JPH06313314A - Foundation ground improving construction method for low storied building - Google Patents

Abstract

PURPOSE:To provide a foundation supporting ground for a low storied building which has sufficient supporting power, and is easily formed, and can produce labor saving such as the shortening of the term of work. CONSTITUTION:After excavating the ground 1 as wide as a fixed extent to a fixed depth (H), a cement system hardener 4 is scattered on the bottom of the excavated ground, and next the excavated earth and sand 5 are uniformly spread to a fixed thickness, and agitated with the cement system hardener 4 and compacted to form the compacted layer 8 of the earth and sand mixed with the cement system hardener 10. The compacted layer 8 is formed in one or plural layers to compose a foundation supporting ground for a low layer building. A reinforcement net 9 can be provided between the compacted layers to reinforce the compacted layer. In addition, the earth and sand mixed with the cement system hardener 10 which is produced by mixing the excavated earth and sand with the cement system hardener 4 and agitating them may be spread on the bottom 3 of the excavated ground to fixed thickness and compacted. Thus the excavated earth is increased in strength by the chemical uniting action of the cement system hardener, and the earth and sand are stuck fast to the hardener by compacting and spreadly hardening to increase the strength of the foundation supporting ground and to secure its safety.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-rise building foundation ground improvement method, and more particularly to a low-rise structure foundation ground improvement method capable of easily forming a supporting ground for the foundation of a low-rise structure.

[0002]

2. Description of the Related Art A conventional supporting method for a foundation of a low-rise building is
It is common to support foundation footings with cast-in-place concrete piles or ready-made concrete piles, or to support cloth foundations or solid foundations with split stones or soil concrete.

[0003]

However, the above-mentioned prior art involves large-scale construction such as pile construction, cracked stone construction, and earth concrete placement, resulting in construction costs, material costs, shortened construction period, and labor. Was a bottleneck for labor saving.

An object of the present invention is to provide a low-rise building foundation ground improvement method capable of forming a support ground for a low-rise structure foundation with sufficient support force and easily, and achieving labor saving such as shortening the construction period. Is to provide.

[0005]

[Means for Solving the Problems] The object is to excavate the ground in a predetermined range and to a predetermined depth, then spread a cement-based solidifying material on the excavated ground surface, and then spread the excavated earth and sand to a predetermined thickness. It is achieved by stirring and rolling with the cement-based solidifying material to form a compacted layer of soil mixed with the cement-based solidifying material, and using this rolling layer as a supporting ground for the foundation of the low-rise building.

Further, after excavating the ground to a predetermined range and a predetermined depth, the cement-based solidifying material mixed with the excavated earth and sand is mixed and stirred, and the soil is mixed with the cement-based solidifying material to a predetermined thickness and rolled. This can be achieved by forming a compaction layer of cement-solidified material-mixed earth and sand, and using this compaction layer as a supporting ground for the foundation of the low-rise building.

[0007]

According to the above structure, the chemical solidification action of the cement-based solidifying material causes the excavated soil to have a supporting strength for the low-rise building structure, and by compacting it by rolling it, air bubbles at the time of stirring are removed. The excavated soil and the cement-based solidifying material adhere to each other to increase the strength and ensure stability. Therefore, it is possible to form the supporting ground for the foundation of the low-rise building having a sufficient supporting force with simple construction.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some embodiments of the present invention will be described below with reference to the drawings. First, the work procedure of one embodiment of the present invention will be described. (1) Preparation work Dust, debris, plant roots, etc. are removed from the construction site, drainage of the water pool, etc. is carried out, and the work such as surveying and marking out the construction site and preparing a temporary storage place for cement and excavated soil are carried out. (2) Excavation As shown in FIG. 1, the ground surface 1 of the construction site has a predetermined depth H.
Drill up to. In this embodiment, the backhoe 2 is used for the excavating machine. (3) Dispersion of cement-based solidifying material As shown in FIG. 2, a predetermined amount of cement-based solidifying material 4 is evenly distributed on the excavated bottom surface 3 of the ground. As the cement-based solidifying material 4, ordinary Portland cement, blast furnace cement, or cement-based soil improving material is applied. In this embodiment, ordinary Portland cement is used. As a method for spraying cement, in the case of bag filling (40 kg / bag), cement bags are arranged on the spraying ground at appropriate intervals, opened with a backhoe, sprayed, and then leveled with a scoop or the like. In the case of a flexible container bag (1 t / bag), the container is opened with a truck crane or the like and sprayed with a backhoe or a scoop. In the case of bulk (bulk loading), spray on a conveyor or a dedicated sprayer. (4) Leveling excavated earth and sand As shown in FIG. 3, a predetermined amount of earth and sand 5 excavated by the backhoe 2 and the like are placed on the scattered cement 4 and spread. (5) Mixing and stirring Next, as shown in FIG. 4, the cultivator 6 or the backhoe sufficiently mixes and stirs the cement 4 and the spread excavated earth and sand 5. Judgment of mixing is based on the extent that there is no unevenness of mixing and the color of cement becomes inconspicuous. (6) Compaction As shown in FIG. 5, excavated earth and sand in which cement is mixed and stirred is compacted by the vibrating roller 7 to form the compaction layer 8. In order to make the chemical solidification action more reliable, it is necessary that the cement and the soil are in close contact with each other, and it is important to eliminate air bubbles generated during mechanical stirring. Therefore, after mixing and stirring,
Sufficient pressure loading by the vibrating roller 7, backhoe bucket, etc. is required. This promotes an increase in the density of the mixed soil and a chemical setting action of cement, and an increase in the strength and stability is secured. As a standard for compaction work, the number of times of rolling when the finished thickness is 30 cm is about 4 times with the vibration roller 7 and about 8 times with the tamper or rammer. (7) Facility of Reinforcement Material As shown in FIG. 6, the formation cycle of the compaction layer 8 of the mixed earth and sand is performed a plurality of times to form a plurality of compaction layers. In this case, if a mochi net-shaped assembled reinforcing bar (reinforcing bar net 9) is provided between the rolling layers 8, the supporting strength of the structure is increased. In this embodiment, after the reinforcing bar net 9 is installed before forming the uppermost compaction layer, the uppermost layer is formed and four compaction layers are implemented. In this case, for the layer immediately above the rebar net 9, it is preferable to use earth and sand (premix soil 10) in which cement is mixed in advance in order to avoid damage to the rebar net 9 during stirring. (8) Construction of foundation As shown in FIG. 7, a footing 12 which is a foundation construction of a building is constructed on a multi-layer compaction-improved ground 11 in which a plurality of compaction layers are formed and surface irregularities are evened out.

FIG. 8 is a flow chart showing the basic steps from these steps (preparation) to step (10) (curing). As shown in the figure, the work from step (cement spraying) to step (compacting) is the first cycle, and from step (backfilling leveling) to step (compacting) depending on design conditions and construction conditions. Is performed as a second cycle, and this is repeated for a required cycle.

The above is one embodiment of the present invention, but as another embodiment, a predetermined amount of excavated earth and sand is spread on the excavated surface first, and then cement is sprinkled on the excavated sand and mixed and stirred with a backhoe or the like. You may roll. Also, cement is mixed in advance with excavated earth and sand, and this mixed earth and sand (premixed soil)
Can be laid on the excavation surface and compacted. By preliminarily mixing the cement with the excavated soil, it is possible to prevent the wind from scattering during the spraying of the cement. still,
The number of rolling layers and the presence or absence of the rebar net can be appropriately determined depending on the construction conditions.

Quality control of the compacted stabilized soil is carried out on the basis of the dry density of the specimen of the indoor mixing test in the required addition amount of cement, the compaction degree is 90% or more, and the porosity is 1
The management standard is 5% or less. The sampling frequency for quality control is determined by the purpose of construction. In the case of foundations such as retaining walls and culverts, there is one location with a 20m construction extension, in the case of foundations of low-rise / detached houses, one point per unit, partial improvement of defective ground. In case of, do it each time.

Confirmation of the ground bearing capacity of the improved ground according to the present invention is as follows.
In principle, it is based on flat plate loading at the time of prescribed material, but considering the importance of buildings, etc., when the construction scale is relatively small, or when the purpose is to supplement the flat plate loading test,
According to Swedish sounding. In the flat plate loading test, one place or more is added at a rate of one place for every 2000 m ^{2 of} treated area, and the ground bearing capacity is directly obtained. Swedish-style sounding is conducted for the purpose of small-scale construction and supplementation of flat plate loading test. For foundations such as retaining walls and culverts, one place is provided for every 10m of construction extension, and for low-rise / detached house foundations, 5 units per unit. In case of partial improvement of parts and defective ground, it should be carried out each time.

The ground improvement principle according to the present embodiment aims to increase the strength of the soil by hydration / consolidation action of cement to improve the soil. As an applicable soil, it is most suitable for sandy soil, but is suitable. Applicable to cohesive soil and soil containing organic matter by selecting appropriate solidifying material and uniform stirring. Further, even in a high water content soil in which the solidified material such as cement is mixed in a mud-like state, it is possible to sufficiently solidify the excavated ground by selecting an appropriate solidified material and the addition amount.

The main construction machines used in this method are:
It is also possible to use a mini backhoe for stripping and solidifying material, a tiller (mini tiller) for agitation, a hand dozer for leveling earth and sand, or a mini backhoe with a waste plate. Further, a hand vibration roller, a tamper, a rammer or the like is sufficient for the compaction. The construction management items include material management, performance of the solidified material, confirmation of adaptability, and management during construction includes material measurement management, spray density management, mixing and agitation management, improvement depth management, etc. As a test, a treatment layer thickness inspection, a test piece test, a boring core test, a penetration test, and the like to inspect the strength and uniformity of the treated soil are performed.

As described above, defective soil (soft layer) near the surface of the earth
By adding and mixing cement-based powdery stabilizer to the soil, compacting with a roller, or applying loading pressure with a bucket of a backhoe or a dozer, the soil compression resistance and strength characteristics are improved, that is, the foundation ground is supported. It is possible to improve force and prevent subsidence. Furthermore, by laying a mochi net-shaped assembly rebar, net, etc. to enhance the horizontal integration of the improved soil mass, it is excellent in a wide range of applications such as the following. It is possible to exert the effect.

For the purpose of long-term design load (5 to 10 t / m ² ), low-rise residential fabric foundation ground improvement factory, warehouse soil ground improvement, retaining wall foundation ground improvement, roadbed stabilization, slope stabilization, earthwork machine work ground surface It can be applied to processing.

For these application purposes, the construction period is short and the cost is low.

Adapt to local conditions such as narrow and irregular sites and topography.

Construction management is easy without requiring special construction machines and techniques.

The improvement effect is excellent.

It is possible to deal with soil properties that are usually difficult to improve.

The improved soil has a high resistance to water such as rainfall and groundwater.

There are excellent effects such as

Hereinafter, some application examples will be described with reference to the drawings. (A) When the ground immediately after backfilling is used as the foundation of a building, etc. As shown in FIG. 9, the stabilization processing part 21 which implements this construction method and improves the ground is the backfilling part (embankment) in the retaining wall 22. ), The ground bearing capacity is about the same as that of the ground portion 23. Due to the construction conditions, etc., it is not possible to perform sufficient compaction with a large machine, so this method is applicable when it is expected that the bearing capacity will decrease due to rainfall.

(B) When a soft layer is used as the foundation of a building or the like As shown in FIG. 10, when the building is constructed as a foundation on a soft layer 24 that is shallowly deposited, It is intended to secure bearing capacity and prevent subsidence. Soft layer 24
If the thickness is thick (2 m or more), or if there is a possibility of consolidation or liquefaction of the unimproved part, consider it separately.

(C) In the case of improving a partially defective portion in the construction of a middle-rise house, etc. As shown in FIG. 11, the partially defective portion of the ground is locally improved as a stabilization processing portion 21 to be the same as the surrounding foundation ground. Prevents unequal settlement by increasing the soil bearing capacity.

(D) In the case of being the basis of a civil engineering structure such as a retaining wall constructed on soft ground As shown in FIG. 12, a retaining wall 2 constructed on a soft layer 24.
It can also be used when improving the ground of the foundation of civil engineering structures such as 5 to form the stabilization treatment unit 21, and is also applicable to enhance the ground bearing capacity of the foundation such as culverts and sewer pipes.

Next, the range and depth of the stabilization processing unit 21 will be described. 1) Processing Range As shown in FIG. 13 or FIG. 14, the processing range of the stabilization processing unit 21 is such that the processing depth Z is 1 at the outer periphery of the foundation 26 of the building or the footing 28 of the building such as the retaining wall 27. / 2 is added.

2) Depth of treatment For the long-term design load of buildings and the weight of the stabilized ground, the thickness should satisfy the allowable bearing capacity of the untreated part.
As shown in FIG. 15, considering the stress propagation into the ground as shown in the figure, the vertical stress level σz in the ground at the depth Z is as follows.
It becomes formula (1).

Σz = (B × q) / B × Z (1) where σz: vertical stress level in the ground (t / m ² ) B: minimum width of the base of the foundation (m) q: contact pressure (T / m ² ) z: Improved thickness (m) Df: Depth (m) from the lowest ground surface adjacent to the foundation to the bottom surface of the foundation.

3) Permissible bearing capacity of original ground The permissible bearing capacity qa of the original ground is as shown in the equations (2) and (3) according to Article 14 of the Building Basic Structural Design Standard of the Japan Institute of Architecture. Long allowable bearing capacity of qa = (1/3) · (α · C · Nc + β · γ 1 · B · Nr + γ 2 · Df · Nq) ...... (2) Equation short tolerance bearing capacity of qa = (2/3) · ( α · C · Nc + β · γ 1 · B · Nr + (1/2) · γ 2 · Df · Nq) ...... (3) formula qa: allowable bearing capacity of (t / m ²⁾ C: soil under basal bottom Adhesive force (t / m ² ) γ ₁ : Unit volume weight of the ground below the bottom of the foundation (t /
m ³ ) (If the water level is below the groundwater level, take the unit weight in water) γ ₂ : Unit volume weight of the ground above the bottom of the foundation (t
/ M ³ ) (Unit weight in water is below groundwater level) α / β: Shape factor (see Table 1 below) Nc, Nr, Na: Coefficient of bearing capacity, function of internal friction angle φ (Table 2 below) reference)

[0032]

[Table 1]

[0033]

[Table 2]

4) Design strength The design strength of the stabilized ground is the uniaxial compressive strength qa required by the calculation of the bearing capacity. Generally, the improvement depth to which the present method is applied is usually 1 to 2 m, so it is not necessary to consider the deformation of the stabilized ground. However, if tensile stress occurs in the stabilized ground and the allowable tensile strength of the treated ground is 20% of the uniaxial compressive strength, the design strength should be determined by referring to the relationship with the improved thickness shown in Fig. 16 or 17. You can

5) Determination of the amount of solidifying material In the example of this construction method, as shown in FIG. 18, the addition amount of the solidifying material was set to the uniaxial compressive strength qa based on the design strength as a strength premium considering construction conditions and the like. And the corresponding addition amount is determined based on the indoor compounding test. The additional coefficient α is α = 2.0 when compaction is performed and α = 2.0-5.0 when compaction is not performed, and the larger the water content and the soil content, the larger the soil value. To do. For example, α = 5.0
Corresponds to high water content and high organic soil.

6) Minimum addition amount Considering the uniformity of stirring and mixing of treatment materials on site, a guideline for the minimum addition amount at the time of construction is as follows: Cohesive soil bed: 60 kg / m ³ ,
Sandy soil: Set 50kg / m ³ .

Before carrying out this method, the amount of consolidation settlement is calculated. (B) If there is a consolidation layer deeper than the bottom of the improved ground, calculate the consolidation settlement amount and confirm that it does not exceed the allowable settlement amount.

(B) The immediate settlement amount of the improved ground is calculated assuming that it is an elastic body.

(C) Immediate settlement amount is calculated by regarding cohesive soil and sandy soil that can be ignored for consolidation settlement as elastic bodies.

(D) The allowable subsidence amount is determined in consideration of ground conditions, foundation type, improved column arrangement, superstructure characteristics, surrounding conditions, etc. so as not to cause harmful uneven settlement.

(E) When the spacing between the improved columns is about 3 times the improved diameter or less, a virtual action surface for the load as shown in FIG. 19 or 20 is set and the load action surface is uniformly distributed. It is sufficient to calculate the subsidence amount. FIG. 19 is a diagram showing a virtual action surface of a load when it is supported by soft clay and FIG. 20 is a virtual action surface when it is supported by an intermediate sand layer.

Some design examples of this method will be described below with reference to the drawings. <Design example 1> In the case of building foundation The foundation of a low-rise house is stabilized with cement.

1) Design conditions FIG. 21 shows a bearing capacity examination model of this design example. In addition, FIG. 22 is a stratum map showing soil conditions.

2) Construction conditions The machine used for stabilizing treatment is as follows: Mixing: Backhoe (0.6m ³ ) Pressing pressure: By cover of the backhoe 3) Calculation of design strength of stabilizing ground The long-term allowable bearing capacity of stabilizing ground is qa ₁ , the above (2)
From the formula, qa ₁ = (1/3) · (α · C · Nc + β · γ ₁ · B · Nr + γ ₂ · Df · Nq) (4) Formula Here, α = 1.0 as the continuous footing basis. , Β = 0.5 φ = 0 °, Nc = 5.3, Nγ = 0, Nq =
3.0 γ ₁ = γ ₂ = 1.7 tf / m ² qa ₁ = (1/3) ・ (1.0 × C × 5.3 + 1.7 × 0.5 × 3.0) ...... (5) As shown in the equation 23, the design strength of the stabilized ground is q = 4.1 tf / m ² from qa ₁ > q.

4) Examination of required stable treatment thickness Calculation of long-term allowable bearing capacity of unstable treatment ground Assuming an improved thickness of 1.5 m, Df = H = 1.5 m α = 1.0, β = 0. 5, Nc = 5.3, Nγ =
0, Nq = 3.0 γ ₁ = 1.6 tf / m ³ , γ ₂ = 1.7 tf / m ³ qa ₂ = (1/3) ・ (1.0 × 2.0 × 5.3 + 0 + 1.7 × 0.5 × 3.0) = 1.7 tf / m ² Equation (6) When qa ₂ is rearranged with respect to H, qa ₂ = 3.53
It becomes + 1.7 × H.

Dispersion of load Consideration will be given to dispersion of load due to the thickness H of the stabilized ground.
In that case, the dispersion angle θ is tan θ = 1/2. q: Load degree just under the foundation surface (tf / m ² ) q ': Load degree on the unstabilized soil (tf / m ² ) q ″: Weight of the stabilized soil under the foundation surface acts on the upper surface of the unstabilized soil Load degree (tf / m ² ) q ′ = [(q · B) / {B + 2 · (H−Df) · tan θ}] + q ″ = [(q · B) / {B + 2 · (H−Df) · tan θ}] + (H−Df) · γ (7) Formula B = 1.2, Df = 0.5 m, γ = 1.7 tf / m ³ , tan θ =
1/2, q = When 8tf / m ^2, q '= [(8 × 1.2) / {1.2 + 2 × (H-0.5) · 1/2} ] + (H-0.5 ) × 1.7 (8) formula = {9.6 / (0.7 + H)} + (H-0.5) × 1.7 The above relationship between qa ₂ and q ′ and H is illustrated. , Fig. 2
4 and H satisfying qa ₂ > q 'is the required stable treatment thickness. Here, H = 1.5 m. This value satisfies the conditions for tensile strength in stabilized ground.

B = 1.2, Df = 0.5 m, γ = 1.7 tf /
m ^3, When tanθ = 1/2, q = 8tf / m 2, q '= [(8 × 1.2) / {1.2 + 2 × (H-0.5) · 1/2} ] + ( H-0.5) × 1.7 (8) formula = {9.6 / (0.7 + H)} + (H-0.5) × 1.7 qa ₂ and q ′ and H above Figure 2 shows the relationship between
4 and H satisfying qa ₂ > q 'is the required stable treatment thickness. Here, H = 1.5 m. This value satisfies the conditions for tensile strength in stabilized ground.

5) Indoor Mixing Test FIG. 25 shows the results of the indoor mixing test. Design strength qu is C
From = 0.41 kgf / cm ² , qu = 2 × C = 0.82 kgf / cm ²
Is. The required addition amount is 74 kg / cm ³ as an addition amount corresponding to 2.0 times the design strength, assuming a premium rate of 2.0 without compaction with cement.

6) Summary Stabilization depth: 1.5 m, addition amount: 74 kg / m ³ .

<Example 2 of design> Retaining wall foundation This is a foundation of a reinforced concrete type retaining wall that has been stabilized with cement.

1) Design Conditions FIG. 26 shows a ground pressure distribution map of this example, and FIG. 27 shows a stratum map showing soil conditions. Retaining wall height: L = 4m, foundation width: B = 2.
6 m, depth of penetration: Df = 0.7 m. Depth 1m
Calculate as a hit.

2) Construction conditions The machine used for stabilizing treatment is: mixing: backhoe (0.6 m ³ ) compaction: rammer (80 kg) 3) calculation of long-term allowable bearing capacity of stabilizing treatment section Long-term allowable bearing capacity of stabilizing treatment section Qa is the uniaxial compressive strength q
and u = 14tf / m ^2, In consideration of eccentricity, inclination of the load, Qa = (1/3) A ' · (α · k · C · Nc + k · q · Nq + 1/2 · γ 1 · B'・ Nγ) (tf) (9) where C: Adhesive force (tf / m ² ) of the stabilized part C = qu
/ 2 (tf / m ² ) q: Overlay load (tf / m ² ), q = γ ₂ · Df = 1.7 × 0.7
= 1.19 (tf / m ² ) A ′: Effective loading area (m ² )
A ′ = B ′ × 1.0 = 2.56 m ² γ ₁ , γ ₂ : Unit volume weight of soil of supporting ground and rooting ground. However, the unit volume weight in water is used below the groundwater level.

B ′: Effective loading width (m) of foundation considering eccentricity, B ′ = B-2e = 2.6-2 × 0.02 = 2.56 m B: Foundation width (m), B = 2 .6 e: eccentricity of load e = 0.02 m Df: effective rooting depth (m) of foundation, Df = 0.7 m α, β: shape factor of foundation α = β = 1.0 Nc in case of strip , Nq, Nγ: Bearing capacity coefficient considering the load inclination From the bearing capacity coefficient table, Nc = 3.4, Nq = 1.0, Nγ = 0 (however, tan θ = HD / Y = 4/15 =
0.267) k: Surplus factor for rooting effect k = 1.0 Qa = (1/3) × 2.56 × (1.0 × 1.0 × 7.0 × 3.4 + 1.0 × 1.19 × 1.0 + 0) ＝ 21.3 (tf) …… ( 10) Formula qa = Qa / A ′ = 8.3 tf / m ^{2 When} the trial calculation of the strength of the above-mentioned stabilization processing part is illustrated,
It becomes like FIG. From the figure, C where qa> q ₁ is the design strength C = 5 tf / m ² .

4) Calculation of long-term allowable bearing capacity of unstabilized portion As shown in FIG. 29, assuming that the improved thickness H is 1 m, Df ′ = Df + H = 0.7 + 1.0 = 1.7 m, , Considering the dispersion of the load due to the improved thickness, the dispersion angle θ is
tan θ = 1/2.

C = 4.5 tf / m ² B ₁ ′ = B ′ + 2 · H · tan θ = 2.56 + 2 × 1.0 × 1/2 = 3.56 m A ₁ ′ = B ₁ ′ × 1.0 = 3.86m ² q ₁ ′ = (N / B ₁ ) ・ (1 + 6e / B ₁ ) = 4.31 tf / m ² q = γ ₂ (Df + H) = 1.7 × (0.7 + 1.0) = 2.0
89tf / m ² q ₂ ′ = (N / B ₁ ) · (1 + 6e / B ₁ ) = 4.03 tf / m ² tan θ = (HB) / (V) = 4/15 = 0.267 From Nc = 3. 4, Nq = 1.0, Nγ = 0 Qa ′ = (1/3) × 3.86 × (1.0 × 1.0 × 4.5 × 3.4 + 1.0 × 2.
89 × 1.0 + 0) = 23.4 (tf / m ² ) qa ′ = Qa ′ / A ′ = 6.06 tf / m ² Here, if qa ′ is rearranged with respect to H, then qa ′ = 5.5 + 0.567 · H. .

Further, in the unstabilized ground, the load on the foundation surface and the weight of the stabilized ground below the foundation surface are considered to act as the load.

(B ′ + 2 · H · tan θ) · {(q ₁ ′ + q ₂ ′) / 2} = {B ′ · (q ₁ + q ₂ ) / 2} + (B ′ + 2 · H · tan θ) · γ · H (11) where q ₁₂ ′ = 1/2 (q ₁ ′ + q ₂ ′), q ₁₂ = 1/2 (q ₁ +
q ₂ ), and rearranging about H q ₁₂ ′ = {(B ′ · q) / (B ′ + 2 · H · tan θ)} + γ · H = [{2.56 × (1/2) × (6.04 + 5.5) )} / {2.56 + 2 × H × (1/2)} ] + 1.7H = {14.77 / (2.56 + H)} + 1.7 × H ...... (12) illustrated the relationship between the expression qa 'and q _12' Figure 3
It is 0. From the figure, H satisfying qa ′> q ₁₂ ′ is the required stable treatment thickness. Here, H = 1.0 m.

5) Indoor Mixing Test The required addition amount is the addition amount corresponding to the value obtained by multiplying the design strength C = 5 tf / m ² by the premium rate α. When compacting using cement, if α = 2.0, the target strength is C = 2.0.
It becomes 0 × 5 = 10 tf / m ² . Therefore, from FIG. 31, the required amount of addition at the site is 123 kg / m ³ .

6) Summary Stabilization depth: 1.7 m, compounding amount: 123 kg / m ³ .

<Design Example 3> Next, in the retaining wall construction, since the ground support capacity is not satisfied with respect to the ground contact pressure, surface ground improvement was performed using cement solidifying materials for loam and silt.

1) Design conditions Design load Ground reaction force 7.0 t / m ² Original ground conditions Soil: Clay silt Unit volume weight: γt = 1.7 t / m ³ Underwater unit volume weight: γ't = 0 .7t / m ³ Local board strength: N value = 2 Adhesion force: C = qu / 2 qu = N / 8 ∴C = N / 16 = 0.125kgf / cm ² = 1.25t / m ² Internal friction angle : Φ = 0 ° (from cohesive soil) 2) Examination of vertical stress in the ground The vertical stress σz in the ground indicates the stress propagation to the ground in the underground stress at the depth Z. If you think like this,

Σz = (B × q) / (B + Z) (13) Here, B: base width (m) q: ground pressure (t / m ² ) Z: improved thickness (m).

Permissible Bearing Capacity of Original Ground The allowable bearing capacity of the original ground qa is based on the Building Basic Structural Design Standard, Article 14 of the Architectural Institute of Japan. Equation (14) is applied to long-term loads and Equation (15) is applied to short-term loads. qa = (1/3) · (α · C · Nc + β · γ 1 · B · Nr + γ 2 · Df · Nq) ...... (14) equation qa = (2/3) · (α · C · Nc + β · γ 1 _{^{· B · Nr + 1/2}} · γ 2 · Df · Nq) ...... (15) equation where, qa: allowable bearing capacity of (t / m ²⁾ C: adhesion of the ground under basal bottom (t / m ² ) Γ ₁ : Unit volume weight of the ground beneath the bottom of the foundation (t /
m ³ ) If the water level is below the groundwater level, take the unit volume weight in water. γ ₂ : Unit volume weight of the ground above the base of the foundation (t
/ M ³ ) If the water level is below the groundwater level, take the unit volume weight in water. α / β: Shape factor shown in Table 1 Nc, Nr, Nq: Bearing force coefficient shown in Table 2, function of internal friction angle φ Df: Depth from the lowest ground surface adjacent to the foundation to the bottom surface of the foundation (m) B : Minimum width of the base of the foundation (m) Calculation of the allowable bearing capacity under the improved bottom Since the internal friction angle φ of soil = 0 °, from the bearing coefficient of Table 2, Nc = 5.3, Nr = 0.0, Nq = 3.0 Further, based on the continuous basis of Table 1, the shape factor: α = 1.0, β
= Substituting 0.5 Local Release condition of the equation (14), qa = (1/3) · ( α · C · Nc + β · γ 1 · B · Nr + γ 2 · Df · Nq) = (1/3)・ (1.0 × 1.25 × 5.3 + 0 + 1.7 × 0.9 × 3.0) = 3.74 t / m ² (16) Formula Study of improved thickness Allowable bearing capacity under the improved bottom surface Improve to a depth that balances the dispersion pressure. Expression (13) ≦ Expression (16) σz = (B × q) / (B + Z) ≦ 3.74 = (8.4) / (1.2 + Z) ≦ 3.74 From this, Z ≧ 1.04 m.

Strength of Improved Ground As the target strength quf of the improved soil, the target strength is the adhesive strength with which the allowable bearing capacity of the improved soil balances with the ground contact pressure of the retaining wall. Regarding the shear strength of the improved soil, the internal friction angle is regarded as 0 and only the adhesive force is evaluated. qa = (1/3) ・ α ・ C ・ Nc (q = 7.0t / m ² ) qa = (1/3) ・ α ・ C ・ Nc (q = 7.0t / m ² ) Therefore, C = (3 × 7.0) / (1 × 1.0 × 5.3) =
3.96 t / m ² Letting quf be the target strength of the site, quf = 2 · C = 7.92 t / m ² = 0.79 kgf / cm ² ≒
It becomes 1.0 kgf / cm ² .

3) Determination of addition amount If the ratio of the room strength qul to the field strength quf is 3, then
The indoor strength is qul = 3.0 kgf / m ³ . Therefore, the addition amount is set to 120 kg / m ³ from the indoor mixing test result of FIG. 32.

4) Results Therefore, in this example, the improved depth is 1.1 m or more and the amount of the cement-based solidifying agent added is 120 kg / m ³ .

[0067]

As described above, according to the present invention, a low-rise structure which has a sufficient supporting force and can be easily formed on the foundation ground of the low-rise structure and can save labor such as shortening the construction period. A foundation ground improvement method can be provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing excavation in an embodiment of the present invention.

FIG. 2 is an explanatory cross-sectional view showing the dispersion of the cement-based solidifying material in this example.

FIG. 3 is an explanatory cross-sectional view showing the leveling of excavated earth and sand in the present embodiment.

FIG. 4 is a sectional explanatory view showing mixing and stirring of cement and excavated earth and sand in the present embodiment.

FIG. 5 is an explanatory sectional view showing the compaction of mixed soil in this example.

FIG. 6 is an explanatory cross-sectional view showing the formation of a plurality of compaction layers in this example.

FIG. 7 is an explanatory cross-sectional view showing a multilayer rolling improvement ground according to the present embodiment.

FIG. 8 is a flowchart showing a work procedure of this embodiment.

FIG. 9 is a sectional view showing an example of an application example of the present embodiment.

FIG. 10 is a sectional view showing another example of application of the present embodiment.

FIG. 11 is a sectional view showing still another example of application of the present embodiment.

FIG. 12 is a sectional view showing still another example of application of the present embodiment.

FIG. 13 is a sectional view showing a processing range according to the present embodiment.

FIG. 14 is a sectional view showing a processing range according to the present embodiment.

FIG. 15 is an explanatory diagram showing stress propagation in the ground.

FIG. 16 is a diagram showing the relationship between the improved thickness of the ground and the uniaxial compressive strength.

FIG. 17 is a diagram showing the relationship between the improved thickness of the ground and the uniaxial compressive strength.

FIG. 18 is a graph showing the relationship between uniaxial compressive strength and cement content.

FIG. 19 is an explanatory diagram showing a virtual action surface of a load supported by soft cohesive soil.

FIG. 20 is an explanatory diagram showing a virtual action surface of a load supported by an intermediate sand layer.

FIG. 21 is a diagram showing a bearing capacity examination model in Design Example 1 according to the present invention.

FIG. 22 is a geological map in design example 1.

FIG. 23 is a diagram showing a relationship between an allowable supporting force and design strength in Design Example 1.

FIG. 24 is a diagram showing a relationship between an allowable supporting force, a load degree, and an improved thickness in Design Example 1.

FIG. 25 is a diagram showing the relationship between the design strength of the improved ground and the addition amount of the solidifying material in Design Example 1.

FIG. 26 is a ground pressure distribution map of the retaining wall foundation in Design Example 2 according to the present invention.

27 is a geological map showing soil conditions in Design Example 2. FIG.

28 is a diagram showing the relationship between the allowable load and design strength in Design Example 2. FIG.

FIG. 29 is a diagram showing load distribution in design example 2;

FIG. 30 is a diagram showing a relationship between a load and an effective load in design example 2 and an improved thickness.

31 is a diagram showing the relationship between the design strength of the improved ground and the addition amount of the solidifying material in Design Example 2. FIG.

FIG. 32 is a diagram showing the relationship between the design strength and the addition amount of the solidifying material in Design Example 3;

[Explanation of symbols]

 1 Ground surface 2 Backhoe 3 Excavation bottom surface 4 Cement-based solidifying material 5 Excavated earth and sand 6 Cultivator 7 Rolling roller 8 Rolling layer 9 Reinforcing bar net 10 Premix soil (soil mixed with cement-based solidifying material) 11 Multi-layer rolling ground 12 Footing 21 Stabilization part 22 Retaining wall 23 Rock mass part 24 Soft layer 25 Retaining wall 26 Foundation 27 Retaining wall 28 Footing

Claims (4)

[Claims] 1. After excavating the ground in a predetermined area and a predetermined depth,
Disperse the cement-based solidifying material on the excavated ground surface, then spread the excavated earth and sand to a predetermined thickness and stir it with the cement-based solidifying material to roll the compacted layer of the cement-based solidifying material mixed soil. A low-rise building foundation ground improvement method that is formed and uses this compaction layer as the support ground for the foundation of the low-rise structure. 2. After excavating the ground in a predetermined area and a predetermined depth,
Cement-based solidifying material mixed with the excavated earth and sand is mixed and stirred, and the cement-based solidifying material-containing earth and sand is laid on the excavated ground surface to a predetermined thickness and rolled to form a compacted layer of the cement-based solidified material-containing earth and sand. , Low-rise building foundation ground improvement method using this compaction layer to support the foundation of low-rise building foundation. 3. The low-rise building foundation ground improvement method according to claim 1, wherein a foundation ground for the foundation of the low-rise structure is formed by successively stacking compaction layers of the cement-based solidifying material-containing earth and sand. 4. An assembly rebar net is laid on the compaction layer of the cement-based solidifying material-mixed sand, and a compaction layer of the cement-based solidifying material-containing soil is applied by stacking on the assembled rebar mesh.
4. The low-rise building foundation ground improvement method according to claim 3, wherein a supporting ground for the foundation of the low-rise structure is formed.