JP2009203678A - Soil improvement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soil improvement method for improving the liquefied layer of a sand ground at low cost. <P>SOLUTION: In this soil improvement method, chemical injection holes 2 are excavated in the sand ground under a paved road bed 13, a chemical is injected through the chemical injection holes 2 and an improvement ratio is changed for each improvement depth until the sand ground 1 just below the paved road bed 13 is improved at an improvement factor of 100%. The improvement factor is further lowered as the depth is larger. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a ground improvement method.

The conventional ground improvement method for sandy ground using a chemical solution for liquefaction countermeasures was to inject the chemical solution at a depth of 20 m from the groundwater surface, thereby replacing the sand gaps in these layers with the chemical solution. In other words, the liquefaction of sandy ground due to the earthquake was prevented by injecting the chemical solution at an improvement rate of 100%. This was a method of improving all the liquefied layers of sandy ground. As another ground improvement method, there is an invention of JP-A-2004-346636.
JP 2004-346636 A

  However, the above-mentioned ground improvement method improves all the 20m from the groundwater surface, and there is a problem that the cost is high because all the gaps of sand in this liquefied layer and the same amount of chemicals are injected into the sandy ground. there were.

  The present invention has been made in view of the above problems, and its purpose is to improve the ground improvement method that can improve the liquefied layer at low cost, that is, to improve all the liquefied layer of the sandy ground. Instead, by improving the structure to the extent that the structure can be formed, the deformation due to softening of the ground is prevented, the original rigidity of the ground is maintained, and consolidation settlement caused by drainage of excess pore water to the ground surface is prevented. It is to provide a ground improvement method.

の式で算定される地盤の液状化指数であるＰ_Ｌ値が、一定の値以下になるように改良率αを設定することを含む。またＰ_Ｌ値を求める際に使用される、Ｆ_Ｌ＝Ｒ／Ｌ（Ｒ：地盤の液状化強度比、Ｌ：地震時の地盤内部のせん断応力比）の式で算定される液状化に対する安全率であるＦ_Ｌ値については、未改良時のＦ_Ｌ値に（１一Ｆ_Ｌ）×改良率αを加算して算定することを含むものである。よって、

The ground improvement method to solve the above problems is to drill a chemical injection hole in the sandy ground below the paved roadbed, inject the chemical solution from the chemical injection hole and change the improvement rate for each improvement depth. The sandy ground directly under the roadbed is improved at an improvement rate of 100%, and the improvement rate decreases as the depth increases. Further, the improvement rate that decreases as the depth increases includes a minimum of 53%. Further, when the improvement rate α is lowered as the depth x increases,

P _L value is a liquefaction index of the ground which is calculated by the formula comprises setting the improvement ratio α to be less than a certain value. In addition, the safety against liquefaction calculated by the formula of F _L = R / L (R: ratio of liquefaction strength of the ground, L: ratio of shear stress in the ground during an earthquake) used when calculating the P _L value The F _L value, which is a rate, includes calculating by adding (1 1 F _L ) × improvement rate α to the F _L value when not improved. Therefore,

  Here, the improvement rate α refers to a ratio of an improved region (improved body) in an improved region of a certain cube. Therefore, when the chemical solution is injected into the sandy ground in the improved area, an almost spherical improved body is formed around the injection point. Therefore, when the minimum of the improvement rate α that decreases as the depth becomes deeper is set to 53%, The improved bodies can be in contact with each other to form a structure that can maintain the original rigidity of the ground. However, when the improvement rate α is less than 53%, adjacent spherical improvement bodies do not come into contact with each other.

The improved body a having an improvement rate of 53% is formed in a substantially spherical shape around the injection point as shown in FIG. 1 (1) when a chemical solution having a specific gravity similar to that of water is injected into the saturated ground. Can be confirmed.
As an example of confirming the shape of the improved body a in the soil, it has also been confirmed from an improved form after excavation in an in-situ injection experiment using special silica conducted by the present applicant in Matsuzaka, Mie Prefecture in 2000. Therefore, when the chemical solution is injected from the center of the improved region M having the same vertical, horizontal, and height, as shown in (2) of FIG. 1, an improved body a having an improvement rate of 53% in contact with the boundary of the improved region M is obtained. It is formed.

  Since the improvement bodies a having such an improvement rate of 53% are connected to each other, the force acting on a part of the improvement region is dispersed inside the structure b ((1) in FIG. 2). reference). On the contrary, in a group of improved bodies a of less than 53%, the improved bodies a are not in contact with each other and are independent, so that the structural body b is not formed. Therefore, the force acting on the improved region is not dispersed, and the improved region is greatly deformed (see (2) in FIG. 2).

The P _L values for setting the improvement ratio α of the layer between the improvement ratio from 100 to 53%, refers to the liquefaction index of the ground, is calculated by the following equation.

The P _L values when the liquefaction occurs, has been found to correlate with the amount of deformation of nearby ground surface. Therefore, the F _L value used in determining the P _L value, in the case of improvement of 100% for liquefaction does not occur, the F L _{= 1.} From this _{F L} value refers to a safety factor against liquefaction _is calculated by F L = R / L. Here, R is the liquefaction strength ratio of the ground, and L is the shear stress ratio inside the ground at the time of the earthquake.

However, when the improvement rate is less than 100%, liquefaction occurs in a part of the improvement region, so there is currently no _FL value setting procedure. So the case of examining the relationship between improvement rate and subsidence of the uniform soil improvement rate of less than 100% Shaking experiments, the improvement rate in soil under improvement ratio L00%, improved after the (1-F _L was determined a relationship between the subsidence of the value) ground surface, as shown in FIG. 3, F _L value and subsidence of the improved it has been found that almost proportional.

This result F _L values of ground improvement of less than 100% would in F _L value while not improve (1 one F _L value) × improvement ratio α may be added. Thus, when in the case of improvement of 100% of _{F L} values of unmodified and _{F L} 0, _{F L} value after the modification is _F L 0+ (1 one _F L 0) × 100%, i.e. 1.0. When the improvement rate is 53%, F _L 0+ (1 1 F _L 0) × 53% = 0.53 (1 + F _L ).

Therefore, setting of the improvement ratio is set by using the P _L value is a liquefaction index. For example, in the case of improvement ratio 100%, F _L value is a safety factor against liquefaction, it is greater than F _L values of unmodified value satisfies "1". In the case of improvement ratio 50% to 70%, since the shear strength increases, becomes greater than the original F _L values, F _L value does not improve to "l". Therefore (1 one F _L value) between the F _{L =} l of F _L value and the full improvement value before improvement × improvement ratio α only, calculates the P _L value as to increase from the original F _L value.

Thus the improvement ratio, P _L value is a liquefaction index is set to be below "5". If this P _L value is "5" or less, but the effect on the ground surface, such as a subsidence can be reduced, because the impact on the ground surface, such as a subsidence exceeds "5" is increased. Therefore, P _L value of the order to suppress the influence of the earth's surface is the target the following "5".

  The ground improvement method by injecting chemical liquid into the gap of sandy ground prevents the increase of excess pore water pressure at the time of earthquake by substituting the pore water of the sand in the ground with jelly-like chemical liquid, It is to maintain the original rigidity and to prevent the excess pore water in the surrounding unimproved ground generated by the earthquake from being transmitted to the ground surface in the improved range and deforming it. Therefore, if the ground can be improved at an improvement rate of 53% to the extent that a structure can be formed, the ground can maintain its original rigidity even when the surrounding ground is liquefied. Further, by setting the improvement rate of the ground near the ground surface to 100%, it is possible to prevent the influence of excess pore water on the ground surface. Moreover, even if the surrounding ground and the ground immediately below the improved area are softened by liquefaction, the improved body formed on the lower side of the paved roadbed floats in the liquefied area, so the pavement surface does not deform. In addition, excess pore water generated in the surrounding unimproved ground is not transmitted to the ground surface because there is an improved layer with an improvement rate of 100% having poor water permeability between the ground surface and the ground surface. For this reason, the outfitting roadbed is not easily affected by deformation due to liquefaction. In addition, without improving the entire liquefied layer, because it was limited to the improvement of the portion close to the ground surface, which has a large effect on the paved roadbed, the improvement cost was reduced to about 1/2-1/4 compared to the overall improvement, At the same cost, the ground can be improved 2 to 4 times longer than conventional methods.

  Hereinafter, embodiments of the ground improvement method of the present invention will be described in detail with reference to the drawings. The present invention is intended to improve the sandy ground below the runway or the paved roadbed of the road, and in the present embodiment, the runway will be described.

  4-7 is embodiment of a ground improvement construction method. This ground improvement method reduces the improvement rate as the depth increases, but the improvement rate of the ground at a depth of 2 m from the groundwater surface directly under the runway is 100%. This is to prevent excess pore water in the surrounding unimproved ground generated by the earthquake from being transmitted to the ground surface in the improved area and deforming the ground surface. That is, an improvement layer having an improvement rate of 100% with poor water permeability is formed between the ground surface and the excess pore water so as not to be transmitted to the ground surface.

Then, set in the improvement ratio of the lower layer of the improvement ratio L00% improvement layer, i.e. the range improvements of the layer between the 100-53% P _L value is less than "5". In this example, various combinations (simulations) are performed in advance to set the best improvement rate, but in this embodiment, it is set to 70%. P _L value in this case was calculated by the following equation.

Assume _{F L} values to a depth (GL) l~3m before improvement and 0.9 here. Further up the depth 0~2m improved 100%, up to a depth 2~4m improvement rate of 70% is calculated _{P L} value as an improvement up to a depth 4~6m in improved 53%. Accordingly, the lower layer is improved to 53%, the intermediate layer is improved to 70%, and the uppermost layer is improved to 100%. It shows a calculation table of P _L value after improvement before and this improved below.

  Next, after performing the simulation as described above, the ground improvement in the lowermost layer is performed. First, as shown in (1) of FIG. 4, a chemical solution having a depth of 6 m from the groundwater surface is injected into the sandy ground 1. Hole 2 is l. Drilling at a pitch of 5-2m. This pitch is such that spherical improvement bodies with an improvement rate of 53% can contact each other. Then, a strainer type injection tube 3 is inserted into the chemical solution injection hole 2 to inject a silica-based aqueous solution type chemical solution 4.

As this silica-based aqueous solution type chemical solution 4, Na ₂ O / nSiO ₂ or K ₂ O / nSiO ₂ which is a raw material for producing so-called “water glass”, and inorganic salts, organic salts, metal oxides which are curing agents thereof. Products, metal hydroxides, inorganic acids, organic acids, acid salts, metal oxides, metal hydroxides, basic salts, etc., as well as special silica solutions and their curing agents such as phosphoric acid is there.

  From the groundwater surface to the sandy ground 1 at a depth of 6 m, a chemical solution 4 having an improvement rate of 53%, that is, a chemical solution 4 having a silica content concentration of 1 to 8% and an injection rate set to 10 L / min. When injected, as shown in (2) of FIG. 4, a semi-improved layer 6 in which spherical improved bodies 5 overlap each other in the horizontal direction is formed. Whether or not the spherical improvement body 5 has been formed is confirmed by sampling such as boring. Thus, when the improvement rate is 53%, the adjacent spherical improvement bodies 5 are in contact with each other and entangled with each other, but when the improvement rate is less than 53%, the adjacent spherical improvement bodies 5 are not in contact with each other.

  Next, an improved ground of the intermediate layer is formed. The strainer type injection pipe 3 is pulled up to the sandy ground 1 above the semi-improved layer 6, that is, 4 m deep from the groundwater surface, with an improvement rate of 70%. As shown in FIG. 5, the overlapping range becomes large and becomes a box shape (cube) when the chemical solution 4, that is, the chemical solution concentration of 1 to 8% and the injection speed is set to 10 L / min. An intermediate improvement layer 8 made of the formed improvement body 7 is formed. Thus, when the improvement rate is 70%, the overlapping range of the spherical improvement bodies becomes large, so that the improvement bodies are formed in a shape close to a box shape. And the lower part of the improvement body 7 of the intermediate | middle improvement layer 8 and the upper part of the spherical improvement body 5 of the semi-improvement layer 6 mutually overlap, and are united up and down.

  Next, the strainer type inlet pipe 3 is further pulled up to the upper side of the intermediate improvement layer 8, that is, to the sandy ground 1 having a depth of 2 m from the groundwater surface, and the chemical solution, that is, the chemical solution concentration is set to 1 When the chemical solution 4 with ˜8% and the injection speed set at 10 L / min is injected, as shown in FIG. 6, a uniform and integrated whole surface improvement layer 10 in which the complete improvement bodies 9 are closely overlapped in the horizontal direction is formed. Is done. When the improvement rate becomes 100% in this way, the overlapping range of the spherical improvement bodies 5 is greatly increased, and the spherical improvement body 5 does not retain its original shape. And the lower part of the complete improvement body 9 of the whole surface improvement layer 10 and the upper part of the box-shaped improvement body 7 overlap each other and are united vertically.

  Accordingly, as shown in FIG. 7, an improved layer 11 in which the semi-improved layer 6, the intermediate improved layer 8, and the entire improved layer 10 are integrated vertically is formed over the entire length below the runway 12. A rigged roadbed 13 is formed on the upper surface of the improvement layer 11 with concrete or asphalt.

  When the improvement rate is lowered as the depth increases, the improvement layer 11 that does not liquefy is formed on the sandy ground l in the range of 2 to 6 m from the groundwater surface. For example, immediately below the surrounding ground and the improvement range. Even if the ground is softened by liquefaction, the ground below the runway can be maintained at its original rigidity, and excess pore water can be prevented from being transmitted to the ground surface.

  Moreover, although the said improvement rate made 70% between l00 to 53%, this is not restricted to 70%, and if it is between l00 to 53%, it may be 70% or more or less than 70%.

  In this embodiment, the chemical injection hole 2 is excavated from the upper surface of the sandy ground l. However, the chemical injection hole 2 is excavated from the existing runway pavement 13 or the existing runway is paved. It is also possible to excavate from the side surface (slope) of the roadbed 13.

(1) is a perspective view of an improved body with an improvement rate of 53%, and (2) is a plan view in which the improved bodies with an improvement rate of 53% are in contact with each other. (1) is a front view of a structure made of an improved body having an improvement rate of 53%, and (2) is a front view of an improved body having an improvement rate of less than 53%. It is a graph of the relationship between the (1- _FL value) after improvement and the amount of settlement. (1) is a cross-sectional view in the vertical direction of the semi-improved layer, and (2) is a cross-sectional view taken along line AA of (1). (1) is a cross-sectional view in the vertical direction of the intermediate improvement layer, and (2) is a cross-sectional view along line B-B in (1). (L) is a sectional view in the vertical direction of the completely improved layer, and (2) is a sectional view taken along the line CC of (1). (1) is a vertical sectional view of an improved layer formed by the ground improvement method, and (2) is a perspective view thereof.

Explanation of symbols

M Improvement area a Improvement body b Structure 1 Sandy ground 2 Chemical solution injection hole 3 Strainer type injection tube 4 Chemical solution 5 Spherical improvement body 6 Semi-improvement layer 7, 15, 17, 19 Box-shaped improvement body 8 Intermediate improvement layer 9 Completely improved body 10 Entirely improved layer 11, 21 Improved layer 12 Runway 13 Pavement roadbed

Claims (4)

  Drilling a chemical injection hole in the sandy ground below the paved roadbed, injecting the chemical liquid from the chemical injection hole and changing the improvement rate according to the improvement depth, the sandy ground directly under the paved roadbed with an improvement rate of 100% A ground improvement method that improves and lowers the improvement rate as the depth increases.   The ground improvement method according to claim 1, wherein the improvement rate that decreases as the depth increases is 53% at a minimum. When reducing the improvement rate α as the depth x increases,

Ground improvement method according to claim l where P _L value is a liquefaction index of the ground which is calculated by the formula of and sets the improvement ratio α to be less than a certain value. P _L value is used to determine _{the, F L = R / L (} R: liquefaction intensity ratio of the ground, L: shear stress ratio of ground inside during an earthquake) safety factor against liquefaction is calculated by the formula for F _L value is, ground improvement method according to claim 3, characterized in that to calculate by adding the F _L value during unmodified (l-F _L) × improvement ratio alpha.

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