JP2019163644A - Ground modification method - Google Patents

Abstract

To provide a ground modification method capable of sufficiently modifying a ground even when underground water flow is quick.SOLUTION: In a ground modification method modifying the ground having underground water flow by action of microorganism having urease activity, a liquid containing a thickener and urea is injected into the ground. Since the liquid has viscosity increased by the thickener, stay period in the ground becomes long even in the underground water flow. Thus, time during which a decomposition reaction of the urea by the urease sufficiently progresses can be secured.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ground improvement method.

  Conventionally, a method for culturing a microorganism having urease activity and a ground improvement method using this microorganism are known (see, for example, Patent Document 1). In this ground reforming method, carbonate ions generated by urease decomposition reaction with urease react with calcium ions in the ground to produce calcium carbonate, which binds the soil particles together to solidify the ground, and the strength of the ground Will improve.

Japanese Unexamined Patent Publication No. 2016-220586

  In this ground reforming method, it takes a certain time until the ground is sufficiently reformed. Therefore, depending on the speed of the groundwater flow, even if a chemical solution necessary for the reaction is injected, the chemical solution flows away faster than achieving the desired degree of modification, and the modification may be insufficient.

  Therefore, the present invention provides a ground improvement method using a microorganism having urease activity, and can sufficiently improve the ground even when the flow of groundwater is fast. Objective.

  The present invention relates to a ground reforming method for modifying a ground having a flow of groundwater by the action of a microorganism having urease activity, and injecting a liquid containing a thickener and urea into the ground. I will provide a.

  In this ground reforming method, since the liquid injected into the ground contains a thickener, the viscosity of the liquid is increased, and the period during which the liquid stays on the ground is increased even in the groundwater flow. . Therefore, it is possible to secure time for the urea decomposition reaction by urease to sufficiently proceed, and to sufficiently improve the ground.

  The liquid to be injected preferably further contains at least one selected from the group consisting of microorganisms, microorganism nutrients and calcium sources. When these elements are scarce in the ground, if the scarce elements are added together, microorganisms in the ground can be further activated and solidification of the ground can be promoted.

  In this ground reforming method, a plurality of types of liquids having different compositions may be prepared, and the plurality of types of liquids may be injected into the ground from a plurality of locations. For example, among the element candidates to be included in the liquid, for example, the calcium source preferably reacts with carbonate ions in a state of widespread in the ground. Therefore, before the liquid is injected into the ground, the calcium source includes microorganisms and urea. It is preferable to maintain a state separate from the liquid.

  The liquid to be injected into the ground is preferably injected into the ground after being heated to a temperature suitable for the activity of microorganisms. The temperature of the ground is usually stable at about 15 to 20 ° C., but this temperature is usually lower than the optimum temperature for the activity of microorganisms. Therefore, if the liquid is heated to a temperature suitable for the activity of the microorganism before the liquid is injected, the activity of the microorganism can be increased for a predetermined time immediately after the injection.

  According to the present invention, there is provided a ground improvement method using a microorganism having urease activity, which can sufficiently improve the ground even when the flow of groundwater is fast. Can do.

(A) is a top view which shows the positional relationship of an injection hole and an observation hole. (B) is a cross-sectional view showing the ground to be reformed and the state of the ground reforming system. It is a top view which shows the observation point of the microtremor on the ground surface of the area | region which improved the ground. It is a graph which shows the amplitude ratio of the microtremor on the ground surface. (A) shows the amplitude ratio at the measurement point Q. (B) shows the amplitude ratio at the measurement point R.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same part or an equivalent part, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 1, the ground reforming method of the present embodiment is a reforming method using a ground reforming system 10, in which ground 1 (1a, 1b, 1c) having a flow of groundwater is treated with urease. It is modified by the action of an active microorganism. The ground reforming system 10 includes a plurality of injection holes 5a, 5b and observation holes 7a, 7b provided for the ground 1 to be reformed, and a storage tank 3 for storing a culture solution to be passed through the injection holes 5a, 5b. have. FIG. 1 shows a ground 1 having a first aquifer 1a, a clay layer 1b, and a second aquifer 1c in this order from the ground. In this embodiment, the aquifer is composed of fine sand or the like. The target for reforming is 1c.

  As shown in FIG. 1, a storage tank 3 for storing a culture solution is installed on the ground. Then, as the injection holes 5a and 5b for injecting the culture solution into the aquifer 1c and the observation holes 7a and 7b for measuring the state of the aquifer 1c, the depth of the aquifer 1c is reached. Establish a well. Here, a rod or a double pipe may be used instead of the well. Here, the rod means a hollow tube made of a material such as metal or vinyl chloride. The well into which the culture solution is injected is connected to the storage tank 3 by a pipe, and a measuring instrument M for measuring the flow rate of the culture solution flowing through the pipe and an open / close valve V are provided in the middle of the well.

  1A is a plan view showing the positional relationship between the two injection holes 5a and 5b and the two observation holes 7a and 7b, and FIG. 1B shows the two injection holes 5a and 5b, and It is sectional drawing of the ground 1 in the position of the one observation hole 7a on the same straight line. The two injection holes 5a and 5b and the two observation holes 7a and 7b are separated from each other by 1 m. Here, the thickness of the aquifer 1 a is 2.4 m, the thickness of the clay layer 1 b is 1.0 m, and the aquifer 1 c exists at a depth less than that.

  The wells serving as the injection holes 5a and 5b have a portion where the wall surface is the strainer S in the portion reaching the aquifer 1c, from which water enters and exits the aquifer 1c. The wells which are the observation holes 7a and 7b also have a portion where the wall surface is the strainer S in the portion reaching the aquifer 1c, and water enters and exits the aquifer 1c from here. In addition, measuring instruments 9a and 9b for measuring electrical conductivity are installed in the portion reaching the aquifer 1c of the well, which is the observation holes 7a and 7b. The observation hole 7a is installed at a depth of 3.6 m, and the observation hole 7b is installed at a depth of 4.7 m. A plurality of measuring instruments may be installed per observation hole. In FIG. 1, the observation hole 7 b is not shown as a cross-sectional view, but for convenience of explanation, the measuring instrument 9 b is drawn so that the position of the measuring instrument 9 b can be seen.

  In the ground reforming method of this embodiment, a culture solution that contributes to the activity of microorganisms having urease activity is injected into the aquifer 1c. In this embodiment, the culture solution contains a microorganism, a nutrient source for the microorganism, urea, a calcium source, and a thickener. The culture solution is mixed with water and injected in the form of an aqueous solution, suspension, emulsion, or the like.

  As the microorganism, a microorganism having urease activity is used. The microorganism to be used may be one obtained by culturing a microorganism collected from the ground 1 or may be a microorganism collected or purchased from another place in the country. Urease is an enzyme produced by the microorganism and catalyzes a reaction of hydrolyzing urea to produce carbonic acid and ammonia.

  There is no restriction | limiting in particular in what is used as a nutrient source of microorganisms, For example, polysaccharides, such as meat extract, saccharides, such as glucose, and starch. The content may be 1 to 30 g or 4 to 20 g per liter of water.

  The content of urea may be 0.1 to 10 mol (mol) per liter of water, may be 0.2 to 5 mol, or may be 0.3 to 0.7 mol. Good. If the urea content is too high, the movement of microorganisms will deteriorate and the solidification effect of the ground will tend to be small. However, it is expected that urea will be diluted to an appropriate concentration by groundwater.

  Any calcium source may be used as long as it dissolves in water and releases calcium ions, and examples thereof include calcium chloride, calcium carbonate, calcium hydroxide, and calcium nitrate. The content may be 0.1 to 10 mol (mol) per liter of water, 0.2 to 5 mol, or 0.3 to 0.7 mol. . If the content of the calcium source is too high, the movement of the microorganisms becomes worse and the solidification effect of the ground tends to be reduced. However, it is expected that the calcium source will be diluted by groundwater to an appropriate concentration.

  Any thickener can be used as long as it can increase the viscosity of the culture solution, and a cellulose derivative is preferable. Of these, carboxymethylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose are preferable. As content, it is preferable to contain so that the viscosity of a culture solution may become 1-10 times the viscosity of water, or 2-5 times.

  The culture solution may contain various components in addition to the above. For example, ammonium chloride, sodium hydrogencarbonate, air, etc. are mentioned. When the specific gravity of the culture solution is high, the culture solution tends to sink in the ground water. Therefore, it is possible to prevent the culture solution from sinking by including air.

  The above elements are mixed to prepare a culture solution and stored in the storage tank 3. By completely mixing before injection into the aquifer 1c, it can be expected to cause a desired reaction in the aquifer 1c.

  The electrical conductivity of the culture solution in the storage tank 3 is measured. Then, the opening / closing valve V is opened, the culture solution is supplied to the injection holes 5a and 5b, and the culture solution is injected into the aquifer 1c. The injected culture solution enters and diffuses into the aquifer 1c in the strainer S portion of the injection holes 5a and 5b (diffusion range D shown in FIG. 1). The pressure due to the flow rate of the injection becomes the diffusing force, and also gradually diffuses due to the flow of groundwater.

  The injection amount of the culture solution can be measured with the measuring instrument M.

  In the aquifer 1c, urea is decomposed by urease produced by microorganisms. Carbonate ions generated by this reaction react with calcium ions present in the aquifer 1c or calcium ions derived from the culture solution to produce calcium carbonate. And calcium carbonate couple | bonds soil particles and solidifies a ground, and the intensity | strength of a ground improves.

  Since the injected culture solution contains a thickener, the viscosity is increased, and the period during which the culture solution stays in the aquifer 1c is prolonged even in the flow of groundwater. Therefore, it is possible to secure a time for the urea decomposition reaction by urease to sufficiently proceed, and the aquifer 1c can be sufficiently modified.

  Here, the culture solution to be injected is preferably injected after being heated to a temperature suitable for the activity of the microorganism. The temperature of the ground 1 including the aquifer 1 c is usually stable at about 15 to 20 ° C., but this temperature is usually lower than the optimum temperature for microbial activity. Therefore, when the culture solution is injected before being heated to a temperature suitable for the activity of the microorganism (for example, 25 to 40 ° C.), the activity of the microorganism can be increased for a predetermined time immediately after the injection. .

  The culture solution is injected in an amount corresponding to the flow rate of groundwater, and the injection period can be several hours, several days, or several weeks. If the injection is over a long period of time, or if the injection is resumed after stopping the injection, the roles of the injection hole 5a and the observation hole 7a are changed from the assumption of the diffusion state of the culture solution and clogging of the aquifer 1c, A measuring instrument 9a may be installed in the injection hole 5a, and the culture solution may be injected from the observation hole 7a.

  The electrical conductivity (mS / m) of groundwater is measured over time with the measuring instruments 9a and 9b over a predetermined period after the culture solution is injected. When the diffused culture solution reaches the measuring instruments 9a and 9b, the electrical conductivity of the groundwater increases according to the concentration, and approaches the value of the electrical conductivity of the culture solution measured in the storage tank 3. Based on this change in conductivity, the diffusion range D of the culture solution in the aquifer 1c can be estimated.

  The measurement of electrical conductivity is preferably continued for several days to two weeks. The culture liquid whose viscosity is increased by the thickener has a longer residence time than normal groundwater, and the period during which the ground is modified (solidified here) by the activity of microorganisms is long. After stopping the injection of the culture solution, it is preferable to continue measuring the electric conductivity until the value of the electric conductivity decreases and the rate of change becomes small. Finally, it can be determined that the modification of the aquifer 1c has been completed because the rate of change in electrical conductivity has decreased.

  After the modification is completed, the degree of modification and the modified range can be confirmed, for example, by measuring the fine movement of the ground. As shown in FIG. 2, a ground surface point (measurement point P) that is sufficiently separated from the injection holes 5a and 5b is set as a reference vibration measurement position, and a sufficient distance is separated from the injection holes 5a and 5b. The surface point where the aquifer 1c is considered not to be modified is defined as the first measurement point Q, and the surface point around the injection holes 5a and 5b where the aquifer 1c is considered to be modified is the first. Let it be 2 measurement points R. Here, in FIG. 2, it is assumed that the groundwater flows from the upper right direction to the lower left direction in the figure, and the portion surrounded by the circle D ′ is estimated by the measurement of the flow direction, the flow velocity, and the electric conductivity. 2 shows a region where the aquifer 1c is modified (that is, the shape in plan view of the diffusion range D of the culture solution in FIG. 1).

  When the vertical vibration with respect to the ground surface is measured, the measurement points Q and R show the amplitude ratio as shown in FIG. 3 for each frequency. As shown in FIG. 3A, since the amplitude ratio is about 1.0 at the measurement point Q, the vibration situation is the same as the measurement position of the reference vibration, and therefore the ground strength is one. It turns out that it is like. On the other hand, as shown in FIG. 3B, at the measurement point R, since the amplitude ratio is about 0.4 on the high frequency side, the vibration is smaller than the measurement position of the reference vibration. Therefore, it can be seen that the ground strength has been improved.

  And by measuring such a microtremor at a plurality of locations on the ground surface, it is possible to specify the range in which the ground has been modified and the degree of modification. In FIG. 2, points other than the points marked with P, Q, and R are the measurement point candidates. The measurement interval is desirably as close as possible. For example, the interval may be 1 m inside and around the circle D ′, and may be 2 m away from the circle D ′.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, as the liquid to be injected into the aquifer 1c, in the above embodiment, a culture solution containing microorganisms, microorganism nutrients, urea, calcium sources, and thickeners has been mentioned. In the case where the source is sufficiently contained in the aquifer 1c by a preliminary investigation, the element may not be included in the liquid. On the other hand, an element with a small amount contained in the aquifer 1c is preferable because a large amount of the element can be added to further activate the microorganisms and promote solidification of the ground.

  Moreover, although the example which inject | pours the same culture solution with respect to the two injection holes 5a and 5b was shown in the said embodiment, the culture solution to inject | pour may have a mutually different composition. That is, two types of culture solutions having different compositions may be prepared and injected separately from the injection hole 5a and the injection hole 5b. For example, among the elements included in the culture solution, it is preferable that the calcium source reacts with carbonate ions in a state of being widely distributed in the aquifer 1c. Therefore, before the culture solution is injected into the aquifer 1c, the calcium source is a microorganism or It is preferable to maintain a separate state from the liquid containing urea. That is, it is preferable to inject a culture solution containing a calcium source from one injection hole 5a and to inject a culture solution not containing a calcium source from the other injection hole 5b.

  In the above-described embodiment, the method of constantly measuring the fine movement is given as a method for specifying the extent to which the ground has been modified and the degree thereof, but instead, the ground is excavated and taken out as a test sample, and a strength test is performed. You may confirm strength by doing.

  Moreover, in the said embodiment, although the example which made the aquifer 1c in the deeper part than the clay layer 1b the modification | reformation object was shown, this invention is with respect to the aquifer 1a in the shallower part than the clay layer 1b. Is also applicable.

  The present invention can be used, for example, as a countermeasure for ground liquefaction.

  DESCRIPTION OF SYMBOLS 1 ... Ground, 1a ... 1st aquifer, 1b ... Clay layer, 1c ... 2nd aquifer, 3 ... Storage tank, 5a, 5b ... Injection hole, 7a, 7b ... Observation hole, 9a, 9b ... Measuring instrument, 10 ... Ground reforming system, D, D '... Diffusion range, M ... Measuring instrument, P, Q, R ... Measuring point, S ... Strainer, V ... Open / close valve.

Claims (4)

A ground modification method for modifying ground having a flow of groundwater by the action of microorganisms having urease activity,
A ground reforming method in which a liquid containing a thickener and urea is injected into the ground.   The ground improvement method according to claim 1, wherein the liquid further includes at least one selected from the group consisting of the microorganism, a nutrient source for the microorganism, and a calcium source. Preparing a plurality of liquids having different compositions from each other;
The ground improvement method according to claim 1 or 2, wherein the plurality of kinds of liquids are respectively injected from a plurality of locations into the ground.   The ground improvement method according to any one of claims 1 to 3, wherein the liquid is injected into the ground after being heated to a temperature suitable for the activity of the microorganism.

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