JPS62197516A - Soil cement composite pile - Google Patents

Abstract

PURPOSE:To increase the frictional resistance of a soil cement composite pile by a method in which the blending proportion of a soil cement is determined so that the bonding strength per unit area between soil cement and steel tubular pile meets specific conditions. CONSTITUTION:The outside diameter Dp of a steel tubular pile 4 to be penetrated and erected in a soil cement column 3 is determined to meet the relationship Dp<=0.85Ds, where the outside diameter of the column 3. Also, the bonding strength S2 per unit area between the column 3 and the pile 4 is determined to meet the relationship S2>=S1(Ds/Dp), where S1 is the surface frictional force between soft ground layer 1 and the column 3. The bearing capacity of the pile 4 can thus be utilized almost 100%.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a soil-cement composite pile using a soil-cement construction method using ready-made piles, and in particular to effective utilization of the strength of steel pipes and the like.

[Conventional technology]

In the soil cement method, an auger or stirring rod mounted on a traveling vehicle is screwed into the ground using electric power or the like to drill holes, and an injection material such as cement milk made of a cement-based hardener is poured from the center of the tip of each auger or stirring rod. Then, form a soil cement column while forcibly stirring with a stirrer or the like. Support piles using the soil cement construction method are constructed by press-fitting pre-hardened Km pipe piles or ready-made concrete piles into the soil cement columns. That is,
As shown in Figure 10 (, ), this support pile uses a drilling fluid with a comparatively low cement mixing ratio, called peripheral fixative, as the injection material for soft N1, and for support layer 2, it uses a drilling fluid with a relatively low cement mixing ratio. A uniaxial soil cement column 6 is formed using a liquid, and before the cement of this soil cement column 3 hardens, a steel pipe pile 4 or a ready-made concrete pile is erected to form a supporting pile as shown in FIG. 10(b). are doing.

For support piles made using the conventional soil cement construction method, the outer diameter Dp of the steel pipe pile 4 or ready-made concrete pile is set to a value as close as possible to the outer diameter D8 of the soil cement column 3, for example, the difference is 5.
~100L, and the circumferential friction strength of the pile is not the outer circumference of the soil cement with a diameter Ds, but the outer circumference of the ready-made pile 4 with an outer diameter Dp, and the circumferential friction force is the same as that of the ready-made pile 4 and the soft layer 1lIJ.
It was calculated using the value of J. In this case, whether the pile supporting capacity was calculated using the outer diameter D3 of the soil cement column 6 or the outer diameter Dp of the steel pipe 4, there was a difference of 10 to 20%, which was not a big difference. That is, in the soft layer, the strength of soil cement was expected to be only about the same as that of the soft layer.

[Problem that the invention seeks to solve]

When a steel pipe is used as an antibody in a soil-cement composite pile made by the conventional soil-cement construction method described above, the M-pipe plate thickness t is t relative to the M-pipe outer diameter Dp to prevent local buckling of the steel pipe.
/Dp > 1/100. Therefore, unless the ground is very strong, the yield strength πDptσa of the pile body is much larger than the normal support capacity of the pile determined by the ground, and it is usually Proof strength πDptσa
In many cases, only about 50% of the amount is used. Note that σa
is the constant allowable compressive stress of the steel pipe.

Also, in PC piles, the inner diameter DI of the pile body is generally about 5 to 0.7 Dp, where Di=Q with respect to the outer diameter DpK.
In this case as well, the cuff resistance of the antibody, (Dp”-Di”)σaf
is far greater than the normal support capacity of piles, which is determined by the soil, and in most cases only about 50% of the pile's bearing capacity is used in general soil. Note that σa1 is the constant permissible bearing capacity of concrete.

That is, support piles made using the conventional soil-cement construction method have a problem in that they are not utilized in general ground because the strength of steel pipes or ready-made concrete piles is insufficient.

This invention was made in order to solve such problems, and the purpose is to propose a soil cement composite pile using the soil cement construction method that can effectively utilize the bearing capacity of steel pipe piles or ready-made concrete piles. It is something.

[Means for solving problems]

The soil-cement composite pile according to the present invention has an outer diameter Dp of a general shaft portion of a steel pipe pile or a prefabricated concrete pile to be erected in a soil-cement pile such that Dp≦0.85D@ with respect to the outer diameter of a soil-cement column. Circumferential surface friction strength S1 per unit area between the layer and soil cement and adhesion strength S per unit area between the soil cement and the steel pipe pile or the prefabricated Funkrete pile.

The soil cement mixture in the soft layer is determined to satisfy the following conditions, and the supporting piles are formed.

[For production]

In this invention, first, the adhesion strength between soil cement and steel pipe piles or ready-made concrete piles is 51Ds /
By determining the mix and strength of the soil cement to be greater than Dp, the soft layer and the soil cement will slip, and the friction between the soil cement and the steel pipe pile or ready-made concrete pile will slide until the circumferential frictional force reaches its strength S. will not slip. In other words, when determining the circumferential friction strength of a pile,
Unlike the conventional method, the outer circumference πDs of the soil cement can be used instead of the outer circumference πDp of the pile, and the friction resistance can be increased compared to the conventional method.

Next, the outer diameter D of the steel pipe pile is adjusted to satisfy Dp≦0.850s.
By making p smaller than the soil cement column diameter Ds, nearly 10% of the yield strength of the steel pipe pile can be utilized while satisfying the restriction t≧Dp/100 for preventing local buckling. Similarly, with ready-made concrete piles, nearly 100% of the pile capacity can be utilized. That is,
This invention has the effect of increasing the circumferential friction resistance and utilizing nearly 100% of the antibody resistance.

〔Example〕

FIG. 1 shows an embodiment of the present invention, in which 1 is a soft layer of the ground, 2 is a support layer, 3 is a soil cement column with an outer diameter Ds formed in the soft lagoon layer 1 and the support layer 2, 4 is a steel pipe pile with an outer diameter Dp that is press-fitted and built into the soil cement column 6.

The composition and strength of the soil cement pillar 6 in the soft layer are those of the soft layer 1.
and the surface friction force S1 between the soil cement column 3 and the adhesion force S between the soil cement column 6 and the steel pipe pile 4.

is πDs a Sl ≦ffDp-8° - Therefore, S! Pressure is determined to satisfy ≧S1 copy. That is, by making the adhesion force S between the steel pipe pile 4 and the soil cement column 3 larger than the friction force S1 on the circumferential surface 111 between the soft layer 1 and the soil cement column 3 so as to satisfy the above equation, the soil cement column 6 and It slides between the ground and obtains local frictional force here.

In addition, the outer diameter Dp of the steel pipe pile 4 is determined to satisfy the relationship Dp≦0.85 Ds with respect to the outer diameter Ds of the soil cement column 3, and the plate thickness t of the steel pipe pile 4 is
is the plate thickness to prevent local buckling, that is, t/Dp>1/
100% relationship is ensured and at the same time the antibody tolerance is 100%
I am using it soon. here.

The outer diameter Dp of the steel pipe pile 4 was determined based on the above relationship for the reason indicated in the arrow.

(・If the strength of the first phase friction force is f, the ultimate bearing capacity of the support layer 2 is L, and the pile length is L, then πDptCa=1(πDSL−f+1DS2・fp)・
...(1) is obtained. Note that in equation (1), 1
, 4 indicates the safety factor.

Except when the tip support layer 2 is extremely good, such as rock.

The ground commonly encountered is the ground shown in the first bramble.

Table 1 For each of these soils, pile length LelOm and 60m r
fJIi If the plate thickness t of the pipe pile 4 is "-Dp, and the soil cement diameter Ds is 100 cm, 120 cm, 150 m, and 200 c1n, the outer diameter Dp of the steel pipe pile 4 is determined by the above equation (1), and the black dot in Fig. 2 is obtained. It will be shown as follows. In addition, the constant allowable stress σa of the copper pipe pile 4 is 1600~
And so. As is clear from FIG. 2, the outer diameter Dp of the # pipe pile 4 that satisfies equation (1) almost satisfies the relationship Dp≦o, 5 sps.

Further, when using PC anti-antibody as the antibody, when the constant antibody resistance and the soil bearing capacity are in equilibrium, the following is obtained. In this case as well, for the ground shown in Table 1, the pile length is Ion and 5
0m, the outer diameter Ds of the soil cement column 6 is 100c.
The results of determining the outer diameter Dp of the PC pile from equation (2) for the cases of 120 cm, 120 boxes, and 150 cm are shown by black dots in FIG. Here, the inner diameter DI of the PC pile was set to Q, 7D, and the constant allowable compressive stress σ, J of the concrete was set to 170. As is clear from Fig. 6, in the case of PC piles, the outer diameter Dp of PC piles that satisfy equation (2) is almost always Dp≦0.85D.
Satisfies the relationship I.

Therefore, by determining the outer diameter Dp of the steel pipe pile 4 or the PC pile with respect to the outer diameter DsK of the soil cement column 3, Dp≦0.85 D@! In the case of l pipe pile 4, the yield strength πDptσ1 of the pile body was set to 100 while ensuring the plate thickness to prevent local buckling.
% can be used. Similarly, in the case of PC piles, it is possible to use nearly 100% of the antibody's dreg resistance (Dp! - DI") σa while satisfying Di = 0.5 to 0.7 Dp.

The formulation of the root hardening solution in the support layer 2 and the reinforcement of the pile tip are determined so that the pile axial force W at the upper end of the support layer 2 is sufficiently transmitted to the support layer 2, as shown in FIG. 4(a). In other words, as shown in Figure 4(b), the ground support capacity is determined so that the soil cement (K/soil cement in support layer 2) ABCD is considered as the foundation. Here, the ground supporting force consists of the tip supporting force G of the soil cement in the supporting layer and the circumferential surface friction force f1.

Although the outer diameter Dp of the steel pipe pile 4 is in the range of Dp≦0.85Ds, if Dp is close to 0.85Ds and is a relatively large value, the difference between the soil cement 6 in the support layer 2 and the steel pipe pile 4 The adhesive strength can be sufficiently large, and the pile axial force W at the upper end of the support layer can be transmitted to the support layer 2 via the adhesive force F without reinforcing the tip of the pile, as shown in FIG. The ground support force G+f of the support layer 2 can be ensured.

In addition, when using a ready-made concrete pile as an antibody and the pile diameter Dp is relatively large, as shown in FIG. can transmit the pile axial force W to the support layer 2.

In this case, soil cement 6 and ready-made concrete pile 4a
The pile axial force W is transmitted to the support layer 2 via the adhesion force F and the thick-walled support force G of the ready-made concrete pile 4&.

When the pile diameter Dp is relatively small under the condition of Dp≦0.85 Ds, it is possible to secure the ground bearing capacity c+fs of the support layer 2 and transmit the pile axial force W at the upper end of the support layer to the support layer 2. It will be difficult without tip reinforcement. In this case, Figure 7 (A) #
As shown in (b), by providing reinforcement consisting of cylindrical steel plates 5 and radial steel plates 5a on the outside of the steel pipe piles 4 in the support layer 2, the ground bearing capacity of the support layer is increased by adding soil cement and steel plates 4. This can be obtained by the adhesive force F of the steel plates 5 and 5a, and the pile axial force W at the upper end of the support layer can be transmitted to the support layer 2.

In addition, FIG. 7(4) is a sectional view of the pile for 2s of support layers, and FIG. 7(b) is a sectional view taken along the line AA in FIG. 7(a).弗7 (
In a), fl is the supporting ground surface friction force.

In addition, in the above embodiment, the steel pipe pile 4. Although we have explained the case where the outer surface of the ready-made concrete pile 4 is flat, the outer surface of the steel pipe pile 4 has striped protrusions 6 as shown in FIG. 8 (jL).
Alternatively, by creating checkered projections 6a shown in FIG. 8(b) by rolling, or by providing projections on the outer surface of the steel pipe 4 by welding beads or reinforcing bar welding after creating the steel pipe 4, it is possible to create a gap between the m-pipe 4 and the soil cement. can increase the adhesion of

In the case of ready-made concrete piles such as PC piles, depending on the formwork used when making the ready-made concrete piles,
As shown, by providing projections 7 and depressions 8 on the outer surface of the ready-made concrete pile 4b, the adhesion between the ready-made concrete pile 4b and the soil cement can be increased.

〔Effect of the invention〕

As explained above, this invention obtains the bearing capacity of a pile by the circumferential friction force between the soil cement and the ground and the tip bearing capacity when the soil cement in the supporting layer is regarded as the foundation, and the steel pipe pile Or 100% of the bearing capacity of ready-made concrete piles.
Since it is designed so that it can be used soon, the strength of steel pipe piles or ready-made concrete piles and the strength of soil cement can be effectively utilized, and the pile foundation can be installed at a low cost.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of the present invention, Fig. 2 is a characteristic diagram of soil cement column outer diameter Ds and steel pipe pile outer diameter Dp, and Fig. 3 is a characteristic diagram of soil cement column outer diameter D$ and PC pile outer diameter. A characteristic diagram of the diameter Dp, Figures 4 (a) and (b) are explanatory diagrams for ensuring the ground bearing capacity of the support layer, Figures 5 and 6 are cross-sectional views of the pile in the support layer, and Figure 7 Figures (a) and (b) show the piles in the support layer, Figure 7 (a) is a cross-sectional view, and Figure 7 (b) is a cross-sectional view.
) is A-, A sectional view of Figure iq (a), Figure 8 (&),
(b) is an explanatory diagram showing another embodiment, FIG. 9 (jL)
, (b) is a sectional view showing an antibody of another example, and FIGS. 10(a) and (b) are explanatory views showing a support pile using the conventional soil cement construction method. DESCRIPTION OF SYMBOLS 1... Soft layer, 2... Supporting layer, 6... Soil cement column, 4... Steel pipe pile, 4a... Ready-made Funkrete pile. Agent Patent Attorney Masaru Sato Year 2: Arrow General Figure 4 (a) (b) Figure 5 Figure 6

Claims (2)

[Claims] (1) A soil-cement column is formed by injecting an injection material such as cement milk into the ground and forcibly mixing it with the soil using a stirring lot, and a steel pipe pile or a ready-made concrete pile is pressed into the soil-cement column before the cement hardens. In the soil-cement composite pile to be formed, the shaft outer diameter Dp, which is the outer diameter of the middle part of the pile excluding the pile head and pile tip of the steel pipe pile or ready-made concrete pile, is Dp≦ with respect to the outer diameter Ds of the soil-cement column. 0.85Ds, and the circumferential surface friction strength S_1 per unit area between the soft layer and soil cement and the adhesion strength S_2 per unit area between the soil cement and steel pipe piles or ready-made concrete piles are S_2≧S_1 (Ds/Dp). A soil cement composite pile characterized in that the soil cement composition is determined to satisfy the requirements. (2) The soil-cement composite pile according to claim 1, wherein the outer surface of the steel pipe pile or the ready-made concrete pile is provided with irregularities.