JP4803531B2 - Evaluation method of water permeability - Google Patents

Description

  The present invention relates to a water permeability evaluation method capable of evaluating the water permeability of a ground in situ.

  Generally, before injecting grout into the ground, a lugion test is performed using a grout device, and the hydraulic conductivity of the ground is calculated. And based on this water permeability coefficient, specifications such as a grout injection method, an injection amount, and an injection material are determined.

  However, when the amount of water injected cannot be measured in the Lugion test, the optimum grout injection was determined because it was determined as 0 (zero) Ludion and the specification of the grout was determined without quantitative evaluation of water permeability. There was a problem that it might not have been done.

Therefore, for example, in Non-Patent Document 1, two packers installed at predetermined intervals in the depth direction in the borehole and a pump for supplying water to the evaluation target section closed by both packers A supply pipe for supplying water discharged from the pump into the evaluation target section, a flow meter for measuring an injection amount of water supplied from the pump, and an injection pressure of water supplied from the pump A method is disclosed in which a permeability test is performed using a permeability test apparatus including a pressure gauge for measuring the pressure and a valve for closing the evaluation target section, and the permeability coefficient in the evaluation target section is calculated. Yes. In this method, water is injected from the pump into the evaluation target section to bring the evaluation target section to a predetermined pressure, and then the water injection is stopped and at the same time the valve is closed to change the pressure in the evaluation target section over time. Based on the measurement result, a professional engineer calculates the hydraulic conductivity using a dedicated analysis tool such as inverse analysis.
NAGRA TECHNICICAL REPORT 93-38, Hydraulic Packer Testing in the Wellenberg Boreholes SB1 and SB2, Methods and Field Results, February 1994, Solexbertsport

  However, since the method of calculating the hydraulic conductivity using the dedicated analysis tool takes about two days, there is a problem that the work must be stopped after the hydraulic test and the work efficiency is poor. Therefore, in order to evaluate water permeability, there are problems such as costs for personnel and equipment, and a long construction period.

  Therefore, the present invention has been made in view of the conventional problems as described above, and can perform a water permeability test continuously after the Lugion test, and quantitatively measure the water permeability in a short time on site. An object is to provide an evaluation method for water permeability that can be evaluated.

To achieve the above object, the present onset Ming, the evaluation method of the permeability of the ground,
One or more packers installed in a borehole drilled in the ground, a pump for supplying water into an evaluation target section closed by the packer, and water discharged from the pump A supply pipe for feeding into the target section, a flow meter for measuring the injection amount of water supplied from the pump, and a pressure gauge for measuring the injection pressure of water supplied from the pump; A press-fitting step of press-fitting water into the evaluation target section from the pump by a water permeation test apparatus in which a valve for closing the evaluation target section is attached to the supply pipe of the grout device constituted by:
A calculation step of calculating a relationship between an elapsed time until the pressure in the evaluation target section decreases from a predetermined pressure by a predetermined degree and a permeability coefficient of the evaluation target section;
By the permeability test apparatus, a measuring step after closing the valve, the pressure in the evaluation target section measures the elapsed time until reduced by the predetermined degree,
Based on the relationship between the calculated elapsed time and the permeability coefficient, a permeability coefficient acquisition step including the permeability coefficient corresponding to the measured elapsed time as the permeability coefficient of the evaluation target section,
In the calculation step,
Assuming a plurality of values for the hydraulic conductivity in the evaluation target section ,
Calculate the change over time of the pressure in the evaluation target section corresponding to each value assumed for the hydraulic conductivity,
Based on the time-dependent change of the calculated pressure, a relationship between an elapsed time until the pressure in the evaluation target section decreases by the predetermined degree and a hydraulic conductivity of the evaluation target section is calculated ( First invention).

  According to the method for evaluating water permeability according to the present invention, the relationship between the elapsed time until the pressure in the evaluation target section where the water permeability test is performed decreases from the predetermined pressure by a predetermined degree and the hydraulic conductivity of the evaluation target section is expressed as follows. A calculation process for calculating, a press-fitting process for injecting water into the evaluation target section from the pump of the water permeability test apparatus with a valve attached to the grout device, and closing the valve to reduce the pressure in the evaluation target section by a predetermined degree. A measurement step for measuring the elapsed time up to and a permeability coefficient obtaining step for setting the permeability coefficient corresponding to the measured elapsed time as the permeability coefficient of the evaluation target section based on the relationship between the calculated permeability coefficient and the elapsed time. In order to prepare, it becomes possible to calculate the hydraulic conductivity of the evaluation target section.

  In addition, after calculating the relationship between the permeability coefficient and the elapsed time in advance, the elapsed time until the pressure in the evaluation target section decreases by a predetermined degree is measured on site, and the relationship between the calculated permeability coefficient and the elapsed time is calculated. In order to set the hydraulic conductivity corresponding to the result measured based on the hydraulic conductivity of the evaluation target section, the hydraulic conductivity can be acquired in a short time. Therefore, immediately after completion of the water permeability test, it is possible to determine the specifications of the grout injection method, the injection amount, the injection material, and the like, and to start the grout injection operation. And in order to implement grout injection | pouring operation | work based on this hydraulic conductivity, it becomes possible to construct the optimal grout to the ground for grout injection | pouring.

  According to a second aspect, in the first aspect, in the press-fitting step, water is injected until the pressure in the evaluation target section becomes the predetermined pressure.

  According to the method for evaluating a hydraulic conductivity according to the present invention, by making the pressure in the evaluation target section the same as the predetermined pressure, the elapsed time and the hydraulic conductivity calculated in the calculation step from the result measured in the measurement step, Based on this relationship, the water permeability can be immediately evaluated, and the water permeability test can be carried out efficiently.

A third invention is characterized in that, in the first or second invention, in the press-fitting step, a Luzione test for increasing the water injection pressure stepwise is performed.

  According to the method for evaluating water permeability according to the present invention, when the water permeability test according to the present invention is performed after the Lugion test, it is possible to perform the water permeability test without replacing the water permeability test apparatus. And, since the grouting operation can be performed using the permeable test device after the permeable test, the grouting operation can be performed without performing the operation of replacing the permeable testing device with the grouting device. Become. Therefore, a series of operations from the water permeability test to the grout injection can be performed efficiently.

A fourth invention is characterized in that, in the third invention, the Lugion test is performed, and when the permeability coefficient cannot be obtained by the Lugion test, the measurement step and the permeability coefficient acquisition step are performed.

  According to the method for evaluating water permeability according to the present invention, it is possible to obtain a water permeability coefficient of a low water permeability section in which water permeability could not be evaluated in the conventional Lugeon test.

  By using the method for evaluating water permeability and the method for calculating the water permeability coefficient of the present invention, it is possible to quantitatively evaluate the water permeability of a low water permeability ground, which cannot be evaluated for water permeability in the Lugion test. Become.

  Hereinafter, preferred embodiments of a water permeability evaluation method and a water permeability calculation method according to the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, the water permeation test apparatus 1 is obtained by attaching a valve 7 to a general grout apparatus 3. The grouting device 3 evaluates the packer 11 installed in the boring hole 9, the pump 13 for supplying water into the evaluation target section 12 closed by the packer 11, and the water discharged from the pump 13. A supply pipe 5 for feeding into the target section 12, a flow meter 15 for measuring the amount of water supplied from the pump 13, and a pressure for measuring the injection pressure of water supplied from the pump 13 And a pressure gauge 17.
When the valve 7 is closed, the movement of the fluid such as water and gas in the supply pipe 5 is suppressed and the evaluation target section 12 is closed.
In the present embodiment, the length from the lower end of the packer 11 to the bottom of the boring hole 9 and the hole diameter of the boring hole 9 are, for example, 5.0 m and 0.075 m, respectively.

The water permeability evaluation method of the evaluation target section 12 using this water permeability test apparatus 1 will be described below.
FIG. 2 is a diagram illustrating a flow of the water permeability evaluation method for the evaluation target section 12. FIG. 3 is a diagram showing a change with time in pressure in the evaluation target section 12 during a Lugion test using the grout device 3. In the present embodiment, it is assumed that the hydrostatic pressure in the evaluation target section 12 is 0.4905 MPa, for example.

  In step S1 of FIG. 2, as shown in FIG. 3, the injection pressure of the water injected into the evaluation target section 12 is stepwise from 0.4905 MPa (effective pressure 0 MPa) to 2.4905 MPa (effective pressure 2.0 MPa). While increasing the pressure in the evaluation target section 12 to be constant for a predetermined time, a Luzione test is performed to measure the amount of water injected into the evaluation target section 12. The Lujion test is conducted according to the method described in “Ground Survey Method and Explanation” (“Ground Survey Method and Explanation”, Geotechnical Society of Japan, issued on June 1, 2004). If the water injection amount cannot be measured at each stage where the pressure in the evaluation target section 12 is kept constant, the pump 13 is stopped after the maximum injection pressure (2.4905 MPa) test to stop the water supply. At the same time, in step S2, the valve 7 is closed (hereinafter referred to as shut-in) to close the evaluation target section 12.

  In the present embodiment, the injection pressure of the lugion test is set to 0.4905 MPa (effective pressure 0 MPa) to 2.4905 MPa (effective pressure 2.0 MPa), but is not limited to this pressure range. Change according to the conditions such as the groundwater level at the site.

  Next, in step S3, an elapsed time Tt until the pressure in the evaluation target section 12 at the time of shut-in decreases from 2.4905 MPa by a predetermined degree is measured.

  Step S1 corresponds to the press-fitting process of the present invention, and steps S2 and S3 correspond to the measuring process of the present invention.

  Here, FIG. 4 is a diagram showing a change with time of the pressure in the evaluation target section 12 after the shut-in. As shown in FIG. 4, the pressure in the evaluation target section 12 after shut-in gradually decreases because the water in the evaluation target section 12 permeates into the ground little by little. In this embodiment, the elapsed time until the pressure in the evaluation target section 12 decreases by 1.8 MPa from 2.4905 MPa, assuming that the predetermined degree is 90% of the effective pressure 2.0 MPa in consideration of the characteristics of the pressure gauge. Tt was measured. And based on the measured elapsed time Tt, based on the relationship between the elapsed time Tc calculated before or during the Lugeon test and the hydraulic conductivity Kc (calculated in step S4 and step S5, details will be described later). In step S6, the hydraulic conductivity Kt of the evaluation target section 12 is obtained. Step S6 corresponds to the water permeability coefficient acquisition step of the present invention.

  In the present embodiment, the case where the predetermined degree is set to 90% of the effective pressure has been described. However, the present invention is not limited to this value, and the degree of pressure decrease is within the evaluation target section 12 at the time of shut-in. It will be changed appropriately according to the site conditions such as the pressure, geological conditions, construction period, etc. and the equipment conditions such as the characteristics of the pressure gauge.

Hereinafter, a method for calculating the relationship between the elapsed time Tc and the hydraulic conductivity Kc will be described.
In step S4, first, an approximate value of the hydraulic conductivity Kc is estimated based on the geological survey results, the site conditions such as the excavation status of the borehole 9 and the water level recovery status in the borehole 9, and 10 ² is the center of this value. A minimum value and a maximum value are set with a width of about (m / s), and a plurality of hydraulic conductivity Kc are set by dividing the minimum value and the maximum value at equal intervals. In the present embodiment, for example, the approximate value of the hydraulic conductivity Kc is estimated to be 5.0 × 10 ⁻⁸ (m / s), the minimum value is 1.0 × 10 ⁻⁹ (m / s), and the maximum value. ^Is set to 1.0 × 10 ⁻⁶ (m / s), and this interval is divided by 0.5 (m / s) intervals to obtain 1.0 × 10 ⁻⁹ , 5.0 × 10 ⁻⁹ , Seven types of hydraulic conductivity of 1.0 × 10 ⁻⁸ , 5.0 × 10 ⁻⁸ , 1.0 × 10 ⁻⁷ , 5.0 × 10 ⁻⁷ , 1.0 × 10 ⁻⁶ (m / s) Kc was set.

  The relationship between the pressure in the evaluation target section 12 at each permeability coefficient Kc and the elapsed time Tc is expressed by the basic equation of osmotic flow and the graphical theory (GTFM-User DOCUMENTATION, Functional Development, Theoretical Investment, and Software Architecture. 0, INTERConsultants, 22 August 1996). For this analysis, parameters such as on-site conditions and analysis conditions shown in FIG. 5 are used. In addition, the actual length is used for the evaluation target section length, borehole radius, and hydrostatic pressure shown in FIG. 5, and the flow dimension, the influence radius, the evaluation target section compression rate, and the non-retention coefficient are estimated as appropriate according to the field situation. (FIG. 5). Moreover, although the value of the injection pressure at the time of the lugion test was used as the pressure value within the evaluation target section 12, it is not limited to this, and the value of the effective pressure at the time of the lugion test (for example, 2 in this embodiment). 0.0 MPa) may be used.

FIG. 6 is a diagram illustrating a result of calculating the relationship between the pressure in the evaluation target section 12 and the elapsed time Tc at each hydraulic conductivity Kc.
As shown in FIG. 6, in all the hydraulic conductivity Kc, the pressure in the evaluation target section 12 after shut-in decreases with the passage of time, but the elapsed time Tc required to decrease the predetermined pressure value varies depending on the hydraulic conductivity Kc. . Therefore, the water permeability of the evaluation target section 12 can be evaluated by measuring the elapsed time Tc required for lowering the predetermined pressure value on site and obtaining the water permeability coefficient Kc corresponding to the elapsed time Tc.

  Therefore, in step S5, based on the relationship between the calculated pressure in the evaluation target section 12 and the elapsed time Tc, the pressure in the evaluation target section 12 is reduced by 1.8 MPa from the pressure at shut-in of 2.4905 MPa. The relationship between the elapsed time Tc until reaching 0.6905 MPa and each hydraulic conductivity Kc is obtained.

Steps S4 and S5 correspond to the calculation process of the present invention.
The relationship between the obtained elapsed time Tc and each water permeability coefficient Kc is output to a screen such as paper or PC, and the water permeability coefficient Kt is obtained with reference to the output result. However, the relationship between the obtained elapsed time Tc and each permeability coefficient Kc is stored in the memory of the computer, and when the value of the elapsed time Tc is input, the computer determines the permeability coefficient Kt with reference to the relationship stored in the memory. You may do it.

  FIG. 7 is a diagram in which an example of the relationship between the elapsed time Tc until the pressure in the evaluation target section 12 decreases by 1.8 MPa from the pressure at the time of shut-in and the hydraulic conductivity Kc is output.

  As shown in FIG. 7, the elapsed time Tc until the pressure in the evaluation target section 12 decreases by 1.8 MPa, which is 90% of a predetermined degree, from the pressure at the time of shut-in becomes longer as the water permeability coefficient Kc decreases. ing. The curve connecting the points indicating the relationship between the water permeability coefficient Kc and the elapsed time Tc in the figure is calculated by a general approximation method such as the least square method.

In step S6, the permeability coefficient Kc corresponding to the elapsed time Tc is obtained with reference to the relationship illustrated in FIG. 7 obtained in step S5, and this value is set as the permeability coefficient Kt in the evaluation target section 12. In the example of FIG. 7, for example, if the elapsed time Tc is 800 seconds, the value of the permeability coefficient Kc corresponding to this is 1.0 × 10 ⁻⁹ (m / s), and this value is the evaluation target section. 12 is a water permeability coefficient Kt. Based on the water permeability coefficient Kt thus obtained, the grout material, the injection amount and the like are determined, and the water injection test apparatus 1 is used to carry out grout injection.

  Moreover, in this embodiment, in order to make description easy, the process of calculating the relationship between the pressure in the evaluation object section 12 in the estimated permeability coefficient Kc and the elapsed time Tc, the permeability coefficient Kc and the elapsed time Tc. The steps illustrating the relationship have been described after steps S1 to S3 as step S4 and step S5, respectively, but these steps are performed in order to derive the water permeability coefficient Kt in step S6 immediately after measuring the elapsed time Tt in step S3. It is desirable to finish in advance before the steps S4 and S5.

  Furthermore, in this embodiment, although the case where the relationship between the pressure in the evaluation object area 12 and the elapsed time Tc was calculated using seven kinds of permeability coefficients Kc was described, it is limited to the values of these permeability coefficients Kc. Not appropriate, but set appropriately according to site conditions such as geological conditions.

  As described above, according to the water permeability evaluation method of the present embodiment, the pressure in the evaluation target section 12 where the water permeability test is performed is decreased by 1.8 MPa which is 90% of a predetermined degree from 2.4905 MPa. The process of calculating the relationship between the elapsed time Tc until the evaluation and the permeability coefficient Kc of the evaluation target section 12 and the permeability test apparatus 1 in which the valve 7 is attached to the grout apparatus 3 in the field are used to perform the permeability test. The step of measuring the elapsed time Tt from the pressure in the evaluation target section 12 of 2.4905 MPa to a drop of 1.8 MPa, which is 90% of a predetermined degree, and the relationship between the calculated permeability coefficient Kc and the elapsed time Tc In order to provide a process for setting the permeability coefficient Kc corresponding to the elapsed time Tt measured in the field to the permeability coefficient Kt of the evaluation target section 12, It is possible to calculate the permeability Kt evaluated section 12 is a low permeability zone it has not been possible to evaluate the permeability. Further, after calculating the relationship between the water permeability coefficient Kc and the elapsed time Tc in advance, the elapsed time Tt is measured on site, and the measured elapsed time Tt is calculated based on the calculated relationship between the water permeability coefficient Kc and the elapsed time Tc. Since the corresponding permeability coefficient Kc is set to the permeability coefficient Kt of the evaluation target section, the permeability coefficient Kt can be acquired in a short time. Therefore, immediately after completion of the water permeability test, it is possible to determine the specifications of the grout injection method, the injection amount, the injection material, and the like, and to start the grout injection operation. And in order to implement grout injection | pouring operation | work based on this water permeability coefficient Kt, it becomes possible to construct the grout optimal for the grout injection | pouring object ground.

  Further, seven kinds of hydraulic conductivity Kc in the evaluation target section 12 are set, and the temporal change of the pressure in the evaluation target section 12 corresponding to each of the hydraulic conductivity Kc is calculated, and based on the calculated temporal change of the pressure. In order to illustrate the relationship between the elapsed time Tc and each permeability coefficient Kc, the permeability coefficient Kc corresponding to the result of the elapsed time Tt measured in the field is read from this figure and used as the permeability coefficient Kt of the evaluation target section 12. Therefore, the water permeability coefficient Kt can be easily obtained visually. In addition, anyone can easily obtain the permeability coefficient Kt and does not require specialized workers and specialized analysis tools for assessing permeability, thus reducing labor costs and equipment costs. It becomes possible.

  Furthermore, since the final injection pressure in the Luzione test was the same as the predetermined pressure (2.4905 MPa in this embodiment) used when calculating the elapsed time Tc and the hydraulic conductivity Kc of the evaluation target section, If the water permeability coefficient cannot be measured by the Lugion test, the water permeability can be evaluated by the method of the present invention following the Lugion test, and the water permeability test can be carried out efficiently.

  In addition, when the water permeability test according to the present invention is performed after the Lujion test, it is not necessary to perform the replacement work of the water permeability test apparatus 1. And, since the grouting operation can be performed using the permeable test device 1 after the permeable test, the grouting operation can be performed without performing the operation of replacing the permeable testing device 1 with the grouting device. It becomes possible. Therefore, a series of operations from the water permeability test to the grout injection can be performed efficiently.

It is sectional drawing which shows the state which installed the water-permeable test apparatus which concerns on this embodiment in the boring hole. It is a figure which shows the flow of the water-permeable evaluation method of an evaluation object area. It is a figure which shows the pressure time-dependent change in the evaluation object area at the time of the lugion test using a grout apparatus. It is a figure which shows the time-dependent change of the pressure in the evaluation object area after shut-in. It is a figure which shows parameters, such as on-site conditions and test conditions used when calculating the time-dependent change of the pressure in an evaluation object area. It is a figure which shows the result of having calculated the relationship between the pressure in the evaluation object area in each hydraulic conductivity, and elapsed time. It is a figure which shows the relationship between the elapsed time Tc until the pressure in the evaluation object area 12 falls by 1.8 Mpa from the pressure at the time of shut-in, and the hydraulic conductivity Kc.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Permeability test apparatus 3 Grout apparatus 5 Supply pipe 7 Valve 9 Boring hole 11 Packer 12 Evaluation object section 13 Pump 15 Flow meter 17 Pressure gauge Tc, Tt Elapsed time Kc, Kt Permeability coefficient

Claims (4)

In the evaluation method of water permeability of the ground,
One or more packers installed in a borehole drilled in the ground, a pump for supplying water into an evaluation target section closed by the packer, and water discharged from the pump A supply pipe for feeding into the target section, a flow meter for measuring the injection amount of water supplied from the pump, and a pressure gauge for measuring the injection pressure of water supplied from the pump; A press-fitting step of press-fitting water into the evaluation target section from the pump by a water permeation test apparatus in which a valve for closing the evaluation target section is attached to the supply pipe of the grout device constituted by:
A calculation step of calculating a relationship between an elapsed time until the pressure in the evaluation target section decreases from a predetermined pressure by a predetermined degree and a permeability coefficient of the evaluation target section;
By the permeability test apparatus, a measuring step after closing the valve, the pressure in the evaluation target section measures the elapsed time until reduced by the predetermined degree,
Based on the relationship between the calculated elapsed time and the permeability coefficient, a permeability coefficient acquisition step including the permeability coefficient corresponding to the measured elapsed time as the permeability coefficient of the evaluation target section,
In the calculation step,
Assuming a plurality of values for the hydraulic conductivity in the evaluation target section ,
Calculate the change over time of the pressure in the evaluation target section corresponding to each value assumed for the hydraulic conductivity,
Based on the time-dependent change of the calculated pressure, the relationship between the elapsed time until the pressure in the evaluation target section decreases by the predetermined degree and the hydraulic conductivity of the evaluation target section is calculated. Evaluation method of sex. The water permeability evaluation method according to claim 1, wherein in the press-fitting step, water is injected until the pressure in the evaluation target section becomes the predetermined pressure.   3. The water permeability evaluation method according to claim 1, wherein in the press-fitting step, a Luzione test is performed in which the water injection pressure is increased step by step. The water permeability evaluation method according to claim 3 , wherein the Lugeon test is performed, and the measurement step and the water permeability coefficient acquisition step are performed when a water permeability coefficient cannot be obtained by the Lugeon test.

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