JPH04330112A - Constructing method for concrete strip footing - Google Patents

Abstract

PURPOSE:To modify the soil quality effectively, at site, and with low costs of execution of works in case the ground, on which a concrete strip footing of a wooden building is to be constructed, is soft, by applying the soil modification work only to the ground portion which should bear the strip footing. CONSTITUTION:A hole 3 is excavated in the ground in the direction in which a concrete strip footing A is constructed, wherein the hole 3 shall be wider than the base board 2 of the strip footing A. A number of liquid passing holes 4 are provided at certain intervals in the bearing layer under the bottom of this hole 3. A water solution of soil quality modifying agent is poured into this bearing layer through the holes 4 so as to form a modified bearing layer 5. The soil at site and the soil quality modifying agent are mixed together and subjected to a rolling process, and thereby a modified base 6 is constructed at the bottom of the hole 3. The concrete strip footing A is constructed in the condition that the base board 2 at the lower end is placed upon the oversurface of this modified base 6.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of strengthening and improving soft ground to construct concrete foundations for mainly wooden houses.

0002

[Prior Art] When constructing a concrete foundation for a wooden house, if the ground of the site is weak (for example, the bearing capacity of the ground is 5 tons/m2 or less), ■Pile foundation by driving piles■ The building site should be laid to a thickness of about 20 cm. A solid foundation completely covered with concrete ■ The ground of the site has been completely improved, and one of the foundations that have been completely improved to increase the bearing capacity of the site has been applied.

[0003] Of these, to give an overview of the complete site improvement foundation (2), which is closer to the present invention, the entire site is dug down by about 1 meter on all sides, and after improving the ground by mixing soil conditioner with the excavated soil. A concrete foundation is being constructed on the improved ground. This also improves the soil quality of the ground and increases its bearing capacity, making it satisfactory in terms of strength.

0004

The problem is that all conventional foundations are extremely expensive in terms of construction costs. In the case of foundations with complete site improvement, the soil quality is improved by excavating not only the area where the concrete cloth foundation will be laid, but also the entire site, which requires a lot of manpower and labor, and the construction costs are extremely high. It's expensive. Pile foundation (2) also requires a large number of piles, and it takes a lot of effort to drive the piles. Similarly, the problem with the solid foundation (2) was that the construction cost was high.

[0005] Therefore, the inventors of the present invention have investigated alternatives to conventional foundations, which are generally expensive to construct. In that case, Figure 5 shows the relationship between the load on the foundation and the underground strength. Based on this, when the width of the foundation plate 2 of the concrete cloth foundation A is a (generally 40 cm), the uniformly distributed load Q is 100 cm on the surface immediately below the foundation plate 2 underground.
%, the load Q is 60% at a depth that is half the width a (1/2a), the load Q is 30% at the depth that is the same as the width a (1a), and the load Q is 30% at a depth that is twice the width a (2a). Load Q is 10 at depth
It is said that the load Q becomes 0% at a depth of three times the width a (3a) (Iwao Yoshida, Visual Foundation and Ground Engineering). As a result, it can be seen that the bearing capacity underground is, in principle, most problematic up to a depth of at least three times the width a of the foundation plate 2, and that it is sufficient to take some safety into account. In other words, the normal width b is 40cm
In basic version 2, the support layer directly below this is 120
It would be sufficient to improve the strength by a cm or so.

[0006] Based on this viewpoint, the present invention aims to efficiently improve the soil quality of the ground immediately below the foundation slab of a concrete cloth foundation. Another object of the present invention is to provide a method for constructing a concrete cloth foundation that can be safely and efficiently constructed on-site and at significantly reduced construction costs.

[0007]

[Means for Solving the Problems] The present invention constructs a concrete cloth foundation through the following steps. As shown in Fig. 2, a hole 3 wider than the width of the foundation slab 2 at the lower end of the concrete cloth foundation A is dug in the ground at the site of the first step along the construction direction of the concrete cloth foundation A. The width of this hole 3 (root cutting width dimension) is approximately 1.5 to 2.0 of the width of the base plate 2, and the hole depth (root cutting depth) is sufficient to be 50 cm to 100 cm. Second step: A large number of liquid passage holes 4 are bored at appropriate intervals in the support layer below the bottom of the holes 3. The drilling depth of each liquid passage hole 4 is 80 to 12
It should be about 0 cm.

Third step: An improved support layer 5 is formed by injecting a soil conditioner aqueous solution into the support layer at the bottom of the hole 3 through each liquid passage hole 4. that time,
It is advantageous to promote the permeability of the soil conditioner aqueous solution into the supporting layer while applying vibration with a vibrator. This makes the compressive strength of the improved support layer 5 approximately 3 to 6 kg/cm2. Fourth step: A soil improving base 6 is constructed at the bottom of the hole 3 by mixing soil and a soil improving agent and rolling the mixture. The soil used here can be backfill soil that has been excavated at the site in advance, and it is recommended to use a granular soil improver and add water as appropriate to promote diffusion and permeability. It is desirable to mix the soil conditioner here in an amount of 150 kg or more per 1 m3 of soil. The compressive strength of the soil improvement base 6 tamped by compaction is approximately 7 to 15 kg/cm2. The thickness of the soil improvement base 6 is 25 to 40 cm when the width of the base plate 2 is the standard width of 40 cm.

Fifth Step A concrete cloth foundation A is constructed with the lower end foundation plate 2 placed directly on the upper surface of the soil improvement base 6. Finally, the hole 3 is backfilled with the soil excavated at the previous site flush with the ground line (GL) to complete the foundation work. In other words, the sum of the depth of the improved support layer 5 and the thickness of the soil improvement base 6 is the basic version 2.
The width should be three times or more, more preferably about four times in consideration of safety.

[0010] The soil bearing capacity of the concrete cloth foundation A in a normal wooden house should be 1.5 to 2.5 tons/m2;
Considering safety, 6 tons/m2 is more than enough. In contrast, according to the method of the present invention, the compressive strength of the improved support layer 5 is 3 to 6 kg/cm2, and the compressive strength of the soil improvement base 6 is 7 to 15 kg/cm2, and the load applied to the cloth foundation A is first Received at soil improvement base 6, which has excellent soil quality.
Since the soil is then supported by the improved support layer 5, the overall soil bearing capacity can be secured to be at least 8 tons/m2 or more and about 10 tons/m2.

[0011]

[Effect of the invention] According to the present invention, concrete cloth foundation A
forming an improved support layer 5 by cutting roots only in the construction part;
Next, all you have to do is build the soil improvement base 6.
Compared to conventional foundations that completely improve the site, the construction area is smaller, and on-site construction can be carried out safely and efficiently.

Furthermore, since the improved support layer 5 below the bottom of the hole is injected with the soil conditioner aqueous solution after the liquid passage holes 4 are provided, the ground support capacity of the important support layer can be enhanced satisfactorily. In addition, even if the land improvement base 6 has a small thickness, it becomes denser due to compaction and becomes a stronger ground than the improved support layer 5. In combination with these factors, the load of the building applied to the concrete foundation A is first received by the strong land improvement base 6 and then by the improved support layer 5 while being gradually attenuated, and the bearing capacity required for the target ground is can be more than adequately secured.

[0013]

[Example] Foundation plate 2 with a width of 40 cm at the bottom end of foundation wall 1
To construct concrete cloth foundation A with
Root cutting width 70 cm, root cutting depth 57 along the construction direction.
Drill hole 3 cm.

[0014] A large number of liquid passage holes 4 are provided in the support layer directly below this hole 3, perpendicularly from the bottom of the hole. Each liquid passage hole 4 has a hole diameter of 5 cm,
The depth is 100 cm, and holes are drilled at equal intervals of 25 cm in the width direction of the hole bottom and 50 cm in the longitudinal direction as shown in FIG.

An improved support layer 5 is formed by pouring an aqueous soil conditioner solution into the support layer immediately below the holes 3 through the respective liquid passage holes 4 while applying vibration with a vibrator, as shown in FIG. The soil conditioner aqueous solution is prepared by mixing 600 to 800 kg of a known soil conditioner in 1 m3 of water and, if necessary, an additive for promoting permeability such as bentonite or sunsalt. The compressive strength of the improved support layer 5 at this time was 3 to 6 kg/cm2.

After the improved support layer 5 has solidified, as shown in FIG. 4, the soil from the site excavated earlier is used at the bottom of the hole 3, and 150K of a granular soil conditioner is applied per 1 m3 of this soil.
A soil improvement base 6 is constructed along the longitudinal direction of the hole 3 by mixing more than 100 g of the mixture and compacting it by tapping with a tapping compactor. In addition, in order to promote mixing of the soil and soil conditioner, a small amount of water is added as necessary. The soil improvement base 6 had a width of 70 cm, a thickness of 30 cm, and a compressive strength of 7 to 15 kg/cm2.

After the soil improvement base 6 has solidified, the above-mentioned concrete cloth foundation A is constructed in the usual manner so that its foundation plate 2 rests directly on the base 6, and the soil previously excavated is placed in the hole 3. The hole was backfilled to make it flush with the ground line (GL) as shown in Figure 1, and construction was completed. Reference numeral 7 in the figure indicates the backfill soil. In such a case, the concrete cloth foundation A is connected to the improved support layer 5 via the soil improvement base 6.
Under the above conditions, the soil bearing capacity was at least 8 tons/m2 or more, and approximately 10 tons/m2.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional front view showing the completed construction of a concrete cloth foundation.

FIG. 2 is a longitudinal front view illustrating a hole drilling process after a root cutting process.

FIG. 3 is a plan view showing a hole drilling state.

FIG. 4 is a longitudinal front view illustrating the construction process of the land improvement base.

FIG. 5 is a longitudinal front view illustrating the relationship between the width of the foundation slab of a concrete cloth foundation and the bearing capacity of the ground.

[Explanation of symbols]

1 Foundation wall 2 Basic version 3 holes 4 Liquid passage hole 5 Improved support layer 6 Soil improvement base A. Concrete cloth foundation

Claims (1)

[Claims] Claim 1: A root cutting step of digging a hole 3 wider than the width of the foundation plate 2 of the concrete cloth foundation A in the ground along the direction of construction, and a root cutting step of digging a hole 3 wider than the width of the foundation plate 2 of the concrete cloth foundation A in the construction direction; a step of drilling holes 4 to provide them at appropriate intervals; a step of pouring an aqueous soil conditioner solution into the support layer below the holes 3 through each of the holes 4 to form an improved support layer 5; A process of constructing a soil improvement base 6 at the bottom of the hole 3 by mixing soil and a soil improvement agent and subjecting it to compaction treatment, and a step of constructing a soil improvement base 6 on the top surface of the soil improvement base 6 with the foundation plate 2 at the lower end placed on it. A method for constructing a concrete cloth foundation, comprising the steps of constructing a cloth foundation A.