JP4511400B2 - Determination method of strength and thickness of improved layer of backfill sand by cement-type solidifying material injection mixing - Google Patents

Description

  The present invention relates to a method for determining the strength and thickness of an improved layer of backfill sand by injecting and mixing cement-based solidifying material, and more specifically, an improved layer suitable for the construction site can be formed to prevent backfill sand from being sucked out. The present invention relates to a method for determining the strength and thickness of an improved layer of backfill sand by cement-based solidifying material injection mixing.

  As a construction method for preventing the back sand from sucking off the offshore structure such as caisson, there is a method for preventing the suction by injecting a chemical solution to improve (harden) the back sand. Concerning this chemical injection method, the concentration of the backside sand improved by the chemical solution, the strength at which suction does not occur, and the obtained strength can be obtained by experiments using this sample. A method of injecting a chemical solution has been proposed (see Patent Document 1).

  In this proposal, by changing the concentration of the chemical to be injected, only the strength of the back sand is changed, and in the experiment in which the sample is subjected to variable water pressure over a certain period of 24 hours, only the result of the presence or absence of suction is verified. The optimum intensity that does not cause suction is detected. That is, given the layer thickness of the back sand to be improved, it is only possible to form the improved back sand by chemical injection that can prevent sucking in a certain period (24 hours), and the appropriate layer thickness etc. can be clearly defined. There was a problem of not becoming.

When high strength is required for the improved layer, etc., there is a method of forming the improved layer by injecting cement-based solidified material into the in-situ back sand and mixing it by spray stirring, mechanical stirring, etc. In the above proposal, an appropriate layer thickness cannot be determined and the construction method is different, so that it cannot be applied as it is, and it is difficult to form an improved layer using a cement-based solidifying material optimal for the construction site.
JP 2002-322639 A

  It is an object of the present invention to provide a method for determining the strength and thickness of an improved layer of back sand by injecting and mixing cement-based solidifying material that can prevent the back sand from being sucked out by forming an improved layer suitable for the construction site. There is to do.

  In order to achieve the above object, the method for determining the strength and thickness of the improved back sand layer by injecting and mixing the cement-based solidifying material of the present invention is a cement-based solidifying material that prevents the back-sand from sucking out of the structure such as caisson. This is a method for determining the strength and thickness of the improved layer of backfill sand by injection mixing, collecting the backfill sand to be improved from the construction site, and adding the cement-based solidified material to be injected per unit volume of backfill sand. The process of producing an improved layer sample under atmospheric pressure by mixing in different amounts, and the relationship between the cement-based solidifying material addition amount and strength using the improved layer sample mixed by changing the added amount of the cement-based solidifying material The process of acquiring data, and changing the layer thickness for each addition amount of the cement-based solidifying material and applying a variable hydraulic pressure until it breaks under predetermined conditions, the layer thickness and the number of times or time until breakage Process for obtaining related data , It is characterized in that a step of selecting the strength and thickness of satisfying improvement layer required in the construction site based on both relationship data the acquired.

  In the present invention, the backfill sand means soil to be backfilled and includes backfill soil.

  According to the method for determining the strength and thickness of the improved back sand layer by the cement-based solidifying material injection and mixing of the present invention, the back-ground sand to be improved is collected from the construction site and injected. By changing the amount of added sand per unit volume and mixing to produce an improved layer sample under atmospheric pressure, the sample can be produced with the actual backfill sand and cement-based solidified material, making the reality more realistic Thus, accurate data can be acquired.

  In addition, in the process of obtaining the relationship data between the cement-based solidifying material addition amount and the strength using the improved layer sample mixed by changing the cement-based solidifying material addition amount, the cement-based solidifying material addition amount and the strength of the improvement layer Can be grasped. In the process of obtaining the relationship data between the layer thickness and the number of times or the time until destruction by giving a variable hydraulic pressure until the improved layer sample is destroyed under predetermined conditions by changing the layer thickness for each cement-based solidifying material addition amount, The correlation between the layer thickness and strength of the improved layer for each cement-based solidifying material addition amount can be grasped by an experiment that approximates the conditions that actually act on the improved layer at the construction site.

  Based on the acquired relationship data, an optimal combination is selected from the combinations of the strength and thickness of the improved layer that satisfies the conditions by the process of selecting the strength and thickness of the improved layer that satisfies the requirements at the construction site. Can be selected.

  When the cement-type solidified material of the added amount C per unit volume of the back sand, which becomes the strength of the improved layer selected and determined by the above process, is injected to form the improved layer with the determined layer thickness, It is possible to satisfy and prevent sucking back sand.

  Hereinafter, a method for determining the strength and thickness of an improved layer of backfill sand by cement-based solidifying material injection and mixing according to the present invention will be described based on the embodiments shown in the drawings.

  FIG. 9 is a cross-sectional view illustrating an example of a construction site where a cement-based solidifying material is injected and mixed into the back sand 5. The caisson 1 is installed on the foundation rubble 2 at the construction site, the backside stone 3 is laid on the back of the caisson 1, the top surface is covered with the sandproof sheet 4, and the backside sand 5 is buried on it. The uppermost surface is the pavement surface 7. A plurality of the caisson 1 are installed in the extending direction of the revetment, and a joint is formed with a gap between adjacent caisson 1, and the gap is closed by a joint plate.

  Here, when the joint plate of the caisson 1 is damaged, a so-called sucking phenomenon occurs in which the back sand 5 is sucked out to the sea side by the wave motion of the seawater W on the front surface of the caisson 1. Therefore, an improved layer 6 is formed by injecting, mixing and hardening a cement-based solidified material into the back sand 5 vertically along the back surface of the caisson 1 to prevent sucking. For this purpose, it is necessary to form the improved layer 6 having the optimum strength and thickness H that satisfies the requirements of the construction site.

  For example, as shown in FIG. 10, the improved layer 6 is formed by rotating and injecting a slurry-like cement-based solidified material mixed with water by a jet jet from a discharge port 24 at the tip through a stirring shaft 22 rotated by an electric motor 25. It is possible to use a jet stirring method in which the cement-type solidified material is supplied and stirred with the back sand 5 while cutting the improved layer forming range by moving the material up and down. In this method, the improvement layer 6a is gradually formed on the back surface along the longitudinal direction of the caisson 1 as shown in the plan view of FIG.

  As another method for forming the improved layer 6, for example, as shown in FIG. 11, a slurry-like cement-based solidified material mixed with water is discharged from a discharge port 24 on the tip side through a stirring shaft 22 rotated by an electric motor 25. The improved layer 6b is formed by a mechanical stirring method in which the back sand 5 and the cement-based solidified material are stirred and mixed by the stirring blade 23 while being discharged, and the improved layer 6a in contact with the back surface of the caisson 1 is formed by the jet stirring method on the outer side. It is also possible to use a combination of mechanical and jet stirring. With only the mechanical stirring method, the stirring blade 23 comes into contact with the back surface of the caisson 1, so it is difficult to form the improvement layer 6 without a gap on the back surface of the caisson 1, but this combined method is shown in FIG. As shown in the plan view, the inner layer is an improved layer 6b formed by mechanical stirring, the outer side is an improved layer 6a formed by jet stirring, and the improved layer 6 is formed on the back surface along the longitudinal direction of the caisson 1. .

  In order to form the improved layer 6 by these methods, the strength and the layer thickness H of the improved layer 6 are determined by the procedure shown in FIG. First, the back sand 5 to be improved is collected from the construction site, and the amount C of the cement-based solidification material per unit volume of the back sand is changed in several ways and mixed to obtain the improved layer sample S under atmospheric pressure. Manufacture (first step). This improved layer sample S is prepared by mixing backfill sand 5, cement-type solidified material of each addition amount C and water, filling the container with a mold or the like, and then curing and improving at atmospheric pressure, for example, for 28 days. A layer sample S is produced.

  In order to manufacture the improvement layer sample S, until now, using the specimen manufacturing method described in the Geotechnical Society standard “Method of preparing specimen without compaction of stabilized soil (JGS 0821-2000)”, It is preferable because knowledge and data accumulated in the database can be used.

  Since this improved layer sample S is manufactured using the back sand 5 at the construction site where the improved layer 6 is actually formed, the improved layer sample S can be used for experiments to reproduce the reality more accurately. Good data can be acquired. Since the improved layer sample S is used for the strength test and the fluctuating hydraulic pressure test, several or more types and several types having different layer thicknesses are manufactured for the strength test for each addition amount C of the cement-based solidified material.

  Next, the relationship data of the addition amount C and the strength q are acquired using the improved layer sample S in which the addition amount C of the cement-based solidifying material per unit volume of the back sand is changed (second step). Specifically, when the uniaxial compressive strength test of the improved layer sample S is performed and the relationship between the strength q and the addition amount C is plotted, the proportional relationship data between the strength q and the addition amount C as illustrated in FIG. Can be obtained. Accordingly, it is possible to grasp and estimate the strength q of the improved layer 6 formed at the construction site by the addition amount C per unit volume of the back sand of the cement-based solidified material to be injected and mixed.

  Next, a variable water pressure experiment is performed in which a variable water pressure P is applied until the improved layer sample S is broken under predetermined conditions by changing the layer thickness h for each addition amount C. Data related to time t is acquired (third step).

  This fluctuating water pressure experiment is conceptually shown in FIG. 3, and the improvement layer sample S is accommodated in a sealed container 8 having a fluctuating pressure unit connected to the upper part and a water flow pipe 12 connected to the lower part. To do. Glass beads G are laid at the bottom of the sealed container 8 in order to ensure water flowability.

  The improvement layer sample S is loaded with a predetermined pressure by the water W in the upper conduit 11 and the water W in the lower water circulation pipe 12. This predetermined pressure is a pressure corresponding to the pressure received at the position where the improvement layer 6 is formed, and is, for example, the pressure at the representative depth point D where the improvement layer 6 is formed.

  In this state, a fluctuating pressure P for moving the water W in the upper conduit 11 up and down is applied. The fluctuating pressure P is obtained in advance as wave data of waves generated at the construction site, and based on this data, for example, is set to the same pressure amplitude and frequency as the most frequent waves as shown in FIG. The fluctuating pressure P is a value that changes due to the vertical movement caused by the most frequent wave to the pressure at the representative depth point D.

  Due to this fluctuating pressure P, the water W in the conduit 11 permeates the improved layer sample S and flows in and out of the water circulation pipe 12, and the improved layer sample S is gradually destroyed by repeated permeation of the water W, and the repetition until the destruction is repeated. The number of times N or time t is measured.

  That is, it is possible to reproduce the state approximate to the construction site where suction of the back sand 5 is generated, and to acquire accurate data on the durability of the improved layer sample S.

  As shown in FIG. 2, the fluctuation water pressure experimental device includes a fluctuation water pressure device 8, a flow rate measurement device 13, and a water flow pipe 12 that connects both devices 8 and 13. The fluctuating water pressure device 8 includes a sealed container 9 in which glass beads G are laid at the bottom, and a fluctuating pressure unit. The fluctuating pressure unit includes a conduit 11, an electropneumatic converter 20a, and a compressed air generating device 17. It is controlled by the control device 18. For example, a sealed container 9 having an outer diameter of about 100 mm and a height of about 100 mm is used. The compressed air generator 17 includes a compressor, a regulator, and the like.

  The flow rate measurement device 13 includes a micro load meter 15 installed in the sealed container 14 and connected to the measurement unit 19, a water storage tank 16 suspended from the pressure meter, and a pressure unit. The unit includes a sealed container 14, an electropneumatic converter 20 b, a pressure gauge 21 b, and a compressed air generator 17, and is controlled by a controller 18.

  One end of the water distribution pipe 12 is connected to the bottom of the sealed container 9 of the variable water pressure device 8, and the other end is disposed in the water storage tank 16 of the flow rate measurement device 13, so that the measurement unit 19 constituting the pipe water pressure measurement device is provided. It has a connected pressure gauge 21c.

  The fluctuating water pressure experiment is carried out by containing the improvement layer sample S in the airtight container 9 of the fluctuating water pressure device 8 with the wire mesh 10 sandwiched between the water W and the air A. By adjusting the inside of the sealed container 14 to a predetermined pressure with the compressed air generator 17 and the electropneumatic converter 20 a of the flow rate measuring device 13, the inside of the sealed container 9 is maintained at a predetermined pressure via the water circulation pipe 12. This predetermined pressure is an equivalent pressure received at the position where the improvement layer 6 is formed as described above, and this predetermined pressure is measured by the pressure gauge 21 b connected to the measurement unit 19.

  Then, by causing the compressed air generator 17 and the electropneumatic converter 20a to flow the air A into and out of the sealed container 9 through the conduit 11, the fluctuation in accordance with the waves generated at the construction site as described above in the water W is achieved. Water pressure P1 is applied. This fluctuating water pressure P1 is measured by the pressure gauge 21a. The method of giving the fluctuating water pressure P1 is not limited to this, and other methods may be used.

  Due to the fluctuating water pressure P1, the water W in the sealed container 9 permeates the improved layer sample S and flows into and out of the water storage tank 16 of the flow rate measuring device 13 through the water flow pipe 12, and the flow rate of the water W is a minute load. The water pressure P2 in the water distribution pipe 12 is measured by the pressure gauge 21c. The wire mesh 10 installed above and below the improvement layer sample S is for protection when the improvement layer sample S is fragile, and the installation can be omitted.

  When the flow rate measured by the flow rate measuring device 13 is shown with time, the outflow flow rate Q rapidly increases while vertically moving due to pressure fluctuation as shown in FIG. As the outflow flow rate Q on the vertical axis in FIG. 6 becomes negative (downward), it means that the water W flows from the storage tank 16 of the flow measurement device 13 into the sealed container 9 through the water flow pipe 12. Yes. That is, it is shown that the improvement layer sample S is broken and the outflow flow rate Q is increased. Thus, based on the flow rate data, for example, it is determined that the improvement layer sample S has been destroyed at the point B1 at which the outflow rate Q has increased rapidly. In the present invention, the destruction of the improved layer sample S (improved layer 6) includes not only the occurrence of cracks and the like, but also the case where the water permeation amount increases and the water stop function is not performed.

  Further, when the data of the fluctuation water pressure P1 measured by the pressure gauge 21a and the water pressure P2 on the lower surface of the improved layer sample S of the water flow pipe 12 measured by the pressure gauge 21c are shown with time, the vertical displacement due to the pressure fluctuation as shown in FIG. The water pressure P2 starts to increase while the water pressures P1 and P2 coincide with each other. This has shown that the improvement layer sample S destroyed and the pressure became uniform. In FIG. 7, in order to clarify the data (solid line) of the water pressure P2, the data (dotted line) of the water pressure P1 is omitted in the middle. It is confirmed that the point B2 when the water pressure P2 on the lower surface of the improvement layer sample S increases coincides with the point B1 when the flow rate Q rapidly increases. It can also be determined that 6 and 7, the horizontal axis represents time t, but the number of times the fluctuating water pressure P1 is applied (the number of repetitions N) may be used.

  The order of performing the second step and the third step may be either, and it is preferable to perform the steps at the same time to shorten the experiment time.

  Then, based on the relationship data between the addition amount C and the strength q acquired earlier and the relationship data between the layer thickness h and the number of times of destruction N or the failure time t, the strength of the improved layer 6 that satisfies the conditions required at the construction site. Then, the layer thickness h is selected (fourth step). Specifically, when the acquired data is plotted for each strength q (that is, the addition amount C per unit volume of the back sand of the cement-based solidified material), the relationship between the layer thickness h and the number N of repetitions until fracture is shown in FIG. The relational data of the quadratic curves of the curves q1 to q3 can be acquired for each of the strengths q1 to q3 as exemplified in FIG.

Multiplying the number N of repetitions until destruction by the frequency (fluctuation frequency of fluctuating water pressure) gives time t until destruction. Therefore, in FIG. For example, when the data is subjected to regression analysis, the following equations (1) and (2) can be obtained.
h = A + BlogN + C (logN) ² (1)
h = A + Blogt + C (logt) ² (2)
Where h: layer thickness of improved layer sample A, B, C: coefficient N: number of repetitions until failure t: repetition time until failure

  Thus, the correlation between the layer thickness h for each strength q (that is, the amount C of the cement-based solidifying material added per unit volume of the back sand) and the durability (the number of repetitions N and time t until breakage) is grasped. The durability can be estimated by the strength q and the layer thickness h. From this plot data, an optimum combination of the layer thickness H (= h) and the strength q that satisfies the requirements of the construction site is selected. For example, when there is a requirement for the durable years, a combination of the layer thickness H and the strength q that clears the repetition number N corresponding to the durable years is selected. When there are a plurality of combinations that satisfy the conditions, the combination that achieves the lowest cost by calculating the cost or the layer thickness H is selected when there is a restriction on the layer thickness H.

  After the combination of the layer thickness H and the strength q of the improved layer 6 is determined by the above steps, the strength is lower than the laboratory test in actual construction. Therefore, the strength αq obtained by multiplying the determined strength q by the safety factor α. An improved layer 6 having a layer thickness H determined by injecting and mixing an added amount C of cementitious solidifying material per unit volume of the back sand is obtained. Thereby, the optimal improvement layer 6 which satisfy | filled the requirements of a construction site is formed, and it becomes possible to prevent the back sand 5 from being sucked out.

It is a flowchart which illustrates the determination method of the intensity | strength and layer thickness of the improvement layer of backfill sand by the cement-type solidification material injection | pouring mixing of this invention. It is explanatory drawing which illustrates the whole outline | summary of the fluctuation | variation water pressure experiment apparatus of this invention. It is explanatory drawing which shows notionally the method of giving a fluctuation | variation water pressure to an improvement layer sample. It is a graph which illustrates the fluctuating water pressure given to an improvement layer sample. It is a graph which shows the relationship between the addition amount per unit of a cement-type solidification material, and uniaxial compressive strength. It is a graph which shows the time-dependent fluctuation | variation of the flow volume of the water which permeate | transmits an improvement layer sample with a fluctuation | variation water pressure. It is a graph which shows the time-dependent fluctuation | variation of the water pressure of the water which flows in and out of a water circulation pipe with a fluctuation | variation water pressure. It is a graph which shows the relationship between the layer thickness of an improvement layer sample, and durability. It is sectional drawing which shows an example of the construction site which inject | pours and mixes a cement-type solidification material to backfill sand. It is a longitudinal cross-sectional view explaining the injection stirring system which inject | pours and mixes a cement-type solidification material to backfill sand. It is a longitudinal cross-sectional view explaining the mechanical stirring system which inject | pours and mixes a cement-type solidification material to backfill sand. FIG. 12A is a plan view showing a process using an injection stirring method, and FIG. 12B is a plan view showing a process using a combined mechanical and jet stirring method.

Explanation of symbols

1 Caisson 2 Basic rubble 3 Back lining stone
4 Sediment prevention sheet 5 Backfill sand 6 Improved layer of backfill sand
6a Improved layer formed by spray stirring method
6b Improved layer formed by mechanical stirring method 7 Pavement surface 8 Fluctuating hydraulic device
9 Sealed container 10 Wire mesh 11 Conduit 12 Water flow pipe 13 Flow rate measuring device 14 Sealed container
15 Micro load cell 16 Water storage tank 17 Compressed air generator
DESCRIPTION OF SYMBOLS 18 Control apparatus 19 Measurement unit 20a-20b Electropneumatic converter 21a-21c Pressure gauge 22 Stirring shaft 23 Stirring blade 24 Discharge port 25 Electric motor A Air G Glass bead S Improvement layer sample W Water

Claims (3)

  A method for determining the strength and thickness of an improved layer of backfill sand by injecting and mixing cement-based solidifying material that prevents sucking out the backfill sand of caisson and other structures. Then, changing the addition amount of the cement-based solidified material per unit volume of the back sand and mixing the mixture to produce an improved layer sample under atmospheric pressure, and mixing the cement-based solidified material while changing the addition amount The process of acquiring the relationship data between the cement-based solidifying material addition amount and strength using the improved layer sample, and changing the layer thickness for each cement-based solidifying material addition amount until the layer is destroyed under predetermined conditions The process of obtaining the relational data between the layer thickness and the number of times or the time until destruction by giving a fluctuating water pressure, the strength of the improved layer that satisfies the conditions required at the construction site based on the obtained both relational data and Select the layer thickness Strength and thickness determination method of improving layer of Urakomi sand by cement solidifying material injection mixture and a step.   In the step of acquiring the relational data between the layer thickness and the number of times or time until destruction, the flow rate of water that permeates the improved layer sample is measured by the fluctuating water pressure, and the destruction is performed based on the measured flow rate data. The method for determining the strength and thickness of the improved layer of back sand by cement-solidifying material injection and mixing according to claim 1, wherein the number of times or time until the determination is determined.   In the step of obtaining the relationship data between the layer thickness and the number of times or time until failure, the pressure of water that permeates the improved layer sample by the fluctuating water pressure is measured, and based on the measured water pressure data, The method for determining the strength and layer thickness of an improved layer of back sand by cement-based solidifying material injection and mixing according to claim 1, wherein the number of times or time until destruction is determined.

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