JP6059029B2 - Vibration compaction method of sand layer and its management method - Google Patents

Description

  The present invention relates to a vibration compaction method for a sand layer using vacuum suction and a management method thereof.

  During an earthquake, a saturated loose sand layer can liquefy and cause severe damage. Measures for liquefaction of sand layers include density increase, drainage (at the time of earthquake), solidification treatment, shear deformation suppression (lattice solidification improvement), desaturation, and the like. Of these, paying attention to the compaction method for increasing the density and excluding the SCP method with sand supply in the ground, the compaction method includes the vibration rod compaction method (RC method) and the water absorption vibration compaction method. There is a construction method (water absorption RC construction method) (see Non-Patent Document 1). There are Patent Documents 1 to 3 as well-known documents of the vibration compaction method. In addition, there are gravel drain method (formation of crushed stone drainage layer) and grid drain method (GD method, large cross section PBD: placement of width 161mm x thickness 30mm) for drainage (earthquake).

  The RC method is a method in which a vibration rod is inserted into the ground, the initial structure of the ground is destroyed by vibration energy, and the ground is compacted. On the other hand, as shown in FIG. 9, the water absorption RC method is arranged in the loose sand layer G0 and vibrated near the tip of the vibrating rod 100 while vibrating the vibrating rod 100 connected to a vibration source (not shown). In this method, water is absorbed by the water supply pipe 101. This water absorption RC method includes a rod compaction type SIMAR method (registered trademark) using the vertical vibration of the vibrating rod and a vibro flot type SVF method using the horizontal vibration of the rod tip.

  The GD method is a method of placing a large cross-section PBD (plastic board drain) to dissipate excess pore water pressure generated during an earthquake through the drain, and it is effective when an earthquake occurs. Different from compaction method.

Japanese Patent Laid-Open No. 04-161608 Japanese Unexamined Patent Publication No. 04-272313 JP 04-272314 A

"Water absorption type vibration compaction method" pamphlet (published by the water absorption type vibration compaction method association)

  However, the above conventional methods have the following problems (1) to (4).

  (1) Since the RC method has a large attenuation of vibration energy, the improvement range per place is small and the compaction effect is also small.

  (2) The vibration compaction method may cause sedimentation of the sand layer that does not require liquefaction countermeasures, which may be undesirable.

  (3) The water absorption RC method is a method that improves the improvement effect by improving the RC method and using water absorption during vibration. However, (a) the fine particles stick to the water suction port attached to the tip of the vibrating rod, and the bulky sand lowers the hydraulic conductivity and lengthens the compaction time. (B) Removes the sand stuck after compaction. The construction efficiency may be greatly reduced, such as necessity.

  (4) The compaction principle of the water absorption RC method is to dissipate the excess pore water pressure generated by liquefaction at the same time by liquefying the sand layer (for example, vibration influence range A in FIG. 9) that requires liquefaction countermeasures. There is. However, in the case of a sand layer having a high fine particle content Fc, the management method of vibration and water absorption time for obtaining a sufficient compaction effect is unknown. Moreover, the application range of the above SIMAR method is Fc of 30% or less, and cannot be applied to sand having a high fine particle content Fc.

  In view of the problems of the prior art as described above, the present invention can reduce the settlement of other sand layers and can obtain a sufficient compacting effect even in the case of a sand layer having a high fine particle content Fc. The object is to provide a vibration compaction method and its management method.

In order to achieve the above object, the vibration compaction method of the sand layer according to the present embodiment includes a step of placing a plastic drain with a cap on a sand layer that requires countermeasures against liquefaction, and the above-mentioned via the plastic drain with a cap. A step of sucking pore water by applying a negative pressure to the sand layer, a step of sucking excess pore water generated by applying vibration to the sand layer in a state of applying the negative pressure, and a function of the negative pressure. A step of measuring the amount of sucked water and determining completion of the vibration / suction step when an incremental amount of sucked water, which is an incremental value according to the time of the amount of sucked water measured after applying the vibration, converges to a substantially constant value ; , Including.

According to this vibration compaction method for sand layers, sand compacts that require countermeasures against liquefaction can improve the compaction effect by using not only vibration but also water absorption by negative pressure suction. Water absorption is performed only for the sand layer that needs to be liquefied by the plastic drain, so that settlement of other sand layers can be reduced. In addition, since the completion of the vibration / suction process is determined based on the measurement result relating to the amount of water by negative pressure suction, a sufficient compaction effect can be obtained even in the case of a sand layer having a high fine particle content Fc. The final stage of the vibration compaction process can be managed accurately. As the measurement result for the water volume by negative pressure suction, an incremental value by the time of the measured suction water volume is used, and the time when this incremental suction water volume becomes almost zero or almost constant (when there is an osmotic flow in the sand layer) is vibrated. It can be determined that the suction process is completed.

In the vibration compaction method of the sand layer, it is preferable to determine the completion based on a temporal change in the amount of excess pore water sucked after the vibration is applied in the determination step . It can be determined that the vibration / suction process is completed when the time variation of the incremental suction water amount of the excess pore water becomes almost zero. Further, it may be a point in time when the incremental suction water amount of the excess pore water becomes substantially zero or substantially constant.

  The plastic drain with cap is connected to a drain material and a non-permeable drainage hose via a cap, and the drain material has a lower end of the drain material near the bottom of the sand layer and an upper end. By being placed so as to be located in the vicinity of the uppermost part of the sand layer, it is possible to reliably perform water absorption only for the sand layer that requires liquefaction countermeasures, and there is a sand layer that does not require liquefaction countermeasures on the upper part. Even if it is present, the non-water-permeable drainage hose is used, so this effect is further ensured.

  The sand layer is vibrated by a vibration device inserted into the sand layer, and the plurality of plastic drains with caps are arranged away from the vibration device, so that the sand layer has a high fine particle content Fc. However, unlike the prior art, sand does not stick to the water inlet in a lump shape, so that the construction efficiency can be improved. In addition, it is preferable to arrange a plurality of plastic drains with caps so as to surround the vibration device.

  It is preferable to apply vibration to the sand layer while moving the vibration part of the vibration device up and down in the sand layer.

The management method of the vibration compaction method of the sand layer according to the present embodiment includes a step of placing a plastic drain with a cap on a sand layer that requires countermeasures against liquefaction, and a negative pressure is applied to the sand layer through the plastic drain with a cap. A method for managing the vibration compaction method of the sand layer, comprising: a step of sucking pore water by acting; and a step of sucking excess pore water generated by applying vibration to the sand layer in a state where the negative pressure is applied. The amount of water sucked by the action of the negative pressure is measured, and the vibration when the incremental suction water amount, which is an incremental value according to the time of the suction water amount measured after applying the vibration , converges to a substantially constant value. -It is characterized by judging completion of the suction process.

  According to the management method of the vibration compaction method of the sand layer, the completion of the vibration / suction process is determined based on the measurement result regarding the amount of water by negative pressure suction, so that the final stage of the vibration compaction process can be accurately managed. .

  According to the present invention, there is provided a vibration compaction method and its management method capable of reducing settlement of other sand layers and obtaining a sufficient compaction effect even in the case of a sand layer having a high fine particle content Fc. Can be provided.

It is a figure which shows roughly the longitudinal cross-section of the ground for improvement for demonstrating the vibration compaction construction method by this embodiment. It is a figure which shows schematically the plane of the ground of FIG. It is a graph for demonstrating an example of the construction cycle of the vibration compaction construction method by this embodiment. It is a flowchart for demonstrating each process of the vibration compaction construction method by this embodiment. It is a figure which shows schematically the experimental apparatus used for this experiment example, Comprising: It is the top view (a) and longitudinal cross-sectional view (b) of an experimental apparatus. It is a figure which shows roughly the vacuum pump equipment used for the experimental apparatus of FIG. It is a graph which shows the relationship between the vibration and negative-pressure water absorption time obtained by this experiment example, and the amount of suction water. It is a graph which shows the relationship between the incremental suction water amount for every minute calculated | required from the integrated suction water amount of FIG. 7, and a vibration and negative pressure water absorption time. It is the schematic which shows the conventional water absorption RC construction method.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a longitudinal section of a ground to be improved for explaining the vibration compaction method according to the present embodiment, FIG. 2 is a diagram schematically showing a plane of the ground of FIG. 1, and FIG. FIG. 4 is a flowchart for explaining the steps S01 to S11 of the vibration compaction method according to this embodiment.

  The vibration compaction method and its management method according to this embodiment will be described with reference to FIGS.

  Referring to FIG. 4, first, a soil survey (standard penetration test, grain size test, etc.) is conducted in the ground improvement target area where liquefaction measures are required (S01), and the results of this soil survey (N value and The possibility of liquefaction of each sand layer is determined from the particle size distribution (S02).

Conducted maximum / minimum density (maximum / minimum gap ratio emax / emin) tests for sand layers that have been determined to have high liquefaction potential, and the sand layer has a relative density Dr = 80% (assumed density when compaction is completed) The amount of drainage VW is calculated by the following formula (1).
VW = V0 × (0.8-Dr) (emax-emin) / {1+ Dr × (emax-emin) + emin} (1)
However, Dr: Relative density of local soil that can be converted from N value, V0: Value determined by drain placement interval and sand layer thickness to be improved. For example, drain placement plane interval (m) is 2 × 2, sand layer When the thickness (m) is 3, 2 × 2 × 3 = 12 m ³ .

  As described above, the compaction specification is determined by determining the amount of drainage VW, the interval between drains, the sand layer to be improved for liquefaction countermeasures, and the like (S03). For example, as shown in FIG. 1, in the ground G to be improved, in the order from the top, when it is determined that there are a sand layer G1, which does not require liquefaction countermeasures, a sand layer G2 that requires liquefaction countermeasures, and a hard sand layer G3. The specifications are determined so that the sand layer G2 is compacted. Based on such specifications, compaction is performed as follows (S04).

  In this embodiment, a plastic board drain 10 with a cap (PBD with a cap) is used. The PBD 10 with a cap is a plastic that is placed in the ground and sucks pore water in the ground as shown in FIG. A drain member 11 made of a board, a water-impermeable drain hose 13, and a cap 12 connecting the upper end of the drain member 11 and the end of the drain hose 13 are provided. A specific example of such a cap-equipped PBD is disclosed in, for example, Japanese Patent Laid-Open No. 2006-241872.

  A plurality of PBDs with caps (for example, width 94 mm × thickness 3.6 mm) 10 are placed in the ground to be improved in a square arrangement such that the drain interval a is 2 m, for example, as shown in FIG. 2 (S05).

  If the sand layer G2 requiring liquefaction measures is, for example, between -5.0 and -8.0 m, the PBD 10 with a cap has a lower end of the drain material 11 at a position of -8 m and an upper end of -5 m as shown in FIG. It is placed so as to be in position. As shown in FIGS. 1 and 2, the cap 12 is directly above the sand layer G <b> 2, and a drain hose (for example, a diameter of 19 mm) 13 extends from the upper part to the ground and is connected to the vacuum pump facility P. In this way, the drain material 11 of the cap-equipped PBD 10 is disposed from the bottom to the top of the sand layer G2 that requires countermeasures against liquefaction, and the upper sand layer G1 that does not require countermeasures for liquefaction does not need to be improved. A water-permeable drainage hose 13 is provided.

  As shown in FIG. 1 and FIG. 2, as a vibration source, a vibration including a vertical vibration device 21 disposed on the ground and vibrating in the vertical direction V and a horizontal vibration device 22 disposed in the ground and vibrating in the horizontal direction H is provided. Device 20 is used. As such a vibration device 20, for example, a vibration rod made of a steel pipe rod having a diameter of 300 mm and equipped with a vibro hammer at the upper portion and a vibro flot at the lower portion can be used. A specific example of such a steel pipe rod is disclosed in, for example, a paper by Yasuhiro Okubo et al. “Development and Field Experiment of Water Absorption-Type Vibration Compaction Method” (35th Geotechnical Research Conference (June 2000)).

  The vibration rod of the vibration device 20 is set at the center of the square arrangement of the PBD with cap as shown in FIG. 2, and is inserted into the ground G as shown in FIG. 1 using the vertical vibration of the vibrator hammer of the vertical vibration device 21. (S06). As a result, the vibration device 20 is separated from the plurality of drain materials 11 and surrounded by the plurality of drain materials 11 in the sand layer G2.

The PBD 10 with a cap placed on the ground is connected to a vacuum pump facility P equipped with a vacuum pump or the like. Next, the vacuum pump facility P is operated, for example, a negative pressure of −60 kN / m ² is applied. Acting on the sand layer G2 (S07), the sand layer G2 is tightened by sucking pore water from the sand layer G2 in the direction of the arrow in FIG. The absolute value of the negative pressure may be 60 kN / m ² or more.

  Subsequently, in the state in which the negative pressure is applied, the vibratory lot of the horizontal vibration device 22 that has reached the vicinity of the lower end of the sand layer G2 that needs countermeasures against liquefaction is operated, and the sand layer G2 is caused by the lateral vibration of the vibratory lot part. 1 is liquefied, and excess pore water generated when the sand structure is destroyed (sinking) is sucked in the direction of the arrow in FIG. 1 by the cap-equipped PBD 10 to compact the sand layer G2 (S08).

  In the step S08, the vibro flot portion of the horizontal vibration device 22 is reciprocated up and down 1 to 1.5 within the sand layer G2. For example, as shown in FIG. 3, the vibratory lot portion of the horizontal vibration device 22 is laterally vibrated with the vibration time T while moving from the lower end → the upper end → the lower end → the upper end of the sand layer G2.

  The water drained by the negative pressure suction by the vacuum pump equipment P in steps S07 and S08 is stored in the tank of the vacuum pump equipment P, and the integrated suction water amount is measured. An incremental suction water amount at a predetermined time interval is obtained from this cumulative suction water amount, and if it is determined that the incremental suction water amount has converged to a substantially constant value (S09), the vacuum pump equipment P and the horizontal vibration device 22 are stopped.

  Next, the vibration rod of the vibration device 20 is pulled up from the ground G (S10). Next, sand is poured into the recessed portion after the vibration rod is pulled out (S11).

  As described above, according to the vibration compaction method of the present embodiment, the compaction effect is improved by using not only vibration but also water absorption by negative pressure suction for the sand layer that requires countermeasures against liquefaction. Can do.

  Further, water absorption is performed only for the sand layer that needs to be liquefied by the PBD with a cap, so that settlement of other sand layers can be reduced.

When a negative pressure is applied to the PBD, the water guide gradient i acting between the distance (L) between the drain material of the PBD and the vibration source is expressed by the following equation (2).
i ＝ (u1 + u2) / L (2)
However, u1: Excess pore water pressure generated at the vibration source, u2: Working negative pressure

  Therefore, even when the massive sand has a reduced hydraulic conductivity, the water guide gradient i is increased by applying a negative pressure, so that excess pore water can be drained promptly.

  In this embodiment, the water inlet at the tip of the vibrating rod (the water inlet of the water supply pipe 101 in FIG. 9) is not repeatedly used as in the prior art, but a large number of PBDs with caps are placed as shown in FIG. The water suction port is provided separately from the tip of the vibrating bar so as to surround the vibrating bar. For this reason, since sand does not stick to the water inlet in a lump shape, construction efficiency can be improved. The PBD is economical because it does not use a large-section PBD, but can use a general drain material having a width of 94 mm and a thickness of 3.6 mm, which is used for consolidation consolidation of clay ground.

  First, negative pressure is applied to suck the pore water to tighten the sand layer, and then the sand layer is liquefied by vibration by the vibration source to suck the excess pore water generated when the sand structure is destroyed (subsidence) by negative pressure. By compacting the sand layer, the sand layer can be compacted efficiently.

  Also, by measuring the cumulative amount of suction water by negative pressure suction, obtaining the incremental amount of suction water at a predetermined time interval from the cumulative amount of suction water, and determining that the vibration / suction process is complete when the incremental amount of suction water converges to a substantially constant value. It is possible to accurately grasp the end time of the vibration / suction process.

  As described above, the vibration compaction process can be accurately managed by using the measurement result of the integrated suction water amount for the management of the vibration / suction process (vibration tightening process). Further, the sand layer having a high fine particle content Fc that requires a long time for compaction can be sufficiently compacted. For this reason, sufficient compaction can be realized even with a sand layer having a high fine particle content Fc.

  According to the vibration compaction method similar to that shown in FIG. 4 actually conducted by the present inventors, the standard penetration test was conducted before and after the construction to examine the change in the N value. It was confirmed that a sand layer having a value of about 2 to 5 had an N value of 20 to 24 after compaction, and a large compaction effect could be obtained.

<Experimental example>
Next, the effect of the vibration compaction method according to the present embodiment was confirmed by experiments.

An experimental apparatus is shown to Fig.5 (a) (b). In a cylindrical container with a diameter of 30 cm and a height of 1.0 m, two vibrating bars (for concrete) are installed at 1/4 flat positions, and then quartz sand No. 5 is dropped in water, relative density Dr = 51%, It was produced with a height of 65 cm, and then a PBD with a cap was inserted into the center of the soil layer using jet water. A 20 cm thick clay layer was provided on the top of the sand layer to ensure the maintenance of negative pressure. When a negative pressure of -60 kN / m ² was applied to this sand layer using the vacuum pump equipment shown in Fig. 6, 2.1 L (liter) of pore water was discharged, but the settlement was almost zero (no sand layer failure). Saturation and effective stress increase).

  Next, the vibrating rod was operated with the negative pressure applied, and the sand structure was destroyed by liquefaction and the excess pore water was sucked. FIG. 7 shows the relationship between the vibration / negative pressure water absorption time and the cumulative suction water volume at that time. The cumulative suction water volume of the pore water was 5.1 L (liter) and the final height was 60.4 cm. FIG. 8 shows the relationship between the incremental suction water amount per minute obtained from the integrated suction water amount in FIG. 7 and the vibration / negative pressure water absorption time. The main results of this experiment are as follows.

  (1) The relative density Dr of the sand layer after compaction determined from the amount of settlement was 91%, and a sufficient compaction effect was obtained.

  (2) From the relationship between the vibration / negative pressure water absorption time and the amount of incremental suction water in FIG. 8, it can be seen that when the compaction is completed, the change in the amount of incremental suction water with time decreases rapidly and then becomes almost zero. . 7 and 8, the increase in the accumulated suction water amount with time (incremental suction water amount) becomes almost zero when compaction is completed (between 2 and 3 minutes in FIGS. 7 and 8). However, the amount of the incremental suction water becomes almost zero because of the experimental apparatus, and it is considered that the incremental suction water amount is actually a constant value (not zero) due to the steady osmotic flow in the sand layer.

  As described above, the modes for carrying out the present invention have been described. However, the present invention is not limited to these, and various modifications can be made within the scope of the technical idea of the present invention. For example, although the placement distance a (FIG. 2) on the plane of the PBD with cap is 2 m, this is an example, and may be a square arrangement within a range of about 1.0 to 5.0 m, for example.

  According to the vibration compaction method and its management method of the present invention, an economical liquefaction countermeasure can be taken for a sand layer, and it is also effective for a sand layer having a high fine particle content Fc.

10 Plastic board drain with cap, PBD with cap
11 Drain material 12 Cap 13 Drainage hose 20 Vibration device 21 Vertical vibration device 22 Horizontal vibration device a Drain interval, placement interval G1 Sand layer G2 that does not require liquefaction measures Sand layer P that requires liquefaction measures Vacuum pump equipment

Claims (5)

A process of placing a plastic drain with a cap on a sand layer that requires countermeasures against liquefaction;
A step of sucking pore water by applying a negative pressure to the sand layer through the plastic drain with the cap;
Sucking excess pore water generated by applying vibration to the sand layer in a state where the negative pressure is applied;
The amount of water sucked by the action of the negative pressure is measured, and the incremental suction water amount, which is an incremental value according to the time of the suction water amount measured after applying the vibration, converges to a substantially constant value when the vibration / suction process is completed. A sand compaction method comprising: a step of judging completion. The plastic drain with cap is connected to a drain material and a non-water-permeable drainage hose via a cap. The sand compaction vibration compaction method according to claim 1 , wherein the sand compaction is placed so as to be positioned in the vicinity of the uppermost portion of the sand layer. The vibration to the sand layer is performed by a vibration device inserted in the sand layer,
The sand compaction compaction method according to claim 1 or 2 , wherein the plurality of plastic drains with caps are arranged apart from the vibration device. The sand compaction method according to claim 3 , wherein the sand layer is vibrated while moving a vibration part of the vibration device up and down in the sand layer. A process of placing a plastic drain with a cap on a sand layer that requires countermeasures against liquefaction;
A step of sucking pore water by applying a negative pressure to the sand layer through the plastic drain with the cap;
A step of sucking excess pore water generated by applying vibration to the sand layer in a state in which the negative pressure is applied, and a management method of the vibration compaction method of the sand layer,
The amount of water sucked by the action of the negative pressure is measured, and the incremental suction water amount, which is an incremental value according to the time of the suction water amount measured after applying the vibration, converges to a substantially constant value when the vibration / suction process is completed. A management method for the vibration compaction method of the sand layer, characterized by judging completion.