JP5158652B2 - How to install the floor - Google Patents

Description

  The present invention relates to a building construction method, and more particularly to a method for constructing a soil floor on soft ground.

As is well known, the interstitial floor that is directly constructed and supported directly on the ground is simpler in construction and easier to construct than a general structural floor constructed by being supported by beams and piles. Therefore, there is a great merit in terms of construction cost and construction period, but if the ground is soft, there is a concern of dissimilar subsidence, so at least the surface ground must be a sufficiently stable high-quality ground. It is only adopted in such cases.
In other words, when the soil floor is constructed even though the surface ground is soft ground, there is a concern that uneven settlement will occur on the soil floor, causing problems in building use. In addition, when the surface ground is sand ground, even if sufficient bearing capacity can be expected for a constant load, if liquefaction occurs in the sand ground during an earthquake, the bearing capacity is lost or excessive pore water pressure is dissipated. There is concern that subsidence will occur, and it is also assumed that uneven subsidence will occur on the soil floor.

Therefore, in general, as a guideline of the ground that can be used to construct a soil floor that does not cause uneven settlement in general, it is said that N value = 10-15 or more in sandy ground, N value = 3 to 5 or more in viscous soil, In the case of such a high-quality ground, it is necessary to take measures as shown in, for example, Patent Documents 1 to 3 when a structural floor is used, or when it is intentionally used as a dirt floor.
That is, as shown in Patent Document 1, a low density, high compressive strength filler is interposed between the soft ground and the soil concrete slab, or as shown in Patent Document 2, the foam mortar is placed on the soft ground. After the layer is provided, the soil is provided on it, or the soil concrete slab is supported by a small-diameter soil cement column as shown in Patent Document 3, thereby preventing the uneven settlement of the soil floor (soil concrete slab). It is said that it is necessary.

JP-A-64-71924 Japanese Patent Laid-Open No. 4-185808 JP 2003-119798 A

However, applying special measures such as those shown in Patent Documents 1 to 3 to the dirt floor is the original merit of the dirt floor, the simplicity of the structure and the simplicity of construction, that is, superiority to the structure floor It is not preferable because it impairs sex, and it is not realistic.
And in recent years, as mentioned above, there are many requests for more aggressive and widespread use of the floors with great structural and construction benefits without losing the benefits, and in order to meet such demands, It is said that it is necessary to develop an effective and appropriate means that makes it possible to construct a stable soil floor with no fear of uneven settlement even on soft ground.

  In view of the above circumstances, the present invention is constructed by adding ingenuity in the process of constructing the floor to the soft ground without taking any special measures in the structure of the floor. An object of the present invention is to provide an effective and suitable method for constructing a floor between floors that can prevent and prevent subsequent uneven settlement.

  In the present invention, when constructing a floor with soft surface layer, prior to the construction of the floor, construct a water shielding wall that surrounds the construction range, pumping groundwater from the inside of the water shielding wall, By reducing the groundwater level inside the impervious wall from the natural groundwater level, the effective earth pressure is increased, and a preceding load corresponding to the soil load on the soil floor after construction is applied to the ground to cause subsidence in advance. After that, by starting the construction of the interstitial floor and gradually recovering the groundwater level in response to the increase in the interstitial load accompanying the progress of construction, the increase in the interstitial load and the recovery of the groundwater level during the construction It is characterized by suppressing the settlement of the interstitial floor after construction by balancing the decrease in effective underground stress due to the construction.

  In the present invention, the thickness of the non-liquefied layer to be secured on the surface layer of the ground is determined based on the relationship with the maximum acceleration of the assumed earthquake, and the groundwater level is lowered when the groundwater level inside the impermeable wall is lowered. It is preferable to lower the position to a depth deeper than the non-liquefied layer.

According to the present invention, the groundwater level is lowered prior to the construction of the interstitial floor, and the construction of the interstitial floor is performed only by gradually recovering the groundwater level while balancing the increase in the interstitial load when constructing the interstitial floor. It is possible to effectively prevent the subsequent uneven settlement.
Therefore, according to the present invention, no special measures are required for the structure of the dirt floor itself, and it is only necessary to temporarily lower the groundwater level during the construction, and no extra construction cost is required. Therefore, it is possible to construct a stable interstitial floor that does not cause uneven settlement even on soft ground that cannot be used as an interstitial floor conventionally.

  Further, according to the present invention, liquefaction hardly occurs naturally due to the desaturation of the ground accompanying temporary lowering of the groundwater level, and therefore the soil floor is caused to be unevenly subsidized due to the liquefaction of the ground. This can also be effectively prevented.

  Furthermore, in the present invention, since the surroundings of the building are surrounded by the impermeable walls, it is possible to prevent the movement of pore water from the external ground of the impermeable walls and the lateral flow of the ground in the event of an earthquake. The effect which can prevent damage is acquired.

The embodiment of the present invention is shown and is a diagram showing an outline of the method of the present invention. It is a figure which shows the transition of the groundwater level under construction, soil load, underground effective stress, and ground subsidence during construction, respectively. It is a figure which shows the relationship between the layer thickness of the non-liquefaction layer of a surface layer part, and maximum acceleration similarly.

An embodiment of the method of the present invention will be described with reference to FIGS.
In this embodiment, as shown in FIG. 1, there is a soft ground 2 on a high-quality ground 1, and concrete is directly supported by the ground when a building is constructed on the ground where the natural groundwater level w1 is relatively shallow. It is an application example when constructing a built-in earth floor 3. The soil load per unit area of the soil floor 3 to be constructed is finally set to L (kN / m ² ) (total of dead load and live load).
In addition, the code | symbol 4 in FIG. 1 is a pillar as an upper structure, 5 is a support pile which is driven to the high quality ground 1 and supports the pillar 4, These are structurally separated from the dirt floor 3 and those construction Basically, it may be carried out as appropriate independently or in succession irrespective of the construction process of the floor 3 described below.

  In this embodiment, prior to the construction of the floor 3, the impermeable wall 6 that surrounds the construction range is first constructed. It is assumed that the depth GL-d1 (m) of the impermeable wall 6 reaches at least deeper than the groundwater level GL-w2 (m) that is lowered in the subsequent stage (that is, d1 ≧ w2).

Then, a pumping well 7 is installed inside the impermeable wall 6, and groundwater is pumped from the pumping well 7 prior to the construction of the interstitial floor 3, and the groundwater level inside the impermeable wall 6 as shown in FIG. Is reduced from the natural groundwater level GL-w1 (m) to the above-mentioned water level GL-w2 (m). As a result, as shown in (c), the effective earth pressure increases with a drop in water level, which is equivalent to the fact that the preceding load has acted on the ground. Arise.
Here, the preceding load acting on the ground by ground water level drops, the relationship 1mAq ≒ 10kN / m ^2, since the 10 × As shown in (c) (w2-w1) (kN / m 2), the basic In reality, it should be equal to the soil load L (kN / m ² ) (ie, set so that 10 × (w2−w1) = L), but slightly larger than that as shown in the example. It is preferable to set.
That is, as shown in (c), the preceding load 10 × (w2−w1) due to the lowering of the groundwater level is slightly larger than the final soil load L so that 10 × (w2−w1) ≧ L. It is only necessary to set the difference 10 × (w2−w1) −L to the ground as a preload load. As a result, as shown in (d), the ground sinks excessively by the amount corresponding to the preload load. Therefore, when the construction of the subsequent floor is started, adjustment is made so that the preload load is canceled and the excess settlement is restored. It ’s fine.
The preceding load due to the drop in groundwater level can be expressed as (w2−w1) (mAq) in units of water head. In that case, if the final soil load is 0.1 × L (mAq) good.

After that, as shown in FIG. As a result, the soil load gradually increases as shown in (b). Accordingly, the groundwater level is gradually recovered as shown in (a), and effective earth cover pressure (underground) The effective stress is gradually reduced. In other words, the soil floor is constructed while controlling the groundwater level so that the effective underground stress is kept constant before and after the construction of the soil floor.
In this way, construction of the soil floor is carried out while balancing the increase in soil load accompanying the progress of construction and the reduction in effective underground stress due to recovery of the groundwater level, while maintaining the effective underground stress constant. By performing the construction of the floor, as shown in (d), it is possible to prevent the settlement of the ground during construction and after the construction, and therefore it is possible to effectively prevent the uneven settlement of the soil floor after the construction.
In addition, when a preload load is applied as described above, as shown in (a) and (c), an adjustment is made so as to eliminate the preload load at the start of construction of the floor between floors, and as shown in (d) In this way, some settlement recovery occurs at the beginning, but when no extra preload load is applied (when 10 × (w2−w1) −L = 0), the settlement remains stable without recovery.

As described above, in the present invention, as a condition for preventing the settlement of the soil floor due to the soil load, prior to construction of the soil floor, w2−w1 ≧ 0.1 × L (mAq) or 10 × (w2−w1) ≧ L (kN / m ² ) The groundwater level is lowered in advance to the water level w2 set so as to satisfy the relationship, and the groundwater level is gradually recovered while balancing with the increase in the soil load when constructing the soil floor. It is possible to prevent uneven settlement after construction of the soil floor only by performing an operation that reduces the intermediate stress.
Therefore, according to the present invention, there is no need for special measures for the structure of the floor between floors as in the prior art, and it is only necessary to temporarily lower the groundwater level and gradually recover it during the construction. In this case, it is only necessary to construct the impermeable wall 6 and the pumping well 7 so as to reach the water level w2 or more to be lowered.
As described above, according to the present invention, it is possible to construct a stable interstitial floor that does not cause uneven subsidence without trouble even on soft ground that cannot be used as an interstitial floor in the past. It becomes.

In addition to the basic effects described above, according to the present invention, since the groundwater level inside the impermeable wall 6 is temporarily lowered and then recovered, liquefaction at the surface layer portion of the ground can be achieved. Therefore, it is difficult to naturally occur, so that it is possible to effectively prevent the deformation and uneven settlement of the interstitial floor 3 caused by the liquefaction of the surface ground during an earthquake.
That is, in the present invention, it is substantially the same as the operation of the groundwater level in the “method for preventing ground liquefaction” in Japanese Patent No. 3374224 (Japanese Patent Laid-Open No. 8-3975) that the groundwater level is temporarily lowered and then recovered again. Therefore, even in the present invention, as in the same patent, the desaturation of the surface ground due to a temporary drop in the groundwater level is maintained for a long time after the groundwater level is restored, thereby increasing the liquefaction strength of the ground. The effect of being naturally enhanced is obtained.
Therefore, in the present invention, in order to sufficiently obtain such an effect of preventing liquefaction, the groundwater level w2 to be lowered is set to be larger than the layer thickness h1 of the non-liquefied layer 8 to be secured in the surface layer portion. Hereinafter, this point will be described with reference to FIG.

Fig. 3 (a) shows the maximum acceleration of "Relationship between liquefied layer thickness H2 and surface non-liquefied layer thickness H1" in order to prevent deformation of the surface layer ground when the underground sand ground liquefies. As a parameter (quoted from Yoshimi and Fukutake (2005): Geophysical liquefaction physics and evaluation and countermeasure technology, Gihodo Publishing, p.192). From this figure, it can be seen that, for example, when the maximum acceleration is 200 Gal, earthquake damage due to liquefaction will not occur if the thickness of the surface non-liquefied layer is 3 m or more. Similarly, if the maximum acceleration is 300Gal, the non-liquefied layer thickness is 6m or more, and if the maximum acceleration is 400Gal or more, the non-liquefied layer thickness is 9m or more. It turns out that does not occur.
FIG. 3 (b) is a graph directly showing the above relationship. When the underground sand ground is liquefied, no deformation occurs in the surface layer ground. The relationship with the layer thickness h1 ”is shown, and the layer thickness h1 of the non-liquefied layer corresponding to the maximum acceleration α assumed from this figure (in order to prevent liquefaction damage even during earthquakes with the maximum acceleration α) The layer thickness of the non-liquefied layer to be secured in the surface layer portion can be determined immediately.

  Therefore, in the present invention, the layer thickness h1 of the non-liquefied layer 8 corresponding to the assumed maximum acceleration α is obtained from FIG. 3B, and the groundwater level w2 is at least deeper than the layer thickness h1 as shown in FIG. By lowering, that is, by setting the groundwater level w2 in the relationship of w2 ≧ h1, the range up to the water level w2 becomes the non-liquefied layer 8 where liquefaction hardly occurs. Therefore, even if liquefaction occurs in the deep part of the ground due to the earthquake of the assumed scale, the non-liquefaction layer 8 having a sufficient layer thickness is secured in the surface layer part, so there is no deformation there, Therefore, it is possible to prevent the soil floor 3 from causing uneven settlement due to liquefaction of the ground.

  Furthermore, in the present invention, since the periphery of the building is surrounded by the impermeable wall 6, it is possible to prevent the movement of pore water from the external ground of the impermeable wall 6 and the lateral flow of the ground in the impermeable wall during an earthquake. This also has the effect of preventing building foundation damage and soil damage.

DESCRIPTION OF SYMBOLS 1 Good quality ground 2 Soft ground 3 Drum floor 4 Pillar 5 Pile 6 Impermeable wall 7 Pumping well 8 Non-liquefied layer

Claims (2)

When constructing a clay floor on the ground where the surface layer is soft,
Prior to the construction of the dirt floor, we constructed a water-impervious wall that surrounds the construction area,
The groundwater is pumped up from the inside of the impermeable wall, and the effective ground cover pressure is increased by lowering the groundwater level inside the impermeable wall from the natural groundwater level, which corresponds to the soil load on the soil floor after construction. Apply a load to the ground to cause subsidence in advance,
After that, by starting construction of the interstitial floor and gradually recovering the groundwater level in response to the increase in interstitial load accompanying the progress of construction, it is effective by increasing the interstitial load during the construction and recovering the groundwater level. A method for constructing an interstitial floor, characterized in that the settlement of the interstitial floor after construction is suppressed by balancing the decrease in underground stress. It is a construction method of the dirt floor according to claim 1,
The layer thickness of the non-liquefied layer to be secured on the surface layer of the ground is determined based on the relationship with the maximum acceleration of the assumed earthquake, and the groundwater level is reduced when the groundwater level inside the impermeable wall is lowered. A method for constructing an interstitial floor, characterized in that it is lowered to a deeper depth.

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