JP7385849B2 - Ground improvement method - Google Patents

Description

The present invention relates to a ground improvement method as a measure against liquefaction that takes into account the anchor effect of injection pipes used in chemical injection methods.

As one of the ground improvement methods aimed at preventing liquefaction, a chemical injection method using a solution type injection material whose main ingredient is non-alkali silica grout is generally known. In liquefaction countermeasures using 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.

In particular, in recent years, consideration has been given to level 2 earthquake motion, so the liquefaction strength ratio required as a liquefaction countermeasure is 0.5 to 1.0, and the design strength is 200 to 500 kN/ ^m2 in unconfined compressive strength, so the safety factor is The target strength in the pre-mixing test multiplied by (2.0) is 400 to 1,000 kN/ ^m2 .

In order to satisfy this target indoor strength, the silica concentration of the injection material must be 8% or more, which may increase the construction cost or may not satisfy the target even if the silica concentration is set high.

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

However, for port quays, which serve as supply bases for relief supplies in the event of an earthquake, simply suppressing lateral flow is not a sufficient countermeasure. must be done.

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

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

Japanese Patent Application Publication No. 2013-194418 Patent No. 5569849

Permanent grouting method technical manual, Ground Injection Development Organization, 2017 Ryozo Yonekura, Shunsuke Shimada, "Recent trends in long-term durable ground grouting methods - Prospects from research on the durability of chemical injection to permanent grouting technology," Foundation Engineering, Vol. 43, No. 2015. 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 Engineering Research Conference, pp. 1809-1810 Kyohei Ofuji, Naoaki Suemasa, Takamitsu Sasaki, Shunsuke Shimada, "Research on seismic stability of self-supporting steel sheet piles treated with chemical injection method", 2006, 41st Geotechnical Research Conference, pp. 1681-1682

According to Non-Patent Document 1, when designing liquefaction countermeasures using the chemical injection method, the required liquefaction intensity ratio is 0.5 to 1.0 in a check against level 2 earthquake motion, so it is necessary to set the silica concentration of the injection material high. Therefore, economic efficiency tends to decline.

In contrast, in the invention described in Patent Document 1 or Patent Document 2, in order to reduce lateral flow due to liquefaction, an improved body is constructed using a chemical injection method in the flow direction, and a tensile reinforcing material is embedded in the improved body. Countermeasures with improved economic efficiency have been proposed. However, the invention described in Patent Document 1 or Patent Document 2 has a limited scope of improvement and allows some degree of liquefaction, so it cannot be said to be a sufficient countermeasure for important structures such as port facilities and hazardous materials tanks. do not have.

Figure 1 shows the results of a triaxial cyclic loading test conducted on unimproved sand and sand improved with chemical _solutions . (positive value), and when the value reaches approximately 0.9, axial strain ε occurs in a brittle manner. This is generally called the liquefaction phenomenon. On the other hand, in chemically modified sand, an excess pore water pressure ratio Δu/σ' _c occurs from the beginning of repeated loading, but it shows a positive value on the compression side and a negative value on the tension side in the loading direction, and it shows a negative value on the tension side. There is no accumulation of pore water pressure.

Furthermore, although the axial strain ε also occurs at the initial stage of loading, it tends to converge to a constant value. In this way, the deformation characteristics of chemically modified sand due to repeated loading are significantly different from those of unimproved sand, and even though liquefaction has not occurred, the liquefaction strength ratio R _{L20 (DA = 5%)} (number of repeated loadings) (stress ratio at which both amplitude strain reaches 5% after 20 cycles), the tenacity against deformation is not evaluated.

In addition, the liquefaction strength ratio R _{L20 (DA=5%)} has a correlation with the unconfined compressive strength q _u as shown in Figure 2, and the liquefaction strength ratio tends to increase as the unconfined compressive strength increases. Therefore, design strength settings and quality control in current design methods are performed using 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 seismic shear stress ratio L, is set to be 1 or more. do. Therefore, the liquefaction strength R required for level 1 earthquake motion is approximately 0.2 to 0.5, and the design strength at this time is 40 to 200 kN/m ² in unconfined compressive strength q _u .

On the other hand, for level 2 earthquake motion, the liquefaction strength ratio R is required to be approximately 0.5 to 1.0, and the design strength is 200 to 500 kN/m ² in unconfined compressive strength. In the pre-mixing test to determine the silica concentration of the injection material to be applied, the target strength is the value obtained by multiplying these design strengths by a safety factor of 2.0.

Figure 3 shows the relationship between the silica concentration SiO ₂ (%) of the injection material and the unconfined compressive strength _q u.As the silica concentration increases, the unconfined compressive strength increases, but the rate of increase tends to differ depending on the sand. be.

As shown in Figure 4, the influence on this increase rate includes the average grain size _D50 and relative density _Dr of the sand, and as the average grain size increases and the relative density decreases, the strength The expression rate of

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

The present invention aims to solve the above-mentioned problems in the conventional technology, and by incorporating the anchor effect of the injection pipe in liquefaction countermeasures using the chemical injection method, it is possible to achieve an economical improved design against large seismic motions. The purpose is to provide a ground improvement method.

If the unimproved soil has an unconfined compressive strength of about 50 kN/m ² , the brittle fracture caused by liquefaction that occurs with unimproved sand will not occur. However, in the F _L method, which determines liquefaction based on the maximum shear stress ratio that occurs during an earthquake, the target strength is set high.

Therefore, in the present invention, it is assumed that sand improved by chemical injection has increased adhesive strength and no liquefaction phenomenon occurs. Furthermore, this is a construction method in which the injection pipe left in the improved ground is expected to function as an anchor body and resist circular slip, shear deformation, and sliding that are likely to occur due to seismic motion, and this is a design that is verified using the seismic intensity method. It's a method.

That is, the present invention relates to a chemical injection method in which the injection material is injected using an injection pipe inserted into the ground to improve the ground as a countermeasure against liquefaction. The injection pipe left in the ground functions as an anchor to prevent the ground from deforming during an earthquake.

By exerting the anchor effect of the injection pipe, it is possible to further prevent circular sliding, shear deformation, and sliding as a construction method to prevent liquefaction during earthquakes.

The injection liquid is a solution-type silica grout containing non-alkali silica (Registered Trademark No. 6322403 of Reinforced Earth Engineering Co., Ltd.) as an active ingredient. Non-alkali silica grout refers to an injection solution with a pH of 1 to 10 that contains one or more of silica colloid and water glass as active ingredients.

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

Furthermore, 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, the asphalt or concrete surface layer, the injection pipe, and the improved body made by chemical injection can be integrated to prevent earthquakes. It is also possible to suppress the deformation of the ground over time.

Furthermore, the upper ends of the injection pipes may be connected to each other with a tensile reinforcing material, so that the injection pipe and the improved body formed by injection of chemical liquid 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 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 unconfined compressive strength. /m ² or less.

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

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

The present invention enables an economical improved design against large seismic motions by incorporating the anchoring effect of injection pipes in liquefaction countermeasures using the chemical injection method. It can be widely applied to earthquake reinforcement, etc.

The conventional design method is the F _L method, which tends to be less economical because it is designed to have sufficient liquefaction strength against the maximum shear stress ratio during an earthquake.However, according to the present invention, the chemical liquid The injection method gives adhesive force to the sand, increasing shear resistance, and the injection pipe left in the ground functions as an anchor body, which prevents deformation of the improved body. This is a method of designing according to the law. As a result, the concentration of the injection material can be set low, resulting in improved economic efficiency and the ability to satisfy the required performance in the verification of level 2 seismic motion.

It is a graph showing the results of a triaxial cyclic loading test conducted on unimproved sand and sand improved with a chemical solution. It is a graph showing the relationship between uniaxial compressive strength q _u and liquefaction strength R _L . It is a graph showing the relationship between the silica concentration SiO ₂ (%) of the injection material and the unconfined compressive strength q _u . It is a graph showing the influence of average particle diameter D ₅₀ and relative density _Dr on unconfined compressive strength q _u . It is a sectional view in the case of applying the present invention to a pile pile type quay wall as one embodiment of the present invention. FIG. 7 is an explanatory diagram regarding a method of checking shear resistance using a seismic intensity method in an improved cross section. FIG. 7 is an explanatory diagram regarding an inspection method using arcuate sliding in an improved cross section. FIG. 6 is an explanatory diagram of the stress state of the divided pieces during arcuate sliding in the improved cross section. FIG. 7 is an explanatory diagram regarding a verification method for activities in an improved cross section. It is a sectional view showing a construction procedure in one embodiment of the present invention. FIG. 3 is a diagram showing a cross-section for studying liquefaction countermeasures in the present invention. It is a graph showing the relationship between uniaxial compressive strength q _u and design horizontal seismic intensity k _h as a result of the study. FIG. 2 is a diagram showing a cross-section of the design of liquefaction countermeasures by chemical injection at the quay of Takamatsu Wharf in the Nakano area of Sendai Port, which was implemented in 2007. This photo shows liquefaction occurring on a quay where no liquefaction countermeasures were taken during the 2011 Tohoku Pacific Coast Earthquake. This photo shows that no deformation was observed in the ground behind the quay or in the normal line of the quay in the ground where chemical liquid was injected as a measure against liquefaction during the 2011 Tohoku Pacific Coast Earthquake.

An embodiment of the present invention is shown in FIG. 5, taking as an example a sheet pile type quay 11 equipped with retaining piles 12.
In the figure, reference numeral 1 indicates an injection tube, and reference numeral 2 indicates a bag provided at the tip of the injection tube 1.

The scope of improvement for liquefaction by chemical injection is the same as that of the conventional design method, and the depth direction targets the layer with the possibility of liquefaction, and the depth direction of the back side of the sheet pile is aimed at Let the working decay angle be up to the point where it started.

In addition, the installation depth of the injection pipe 1 should preferably be such that the tip of the injection pipe 1 penetrates into the non-liquefaction layer and is fixed, but as a result of inspection, it was found that shear deformation occurs between the non-liquefaction layer and the improved ground. If no arc-like sliding or sliding occurs, the tip of the injection tube 1 may be kept within the improved range.

Further, as the material of the injection tube 1 to be used, the injection tube made of vinyl chloride used in conventional construction methods can be used, and the diameter of the injection tube can be selected in order to expect 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 reduce economic efficiency, so it is useful to use a steel pipe with high rigidity.

In addition, as a method to further enhance the anchoring effect of the injection tube 1, a bag body 2 made of cloth, rubber, vinyl, etc. is provided at the tip of the injection tube, and this bag body 2 is filled with a hardening suspension. The tip of the injection pipe 1 is fixed to the non-liquefaction layer while compacting the ground.

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

The weight W of the clod at this time is expressed by equation (1), and the stress N perpendicular to the sliding surface is expressed by equation (2). Therefore, the force T _D that tends to shear deform the soil mass is determined by formula (3), and the force T _R that resists this is determined by formula (4).

Here, c is the adhesive force of the chemically improved soil, φ is the internal friction angle of the improved soil, β is the shear slip angle, σ _T is the tensile strength of the improved soil, n is the number of injection pipes in the shear area, F is the vertical resistance force per injection tube.

The resistance force F per injection tube is
a. The pull-out resistance obtained from the frictional force between the improved soil below the shear surface of the soil clod and the injection pipe,
b. Pull-out resistance obtained from the frictional force between the non-liquefied layer and the injection tube,
c. The pull-out resistance of the enlarged bag,
Anticipate either. Further, this resistance force F is compared with the tensile strength of the injection tube, and the 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 T _D becomes 1, as shown in equation (5).

Here, since the internal friction angle φ of the improved soil used for calculation is not significantly different from that of unimproved sand, that value can be used. In addition, the tensile strength σ _T is set to 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 determined by equation (6) from the geometric conditions in the Mohr-Coulomb failure criterion. You can ask for it.

Figures 7 and 8 show the verification method using arcuate slip, but the stress state generated on the slip surface in one segment of arcuate slip is the same as Equation (3) and Equation (4) used in the verification of shear deformation; Examinations are performed using the Fellenius method, Bishop method, etc.

Figure 9 shows a method for checking sliding, and the friction resistance of the bottom of the improved body obtained from the weight of the improved body and the anchor effect of the injection pipe are The stability against sliding in the opposite direction will be investigated.

In this way, the stability against shear deformation, circular sliding, and sliding is checked, and the adhesive strength c that ensures stability in all items is determined as the standard value for design and construction management.

FIG. 10 shows the construction procedure, which will be explained next.
(a) Drill a hole to install the injection pipe. Note that when using a bag anchor, the hole is drilled deeper than the target depth for injection.
(b) Insert the injection pipe with the bag attached, apply seal grout, and pull out the drilling pipe.
(c) Press-fit a hardening filler into the bag anchor and inflate the bag.
(d) Cracking the sealing material.
(e) Inject the injection material.
(f) Backfill the drilled holes with paving material so that the paving, injection pipe, and improvement body are integrated.

〔Example〕
Figure 11 is a cross-sectional view of the study of liquefaction countermeasures. The object of consideration is a pile-type sheet pile quay with a sheet pile height of 6.75 m. In addition, the wet density _ρT of the improved soil was 20.0 kN/m ³ and the internal friction angle φ was 35°. In addition, the injection pipes were arranged in a square arrangement with an interval of 1 m, and the pulling resistance was 20 kN/tube.

In addition, the stability against shear slippage proposed in this patent was calculated using the F _L method and the seismic intensity method, and the presence or absence of the anchor effect of the injection pipe was also calculated using the seismic intensity method. In addition, in the study using the seismic intensity method, it was assumed that the shear slip angle β coincided with the active collapse angle during an earthquake, and here β = 60°.

As a result of the study, Figure 12 shows the relationship between the uniaxial compressive strength q _u and the design horizontal seismic intensity k _h . Under conditions where the uniaxial compressive strength is relatively low, the required uniaxial compressive strength is the same as the design horizontal seismic intensity, but in the range of design horizontal seismic intensity of 0.5 or higher where level 2 earthquake motion is expected, the F _L method is used. High unconfined compressive strength is required. On the other hand, when using the seismic intensity method, the required unconfined compressive strength is lower than that using the F _L method for the same design horizontal seismic intensity; It becomes possible to set the strength to 200kN/ ^m2 or less.

Figure 13 is a design cross-section of the liquefaction countermeasures implemented in 2007 by chemical injection at the Takamatsu Wharf quay in the Nakano area of Sendai Port. The design horizontal seismic coefficient k _h for this improvement work was 0.25, and the unconfined compressive strength was 50 kN/m ² as a management standard value.

During the 2011 off the Pacific coast of Tohoku Earthquake, seismometers near the improved ground measured accelerations of about 400 to 1,000 gal, and as shown in Figure 14, liquefaction occurred on quays where no liquefaction countermeasures had been taken. is occurring. On the other hand, although the ground where the chemical solution was injected was subjected to seismic motion that far exceeded the design, no deformation was observed in the ground behind the quay or in the normal line of the quay, as shown in Figure 15.

One of the reasons why no ground deformation was observed despite the expected earthquake motion is that the injection pipe had a suppressive effect on shear deformation.

1... Injection tube, 2... Bag body,
11...Sheet pile type quay, 12...Support pile

Claims (10)

In the chemical injection method, which improves the ground as a liquefaction countermeasure by injecting an injection material using an injection pipe inserted into the ground, the tip of the injection pipe is penetrated to the non-liquefaction layer, and the injection material is poured into the ground. After the injection, the injection pipe is left in the ground, and the injection pipe itself left in the ground functions as an anchor body, thereby suppressing deformation of the ground during an earthquake. Improved construction method. 2. The ground improvement method according to claim 1 , wherein the injection pipe is a vinyl chloride pipe. 2. The ground improvement method according to claim 1 , wherein the injection pipe is a steel pipe. In the ground improvement method according to any one of claims 1 to 3 , a bag is provided at the tip of the injection pipe, and a hardening filler is filled in the bag and expanded in the ground. A ground improvement method characterized by increasing the anchoring effect. In the ground improvement method according to any one of claims 1 to 4 , by backfilling the drill hole formed at the top end of the injection pipe with asphalt or concrete together with the injection pipe, the asphalt or A ground improvement method characterized in that the surface layer of concrete, the injection pipe, and the improvement body formed by injecting a chemical solution work together to suppress deformation of the ground during an earthquake. The ground improvement method according to any one of claims 1 to 5 , characterized in that the upper ends of the injection pipes are connected to each other by a tensile reinforcing material. The ground improvement method according to any one of claims 1 to 6 , characterized in that the design strength of the ground improved by the injection material is set to be 200 kN/m ² or less in unconfined compressive strength. Ground improvement method. In the chemical injection method, which improves the ground as a liquefaction countermeasure by injecting an injection material using an injection pipe inserted into the ground, the tip of the injection pipe is penetrated to the non-liquefaction layer, and the injection material is poured into the ground. A design for a ground improvement method in which the injection pipe is left in the ground after injection into the ground, and the injection pipe itself left in the ground functions as an anchor body to suppress deformation of the ground during an earthquake. 1. A design method for a ground improvement method, characterized in that the unconfined compressive strength of the ground improved by the injection material is set in consideration of the anchor effect of the injection pipe. 9. The design method for a ground improvement method according to claim 8 , wherein the unconfined compressive strength is set to be 200 kN/m ² or less. 5. The injection pipe used in the ground improvement method according to claim 4 , wherein a bag is provided at the tip of the injection pipe, and the bag is filled with a hardening filler. An injection pipe for use in ground improvement methods, characterized in that its body expands within the ground.