefore, in the present invention, based on the relationship data between the soil particle-polymer ratio and the initial drainage evaluation ratio, the addition amount of the polymer flocculant to be mixed with the raw soil and sand to be dehydrated is determined. The weight of the soil particles of the raw soil and sand described above is the weight obtained by subtracting the weight of the moisture contained in the raw soil and sand from the weight of the raw soil and sand (soil particles + moisture) in the state containing moisture. Hereinafter, the weight of the polymer flocculant in the soil particle-polymer ratio is the weight including moisture and the like other than the polymer component contained in the polymer flocculant. Since there is a high correlation with the initial drainage evaluation ratio mainly due to the weight ratio of the soil particles of the raw soil and sand to the weight of the polymer component contained in the polymer flocculant, for example, the soil particle-polymer ratio can also be calculated by using only the weight of the polymer component contained in the polymer flocculant as the weight of the polymer flocculant.

[0022] Specific examples of data showing the correlation between the activity of the raw soil and sand and the degree of improvement in drainage efficiency during the initial period of production by mixing a polymer flocculant with the raw soil and sand to produce treated soil and sand will be described below.

[0023] Using the drainage test apparatus 1, drainage tests were conducted on a plurality of types of raw soil and sand and the treated soil and sand produced from each of the raw soil and sand, and time-dependent change data of the drainage volume under predetermined conditions set in advance for the raw soil and sand and the treated soil and sand, as illustrated in FIG. 4, were created respectively. Then, the final drainage volume of each soil (raw soil and sand, treated soil and sand) was estimated by hyperbolic approximation for the time-dependent change data of the drainage volume.

[0024] As illustrated in FIG. 4, in both the raw soil and sand and the treated soil and sand, the drainage volume per unit time is large during a period not exceeding approximately 6 hours from the start point (t = 0) of soil drainage, and as time passes after exceeding approximately 6 hours from the start point of drainage, the drainage volume per unit time gradually decreases. Then, when exceeding approximately 20 hours from the start point of drainage, the drainage volume per unit time significantly decreases, and eventually the final drainage volume W f is reached. Therefore, if the time-dependent change data of the drainage volume from the start point of drainage to about 20 hours is obtained, the final drainage volume W f of the soil (raw soil and sand, treated soil and sand) can be estimated by hyperbolic approximation.

[0025] As shown in FIG. 4, in the present invention, the final drainage volume W of the earth and sand (raw earth and sand, treated earth and sand) f at a predetermined ratio is the intermediate drainage volume W m , and the elapsed time from the start point of drainage of the earth and sand to the point when the intermediate drainage volume W m is reached is the intermediate elapsed time t m . Then, as shown by the dashed line in FIG. 4, the value obtained by excluding the intermediate drainage volume W m by the intermediate elapsed time t m is the initial drainage gradient E d (= W m / t m ). That is, the origin (0, 0) of the graph indicating the start point of drainage and the point P (t m , W m , W m ) corresponding to the intermediate drainage volume W on the graph, the gradient of the secant line passing through is the initial drainage gradient E d .

[0026] In this embodiment, 50% of the final drainage volume W of the earth and sand f is taken as the intermediate drainage volume W m (= W f / 2). The intermediate drainage volume W m is appropriately set, for example, within the range of 30% or more and 70% or less of the final drainage volume W f . The magnitude of the initial drainage gradient E d indicates the ease of drainage from the start point of drainage of the earth and sand to the point when the intermediate drainage volume W m is reached, and shows that the higher the initial drainage gradient E d , the higher the drainage efficiency of the earth and sand in the initial period of drainage.

[0027] Figure 5 shows the data obtained by graphing the relationship between the activity of the original soil and sand and the initial drainage evaluation ratio of the treated soil and sand produced from the original soil and sand. The data K in the figure shows the data of the treated soil and sand produced by mixing a cationic polymer (Hymolock MX-9134A: manufactured by Hymol Co., Ltd.) and polyaluminum chloride as a polymer flocculant with the original soil and sand at the predetermined mixing ratio described above. In Figure 5, the data is shown for the case where the loading stress applied to the treated soil and sand is varied at a plurality of levels (when the magnitudes of the loading stress are 10 kPa, 20 kPa, and 30 kPa).

[0028] The initial drainage evaluation ratio of the treated soil and sand described above is the ratio of the initial drainage gradient E d of the treated soil and sand to the initial drainage gradient E d of the original soil and sand, and indicates the degree of improvement in the drainage efficiency during the initial production period by mixing a polymer flocculant with the original soil and sand to produce the treated soil and sand. The initial drainage evaluation ratio is calculated by dividing the initial drainage gradient E d of the treated soil and sand by the initial drainage gradient E d of the original soil and sand. When the initial drainage evaluation ratio is greater than 1, there is a drainage promotion effect by mixing a polymer flocculant with the original soil and sand, and the higher the initial drainage evaluation ratio, the higher the degree of improvement in the drainage efficiency during the initial production period by mixing a polymer flocculant. When the initial drainage evaluation ratio is 1 or less, it indicates that there is no drainage promotion effect by mixing a polymer flocculant with the original soil and sand.

[0029] As can be seen from the data in Figure 5, the initial drainage evaluation ratio has a correlation with the activity of the original soil and sand. The higher the activity of the original soil and sand, the higher the initial drainage evaluation ratio, and the greater the drainage promotion effect by mixing a polymer flocculant. In particular, it can be seen that when a polymer flocculant is mixed with the original soil and sand having a high activity, the degree of improvement in the drainage efficiency during the initial production period of the treated soil and sand is significantly increased.

[0030] Thus, there is a correlation between the activity of the original soil and sand and the drainage promotion effect by mixing a polymer flocculant with the original soil and sand. Therefore, by grasping the activity of the original soil and sand, it is possible to determine whether mixing a polymer flocculant with the original soil and sand is effective in enhancing the drainage efficiency during the initial period of manufacturing the treated soil and sand.

[0031] Figure 6 shows the relationship data between the weight ratio of the soil particles of the original soil and sand to the weight of the polymer flocculant mixed in the original soil and sand (soil particle-polymer ratio) and the initial drainage evaluation ratio indicating the degree of improvement in the drainage efficiency of the treated soil and sand with respect to the drainage efficiency of the original soil and sand at the initial stage of drainage. The data X (triangle symbol), data Y (circle symbol), and data Z (square symbol) in the figure respectively show the data of the treated soil and sand produced by mixing a cationic polymer (Hymolock MX-9134A: manufactured by Hymol Co., Ltd.) and polyaluminum chloride as a polymer flocculant with the original soil and sand. The data X, Y, and Z respectively show the cases where the initial water content ratio of the original soil and sand is 1.1 times, 1.6 times, and 2.5 times the liquid limit. Furthermore, in Figure 6, for the data X, Y, and Z respectively, three sets of data (open symbols, filled symbols, double-line symbols) are shown for the case where the loading stress applied to the treated soil and sand is varied at multiple levels. Also, in Figure 6, the relationship between the soil particle-polymer ratio and the initial drainage evaluation ratio predicted from the test results when the loading stress is set to the condition indicated by the open symbols is shown by a dashed curve.

[0032] The polymer flocculant has the property of acting on the soil particles of the original soil and sand. In the treated soil and sand with an appropriate weight of the polymer flocculant mixed with respect to the weight of the soil particles of the original soil and sand, a large number of flocs are formed by the flocculation action of the polymer flocculant, and a part of the moisture in the soil is retained between the soil particles forming the flocs, resulting in a state where the fluidity is moderately reduced. Also, the remaining moisture in the soil that is not taken in between the soil particles forming the flocs becomes free water, and this free water is easily drained to the outside. Therefore, as exemplified in Figure 6, the initial drainage gradient ratio of the data Y with an appropriate value of the soil particle-polymer ratio, which is the weight ratio of the soil particles of the original soil and sand to the weight of the polymer flocculant mixed in the original soil and sand, shows a high value.

[0033] When the polymer flocculant is insufficient for the soil particles of the original soil and sand, the flocs that retain the moisture in the soil cannot be sufficiently formed by the polymer flocculant. Therefore, the fluidity of the treated soil and sand does not decrease sufficiently, and the dehydration efficiency at the initial stage of drainage of the treated soil and sand is relatively low. For this reason, the initial drainage gradient ratio of data X with an excessive soil particle-polymer ratio is relatively low. On the other hand, when the polymer flocculant is added excessively to the soil particles of the original soil and sand, excessive flocs are formed in the soil and sand by the polymer flocculant. And a lot of moisture in the soil is retained in the flocs, and the amount of free water not incorporated into the flocs decreases. Therefore, it becomes difficult for the moisture in the treated soil and sand to be discharged to the outside, and the dehydration efficiency at the initial stage of drainage of the treated soil and sand is relatively low. For this reason, the initial drainage gradient ratio of data Z with an excessively small soil particle-polymer ratio is relatively low.

[0034] Thus, there is an appropriate soil particle-polymer ratio, or a range thereof, for enhancing the drainage promoting effect at the initial stage of drainage of the treated soil and sand. Therefore, in the present invention, by using the relationship data between the soil particle-polymer ratio and the initial drainage evaluation ratio, it is possible to easily and accurately determine an appropriate addition amount of the polymer flocculant to the original soil and sand that is advantageous for enhancing the drainage efficiency at the initial stage of drainage. As a result, it is possible to efficiently dehydrate the soil and sand containing a large amount of moisture at an early stage by using the polymer flocculant.

[0035] Specifically, for example, as shown in FIG. 6, a threshold value T of the initial drainage evaluation ratio is set in the relationship data between the soil particle-polymer ratio and the initial drainage evaluation ratio. The threshold value T can be appropriately determined according to the target drainage volume, construction period, and the like. Then, the addition amount of the polymer flocculant to the original soil and sand is determined so as to be within the allowable range R1 of the soil particle-polymer ratio at which the initial drainage evaluation ratio is equal to or higher than the set threshold value T.

[0036] In order to reduce the amount of sediment after drainage treatment, it is preferable to increase the drainage efficiency of the treated sediment while minimizing the amount of polymer flocculant added. Therefore, for example, within the aforementioned allowable range R1, when determining the amount of polymer flocculant added to the raw sediment so that the soil particle-polymer ratio is within the upper 50%, more preferably within the upper 30% in the range R2, it is possible to increase the drainage efficiency of the treated sediment while reducing the amount of polymer flocculant added. This is advantageous for efficiently dehydrating sediment containing a large amount of moisture at an early stage. For example, when attaching the utmost importance to the drainage efficiency at the initial stage of drainage of the treated sediment, it is advisable to adopt the soil particle-polymer ratio at which the initial drainage evaluation ratio is the highest in the relational data between the soil particle-polymer ratio and the initial drainage evaluation ratio.

[0037] As shown in FIG. 5, the initial drainage evaluation ratio of the treated sediment varies depending on the activity of the raw sediment. Also, the appropriate soil particle-polymer ratio for enhancing the drainage promotion effect in the initial stage of drainage of the treated sediment also varies depending on the magnitude of the activity of the raw sediment. Therefore, it is advisable to obtain in advance the relational data between the soil particle-polymer ratio and the initial drainage evaluation ratio for each magnitude of the activity of the raw sediment, and determine the amount of polymer flocculant to be mixed into the raw sediment based on the relational data corresponding to the activity of the raw sediment to be dehydrated.

[0038] If the types of clay matrix materials constituting the raw sediment are the same, the activity of the raw sediment will be approximately the same value. Therefore, if the clay matrix material constituting the raw sediment is a type for which the activity has been previously grasped, it is possible to easily grasp the activity of the raw sediment without conducting a liquid limit-plastic limit test or a particle size test for grasping the activity of the raw sediment.

[0039] If relationship data between the activity of the original soil and sand and the initial drainage evaluation ratio, as shown in Fig. 5, is obtained in advance, just by grasping the activity of the original soil and sand to be dehydrated, it is possible to easily determine whether it is appropriate to mix a polymer flocculant into the original soil and sand or not. For example, when the activity of the original soil and sand is high and the initial drainage evaluation ratio is greater than 1, since there is a drainage promotion effect by mixing a polymer flocculant into the original soil and sand, it can be determined that mixing a polymer flocculant into the original soil and sand is effective for shortening the time required for the dehydration treatment. On the other hand, for example, when the activity of the original soil and sand is low and the initial drainage evaluation ratio is 1 or less, since there is no drainage promotion effect by mixing a polymer flocculant into the original soil and sand, it can be determined that it is advantageous for cost reduction to perform the dehydration treatment in the state of the original soil and sand without mixing a polymer flocculant.

[0040] In the above, the case of determining the addition amount of the polymer flocculant to be mixed into the original soil and sand to be dehydrated based on the relationship data between the weight ratio of the soil particles of the original soil and sand to the weight of the polymer flocculant mixed into the original soil and sand (soil particle polymer ratio) and the initial drainage evaluation ratio was exemplified. However, in the present invention, similarly, based on the relationship data between the weight ratio of the polymer flocculant mixed into the original soil and sand to the weight of the soil particles of the original soil and sand (the reciprocal of the soil particle polymer ratio) and the initial drainage evaluation ratio, it is also possible to determine the addition amount of the polymer flocculant to be mixed into the original soil and sand to be dehydrated.

Explanation of reference numerals

[0041] 1 Drainage test device 2 Storage container 3 Drain pipe 4 Loading mechanism 5 Water storage section S Soil and sand W Water

Claims

1. In a method for dewatering earth and sand, wherein treated earth and sand produced by mixing a polymer flocculant with raw earth and sand is dewatered in an initial production period not exceeding 48 hours from the production of the treated earth and sand, when determining the amount of the polymer flocculant to be added to the raw earth and sand to be dewatered, based on the relationship data between the weight ratio of the soil particles of the raw earth and sand to the weight of the polymer flocculant mixed with the raw earth and sand, and the initial drainage evaluation ratio indicating the degree of improvement in the drainage efficiency of the treated earth and sand with respect to the drainage efficiency of the raw earth and sand during the initial production period, for each of the treated earth and sand and the raw earth and sand, a test is conducted in which they are placed in a storage container and the amount of drained water discharged from each of the earth and sand is measured in a state where the same compressive stress is set, the final drainage volume of each of the earth and sand is estimated by hyperbolic approximation for the time-dependent change data of the drainage volume of each of the earth and sand under predetermined conditions set in advance, and the initial drainage gradient of each of the earth and sand is calculated by dividing the intermediate drainage volume by the intermediate elapsed time from the start point of drainage until the time point when the intermediate drainage volume reaches a predetermined ratio of the final drainage volume, and the ratio of the initial drainage gradient of the treated earth and sand to the initial drainage gradient of the raw earth and sand is used as the initial drainage evaluation ratio, the method for dewatering earth and sand, characterized in that the amount of the polymer flocculant added is determined so as to be within the allowable range of the weight ratio at which the initial drainage evaluation ratio in the relationship data is equal to or higher than a set threshold value.

2. The method for dewatering earth and sand according to claim 1, wherein the relationship data is acquired in advance for each magnitude of the activity of the raw earth and sand calculated using the plasticity index of the raw earth and sand and the clay content of particles having a particle size equal to or less than a predetermined value contained in the raw earth and sand, and the amount of the polymer flocculant to be mixed with the raw earth and sand is determined based on the relationship data corresponding to the activity of the raw earth and sand to be dewatered.

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