JP6681115B2 - Method for designing the structure for countermeasures against liquefaction of ground - Google Patents

Description

  The present disclosure relates to a liquefaction countermeasure structure of a ground suitable for an external part other than a supporting ground of a main building, such as a parking lot or a supporting ground of a small building, in a site such as an existing or new apartment house, and a design method thereof. .

  The soil that constitutes the ground consists of soil particles and voids. Usually, water or air is present in the pores, and the pores are filled with water in a portion of the ground below the groundwater level. When soil particles (sand in the case of loose sand ground that causes liquefaction) are loosely bound, when vibration is transmitted to the ground due to an earthquake, the meshing of soil particles (sand) collapses, and the volume of soil including gaps is reduced. Trying to get smaller. At this time, since the gap is filled with water, the water pressure increases. This water pressure is called excess pore water pressure. The load of the structure provided on the ground is transmitted to the deep part of the ground by the total of the force transmitted by the soil particles (sand) and the force transmitted by the pore water. The stress transmitted by soil particles (sand) is called effective stress. When the ground is vibrated by an earthquake, the pressure of pore water increases as described above, so that the force (effective stress) transmitted by soil particles (sand) relatively decreases. It is a phenomenon called liquefaction of the sand ground that the rigidity of the soil is reduced due to the reduction of the effective stress and the soil becomes fluidized.

  When constructing a relatively large building such as an apartment or office building on the ground where a liquefaction layer that causes such liquefaction exists, for the main building, construct a support pile that reaches the support layer or In many cases, sufficient liquefaction measures such as building compacted sand piles directly under the building will be taken with the construction of. On the other hand, since such measures against liquefaction are costly, parking lots and light buildings (buildings other than relatively large buildings such as condominiums and office buildings, for example, Building Standard Act Article 6 In many cases, sufficient measures against liquefaction are not taken for the ground of the exterior part such as the building (so-called No. 4 building) specified in Paragraph No. 4.

  As a liquefaction countermeasure method for the ground, sand piles are created in the layer to be liquefied and the sand ground is compacted (static compaction method (SAVE method), sand compaction pile method), or the ground to be liquefied is gridded. -Like construction, a method of suppressing shear deformation of soil in the division (TOFT method), a gravel drain construction method of forming crushed stone columns with good permeability in the ground and dissipating excess pore water pressure of the liquefaction target layer, There is a shallow layer mixing treatment method that improves soil by mixing the soil in the shallow layer to be liquefied with cement-based solidifying material.

  In the gravel drain method, since the gravel drain is installed over the entire length of the layer to be liquefied, the heavy machinery becomes large and construction may be difficult due to site conditions. Further, since the gravel drain method is based on the design concept of preventing the occurrence of liquefaction, the pitch of the gravel drain is small and the cost is high, and it is difficult to create the gravel drain when the liquefaction target layer is deep. There are cases. In addition, the exterior part and parking lot are considered to be less important facilities, while the gravel drain method is designed to prevent liquefaction from occurring due to its design concept. The cost is high, and the cost balance between the object to be protected and the construction cost for realizing it is poor.

  On the other hand, the shallow layer mixing method mixes the solidifying material such as cement-based solidifying material with the soil of the local soil, so that the boundary between the area where the soil is improved by using the solidifying material and the area where the soil is not improved. Water may gush out (including the boundary of the construction site), and the flow of water may cause the sand of the liquefaction target layer to flow out to the ground surface. This phenomenon is called sand-blowing, and when a large amount of sand-sand flows out, even if the ground surface is not liquefied due to ground improvement, differential subsidence occurs, and the function of the vehicle flow line is lost due to sand-sand. I have something to do. In addition, in the shallow layer mixing process, there is in principle no escape point for excess pore water pressure, and the possibility that sand is generated at the weak points is inevitable.

  The present invention has been made in view of such a background, the cost is relatively low and construction is easy, and by preventing uneven settlement and sand blast during an earthquake, it is possible to prevent the loss of the function of the ground. The purpose is to provide a liquefaction countermeasure structure.

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, this invention is a liquefaction countermeasure structure (20,30,40) of the target ground (10) in which the liquefaction layer (13) exists in the surface layer or near the surface layer, Comprising: 3-7) and at least one of a pavement layer (26) formed of a roadbed (24) and pavement (23, 25) and a shallow improvement layer (21), and the target region (3-7). ), A liquefaction countermeasure structure having a gravel drain (22) which is distributed vertically and has a lower end that does not reach the lower end of the liquefaction layer (13) and is formed substantially vertically with a predetermined depth (H1). To do.

  With such a configuration, it is not necessary to form the gravel drain up to the lower end of the liquefied layer, so that the construction can be performed without using a large heavy machine and the cost can be reduced. Then, in the upper part of the liquefaction layer in which the gravel drain is formed, excess pore water flows into the gravel drain to suppress an increase in excess pore water pressure ratio, so that liquefaction is prevented. That is, the upper part of the liquefied layer becomes the non-liquefied layer. At this time, ground subsidence may occur due to drainage of excess pore water, but since at least one of the pavement layer and the shallow layer improvement layer exists above the non-liquefied layer, the occurrence of differential subsidence is prevented, The function as the ground is maintained. On the other hand, liquefaction can occur below the gravel drain in the liquefaction layer, but since there is a non-liquefaction layer above the liquefaction layer, the effect of liquefaction extends to the ground surface, that is, the occurrence of ground subsidence due to this liquefaction. The occurrence of liquefaction damage on the ground due to the generation of sand and sand is reduced.

  Further, according to one aspect of the present invention, the predetermined depth (H1) may be set according to the depth (H) to the lower end of the liquefaction layer (13).

  According to this configuration, by appropriately setting the depth of the gravel drain according to the depth of the liquefaction layer, the influence of liquefaction occurring below the gravel drain in the liquefaction layer on the ground surface can be prevented. The cost can be reduced after the reduction.

  Further, according to one aspect of the present invention, a gravel mat (formed over the entire target region (3 to 7) below at least one of the pavement layer (26) and the shallow improvement layer (21). 31) is further provided.

  Even in the upper part of the liquefied layer where the gravel drain is formed, the excess pore water pressure ratio temporarily increases during an earthquake, but with such a structure, the excess pore water pressure ratio increased during an earthquake can be reduced early. It is possible to prevent liquefaction damage more reliably.

  Moreover, according to one aspect of the present invention, at least the pavement layer (26) is provided, and through holes (23a, 25a) are formed in the pavement (23, 25), and the through holes (23a, 25a) are formed. A lid member (27) for draining excess pore water to the surface of the surface when the excess pore water pressure of the liquefied layer (13) rises can be attached to the above.

  According to this configuration, it is possible to improve the appearance and maintainability while ensuring the drainage of excess interstitial water during an earthquake.

  Moreover, in order to solve the said subject, this invention is constructed | assembled in the target ground (10) in which the liquefaction layer (13) exists in the surface layer or near the surface layer, and is formed over the whole target area (3-7), At least one of the pavement layer (26) consisting of the roadbed (24) and the pavement (23, 25) and the shallow layer improvement layer (21), and the target region (3 to 7) are dispersedly arranged, and the lower end is the liquefaction. A method for designing a liquefaction countermeasure structure (20, 30, 40) having a gravel drain (22) formed substantially vertically with a predetermined depth (H1) not reaching the lower end of the layer (13), the surface layer In the model ground (50) in which the deep liquefaction layer (52) exists below the surface non-liquefaction layer (51) present in the ground, the influence of liquefaction when the deep liquefaction layer (52) is liquefied by an earthquake Is the surface of the model ground (50) The thickness (H51) of the surface non-liquefaction layer (51) required to reach the depth is the depth (H50) from the surface of the model ground (50) to the lower end of the deep liquefaction layer (52). In accordance with a predetermined relationship (FIG. 6) in which the larger is, the predetermined depth (H1) is set to the depth (H) from the ground surface of the target ground (10) to the lower end of the liquefaction layer (13). Provided is a method for designing a liquefaction countermeasure structure, which is characterized by setting the value of the thickness (H51) of the surface non-liquefaction layer (51) accordingly.

  Further, according to one aspect of the present invention, in the model ground (50), when the deep liquefaction layer (52) is liquefied due to an earthquake, the influence of liquefaction affects the ground surface of the model ground (50). The thickness (H51) of the surface non-liquefied layer (51) required to disappear is set to the predetermined depth (H1) according to a predetermined relationship (FIG. 6) that increases as the maximum acceleration of the earthquake increases. , Setting the value of the thickness (H51) of the surface non-liquefaction layer (51) according to the design value of the maximum acceleration of the earthquake that does not influence the liquefaction on the ground surface in the target ground (10) It can be configured.

  As described above, according to the present invention, it is possible to provide a ground liquefaction countermeasure structure which is relatively low in cost, easy to construct, and capable of preventing the loss of the function as the ground by preventing sand blast during an earthquake.

Plan view of the liquefaction countermeasure structure according to the first embodiment II-II sectional view in FIG. Enlarged view of essential parts in Figure 2 Enlarged view of essential parts in Figure 2 Perspective view showing an example of the lid member shown in FIG. Relationship diagram between surface non-liquefaction layer thickness and deep liquefaction layer thickness in model ground and liquefaction occurrence on the ground surface The graph which shows the experimental result which concerns on 1st Embodiment Sectional drawing of the liquefaction countermeasure structure which concerns on 2nd Embodiment The graph which shows the experimental result which concerns on 2nd Embodiment Sectional drawing of the liquefaction countermeasure structure which concerns on 3rd Embodiment

  Hereinafter, some embodiments of the liquefaction countermeasure structure 20 according to the present invention will be described in detail with reference to the drawings.

«First embodiment»
First, a first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, in addition to a condominium 2 which is a main building, a small building such as a bicycle parking lot 3, an electric room 4 and a garbage storage space 5 is constructed on the site 1. Inside the site 1, in addition to the site of the condominium 2 and such a small building, an approach 6 which is a connecting passageway to the entrance of the condominium 2 and a bicycle parking lot 3, and a parking lot 7 are present as exterior parts.

As shown in FIG. 2, the site 1 is the liquefied ground 10 in which the liquefied layer 13 exists near the surface layer, and the non-liquefied layer 12 and the liquefied layer 13 are deposited in this order above the support layer 11. . FIG. 2 shows the liquefied ground 10 after the construction of the liquefaction countermeasure structure 20, and the liquefaction layer 13 exists up to the ground surface before the construction. The liquefaction ground 10 is a target ground on which the liquefaction countermeasure structure 20 according to the present invention is constructed.

  The liquefaction layer 13 is composed of a sandy soil in a water-containing state, and when the earthquake vibrates, the water saturated between the sand grains flows, the intergranular bonds of the sand grains are broken, and the liquefaction layer behaves like a liquid to support the bearing capacity. Is a layer that loses. When the liquefied layer 13 is liquefied, the fluid pressure of fluidized pore water rises sharply, and excess pore water is generated.

Here, of the site 1, the liquefied ground 10 is targeted to the site of a small building such as a bicycle parking lot 3, an electric room 4, a garbage storage site 5, and an exterior part including the site used as the approach 6 and the parking lot 7. A liquefaction countermeasure structure 20 is constructed on (target ground) . Each region of interest (parking lot 3, electric chamber 4, refuse depot 5, approaches 6 and Parking 7) liquefaction countermeasure structure 20 for, by improving the top of the liquid layer 13 I was I the entire target area A shallow improvement layer 21 formed above the liquefaction layer 13, and a plurality of gravel formed so as to extend from the ground surface to the upper part of the liquefaction layer 13 through the shallow improvement layer 21 in a substantially vertical manner. And a drain 22.

  The shallow improvement layer 21 is a shallow improved ground layer obtained by improving a relatively shallow ground near the ground surface (for example, the liquefied layer 13 1 m from the ground surface), and liquefies a powder-based or slurry-based solidifying material, for example. It is formed by stirring and mixing the layer 13 and compacting and solidifying by rolling. The shallow improvement layer 21 serves as a support ground for the bicycle parking lot 3, the electric room 4, and the garbage storage space 5, and also serves as a roadbed for the approach 6 and the parking lot 7.

  The gravel drain 22 is a crushed stone columnar body for draining upward excess pore water of the liquefaction layer 13 generated during an earthquake. As shown in FIG. 1, the gravel drains 22 are arranged in a distributed manner at a predetermined interval (horizontal direction interval) in plan view over the entire target region of the liquefied ground 10. In the present embodiment, the gravel drains 22 are arranged in a grid pattern in two directions orthogonal to each other on the horizontal plane at a substantially constant interval. In another embodiment, the gravel drains 22 may be arranged in a zigzag arrangement in which two congruent equilateral triangles are combined and arranged continuously in an orthorhombic vertex. The gravel drain 22 is preferably made of single-grain crushed stone having many voids and high drainage capacity.

  FIG. 3 is an enlarged cross-sectional view of the ground of the approach 6 in FIG. Approach 6 has tiled paving 23. The tile pavement 23 is formed by laying a sand cushion on the roadbed 24, laying blocks and tiles on the sand cushion, and filling the joints with sand. Although illustration is omitted, in a place where the gravel drain 22 is located on a supporting ground of a small building such as a bicycle parking lot 3, an electric room 4, and a garbage yard 5, a roadbed 24 is laid under the foundation of the building to function as a gravel mat. Excess pore water is drained to the surface of the earth by draining horizontally through the roadbed 24.

  FIG. 4 is an enlarged cross-sectional view of the parking lot 7 portion in FIG. Asphalt pavement 25 is applied to the parking lot 7. The asphalt pavement 25 is made of water-impermeable asphalt, and is formed on a roadbed 24 made of crushed stone laid above the shallow improvement layer 21. In this specification, the roadbed 24 and the tile pavement 23 or the asphalt pavement 25 are collectively referred to as a pavement layer 26.

  Through holes 23a, 25a are formed in the portions of the pavements 23, 25 where the gravel drains 22 are formed, and excess pore water rising in the gravel drains 22 passes through the through holes 23a, 25a and reaches the pavements 23, 25. It is designed to be drained. The through holes 23a and 25a may be opened so that the gravel drain 22 is exposed, but a lid member 27 capable of draining excess pore water pressure may be attached. By attaching the lid member 27 to the through holes 23a and 25a, aesthetics and maintainability can be improved.

  The through holes 23a and 25a and the lid member 27 are, for example, as shown in FIG. 5 (A), a manhole-like shape including a cylindrical frame 28 defining the through holes 23a and 25a and a lid member 27 attached to the cylindrical frame 28. The lid assembly 29 can be installed on the roadbed 24 (upper end of the gravel drain 22) and the tile pavement 23 can be spread around it or the asphalt pavement 25 can be installed. As another embodiment, as shown in FIG. 5 (B), through holes 23a and 25a are directly formed in the tile pavement 23 or the asphalt pavement 25 by die cutting or core punching, and a lid member 27 that fits the through holes 23a. It can also be installed by fitting. In any of the forms, the lid member 27 is opened with a water pressure smaller than the water pressure that damages the pavements 23 and 25 due to the excess pore water pressure in the gravel drain 22, and the excess pore water passes through the through holes. It is possible to eject from 23a and 25a. Although not shown, as another embodiment, the lid member 27 may be formed in a mesh shape and attached to the pavements 23 and 25 so that excess pore water can be drained at any time.

3 and 4, the gravel drain 22 has a depth H1 (ground surface) smaller than the thickness (depth from the ground surface to the lower end ( lower surface ) of the liquefaction layer 13) H of the liquefaction layer 13. To the lower end). Therefore, in the lower part of the liquefaction layer 13, an untreated layer 14 having a thickness H2 (H2 = H-H1) in which the gravel drain 22 is not formed (a layer which is not liquefaction countermeasure process and liquefies during an earthquake) ) Is present, the upper part of the liquefied layer 13, that is, the upper part of the untreated layer 14 has the same thickness as the depth H1 of the gravel drain 22, which has been subjected to the liquefaction countermeasure treatment of forming the gravel drain 22. It is a treated layer 15 (a liquefaction prevention layer which is an apparent non-liquefied ground).

Here, the design depth (predetermined depth H1) of the gravel drain 22 will be described. FIG. 6 shows the thickness of a non-liquefied layer of the surface layer (hereinafter referred to as a surface non-liquefied layer 51) and the deep liquefied layer (hereinafter referred to as the deep liquefied layer 52 ) proposed by Kenji Ishihara. it is a graph showing the relationship between the thickness of) that. This ground is different from the liquefaction ground 10 shown in FIG. 2, which is the construction target of the liquefaction countermeasure structure 20, and is a ground at the time of designing the liquefaction countermeasure structure 20 constructed on the liquefaction soil 10. Is. Hereinafter, this ground is referred to as the model ground 50. This figure, when the thickness of the table Sohi liquefaction layer 51 in the model soil 50 and H 5 1, the thickness of the deep liquid layer 52 which exists beneath the surface layer non-liquefaction layer 51 was H 5 2 In addition, the relationship between the two that causes liquefaction on the surface is shown according to the maximum acceleration. That is, even if liquefaction occurs in the deep liquefaction layer 52 during an earthquake, the influence of liquefaction does not reach the surface of the model ground 50, and the thickness H51 of the surface non-liquefaction layer 51 is shown. The depth H50 from the ground surface of the model ground 50 to the lower end of the deep liquefaction layer 52 is a value obtained by adding the thickness H51 of the surface non-liquefaction layer 51 and the thickness H52 of the deep liquefaction layer 52.

For example, when the thickness H 5 2 deep liquefaction layer 52 is 3m, the surface non-liquefaction layer to effect the liquefaction even 200gal can not reach the surface of the model soil 50 has a thickness H51 of 3m weak 51 is required, the influence of the liquefaction even 300gal is the surface layer non-liquefied layer 51 must have a thickness H51 of approximately 4.5m in order to not extend to the surface of the model soil 50, the influence of the liquefaction even 400~500gal The surface non-liquefaction layer 51 having a thickness H51 of about 7.5 m is required in order that the area does not reach the surface of the model ground 50 .

Therefore, in the present embodiment, the depth H1 of the gravel drain 22 is set according to the thickness H of the liquefaction layer 13 before the liquefaction countermeasure process of FIGS. 3 and 4 with reference to the relationship diagram of FIG. For example, when the thickness H of the liquefaction layer 13 is 10 m, the thickness of the treatment layer 15 ( the depth of the gravel drain 22 is set when the liquefaction effect is designed so as not to reach the surface of the liquefaction ground 10 even at 200 gal). H1 ) is set to about 3 m, and when the design is such that the influence of liquefaction does not reach the surface of the liquefied ground 10 even at 300 gal, the thickness ( H1 ) of the treatment layer 15 is set to a little less than 6 m, When designing such that the influence of liquefaction does not reach the surface of the liquefied ground 10 even at 400 to 500 gal, the thickness ( H1 ) of the treatment layer 15 is set to a little over 7 m.

  As described above, it is necessary to form the gravel drain 22 up to the lower end of the liquefaction layer 13 by setting the depth of the gravel drain 22 according to the thickness H of the liquefaction layer 13 with reference to the relationship diagram of FIG. 6. Since it is not necessary, the construction can be performed without using a large heavy machine, and the cost can be reduced.

In the treatment layer 15 of the liquefaction ground 10 in which the gravel drains 22 are formed, excess pore water flows into the gravel drains 22 and is discharged to the ground surface during an earthquake. Therefore, in the treatment layer 15, an increase in excess pore water pressure ratio is suppressed, and liquefaction is prevented. On the other hand, liquefaction may occur in the non-treated layer 14, but since the treated layer 15 exists above, the influence of liquefaction extends to the surface of the ground, that is, ground subsidence due to this liquefaction and the occurrence of sand blasts. Liquefaction damage is prevented from occurring. That is, when an earthquake occurs, it is possible to prevent the influence of liquefaction from reaching the ground surface while allowing the liquefaction to occur under the liquefaction layer 13.

  On the other hand, if excess pore water in the treatment layer 15 is drained to the gravel drain 22 during an earthquake, the treatment layer 15 may condense and cause ground subsidence, but the pavement layer 26 and the shallow layer improvement above the treatment layer 15 may occur. Due to the existence of the layer 21, even if some ground subsidence occurs, the occurrence of differential subsidence is prevented. Therefore, the function of the ground such as the parking lot 7 is maintained.

  The inventors of the present application conducted a vibration experiment using a model in order to confirm the operation effect of the liquefaction countermeasure structure 20 of the present embodiment. The outline and results are shown below.

  For the experiment, a model was prepared in which mortar was mixed with the surface layer 25 mm of the liquefaction layer 13 having a thickness of 500 mm and the scale was set to 1/10. In order to confirm the influence of the drain length, the model has a case A without a drain, a case B in which a drain having a depth of half the thickness of the liquefaction layer 13 is formed, and the entire thickness of the liquefaction layer 13 Three cases, Case C in which a drain was formed, were prepared. In the vibration experiment, the liquefaction layer 13 was vibrated in a gravity field with a sine wave of 10 Hz as an input wave, a maximum acceleration of 200 gal, and a vibration time at the maximum acceleration of 6 seconds. During the experiment, the pore water pressure of 1/4 of the thickness of the liquefaction layer 13 was measured from the surface of the earth, and the amount of sand jet was measured.

  FIG. 7 shows the transition of the measured excess pore water pressure ratio in each of the cases A to C. The excess pore water pressure ratio is calculated by dividing the pore water pressure by the initial effective soil cover pressure, and the time history waveform is a moving average. From FIG. 7, the excess pore water pressure ratio of Case B is longer than that of Case C but is much shorter than that of Case A. From this, it is understood that the presence of the gravel drain 22 effectively prevents the liquefaction of the treatment layer 15.

上表からわかるように、ケースＣおよびケースＢにおいても噴砂は発生しているものの、噴砂の量はドレーンなしのケースＡと比較して大幅に減少している。この結果は、大きな過剰間隙水圧比が維持される時間がドレーンの設置で低減したことと調和的である。 The amount of sand flow in each case was as follows.

As can be seen from the above table, although sand is also generated in Case C and Case B, the amount of sand is significantly reduced compared to Case A without drain. This result is consistent with the fact that the time for maintaining a large excess pore pressure ratio was reduced by installing the drain.

  As described above, the liquefaction countermeasure structure 20 is designed to have a depth smaller than that of the conventional gravel drain construction method, so that the liquefaction countermeasure structure 20 can be constructed relatively easily and at low cost without using a large heavy machine. Therefore, of the site 1 of the liquefied ground 10, it is suitable for a site of a building, such as a small building, an approach 6, or a parking lot 7.

«Second embodiment»
Next, a second embodiment of the present invention will be described with reference to FIGS. 8 and 9. It should be noted that description of the same configurations and effects as those of the first embodiment will be omitted. The same applies to the following embodiments.

  In the liquefaction countermeasure structure 30 of the present embodiment, as shown in FIG. 8, a gravel mat 31 is provided below the shallow layer improving layer 21 of the first embodiment. The gravel mat 31 is a crushed stone layer for horizontally draining excess pore water of the liquefaction layer 13 generated during an earthquake. As with the gravel drain 22, the gravel mat 31 is preferably made of single-grain crushed stone having many voids and high drainage capacity.

  As described in the first embodiment, even in the treatment layer 15 in which the gravel drain 22 is formed, the excess pore water pressure ratio temporarily increases during an earthquake, but the liquefaction countermeasure structure 30 has such a configuration. As a result, the excess pore water pressure ratio that has risen during an earthquake decreases early, and liquefaction damage is more reliably prevented.

  The inventors of the present application conducted a vibration experiment using a model similar to that described in the first embodiment in order to confirm the operation and effect of the liquefaction countermeasure structure 30 of the present embodiment. The outline and results are shown below.

  In this experiment as well, in order to confirm the influence of the drain length, the case D without the drain, the case E in which a drain having a depth of 1/2 of the thickness of the liquefaction layer 13 and the thickness of the liquefaction layer 13 were formed. A model was prepared for three cases of case F in which a drain was formed on the whole of the above, and the liquefaction layer 13 was vibrated to measure the pore water pressure of 1/4 of the thickness of the liquefaction layer 13 from the ground surface, The presence or absence of sand-sand was confirmed.

  FIG. 9 shows the transition of the measured excess pore water pressure ratio in each of the cases D to F. From FIG. 9, the dissipation time of the excess pore water pressure ratio is shorter in all the cases D to F than in the corresponding cases A to C of the first embodiment shown in FIG. 7. From this, it is understood that the presence of the gravel drain 22 shortens the time during which the large excess pore water pressure ratio is maintained. Further, as in the first embodiment, the excess pore water pressure ratio of the case E is longer than that of the case F, but is much shorter than that of the case D, so that the gravel drain 22 exists. Can effectively prevent the liquefaction of the treatment layer 15.

  In this experiment, in all cases D to F, no sand generation was observed. From this, the gravel mat 31 is laid between the shallow improvement layer 21 and the treatment layer 15, which shortens the time for maintaining a large excess pore water pressure ratio and makes it difficult for the sand to flow out. Recognize.

<< Third Embodiment >>
Finally, a third embodiment of the present invention will be described with reference to FIG. In the liquefaction countermeasure structure 40 of the present embodiment, a gravel mat 31 is provided below the paving layer 26 instead of the shallow improvement layer 21 of the first embodiment. Even if the liquefaction countermeasure structure 40 is configured as described above, the ground subsidence may occur due to the condensation of the treatment layer 15 during the temporary liquefaction when draining the excess pore water. Since the pavement layer 26 and the gravel mat 31 are present above 15, the differential settlement is prevented.

  Although the specific embodiments have been described above, the present invention is not limited to these embodiments. For example, in the above-described embodiment, the liquefaction countermeasure structures 20, 30, and 40 are constructed for the liquefaction ground 10 in which the liquefaction layer 13 exists on the surface layer, but the non-liquid state is formed on the liquefaction layer 13. It can also be applied to the liquefied ground 10 on which a liquefied layer is deposited. In this case, the shallow non-liquefied layer may be subjected to the shallow layer mixing treatment to form the shallow layer improving layer 21. Further, in the above embodiment, the asphalt pavement 25 is adopted as the pavement for the parking lot 7, but concrete pavement or the like may be adopted, and the shallow improvement layer 21 and the gravel mat 31 are provided below the pavement layer 26. It can also be a non-form. Further, in the above-mentioned embodiment, the excess pore water is drained to the surface of the ground through the gravel drain 22, but a permeable drainage groove is provided at the upper end of the gravel drain 22 to drain the excess pore water to the drainage groove. You may do it. Further, in the third embodiment, the pavement layer 26 is formed above the gravel mat 31, but the gravel mat 31 may be regarded as the roadbed 24 and the pavement may be directly formed on the gravel mat 31. Further, a mode in which a perforated pipe is installed inside the gravel drain 22 and the gravel mat 31 is also possible. In addition, the specific dimensions, arrangement, materials, etc. of each element can be appropriately changed without departing from the spirit of the present invention. In addition, not all of the respective elements of the liquefaction countermeasure structure 20, 30, 40 according to the present invention shown in the above embodiment are necessarily indispensable and can be appropriately selected.

3 Bicycle parking lot (target area)
4 Electric room (target area)
5 Place (target area)
6 Approach (target area)
7 parking lot (target area)
10 Liquefied ground (target ground)
13 Liquefaction layer 14 Non-treatment layer 15 Treatment layer 20, 30, 40 Liquefaction countermeasure structure 21 Shallow layer improvement layer 22 Gravel drain 23 Tile paving 23a Through hole 24 Roadbed 25 Asphalt pavement 25a Through hole 26 Pavement layer 27 Lid member 31 Gravel mat
50 model ground
51 surface non-liquefied layer
52 Deep Liquefaction Layer H Thickness of Liquefaction Layer 13 (depth from the ground surface to the lower end of the liquefaction layer 13)
Depth of H1 gravel drain 22 ( thickness of processing layer 15 )
Thickness of H2 untreated layer 14
Depth from the ground surface of the H50 model ground 50 to the lower end of the deep liquefaction layer 52
H51 Thickness of surface non-liquefied layer 51
H52 Thickness of deep liquefaction layer 52

Claims (1)

At least one of a pavement layer consisting of roadbed and pavement and a shallow improvement layer, which is constructed on the target ground where a liquefaction layer exists on the surface layer or near the surface layer, and is formed over the entire target area, and distributed arrangement in the target area And a method for designing a liquefaction countermeasure structure having a gravel drain that is formed substantially vertically with a lower end having a predetermined depth that does not reach the lower end of the liquefaction layer,
In the model ground where the deep liquefaction layer exists below the surface non-liquefaction layer existing in the surface layer, when the deep liquefaction layer liquefies due to an earthquake, the influence of liquefaction does not reach the surface of the model ground. According to a predetermined relationship, the required thickness of the surface non-liquefaction layer increases as the depth from the surface of the model ground to the lower end of the deep liquefaction layer increases and increases as the maximum earthquake acceleration increases. , The predetermined depth according to the depth from the ground surface of the target ground to the lower end of the liquefaction layer and the design value of the maximum acceleration of the earthquake that does not influence the liquefaction on the ground surface in the target ground A method for designing a liquefaction countermeasure structure, characterized in that the thickness of the surface non-liquefaction layer is set to the value of the thickness.

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