JP4827020B2 - Ground improvement method - Google Patents

Description

  The present invention relates to a ground improvement method using an earth auger.

  Conventionally, this type of ground improvement method has a drive mechanism that can be moved up and down along a frame that stands upright on the ground surface, and has a drilling screw at the lower end and a spiral that is intermittently connected upward. A hollow cylindrical auger provided with stirring and crushing plates, respectively, is connected so as to be reversible by the drive mechanism, and this proposed method consists of a drilling screw at the tip and a stirring and crushing plate in the following part. And using augers constructed by opening quick lime or slaked lime feeding screw conveyors and compressed air passages at the front end portions, respectively, and using auger soil as much as possible to discharge as much as possible. And lime fed by the screw conveyor into the crushed excavated soil. It is ejected with compressed air, and excavated soil and soil water are stirred and mixed, and this lime reacts with excavated soil and soil water to form a columnar body with soft lime and excavated soil in soft ground. And a step of forming a drilling hole having a predetermined depth in the ground by using an earth auger, and a pile tip from the auger head of the earth auger at the tip of the drilling hole. A step of selectively injecting a portion fixing solution, a step of injecting a pile peripheral portion filling solution from the auger head after injecting the pile tip portion fixing solution, and a step of installing a pile in the excavation hole; There is a hole wall ground improvement method in the Cement Milk Gazette comprising the step of fixing the pile to the ground so as to reach a height level. Le tip fixative and pile periphery filling liquid two used but, by suitably selecting the ingredients in each case, the frictional force and the supporting force and the like can be greatly improved. In particular, the pile peripheral portion filling liquid is obtained by adding normal portland cement and cement-based solidified material as main components and adding an appropriate amount of bentonite (for example, Patent Document 2). For example, it is stated that ordinary Portland cement, especially for sandy soil, and cement-based solidification material, for viscous soil, can improve the ground, thereby increasing the ground strength. Has been.

  All of the above conventional ones are intended to improve the ground by forming a columnar body in the ground using a large amount of solidifying material such as lime or cement, and the material costs are increased, and the solidifying material There is also concern about the impact on the environment due to the use. Moreover, since only the excavation part is formed into a strong columnar part, there is a surface inferior in the compaction effect around the excavation part.

  Taking such problems into consideration, a drilling hole having a predetermined depth is formed while the earth auger is rotated forward, and then the earth auger is reversely rotated at a low speed and a vertical axial force is applied to the earth auger. The ground improvement method (for example, patent document 3) which applies the force of a horizontal direction to the aggregate thrown in from the ground surface by the auger and compacts the circumference | surroundings of the excavation hole and the inside of the excavation hole is proposed, and this ground improvement method includes quick lime. Using aggregate, it has excellent compatibility with the environment, and can effectively consolidate around the excavation hole.

In addition, a ground improvement material containing quick lime having a particle size of 5 mm or less (for example, Patent Document 4) and a construction method (for example, Patent Document 5) in which quick lime having a particle diameter of 15 mm or less is preferably used are also known.
Japanese Patent Publication No.52-606 JP 7-216866 A Japanese Patent Laid-Open No. 2001-172756 Japanese Patent Laid-Open No. 11-181424 JP 2001-152149 A

  In the ground improvement method of the said patent document 3, it is excellent in the compatibility to an environment using the aggregate containing quick lime, and the circumference | surroundings of an excavation hole can be effectively consolidated. However, after mixing quicklime and mountain sand, throw it into the drilling hole, and by reverse rotation of the earth auger, apply the force in the horizontal direction of the quicklime and mountain sand to consolidate the circumference of the drilling hole and the inside of the drilling hole. A sand pile in which quick lime, mountain sand and soil water reacted was formed in the hole, but the effect of using quick lime was not sufficiently obtained around the sand pile.

  The present invention solves the above-mentioned problems, and aims to provide a ground improvement method capable of obtaining a wide-range consolidation effect and capable of continuing cementation (chemical effect) with quick lime over a long period of time. To do.

  In the ground improvement method according to claim 1 of the present invention, an excavation hole having a predetermined depth is formed while the earth auger is rotated forward, and then aggregate and quicklime are introduced into the excavation hole from the surface, and the earth auger is While rotating in the reverse direction, by applying a vertical axial force, a horizontal force is applied to the aggregate and quicklime to consolidate the periphery of the drilling hole and the inside of the drilling hole, and move the quicklime to the periphery of the drilling hole. The ground improvement method is characterized in that the quicklime larger than the aggregate is used.

Ground improvement method according to claim 1 of the present invention is a ground plate improved method you wherein the size of the quick lime is 30 mm to 5 0 mm.

  According to claim 1 of the present invention, by rotating the earth auger in reverse, the aggregate and quicklime are pushed into the soft ground around the excavation hole, and an aggregate pile made of aggregate in the excavation hole is created in the ground. In addition to promoting the consolidation effect, a wide range of ground consolidation effects can be obtained using a series of chemical reactions that occur from quicklime, pore water and surrounding soil particles moved around the excavation hole, and for a long time. You can continue cementation across.

According to the first aspect of the present invention, when the earth auger rotates reversely between the aggregate and the quicklime in the excavation hole, the quicklime that is larger than the aggregate moves to the outer peripheral side. Further, by using large quick lime, the quick lime takes time to react with moisture, so that it is easy to move to the outside.

  Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments described below do not limit the contents of the present invention described in the claims. In addition, all of the configurations described below are not necessarily essential requirements of the present invention. In each embodiment, by adopting a new ground improvement method different from the conventional one, an unprecedented ground improvement method is obtained, and the ground improvement method is described.

  Embodiment 1 of the present invention will be described below with reference to the accompanying drawings. 1 to 4 show a first embodiment of the present invention. As shown in FIG. 1 to FIG. 4, a leader 2 is connected to the tip of a boom 1 of a work vehicle such as a tow truck, and the leader 2 is erected on a ground surface portion 3. A rotating means 4 with a speed reducer is provided so as to be movable along the leader 2, and an earth auger 5 is vertically suspended from the rotating means 4. The earth auger 5 has a spiral screw-shaped excavation blade 7 on the outer periphery of a cylindrical portion 6, and a sharp conical portion 8 is provided at the lower end.

  Next, the procedure of the ground improvement construction method of the present invention will be described. First, in the ground surface portion 3 where the ground improvement is performed, boring is performed, a sample is taken from the ground, and a predetermined test is performed. Thereby, various data described later are calculated. First, as shown in FIGS. 1 and 2, the earth auger 5 is rotated in the excavation direction to form an excavation hole 11 having a predetermined depth. Thereafter, the earth auger 5 is reversely rotated at a low speed, and the aggregate 12 is introduced from the surface. In this case, as shown in FIG. 3, the axial force that is the vertical load W applied to the earth auger 5 is about 2 to 3 tons, and the earth auger 5 is 25 rotations per minute or less, preferably about 20 rotations. Further, the aggregate 12 can be excavated soil and sand that has been excavated by excavation of the earth auger 5, and in this case, about 6% to less than 10%, preferably about 6% of the improved ground volume. 7% of aggregate 12 and quicklime 14 will be added. In other words, when adding aggregate 12 and quicklime 14 of about 6% to 10% of the improved ground volume and returning all the excavated soil to the excavation hole 11, the added mountain sand 13 and quicklime 14 are the ground improvement capacity. From about 6% to about 7% is preferable. The improved ground volume is obtained by multiplying the area of the location where the ground is improved by the excavation depth of the excavation hole 11. Specifically, referring to FIG. , Circle 13, circle 17, circle 21, circle 22, circle 23, circle 24, circle 20, circle 16, circle 12, circle 3, circle 8, circle 7, circle 6 and surrounded by the center line of the borehole 11 shown in FIG. The portion (indicated by the alternate long and short dash line in the figure) is the improved ground area of the surface portion 3, and the area obtained by multiplying this area by the depth of the excavation hole 11 shown in FIG. 2 is the improved ground volume. Then, aggregate 12 and quicklime 14 of about 6% to less than 10%, preferably about 6% to 7% of the ground improvement volume are added, and the total additional amount is added to each drilling hole 11. An amount of aggregate 12 approximately equivalent to the amount divided by the number of is added.

  Thus, after rotating the earth auger 5 and putting a predetermined amount of aggregate 12, as shown in FIG. 4, quick lime 14 is put into the excavation hole 11, and the quick lime 14 is reversely rotated by the earth auger 5. The screw is conveyed to the lower part of the excavation hole 11 by the action of the screw conveyor, and reaches the entire depth direction of the excavation hole 11. Even after the quick lime 14 has been charged, the earth auger 5 is rotated in the reverse direction to increase the lateral stress due to the aggregate 12 and quick lime 14 and generate excess pore water pressure around the excavation hole 11 for drainage. Promote consolidation by prompting. Alternatively, a predetermined amount of quick lime 14 may be input after the aggregate 12 that closes the excavation hole 11 is input, and then the aggregate 12 may be additionally input.

  In the excavation hole 11, the aggregate 12 and the quicklime 14 are mainly moved to the outer peripheral side when the earth auger 5 rotates in the reverse direction. This is similar to the fact that the sedimentation speed of particles in liquid is faster as the particle size is larger, and in the case of debris flow, the phenomenon is similar to the fact that larger particles appear on the front surface, and the particle size is increased. As a result, it takes time to react with moisture, so that it can easily move to the outside.

  And in the experiment using normal pile sand as the aggregate 12, when the particle size of the quick lime 14 is less than 30 mm, the movement of the quick lime 14 is not enough, and the quick lime 14 to be introduced is smaller than the aggregate 12 The one having a large diameter, for example, a particle diameter of 30 mm or more and 60 mm or less, preferably 40 mm or more and 50 mm or less is used. The reason why the quick calcined lime 14 having a mass of 40 mm or more and the quick lime 14 less than 30 mm were compared was because quick lime of about 35 mm could not be obtained. In addition, it is preferable to use quick lime 14 of 50 mm or less, and the thing added to the excavation blade | wing 7 of the earth auger 5 when it exceeds 50 mm from the surface of the economy by being difficult to obtain the thing exceeding 50 mm as a commercial item. This is because it becomes difficult to feed to the bottom of the excavation hole 11.

  In addition, a particle size of 30 mm or more and 60 mm or less means passing through a 60 mm sieve without passing through a 30 mm sieve.

The quicklime 14 is produced by using a limestone (CaCO ₃ ) as a raw material and calcining at a high temperature of 900 ° C. or higher to cause a decarburization action (deCO 2).

  By setting the vertical load W applied to the earth auger 5 and the number of revolutions, the aggregate 12 and quicklime 14 can be effectively obtained in the horizontal direction, and the ground around the excavation hole 11 can be effectively obtained. Can be consolidated. If the weight of the earth auger 5 and the rotating means 4 is about 2 to 3 tons, the vertical load W can be obtained in this example without providing a separate weight. When the vertical load W is set to be large, a weight (not shown) is provided on the rotating means 4, a wire (not shown) is connected to the rotating means 4, and the wire is wound up. A downward load may be applied.

  The action will be described in detail. When the clay is stirred, it becomes liquid and soft, and if left in this state, it loses its liquid properties or becomes rigid, but this stirring is random and static. When pressure is applied with a stress that is close (similar to the static earth pressure coefficient), the structural arrangement changes from an incompletely oriented structure to the above-described one close to the oriented structure. This phenomenon is called thixotropy and has been recognized for a long time.

  On the other hand, there is a difference between the actual displacement value and the theoretical value so far in the embankment test on highways, and this difference is explained as an increase in shear strength due to anisotropic consolidation. That is, considering the elements in the ground, isotropic consolidation is a special case, and the effective soil cover pressure and the lateral restraint pressure values are usually different. Therefore, the strain in the ground is generated only in the vertical (vertical) direction, and no strain is generated in the horizontal direction. Therefore, such a consolidation test that matches the stress and strain conditions in the ground is now called the K0 test. The value of the static earth pressure coefficient K0 approximates 0.95-sinΦ ′ (Φ ′ is the internal friction angle in the soil).

  Then, by slowly applying pressure while applying a stress close to horizontal with a force close to the static earth pressure coefficient, the minimum increase in stress occurs almost uniformly in the ground. This pressurization can be adjusted by rotating the earth auger 5 in the reverse direction and controlling its weight and rotation speed.

  By rotating the auger that penetrates into the ground in this way, the aggregate 12 such as mountain sand is pushed into the soft ground, and the sand pile 15 as the sand pile is created in the ground to promote the consolidation effect. Using a series of chemical reactions that occur from quicklime, pore water and soil particles around the sand pile 15, to promote the consolidation effect (physical effect) of the ground over a wide area and to extend cementation (chemical effect) over a long period of time Can do.

  Physically, consolidation is promoted by encouraging drainage by increasing the lateral stress by creating the sand pile 15 and generating excess pore water pressure. The sand pile 15 itself has little consolidation settlement and has a large bearing capacity, which contributes to an increase in the bearing capacity of the ground.

  The series of chemical reactions includes (1) hydration reaction, (2) ion exchange, (3) ethrin guide generation, (4) pozzolanic reaction, and (5) carbonate formation.

  The side consolidation effect of the excavation hole 11 is promoted by introducing the aggregate 12 into the excavation hole 11 and forming the sand pile 15 while rotating the earth auger 5 in the reverse direction. In this case, an excessive pore water pressure is generated in the viscous soil by the sand pile 15, thereby forcibly draining.

Hereinafter, a series of chemical reactions will be individually described.
(1) Hydration reaction Quicklime CaO reacts with moisture in the soil as follows to produce slaked lime Ca (OH) ₂ .

In this reaction, when 10 kg of quicklime becomes slaked lime, about 4.3 kg of pore water in the soil is changed to crystal water. The generated heat promotes the evaporation of pore water. Generally, since soft soil has a high water content, a decrease in the water content greatly contributes to strength development. However, since this reaction occurs only with quicklime, it is considered that the soil with high water content is limited to the vicinity of the place where quicklime is present.

  When mixing soil and quicklime, the amount of each is determined, so the water content change can be calculated.

  When quicklime and soil are mixed, various information can be obtained from the chemical reaction formula. For example, in the quick lime hydration reaction, 32% of the quick lime mass water is used to produce slaked lime. In addition, 45% of the quicklime mass is removed from the water content when the amount of evaporation due to dehydration is added. Moreover, in the reaction of the above formula 1, the mass increases by the amount of water used for the reaction, so the mass of slaked lime produced is 1.32 times that of the added quicklime.

  The effect of the formation of the sand pile 15 and the hydration reaction can be obtained in a relatively short time. This will be described with reference to FIG.

  FIG. 7 illustrates a mechanism for increasing the supporting force of the ground when vertical loading is performed on the ground on which the sand pile 15 is placed. An increase in bearing capacity is an increase in resistance to slip failure. Originally, in the ground where the adhesive strength is c, the frictional resistance against sliding across the sand pile 15 and the relatively fast reaction from quick lime to slaked lime occur, and the water content ratio decreases, thereby increasing the adhesive strength and increasing the sliding resistance.

In contrast, those that react relatively slowly and those that require the movement of elements and molecules appear as delayed effects. The delay effect is described below.
(3) Ion exchange Fine-grained soil such as clay mineral has a lot of electric charge on its surface, and cations are adsorbed there. Further, when Na ions are adsorbed on the particle surface, Ca ions are changed to Na ions. This action is called cation exchange, and this action is more likely to occur in soil with a larger soil cation exchange capacity (CEC). Generally, the smaller the particle size and the higher the active clay, the larger the CEC. The Ca ions dissolved from the lime are combined with water or adsorbed on the soil particles and contribute to the bonding between the particles. As a result, agglomeration may occur easily.

  Water molecules are bipolar and oriented with respect to the charge. In addition, the hydrated ions that have adsorbed water molecules act to convert the negative charge on the surface of the particles to repulsive force between the particles. This also causes aggregation. Furthermore, when Na is exchanged for Ca ions, the original water film on the surface of the particles becomes thin, and consolidation tends to occur. This effect can occur to the periphery by the movement of Ca ions.

  The movement of Ca ions occurs due to the diffusion phenomenon even without water flow. In the case of cohesive soil, since the hydraulic conductivity is small, solutes such as ions are generated by diffusion. The amount of movement at a certain point is proportional to the concentration gradient ΔC / ΔL there, and has the relationship of the following formula 2.

Here, C is the concentration, D _dif is the diffusion coefficient, and L is the distance. That is, the amount of movement of Ca ions between two points increases as the concentration difference between the two points increases. The number 2 is known as Fick's law.
(4) Etrin guide formation Acetic ethrin guide crystals are formed by the reaction of slaked lime with alumina (Al ₂ O ₃ ), gypsum (CaSO ₄ ) and water to crosslink the soil particles. The reaction is as shown in FIG.

(5) Pozzolanic reaction The pozzolanic reaction is a reaction of slaked lime with silica and alumina, as is the case with the Etrin guide. The produced substance is bonded to the soil particles with calcium silicate hydrate or calcium aluminate hydrate. Since silica and alumina are inorganic minerals, they are considered to occur normally in soils other than highly organic soils. The pozzolanic reaction is represented by the following formula 4.

(6) Production of carbonate When carbon dioxide reacts with lime water in which slaked lime is dissolved in water, calcium carbonate is produced. At that time, particle sticking occurs. This reaction occurs normally in nature, and has recently become more important in the field of geotechnical engineering as a cause of cementation. Basically, since Ca ²⁺ and HCO ^{3− in} lime water move far with time, it can be expected that carbonation occurs over a wide area. This reaction helps to fix the CO ₂ in the ground.

  Lime is obtained by firing calcium carbonate (limestone), and at that time, carbon dioxide is generated. The reaction in which calcium carbonate is produced from lime water is shown in the following equation (5).

In this case, since CO ₂ is required, it can be said that carbonation is likely to occur in highly organic soil where organic matter is decomposed and CO ₂ is generated, near the groundwater surface, or where the groundwater level fluctuates greatly.

These phenomena mainly play a role as strength development effect of soft soil. The main difference between this construction method and conventional ground improvement using quick lime is not the purpose of mixing soil and quick lime to be improved, but the construction of sand pile 15 and the creation of quick lime walls around it. is there. In other words, dehydration of soft ground around sand piles, generation of slaked lime, and various chemical reactions due to diffusion of Ca ²⁺ are important factors.

Technical features Particularly in the present invention, the layer of quicklime 14 can be formed around the sand pile 15 as shown in FIG. As a result, the soft ground comes into contact with the quicklime 14, and a hydration reaction takes place, causing a decrease in the moisture content in the soft ground and evaporation due to heat generation. In other words, slaked lime is generated by the reaction of quicklime 14 with water, and in the process, needle-shaped ethrin guides are generated and the ground is hardened. In addition, slaked lime causes a pozzolanic reaction and acts as a cement substance such as clay particles. Calcium ions eluted from lime are exchanged with sodium ions and the like adsorbed on clay particles, and the density is increased (consolidation promotion) by thinning the adsorbed water film and electric double layer. Furthermore, when slaked lime becomes lime water and carbon dioxide is supplied, calcium carbonate is deposited on the contact portion and surface of the soil particles. This acts as soil cementation. As slaked lime is also used as food material, these reactions and products are almost harmless.

  Calcium carbonate is naturally present in large quantities as limestone, and all soils contain a small or large amount of calcium carbonate. Recently, it has been clarified that these calcium carbonates and other carbonates (magnesium carbonate, sodium carbonate, etc.) greatly contribute to the strength of the soil. In addition, it is well known as a diagenesis in the field of geology that calcium ions and bicarbonate ions are crystallized in the pore water of natural ground and aggregate on the particle surface, causing a significant increase in strength. The present technology also has an effect of artificially creating conditions that ultimately cause such a phenomenon.

The relationship between the calcium carbonate content obtained so far and the strength of the soil is as shown in Table 1 above. As a result of investigation, uniaxial compressive strength increases at a rate of about 17 kPa /% when calcium carbonate increases by 1% in the surface soil of the seabed, and increases by 60 to 70 kPa /% when the depth is about 40 m from the seabed. At a depth of 1 to 2.5 m, the uniaxial compressive strength increased at a rate of 260 kPa /%.

  In the case of paddy fields, the influence of glue other than calcium carbonate can be considered, but in this case, it cannot be explained unless there is a correlation between the contents of calcium carbonate and the glue. In the case of sand, a strength increase rate of 65 kPa /% is obtained.

Theoretical verification of the technology As described above, the apparatus used for the ground improvement method comprises an earth auger 5, a rotating means 4 such as a motor for rotating the earth auger 5, and a boom 1 such as a backhoe for hanging the earth auger 5. . FIG. 9 is an explanatory cross-sectional view during construction. As shown in FIG. 9, the earth auger 5 is penetrated to a predetermined depth at a predetermined position, and the earth auger 5 is rotated in the reverse direction, whereby the underground screw conveyor Then, aggregate 12 such as mountain sand and quicklime 14 are fed from the ground surface part 3 into the ground by the earth auger 5 that rotates in reverse.

  The sand pile 15 is formed by the earth auger 5 rotating in the reverse direction. The size of the sand pile 15 formed in the ground is the weight of the earth auger 5 and the rotating means 4 and the original acting on the sand pile 15 to be created. It relates to the balance with the reaction force in the ground (Fig. 9). Under the vertical weight W, the diameter of the sand pile 15 to be created increases as the raw ground becomes softer. The sand pile 15 is constructed until the earth auger 5 is lifted by the reaction force of the aggregate 12 and quicklime 14 at the tip of the earth auger 5, and the balance formula at that time is (the reaction force R of the tip that lifts the auger) ) = (Weight of the auger and motor W) + (peripheral friction F when the auger is lifted upward), and is expressed by the following equation (6).

FIG. 9 shows the balance of force when the earth auger 5 is considered as a stake. In this case, the rotational force is ignored, and the aggregate 12 moving downward by the earth auger 5 is regarded as an integral part of the earth auger 5. It is assumed that circumferential friction occurs between the aggregates 12.

  Here, r is the maximum rotation diameter of the earth auger 5, d is the depth of the portion where the earth auger 5 is in the ground, σ is the lateral side, and φr is the internal friction angle of the aggregate 12. By comparing the reaction force R obtained here with the tip support force (converted from the N value) formula of the sand pile 15, the support force of the sand pile 15 formed can be estimated.

Infiltration of calcium ions Slaked lime (calcium hydroxide) is generated and dissolved in pore water and moves through the soil as Ca ions. A solution of calcium hydroxide dissolved in water is lime water. The amount of calcium hydroxide dissolved in water is 0.18 g (0 ° C.), 0.13 g (50 ° C.), and 0.007 g (100 ° C.) per 100 g of water.

  The movement of ions in the soil is regarded as an advection / diffusion phenomenon, and when adsorption or decomposition can be ignored, it is generally expressed by the following advection / diffusion equation (7).

Here, Dx is a dispersion coefficient in the x direction, C is a Ca ion concentration, vx is an advection velocity, x is a coordinate representing a one-dimensional position, x = L, and t is time (FIG. 10). This general solution is expressed as the following equation (8).

Here, Co is an initial density, erf (β) is an error function, and erfc (β) is a complementary error function.

The values of β and erft (β) are shown in Table 2.1.

In the case of cohesive soil, since the hydraulic conductivity is low, ignoring the advection speed and setting vs = 0, Equation 8 becomes the following Equation 10.

FIG. 11 shows the calcium hydroxide concentration distribution after 30 days calculated from Equation 10 using various dispersion coefficients. It can be seen that the larger the dispersion coefficient, the faster the calcium hydroxide disperses in the form of ions. The initial concentration was 1500 mg / L, which is the maximum concentration at which calcium hydroxide dissolves at room temperature. FIG. 12 is calculated for two years later. In this case, the initial and boundary condition is that the concentration is always 1600 mg / L at x = 0.

Actually, it is not one-dimensional penetration, and there is also an adsorption reaction by ion exchange. Furthermore, if carbon dioxide is present, calcium carbonate is generated and contributes to particle bonding. Therefore, there is a possibility that it is greatly different from the value calculated here. Moreover, if there is advection, the movement speed of Ca ²⁻ increases.

Quick lime particle size and soil particle size When a particle group rotates, the larger the particle size, the more it moves outward. This is similar to the fact that the sedimentation rate of particles in a liquid increases as the particle size increases. In addition, in the case of debris flow, it seems that the larger particles are similar to the phenomenon that comes out on the front.

Experimental example In order to grasp the ground improvement effect by this technology, the experimental construction was conducted in a secret state and the ground survey was conducted. The survey point is an intermediate point on the diagonal of sand piles 15 placed in a grid at intervals of 2 m. The diameter of the sand pile 15 is about 30 cm, and it is considered that the quick lime reacts with water to form slaked lime around the sand pile 15.

  The experimental results are shown in Tables 3 and 4.

As shown in Table 3, it can be said that there is almost no difference in soil constant before and after sand pile driving. It is more appropriate to consider that there is no change in soil quality because the survey is conducted immediately after placement. It seems that consolidation is promoted over time and the water content is lowered. It should be noted that changes in physical properties due to chemical reactions other than hydration reactions do not appear as changes in the physical properties shown in Table 3, but rather are reflected in the mechanical properties.

  Looking at the uniaxial compressive strength, it shows a somewhat higher value after placement than before placement.

From Table 3, the soil particle density exceeds 2.6 g / cm ³ , and it seems that there is not much undecomposed organic matter.

  Looking at the results of the horizontal loading test (Table 4), there is an increase in yield pressure, fracture pressure, ground coefficient, deformation coefficient, etc. before and after placing. Since the loading test was conducted within a short period of time after placing, this result is considered to be due to an immediate effect. As shown in Table 3, the water content at the survey site has not changed so much, so this increase seems to be due to pile driving and immediate hydration. This is because the loading test results are affected by a wide range of ground areas that will be destroyed by loading.

  The feature of this technology is that instead of making a mixed pile of quicklime and sand material, the compaction effect of the surrounding ground by the sand pile, and the hydration reaction and cation exchange that start by dispersing quicklime around the pile It is a point that utilizes the effects of ethrin guide generation, pozzolanic reaction, carbonation, etc. in a complex manner. Therefore, a long-term increase in ground strength can be expected, and the ground where cementation has occurred may be close to natural ground.

  As described above, in this embodiment, in the ground portion 3 of the improved ground for ground improvement, the improved ground sample is collected from the ground by boring, and the moisture content is obtained by the indoor soil test of the collected sample. The sample is subjected to a consolidation test to set the vertical axial force and reverse rotation speed of the earth auger 5 suitable for the improved ground, and the vertical axial force to be set is 2 to 3 tons. The adjacent excavation hole 11 is arranged at the crossing position of the grid, and the improved ground volume is in the area of the surface part 3 of the portion surrounded by the line connecting the centers of the surrounding excavation holes 11. 11 times the depth, adding 6% to 7% aggregate 12 and quicklime 14 to the improved ground volume, and roughly equivalent to the amount divided by the number of drilling holes 11 Aggregate 12 and quicklime 14 are added to each borehole 11, and the aggregate 12 is sand. From, it is possible to effectively consolidate the surrounding borehole 11. Furthermore, since 6-7% of aggregate 12 and quicklime 14 are added to the improved ground volume, it is possible to perform appropriate compaction without the ground collapsing, and stable construction without ground breaking is possible. It becomes.

  In this way, in this embodiment, corresponding to claim 1, after the excavation hole 11 having a predetermined depth is formed while the earth auger 5 is rotated forward, the aggregate 12 and the quicklime 14 are transferred from the surface 3 to the excavation hole 11. The earth auger 5 is rotated in the reverse direction and a vertical load W, which is a vertical axial force, is applied to apply a horizontal force to the aggregate 12 and quicklime 14 so as to surround the drill hole 11 and the drill hole 11. While compacting the inside, the quick lime 14 is moved around the excavation hole 11 and the quick lime 14 larger than the aggregate 12 is used. Since the quick lime 14 is larger than the aggregate, the earth auger 5 is reversely rotated. Then, the aggregate 12 and the quicklime 14 are pushed into the soft ground around the excavation hole 11, and the sand pile 15 composed of the aggregate 12 in the excavation hole 11 is created in the ground to promote the consolidation effect, and the excavation hole 11 A series of occurrences from quicklime 14 moved around, pore water and surrounding soil particles By using a chemical reaction, with consolidation effect of extensive ground is obtained, it is possible to continue the cementation over time.

Further, in the present embodiment in this manner, corresponding to claim 1, since the size of the particle diameter of quicklime 14 is 30 mm to 5 0 mm, within the borehole 11, an aggregate 12 and quicklime 14, When the earth auger 5 rotates in the reverse direction, quick lime 14 that is larger than the aggregate 12 moves to the outer peripheral side. In addition, by increasing the size of the quicklime 14, the quicklime 14 takes a long time to react with moisture, so that it can easily move to the outside.

  Moreover, in the embodiment, instead of constructing a mixed pile mixed with aggregate 12, aggregate 12 and quicklime 14 are introduced separately, and the effect of compacting the surrounding ground by sand pile 15 and around the pile The effects of hydration reaction, cation exchange, ethrin guide generation, pozzolanic reaction, carbonation, etc. starting from the dispersion of quicklime 14 can be combined.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the ground improvement method of the present invention can be used for reinforcement of river levee bodies, road reinforcement, slope stability, landslide areas, etc., other than the embodiment.

It is sectional drawing at the beginning of excavation which shows Example 1 of this invention. It is sectional drawing of the state which formed the excavation hole same as the above. It is sectional drawing of the state which has rotated the earth auger reversely and injected | thrown-in the aggregate. It is sectional drawing of the state which reversely rotates an earth auger same as the above and has put quicklime. It is sectional drawing of the state which is performing the compacting operation | work by reversely rotating an earth auger same as the above. It is a top view of the ground surface part which performs ground improvement same as the above. It is a cross-sectional explanatory drawing explaining the effect by the hydration reaction of an aggregate pile and quicklime. It is a section explanatory view explaining the reaction which arises from quick lime in the soft ground same as the above. It is a cross-sectional explanatory drawing in the middle of construction same as the above. It is explanatory drawing explaining primary diffusion of Ca ion same as the above. It is a graph which shows the dispersion state of the calcium hydroxide 30 days after construction same as the above. It is a graph which shows the dispersion | distribution state of calcium hydroxide two months after construction same as the above.

Explanation of symbols

3 Ground part 4 Rotating means 5 Earth auger
11 Drilling hole
12 Aggregate
14 Quicklime
15 Sand pile (aggregate pile)
W Vertical load

Claims (1)

After forming an excavation hole of a predetermined depth while rotating the earth auger, aggregate and quicklime are put into the excavation hole from the surface, and the earth auger is rotated in reverse and a vertical axial force is applied. By applying a horizontal force to the aggregate and quick lime to consolidate the periphery of the excavation hole and the inside of the excavation hole, the quick lime is moved to the periphery of the excavation hole, and the quick lime larger than the aggregate is used . The ground improvement construction method characterized by that the size of the ground is 30 mm to 50 mm .