JP2019015126A - Estimation method of strength of improved soil - Google Patents

Abstract

To provide an estimation method of a strength of improved soil which can promptly check a strength of improved soil to which a soil improvement chemical is injected.SOLUTION: A fluid is injected into improved soil through an injection hole after completing a step of injecting a soil improvement chemical into the injection hole and an underground gel time t of the soil improvement chemical has passed and before a predetermined time T for a cure time Tof the improved soil, thereby acquiring a relationship between an injection pressure P and an injection flow rate Q in the improved soil. Then, a coefficient k of permeability of the improved soil is calculated based on the acquired relationship between the injection pressure P and the injection flow rate Q, and a uniaxial compressive strength qu after cure of the improved soil is estimated based on the calculated coefficient k of permeability and relation data between the previously grasped uniaxial compressive strength qu after the cure time Tof the improved soil formed by the soil improvement chemical and the coefficient k of permeability.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for estimating the strength of an improved ground, and more particularly to a method for estimating the strength of an improved ground that enables early confirmation of the strength of the improved ground injected with a ground improvement chemical.

  As a ground improvement method for the purpose of liquefaction countermeasures or the like, a chemical solution injection method for injecting a ground improvement chemical solution such as a solution type chemical solution or a cement suspension type chemical solution into the ground is performed. If the strength of the improved ground by this method can be confirmed at an early stage, it will be beneficial from the viewpoint of improving the injection conditions and other aspects. Conventionally, several methods for confirming the uniaxial compressive strength of the ground are known (for example, see Patent Document 1). Patent Document 1 proposes an intrusion test method in which a penetrating rod having a screw point at its tip is rotationally penetrated into the ground, and the rotational torque of the penetrating rod is measured while changing the load applied to the penetrating rod in stages. Yes. However, this test method grasps the uniaxial compressive strength at the time of performing the test. Therefore, even if the improved ground strength is to be confirmed at an early stage, it is necessary to cure until the improved ground has sufficiently developed the strength.

  Alternatively, even in the method of performing core boring on the improved ground and performing a uniaxial compression test using the collected samples, the test can be performed after the improved ground has been sufficiently cured and has developed its strength. It will be disadvantageous to confirm the strength of the early. Furthermore, since it is necessary to carry out an indoor test after collecting the local sediment by boring, it takes a long time to check the improved ground strength. In this method, the sample is disturbed when sampling is performed, and there is also a problem that it is difficult to measure an accurate intensity. Thus, in the conventional method, since the strength at the time when the strength is sufficiently developed cannot be grasped in advance, there is a limit to confirming the strength of the improved ground at an early stage.

JP 2014-134667 A

  The objective of this invention is providing the estimation method of the intensity | strength of the improved ground which can confirm the intensity | strength of the improved ground which injected the ground improvement chemical | medical solution at an early stage.

  In order to achieve the above object, the method for estimating the strength of the improved ground according to the present invention is a method for estimating the strength of the improved ground formed by injecting a ground improving chemical solution through an injection hole formed in the ground, After completing the step of injecting the ground improvement chemical solution into the injection hole, after the soil gel time of the ground improvement chemical solution has elapsed and before the predetermined time before the curing period of the improved ground elapses, the improved ground through the injection hole The fluid is injected into the tank, the relationship between the injection pressure and the injection flow rate of the fluid at that time is acquired, and the hydraulic conductivity of the improved ground is calculated based on the relationship between the acquired injection pressure and the injection flow rate. Based on the water permeability coefficient and the relationship data between the uniaxial compressive strength and the water permeability coefficient after the curing period of the improved ground formed by the previously known ground improvement chemical solution, after the curing of the improved ground And estimating the axial compressive strength.

  According to the present invention, the hydraulic conductivity can be quickly and easily calculated by injecting a fluid using the injection hole into which the ground improvement chemical solution is injected, and acquiring the relationship between the injection pressure and the injection flow rate. Furthermore, since this fluid injection can be performed during the curing period before the improved ground develops strength, the strength of the improved ground should be grasped at an early stage based on the calculated permeability coefficient and previously known data. Can do.

  Here, for example, water is used as the fluid. In the case of using water, since the influence on the improved ground is small, the strength of the improved ground can be estimated without substantially changing the strength of the improved ground before the water is injected.

  Or a ground improvement chemical | medical solution can also be used as said fluid. When the ground improvement chemical solution is used, the ground improvement chemical solution is further injected into the initial improvement ground, so that the strength of the improvement ground can be further improved. Moreover, when the ground improvement chemical | medical solution is surplus, it becomes effective utilization of a ground improvement chemical | medical solution.

When calculating the hydraulic conductivity, specifically, for example, the injection pressure is converted into an effective injection pressure head, and an inclination A of the effective injection pressure head with respect to the injection flow rate is obtained. ), The water permeability coefficient k can also be calculated.
Hydraulic conductivity k = {1 / (2πLA)} ln (2L / D) (1)
Here, L is the length of the portion holding the fluid injected in the injection hole, and D is the diameter of the injection hole.

It is a flowchart which shows an example of the estimation method of the intensity | strength of the improved ground of this invention. It is explanatory drawing which illustrates an on-site injection | pouring test process by a longitudinal cross-sectional view. It is a graph which illustrates the relationship between an injection | pouring flow volume and an effective injection pressure head. It is a graph which illustrates the relationship data of the uniaxial compressive strength after a curing period progress, and a hydraulic conductivity. It is a graph which illustrates the relationship between a curing period and uniaxial compressive strength. It is a graph which illustrates the relationship between a curing period and a hydraulic conductivity. It is explanatory drawing which illustrates the condition which inject | pours a chemical | medical solution into the ground by a longitudinal cross-sectional view.

  Hereinafter, the method for estimating the strength of the improved ground according to the present invention will be described based on the embodiments shown in the drawings.

  The present invention is a method for estimating the strength of an improved ground formed by injecting a ground improvement chemical solution G (hereinafter referred to as a chemical solution G) through an injection hole H formed in the ground as shown in FIG. In this embodiment, an injection hole H having a hole diameter D (m) is formed in the ground by a casing rod extended from the drilling machine, and the chemical solution G is injected into the ground by the chemical solution injection device 10.

As illustrated in FIG. 5, in the improved ground formed by injecting the chemical solution G, the strength (uniaxial compression strength qu) increases until a certain period (for example, about 14 days) after the injection of the chemical solution G, and then Is almost constant. Therefore, the uniaxial compressive strength qu of ground improved after curing period T _E to directly grasp and measure the improved ground makes measurements after at least improved ground has Strength (14 days later) There is a need.

On the other hand, as illustrated in FIG. 6, the permeability coefficient k of the improved ground becomes a constant value after the gel time t in the soil has elapsed. That is, if the soil gel time t later, it is possible even during curing period prior to strength development acquires permeability k of the ground improved after curing period T _E. The present invention includes a permeability k, by utilizing the relationship between the uniaxial compressive strength qu the improved ground after curing period T _E passed the permeability k, even during curing period before Strength However, the strength of the improved ground can be grasped.

  As shown in the flowchart of FIG. 1, the present invention is roughly composed of three processes (on-site injection test process, hydraulic conductivity calculation process, and uniaxial compressive strength estimation process). In the present invention, the on-site injection test process and the permeability coefficient calculation process are performed to acquire the permeability coefficient k of the improved ground, and the uniaxial compression strength qu is estimated from the permeability coefficient k in the uniaxial compression strength estimation process. Details of each step will be described below.

Local injection testing process completes the step of injecting a drug solution G to the injection hole H, and after the lapse of soil gel time t of liquid G, performed before a predetermined time T has elapsed curing period T _E of improved ground. The soil gel time t is the time required until the chemical solution G gels (the liquid solidifies) in the ground. The soil gel time t varies depending on the chemical solution G to be used, and is, for example, 2 hours to 12 hours after the injection of the chemical solution G is completed.

Curing period T _E of the improved ground is generally 28 days from the injection of the drug solution G is completed. The predetermined time T is, for example, 14 to 27 days. That is, in the present invention, after the lapse of the gel time t in the soil of the chemical solution G, the on-site injection test process is performed 28 days before the completion of the injection of the chemical solution G. It is desirable to perform the local injection test process during a period of about 14 days (during the curing period before the improved ground develops strength).

In the on-site injection test process, as shown in FIG. 2, by injecting fluid into the injection hole H formed in the ground, the injection pressure P (Pa) and the injection flow rate Q (m ³ / s) in the improved ground Get relationship. For example, water W or chemical G can be used as the fluid. In this embodiment, the local injection test is performed by injecting water W into the injection hole H using the local injection test apparatus 1.

  The on-site injection test apparatus 1 includes an injection tube 2 having a packer 7 on the outer surface, an injection device 3 connected to the injection tube 2, a flow meter 4 and a water pressure meter 5 connected directly or indirectly to the injection tube 2. And an arithmetic device 6 connected to the injection device 3, the flow meter 4 and the water pressure meter 5 by wire or wirelessly, and a pressurizing device 9 connected to the packer 7 via a pipe 8. The packer 7 is an annular bag.

  The injection tube 2 is a water-tight tube, and has an insertion tube portion 2 a having an outer diameter smaller than the hole diameter D of the injection hole H, and a supply tube portion 2 b that connects the insertion tube portion 2 a and the injection device 3. It consists of and. A water pressure gauge 5 is installed at the upper end portion of the insertion tube portion 2a, and the upper end portion is closed. A flow meter 4 is installed in the middle of the supply pipe 2b.

  The injection device 3 can supply water W to the injection pipe 2 (supply pipe part 2b) at a predetermined injection pressure P or injection flow rate Q. An example of the injection device 3 is a secret water tank that sends out water W using a pump or gas pressure. An accumulator may be attached to the injection device 3 in order to reduce the pulsation of the injection pressure P.

  The flow meter 4 measures the injection flow rate Q of the water W supplied from the injection device 3 to the injection pipe 2. The water pressure gauge 5 measures the injection pressure P when water W is injected into the improved ground. The measurement data of the flow meter 4 and the water pressure meter 5 are input to the sequential calculation device 6.

  The calculation device 6 performs control operations based on the control of the injection device 3, the recording of measurement data of the flow meter 4 and the water pressure meter 5, and the measurement data. An example of the arithmetic device 6 is a personal computer. By injecting gas g or water into the packer 7 from the pressurizing device 9 through the pipe 8, the packer 7 expands.

  A procedure for acquiring the relationship between the injection pressure P and the injection flow rate Q in the improved ground using the local injection test apparatus 1 will be described below. In this embodiment, the test interval is from the bottom of the injection hole H to the position of L (m) on the upper side. Then, water W is injected while increasing the injection pressure P stepwise in the test section, and the injection flow rate Q at the steady state in each step is measured. This on-site injection test process is performed based on JGS1322 (the rock permeability test method by injection) of the Geotechnical Society (JGS).

  First, the insertion tube portion 2a of the injection tube 2 is installed so as to be inserted into the injection hole H. At this time, the lower end portion of the insertion tube portion 2a is not grounded to the bottom of the hole, and the lower end portion of the packer 7 when expanded is arranged at the position L (m) above the bottom of the injection hole H. To do. Next, the packer 7 is expanded by supplying the gas g from the pressurizing device 9, and the gap between the outer peripheral surface of the insertion tube portion 2 a and the hole wall of the injection hole H is tightly closed by the packer 7. That is, the space (test section) from the bottom of the injection hole H to the lower end of the expanded packer 7 is sealed.

  After completing the above preparation, an instruction is input from the arithmetic unit 6 to the injection device 3 so as to inject at a constant injection flow rate Q1, and injection is started. Upon receiving a command from the arithmetic unit 6, the injection device 3 supplies water W to the supply pipe portion 2b, and injects water W into the test section at a constant injection flow rate Q1 from the lower end opening of the insertion tube portion 2a. That is, the length of the portion that holds the injected water W in the injection hole H is L (m).

  The time-dependent change of the injection pressure P when water W is injected at a constant injection flow rate Q1 is sequentially measured by the water pressure gauge 5, and the measurement data is sequentially input to the arithmetic unit 6. The arithmetic unit 6 reads the numerical value when the injection pressure P becomes substantially constant at the constant injection flow rate Q1 (steady state) from the measurement data sequentially input, and records the numerical value as the injection pressure P1 at the injection flow rate Q1. To do.

  When the recording of the injection pressure P1 at the injection flow rate Q1 is completed, the arithmetic device 6 inputs a command to the injection device 3 so as to change the injection flow rate Q1 injected into the target ground to the injection flow rate Q2 having a higher flow rate. Thereafter, the injection pressure P2 at the injection flow rate Q2 is recorded in the same procedure as that performed at the injection flow rate Q1. By repeating the procedure from changing the injection flow rate Q to recording the injection pressure P at the injection flow rate Q while increasing the injection flow rates Q1, Q2, Q3. The relationship between the injection pressure P and the injection flow rate Q is acquired.

  The measurement of the injection pressure P and the injection flow rate Q ends when the injection flow rate Q exceeds the limit injection rate. Specifically, if the injection flow rate Q exceeds a certain value (limit injection rate), the ground will split and the value of the injection pressure P will decrease, so that the arithmetic unit when the injection pressure P falls below the previous measurement. A command is input from 6 to the injection device 3 so as to end the injection.

  In this embodiment, the injection pressure P when water W is injected into the test section at a constant injection flow rate Q is measured, but by measuring the injection flow rate Q when water is injected into the test section at a constant injection pressure P, The relationship between the injection pressure P and the injection flow rate Q can also be acquired. Further, the measurement can be finished before the injection flow rate Q reaches the limit injection speed.

  Although the control of the injection device 3, the measurement of the flow meter 4 and the water pressure meter 5, and the recording of the measurement result can be performed manually by an operator, these operations are performed using the arithmetic device 6 as in this embodiment. If done, work can be done with high accuracy. In addition, lighter labor can be achieved.

  In the next hydraulic conductivity calculation step, the hydraulic conductivity k of the improved ground is calculated based on the relationship between the injection pressure P and the injection flow rate Q acquired in the local injection test step. In this embodiment, the permeability coefficient k is calculated based on JGS1322 (a rock permeability test method by rock injection) of the Geotechnical Society (JGS). A procedure for calculating the hydraulic conductivity k of the improved ground based on the relationship between the injection pressure P and the injection flow rate Q will be described below.

First, the injection pressure P (Pa) is converted into an effective water injection pressure head S (m) by the following equation (2).
S = P / r + h1-h2-h3 (2)
Here, h1 is the difference in height between the hydrometer 5 and the center of the test section (m), h2 is the difference in height between the equilibrium water level and the center of the test section (m), and h3 is the head of loss due to the in-tube resistance of the injection pipe 2 ( m) and r are unit volume weights (N / m ³ ) of water W. The equilibrium water level can be measured based on JGS1311 (measuring method of groundwater level of sandy / gravel ground using a borehole). The loss head h3 due to the in-pipe resistance of the injection pipe 2 can be obtained by a loss head test.

Next, as shown in FIG. 3, a graph is created in which the effective water injection pressure head S is plotted on the vertical axis and the injection flow rate Q is plotted on the horizontal axis, and the measured values at each pressure stage are plotted. Then, an inclination A of the effective water injection pressure head S with respect to the increase amount of the injection flow rate Q is obtained. When the slope A is obtained, it is obtained using the relationship between the effective water injection pressure head S and the injection flow rate Q up to the stage before the injection flow rate Q exceeds the limit injection rate Qcr (Q1 to Q5 in FIG. 3). The inclination A is expressed by the following equation (3).
A = ΔS / ΔQ (3)
Moreover, when calculating | requiring the hydraulic conductivity k from the injection pressure P and injection | pouring flow volume Q of one step, the inclination A is calculated | required from following (4) Formula.
A = S / Q (4)
In this embodiment, a graph is created for convenience of explanation, but the slope A can be obtained without creating a graph.

And the hydraulic conductivity k is calculated by substituting the inclination A calculated | required by (3) Formula or (4) Formula (1) below.
k = {1 / (2πLA)} ln (2L / D) (1)
Here, D is the diameter of the injection hole H (hole diameter of the test section) (m), and L is the length of the test section (m). Thus, the hydraulic conductivity k can be calculated simply and quickly by the work at the construction site.

The following uniaxial compressive strength estimation step, and permeability k calculated in permeability calculation step, the uniaxial compressive strength qu after curing period T _E lapse of improved ground formed by a chemical solution G which has previously been grasped cured based on the relationship data between the permeability coefficient k of the ground improved after the period T _E, it estimates the uniaxial compressive strength qu after curing of improved ground during curing period.

The relationship data between uniaxial compressive strength qu and permeability k after curing period T _E lapse of previously grasped by formed by a chemical solution G in which the improved ground, the use of correlation between both illustrated in FIG. 4 it can. Uniaxial compressive strength of the graph vertical axis of FIG. 4 qu shows a uniaxial compressive strength qu the improved ground in wood age 28 days have elapsed curing period T _E of 28 days from the injection of liquid medicine G. The horizontal axis of the graph in FIG. 4 also shows the hydraulic conductivity k of the improved ground on the 28th day of the material age as a logarithmic coefficient logk.

Relationship data between uniaxial compressive strength qu and permeability k after curing period T _E lapse of improved ground formed by a chemical solution G, for improved ground samples after curing period T _E elapsed created using a chemical solution G It can be obtained by conducting a water permeability test and a uniaxial compression test. More specifically, for example, the hydraulic conductivity k is calculated from the particle size (for example, 20% particle size D ₂₀ ), and the uniaxial compression strength qu is based on JGS0511 (uniaxial compression test of soil) of the Geotechnical Society (JGS). Can be obtained. The relational data between the uniaxial compressive strength qu and the water permeability coefficient k may be arranged in advance in a graph or the like for each type of chemical solution G as shown in FIG.

  In FIG. 4, the respective relationship data of the improved ground sample A formed by the chemical solution G and the improved ground sample B formed by the chemical solution G1 are shown. In this embodiment, since the chemical solution G is used, the relationship data of the improved ground sample A is used.

As illustrated in FIG. 4, the logarithmic function logk and the uniaxial compressive strength qu have a strong correlation, so that the hydraulic conductivity k of the improved ground calculated in the hydraulic conductivity calculation step and the chemical solution that has been grasped in advance. It is possible to estimate the uniaxial compressive strength qu after curing the improved ground by associating the relationship data with the uniaxial compressive strength qu and permeability k after curing period T _E lapse of improved ground formed by G it can.

  In this embodiment, by constructing a work program from the hydraulic conductivity calculation process to the uniaxial compressive strength estimation process in advance in the arithmetic device 6, the injection pressure P and the injection flow rate Q acquired in the local injection test process are calculated. Based on the relational data, the uniaxial compression strength qu when each chemical solution G is used is automatically estimated. In other words, if an arithmetic device 6 in which a work program is constructed in advance is prepared and the relational data between the uniaxial compressive strength qu and the hydraulic conductivity k when each chemical solution G is used is input to the arithmetic device 6, the local injection Operations from the test process to the uniaxial compressive strength estimation process can be automated. In addition, it is also possible for an operator to perform operations from the on-site injection test process to the uniaxial compression strength estimation process without providing the arithmetic device 6.

  According to the present invention, the fluid is injected using the injection hole H into which the chemical solution G has been injected, and the relationship between the injection pressure P and the injection flow rate Q is acquired quickly and easily, so that the permeability coefficient k of the improved ground can be obtained. It can be calculated. Furthermore, since the fluid can be injected during the curing period before the improved ground develops strength, the strength of the improved ground (uniaxial compression) can be quickly determined based on the calculated permeability coefficient k and previously known data. Strength qu) can be grasped.

  As described above, since the strength of the improved ground can be confirmed at an early stage, for example, when the strength of the improved ground is less than a specified value, measures such as injecting the chemical solution G again can be taken early. Moreover, since the relationship between the injection specifications (injection amount, injection speed, etc.) of the chemical solution G when the improved ground is formed and the strength of the improved ground can be confirmed at an early stage, the injection conditions of the chemical solution G can be set for later injection work. Improve early.

  Since the present invention can also be adopted when the injection hole H is bent in the middle, for example, the strength of the improved ground is confirmed even in places where sampling and surroundings are difficult such as directly under the structure. be able to. Therefore, it is more versatile than the conventional method.

  In this embodiment, since water W is used as the fluid, there is little influence on the improved ground. Therefore, the strength of the improved ground can be estimated without substantially changing the strength of the improved ground before the water W is injected.

  The chemical solution G can also be used as a fluid to be injected into the injection hole H. Even when the chemical solution G is used, the same procedure as in the embodiment described above can be performed.

  When the chemical solution G is used as the fluid to be injected into the injection hole H, the chemical solution G is further injected into the original improved ground, so that the strength of the improved ground can be further improved. In addition, when the chemical solution G remains, the chemical solution G is effectively used.

DESCRIPTION OF SYMBOLS 1 On-site injection test apparatus 2 Injection pipe 2a Insertion pipe part 2b Supply pipe part 3 Injection apparatus 4 Flowmeter 5 Water pressure gauge 6 Arithmetic apparatus 7 Packer 8 Pipe 9 Pressurization apparatus 10 Chemical solution injection apparatus H Injection hole W Water G Ground improvement chemical solution g gas

Claims (4)

A method for estimating the strength of an improved ground formed by injecting a ground improvement chemical solution through an injection hole formed in the ground,
Completing the step of injecting the ground improvement chemical solution into the injection hole, and after the gel time in the soil of the ground improvement chemical solution has elapsed and before the predetermined time before the curing period of the improved ground has passed, the improvement through the injection hole A fluid is injected into the ground, the relationship between the injection pressure and the injection flow rate of the fluid at that time is acquired, and the hydraulic conductivity of the improved ground is calculated based on the relationship between the acquired injection pressure and the injection flow rate. Based on the calculated permeability coefficient and the relational data between the uniaxial compressive strength and permeability coefficient after the curing period of the improved ground formed by the ground improvement chemical solution grasped in advance, the uniaxial after the curing of the improved ground A method for estimating the strength of improved ground, characterized by estimating compressive strength.   The method for estimating the strength of the improved ground according to claim 1, wherein water is used as the fluid.   The method for estimating the strength of the improved ground according to claim 1, wherein the ground improvement chemical is used as the fluid. When calculating the hydraulic conductivity, the injection pressure is converted into an effective injection pressure head, the slope A of the effective injection pressure head with respect to the injection flow rate is obtained, and the obtained slope A is introduced into the following equation (1). The estimation method of the intensity | strength of the improved ground in any one of Claims 1-3 which calculates the said hydraulic conductivity k by this.
Hydraulic conductivity k = {1 / (2πLA)} ln (2L / D) (1)
Here, L is the length of the portion holding the fluid injected in the injection hole, and D is the diameter of the injection hole.

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