JP2023069117A - ground improvement method - Google Patents

Abstract

To provide a ground improvement method which takes in an anchor effect of an injection pipe in a liquefaction countermeasure by a chemical injection method, and thereby can perform an economical improvement design for large earthquake motion.SOLUTION: A chemical injection method for injecting an injection material such as a solution type injection material containing a non-alkali-silica grout as a main agent using an injection pipe 1 inserted to a ground, and performing ground improvement as a liquefaction countermeasure, leaves the injection pipe 1 in the ground after injection of the injection material to the ground, causes the injection pipe 1 left in the ground to function as an anchor so as to allow the injection pipe 1 to exhibit an anchor effect for circular arc slipping, shear breakage or sliding generated in earthquake, and suppresses deformation of the ground. As the injection pipe 1, a vinyl chloride pipe or a steel pipe can be used. A bag body 2 is provided on the tip of the injection pipe 1, the bag body 2 is filled with a curable filler, which causes the bag body 2 to expand in the ground, and an anchor effect can be enhanced.SELECTED DRAWING: Figure 5

Description

TECHNICAL FIELD The present invention relates to a ground improvement method as a countermeasure against liquefaction in consideration of the anchor effect of injection pipes used in chemical injection methods.

As one of ground improvement methods for the purpose of liquefaction countermeasures, a chemical injection method using a solution-type grouting material based on non-alkali silica grout is generally known. In the liquefaction countermeasures by the chemical injection method, the ground improvement strength is set so that the liquefaction strength ratio is sufficient for the maximum shear stress ratio that occurs during an earthquake.

Especially in recent years, since level 2 seismic motion is also being studied, the liquefaction strength ratio required as a countermeasure against liquefaction is 0.5 to 1.0, and the design strength is 200 to 500 kN/ ^m2 in uniaxial compressive strength, which is a safety factor. The target strength in the preformulation test multiplied by (2.0) is 400 to 1,000 kN/m ² .

In order to satisfy this indoor target strength, the silica concentration of the injection material must be 8% or more, and there are cases where the construction cost becomes high, or even if the silica concentration is set high, the target cannot be met.

Against this background, Patent Document 1 or Patent Document 2 proposes a method of resisting flow pressure by constructing an improved body in the direction in which lateral flow occurs and embedding a tensile reinforcing material inside the improved body. Is going. In other words, these proposals aim to improve economic efficiency by minimizing the scope of improvement, and to suppress large lateral deformation while allowing liquefaction to some extent.

However, for harbor quay walls that serve as supply bases for relief supplies in the event of an earthquake, simply suppressing lateral flow is not a sufficient measure. must be

The effectiveness of liquefaction countermeasures using the chemical injection method was confirmed in the 2011 off the Pacific coast of Tohoku Earthquake, and in Sendai Port in particular, much larger seismic motion than was assumed in the design occurred. However, the quay remained in good condition and operations resumed after a few days.

Based on these findings and the results of model experiments, we have proposed a countermeasure against liquefaction in which the injection pipe functions as an anchor body and a design method thereof as the present invention.

JP 2013-194418 A Japanese Patent No. 5569849

Technical Manual for Permanent Grouting Method, Ground Grouting Development Organization, 2017 Ryozo Yonekura, Shunsuke Shimada, "Recent Trends in Long-term Durability Ground Grouting Method - From Research on Durability of Chemical Injection to Permanent Grout Permanent Grouting Technology -", 2015, Kisoko, Vol.43, No. 10, pp.1-9 Kimihiko Kuboi, Naoaki Suemasa, Tsuyoshi Tanaka, Takamitsu Sasaki, Shunsuke Shimada, "Earthquake stability of sheet pile quay improved by chemical injection method", 2005, 40th Geotechnical Research Conference, pp.1809-1810 Kyohei Ofuji, Naoaki Suemasa, Takamitsu Sasaki, Shunsuke Shimada, "Study on seismic stability of self-supporting steel sheet piles with chemical injection method", 2006, 41st Geotechnical Research Conference, pp.1681-1682

According to Non-Patent Document 1, in the design of liquefaction countermeasures by the chemical injection method, the required liquefaction strength ratio is 0.5 to 1.0 in comparison with level 2 seismic motion, so it is necessary to set the silica concentration of the injection material high. Therefore, it tends to be less economical.

On the other hand, in the inventions described in Patent Document 1 or Patent Document 2, in order to reduce lateral flow due to liquefaction, an improved body is constructed by a chemical injection method in the flow direction, and a tensile reinforcing material is embedded in the improved body. There have been proposals for countermeasures that improve the economic efficiency of However, the invention described in Patent Document 1 or Patent Document 2 has a limited range of improvement and allows a certain degree of liquefaction, so it is not a sufficient countermeasure method for important structures such as harbor facilities and tanks for hazardous materials. do not have.

Figure 1 shows the results of a triaxial cyclic loading test conducted on unimproved sand and chemically improved _sand . positive value), and when the value is about 0.9, brittle axial strain ε occurs. This is generally called a liquefaction phenomenon. On the other hand, with the chemically modified sand, the excess pore water pressure ratio Δu/σ' _c occurs from the initial stage of cyclic loading. There is no such accumulation of pore water pressure.

Also, the axial strain ε also tends to converge to a constant value, although it occurs at the initial stage of loading. As described above, the deformation characteristics of chemically modified sand under repeated loading differ greatly from those of unimproved sand _. stress ratio at which both amplitude strains reach 5% at 20 times), the tenacity to deformation is not evaluated.

In addition, the liquefaction strength ratio R _{L20 (DA = 5%)} has a correlation with the uniaxial compressive strength q _u as shown in Fig. 2, and the liquefaction strength ratio tends to increase as the uniaxial compressive strength increases. Therefore, the setting of design strength and quality control in the current design method are based on unconfined compressive strength.

In addition, in the design of liquefaction countermeasures using the current chemical injection method, the liquefaction safety factor F _L = R / L, which is the liquefaction strength ratio R of the ground divided by the earthquake shear stress ratio L, is set to be 1 or more. do. Therefore, the liquefaction strength R required for level 1 seismic motion is approximately 0.2 to 0.5, and the design strength at this time is 40 to 200 kN/m ² in uniaxial compressive strength q _u .

On the other hand, level 2 seismic motion requires a liquefaction strength ratio R of about 0.5 to 1.0, and the design strength is 200 to 500 kN/m ² in uniaxial compressive strength. Then, in the preliminary compounding test to determine the silica concentration of the injection material to be constructed, the value obtained by multiplying these design strengths by a safety factor of 2.0 is set as the target strength.

Figure 3 shows the relationship between the silica concentration SiO ₂ (%) and the unconfined compressive strength q _u of the grouting material. be.

As shown in Fig. 4, the average grain size _D50 and the relative density _Dr of sand have an effect on this rate of increase. The expression rate of

Therefore, even though the chemical-improved soil does not cause liquefaction, depending on the type and density of the sand and the strength of the design, the improved design may be less economical, or the construction method itself may not be suitable.

The present invention is intended to solve the above-mentioned problems in the conventional technology, and by incorporating the anchor effect of the injection pipe in the liquefaction countermeasure by the chemical injection method, it is possible to economically improve the design against large seismic motion. The purpose is to provide a ground improvement method.

If the unimproved soil has a uniaxial compressive strength of about 50 kN/m ² , the brittle fracture due to liquefaction seen in unimproved sand does not occur. However, the _FL method, which judges liquefaction based on the maximum shear stress ratio that occurs during an earthquake, sets a high target strength.

Therefore, in the present invention, it is assumed that the sand improved by chemical injection has increased adhesion and does not liquefy. In addition, the injection pipe left in the improved ground functions as an anchor body and is expected to resist arc slip, shear deformation, and sliding that are likely to occur due to seismic motion. The method.

That is, the present invention is a chemical injection method for injecting an injection material using an injection pipe inserted into the ground to improve the ground as a countermeasure against liquefaction, in which the injection pipe is inserted into the ground after the injection material is injected into the ground. It is characterized in that deformation of the ground during an earthquake is suppressed by leaving the injection pipe left in the ground and functioning as an anchor.

The injection pipe exhibits an anchoring effect, and as a countermeasure against liquefaction during earthquakes, it is possible to further suppress circular slips, shear deformation, and sliding motions.

The grout is a solution-type silica grout containing non-alkaline silica (registered trademark No. 6322403 of Kaen Soil Engineering Co., Ltd.) as an active ingredient. The non-alkaline silica grout refers to an injection liquid having a pH of 1 to 10 and containing silica colloid and/or water glass as active ingredients.

As the injection pipe, a vinyl chloride pipe, a steel pipe, or the like used in the chemical injection method can be used.

Further, the anchoring effect of the injection pipe can be enhanced by providing a bag at the tip of the injection pipe, filling the bag with a hardening filler, and expanding it in the ground.

In addition, by backfilling the drilled hole formed at the top of the injection pipe with asphalt or concrete together with the injection pipe, the surface layer of asphalt or concrete, the injection pipe, and the improved body made by injecting chemicals are integrated to prevent earthquakes. It is also possible to suppress the deformation of the ground during time.

Furthermore, it is also possible to connect the upper ends of the injection pipes with a tension reinforcing material so that the injection pipes and the improved body by chemical injection are integrated to suppress deformation of the ground during an earthquake.

In the ground improvement method of the present invention, it is possible to design considering the anchor effect according to the tensile strength of the injection pipe, so the design strength of the ground improved by the injection material of the chemical injection method is 200 kN in uniaxial compressive strength. /m ² or less.

In addition, after injecting the injection material into the ground, the injection pipe is left in the ground, and the injection pipe left in the ground functions as an anchor, thereby suppressing the deformation of the ground during an earthquake. As a design method for slabs, a design method can be used in which the unconfined compressive strength of the ground improved by the grouting material is set in consideration of the anchoring effect of the grouting pipe. In that case, as described above, for example, it is possible to design the improved body so that the uniaxial compressive strength is 200 kN/m ² or less.

As the injection pipe used in the ground improvement method of the present invention, a bag is provided at the tip of the injection pipe, and the bag expands in the ground by filling the inside of the bag with a hardening filler. The injection pipe for the ground improvement method can be used, and by expanding in the ground, a high anchor effect can be exhibited.

In the liquefaction countermeasures by the chemical injection method, the present invention enables an economical improvement design against large seismic motion by incorporating the anchor effect of the injection pipe. It can be widely applied to seismic reinforcement and the like.

The conventional design method is the _FL method, which is designed to have sufficient liquefaction strength against the maximum shear stress ratio during an earthquake, so it tends to be less economical. However, according to the present invention, the chemical solution Adhesion is given to the sand by the grouting method, which increases the shear resistance, and the grouting pipe left in the ground functions as an anchor body, which suppresses the deformation of the improved body. It is a method of designing by law. As a result, it is possible to set the concentration of the injection material to a low level, which brings about the effect of improving the economic efficiency and satisfying the required performance in the verification against the level 2 seismic motion.

It is a graph which shows the result of a triaxial cyclic loading test performed on unimproved sand and sand improved with a chemical solution. 4 is a graph showing the relationship between uniaxial compressive strength q _u and liquefaction strength R _L ; 4 is a graph showing the relationship between the silica concentration SiO ₂ (%) of the injection material and the unconfined compressive strength _qu . Fig. 3 is a graph showing the effect of average particle size _D50 and relative density D _r on unconfined compressive strength q _u . It is a sectional view in the case of applying the present invention to a stay pile sheet pile type quay as one embodiment of the present invention. FIG. 10 is an explanatory diagram relating to a method of checking shear resistance using a seismic intensity method in an improved cross section; FIG. 10 is an explanatory diagram relating to a checking method by circular arc sliding in an improved cross section; FIG. 10 is an explanatory diagram of the stress state of the split piece in circular arc sliding in the modified cross section; FIG. 10 is an explanatory diagram relating to a review method for activities in an improved cross section; It is sectional drawing which shows the construction procedure in one Embodiment of this invention. It is a figure which shows the liquefaction countermeasure examination cross section in this invention. 4 is a graph showing the relationship between the unconfined compressive strength q _u and the design horizontal seismic coefficient k _h as a study result. It is a figure which shows the design cross section of the liquefaction countermeasure by chemical|medical solution injection in Sendai Port Nakano district Takamatsu wharf quay implemented in 2007. FIG. This is a photograph showing that liquefaction occurred at the quay walls where liquefaction countermeasures were not taken during the 2011 Tohoku-Pacific Ocean Earthquake. This is a photograph showing that no deformation was observed in the ground behind the quay wall or in the normal line of the quay wall in the ground where chemical injection was performed as a countermeasure against liquefaction during the 2011 Tohoku-Chihou-Taiheiyo-Oki Earthquake.

FIG. 5 shows an embodiment of the present invention, taking a sheet pile quay wall 11 provided with stay piles 12 as an example.
In the drawing, reference numeral 1 denotes an injection tube, and reference numeral 2 denotes a bag provided at the tip of the injection tube 1. As shown in FIG.

The range of liquefaction improvement by chemical injection is the same as in the conventional design method. It is assumed that the working collapse angle is up to the point where it is raised.

As for the installation depth of the injection pipe 1, it is desirable that the tip of the injection pipe 1 penetrates into the non-liquefaction layer and is fixed. If there is no arc slip or sliding, the tip of the injection tube 1 may be kept within the improvement range.

Also, the material of the injection tube 1 to be used can be a vinyl chloride injection tube used in the conventional construction method, and the diameter of the injection tube can be selected for the purpose of expecting a large shear resistance or tensile resistance.

However, if an injection pipe with a large diameter is selected, the drilling process for installing the injection pipe 1 will lengthen the construction period and lower the economic efficiency, so it is useful to use a steel pipe with high rigidity.

In addition, as a method of further enhancing the anchoring effect of the injection tube 1, a bag 2 made of cloth, rubber, vinyl, or the like is provided at the tip of the injection tube, and the bag 2 contains hardening suspension or the like. is pressed in, and the tip of the injection pipe 1 is fixed to the non-liquefaction layer while compacting the ground.

Fig. 6 shows the verification method for shear resistance using the seismic coefficient method in this improved cross section. When horizontal seismic motion k _h is applied to the back ground of sheet pile height H ₁ , a crack of depth H ₂ occurs in the improved body, and shear deformation occurs in a block state of width B.

The weight W of the soil mass at this time is given by Equation (1), and the stress N perpendicular to the slip surface is given by Equation (2). Therefore, the force T _D that causes the soil mass to shear and deform is obtained by equation (3), and the force T _R that resists it is obtained by equation (4).

where, c is the cohesion of the chemically modified soil, φ is the internal friction angle of the modified soil, β is the shear slip angle, σ _T is the tensile strength of the modified soil, n is the number of injection pipes in the shear zone, F is the vertical resistance per injection tube.

The resistance force F per injection tube is
a. pull-out resistance obtained from the frictional force between the improved soil deeper than the sheared surface of the soil mass and the injection pipe,
b. Pull-out resistance obtained from the frictional force between the non-liquefying layer and the injection tube,
c. the pull-out resistance of the enlarged bag body,
anticipate either Also, this resistance force F is compared with the tensile strength of the injection tube, and calculation is performed using the smaller value.

The calculation method uses H ₂ and β as parameters, and determines the adhesive force c so that the safety factor F _s obtained by dividing _TR by _TD becomes 1, as shown in Equation (5).

Here, the internal friction angle φ of the improved soil used for the calculation is not significantly different from that of the unimproved sand, so that value can be used. In addition, the tensile strength σ _T is a value of 1/8 to 1/10 of the unconfined compressive strength q _u of the improved soil, and the unconfined compressive strength is obtained from the geometric conditions in Mohr-Coulomb's failure criterion by formula (6) can ask.

Figures 7 and 8 show the verification method using circular arc slip. are examined by the Fellenius method, the Bishop method, etc.

Fig. 9 shows a method for checking sliding. We will examine the stability against sliding in one direction.

In this way, the stability against shear deformation, circular slip and sliding is examined, and the adhesion force c that can ensure stability for all items is set as the design and construction control reference value.

FIG. 10 shows the construction procedure, which will be explained below.
(a) Drill holes for installation of injection pipes; When using bag anchors, drill holes deeper than the injection target depth.
(b) Insert the injection pipe with the bag attached, cast the seal grout, and pull out the drill pipe.
(c) Inflate the bag by press-fitting a curable filler into the bag anchor.
(d) Crack the sealing material.
(e) Inject the grouting material.
(f) Backfill the drilled hole with pavement so that the pavement, injection pipe and improvement are integrated.

〔Example〕
FIG. 11 is a cross-sectional view of a liquefaction countermeasure. The subject of the study is a pile pile quay with a sheet pile height of 6.75m. The wet density _ρT of the improved soil was set at 20.0 kN/m ³ and the internal friction angle φ was set at 35°. Also, the injection tubes were arranged in a square arrangement with an interval of 1 m, and the pull-out resistance was 20 kN/tube.

In addition, the stability against shear slip proposed in the _FL method and this patent was calculated by the seismic intensity method. In the seismic intensity method, it is assumed that the shear slip angle β coincides with the active collapse angle during an earthquake, and β = 60° here.

As a result of the study, Fig. 12 shows the relationship between the unconfined compressive strength q _u and the design horizontal seismic coefficient k _h . Under conditions where the unconfined compressive strength _is relatively low, the required unconfined compressive strength is about the same as the design horizontal seismic coefficient. A high uniaxial compressive strength is required. On the other hand, with the seismic coefficient method, the necessary unconfined compressive strength is lower than that with the _FL method for the same design horizontal seismic coefficient. It becomes possible to set the tension to 200 kN/m ² or less.

Fig. 13 shows a design cross-section of a liquefaction countermeasure implemented in 2007 by injecting chemicals at the quay wall of Takamatsu Wharf in the Nakano district of Sendai Port. The design horizontal seismic coefficient k _h in this improvement work was 0.25, and the unconfined compressive strength was 50 kN/m ² as a control standard value.

During the 2011 off the Pacific coast of Tohoku Earthquake, seismometers near the improved ground measured accelerations of 400 to 1,000 gal. is occurring. On the other hand, in the ground where the chemical solution was injected, although the seismic motion far exceeded the design, as shown in Fig. 15, no deformation was observed in the ground behind the quay or in the normal line of the quay.

In this way, one of the reasons why no ground deformation was observed despite the occurrence of the assumed seismic motion was the effect of suppressing shear deformation of the injection pipe.

1... injection tube, 2... bag body,
11... sheet pile quay, 12... stay pile

Claims (11)

In the chemical injection method of injecting the injection material using the injection pipe inserted into the ground to improve the ground as a countermeasure against liquefaction, after the injection material is injected into the ground, the injection pipe is left in the ground, and the ground is A ground improvement method characterized in that deformation of the ground during an earthquake is suppressed by making the injection pipe left inside function as an anchor. 2. A ground improvement method according to claim 1, wherein said solution-type grouting material is a solution-type grouting material containing non-alkali silica grout as a main ingredient. 3. A ground improvement method according to claim 1 or 2, wherein said injection pipe is a vinyl chloride pipe. 3. A ground improvement method according to claim 1 or 2, wherein said injection pipe is a steel pipe. In the ground improvement method according to any one of claims 1 to 4, a bag is provided at the tip of the injection pipe, and the bag is filled with a hardening filler and expanded in the ground. A ground improvement method characterized in that the anchor effect is enhanced by In the ground improvement method according to any one of claims 1 to 5, the drilling hole formed at the top end position of the injection pipe is backfilled with asphalt or concrete integrally with the injection pipe, so that the asphalt or A ground improvement method characterized by suppressing deformation of the ground during an earthquake by integrating the surface layer of concrete, the injection pipe, and the improved body by injection of chemical solution. The ground improvement method according to any one of claims 1 to 6, wherein the upper ends of the injection pipe are connected with a tension reinforcing material, and the injection pipe and the improved body by chemical injection are integrated to deform the ground during an earthquake. A ground improvement method characterized by suppressing the The ground improvement method according to any one of claims 1 to 7, wherein the design strength of the ground improved by the injection material is set to be 200 kN/m ² or less in uniaxial compressive strength. ground improvement method. In the chemical injection method of injecting an injection material using an injection pipe inserted into the ground to improve the ground as a countermeasure against liquefaction, after the injection material is injected into the ground, the injection pipe is left in the ground, A design method for a ground improvement method that suppresses deformation of the ground during an earthquake by making the injection pipe left in the ground function as an anchor, wherein the uniaxial compression of the ground improved by the injection material A design method for a ground improvement method, characterized in that the strength is set in consideration of the anchor effect of the injection pipe. 10. The design method for a ground improvement method according to claim 9, wherein the unconfined compressive strength is set to 200 kN/m ² or less. An injection pipe used in the ground improvement method according to claim 5, wherein a bag is provided at the tip of the injection pipe, and by filling the inside of the bag with a hardening filler, the bag An injection pipe for a ground improvement method, characterized in that the body is made to expand in the ground.

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