JP2001172956A - Soil improvement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soil improvement method excellent in compatibility with an environment and capable of effectively consolidating the circumference of an excavated hole. SOLUTION: The excavated hole 11 with a specific depth is formed while forwarding an earth auger 5. An then, the earth auger 5 is reversed at a low speed and, at the same time, axial force in the direction of excavation is added, and horizontal force is added to aggregate 12 cast from the ground surface 3 by the earth auger 5 to consolidate the circumference of the excavated hole 11 and the inside of the excavated hole. Soil around the excavated hole 11 is effectively compacted to make it possible to carry out soil improvement by reversing the earth auger 5 at a low speed in a state to add axial force to the direction of excavation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground improvement method using an earth auger.

[0002]

Conventionally, as this kind of ground improvement method, Japanese Patent Laid-Open No. 51-136315 discloses
The casing inserted into the ground is filled with sand, the casing is pulled up, the ground is compacted by draining through a sand column formed in the ground, and then the grout material is injected into the sand column and compacted. There is a ground improvement method, and Japanese Patent Publication No. 52-606 has a drive mechanism capable of ascending and descending along a frame structure standing upright on the ground surface. A hollow cylindrical auger provided with a spiral stirring and crushing plate, which is intermittently connected upward, is connected so as to be able to reversibly rotate by the driving mechanism (claims). Excavation screw is provided in the section, stirring and crushing plate etc. are provided in the section following this, and the inside of quick lime or slaked lime (hereinafter referred to as lime) feeding screw conveyor and compressed air And, using an auger configured with each opening at the tip end, excavating the excavated soil in a columnar manner so as not to discharge as much as possible, and at the same time the excavated soil is stirred and crushed in the excavation hole, The lime fed by the screw conveyor is blown out by compressed air into the crushed excavated soil, and the lime is stirred and mixed with the excavated soil and the soil water, and the lime is reacted with the excavated soil and the soil water, In the soft ground, a columnar body is formed by strong lime and excavated soil (Publication, column 3, lines 19 to 32). Further, JP-A-7-216866 discloses the use of an earth auger. Forming a drilling hole of a predetermined depth in the ground; selectively injecting a pile tip fixing liquid from an auger head of the earth auger at a tip of the drilling hole; Injection After pouring the filling liquid around the pile from the auger head, setting a pile in the excavation hole, and fixing the pile to the ground so that the pile has a predetermined height level. There is a perforated wall ground improvement method in the cement milk publication (claims). In this ground improvement method, two types of cement milk are used: a pile tip fixing liquid and a pile peripheral filling liquid. By suitably selecting the composition, the frictional force, the supporting force, and the like can be significantly improved. In particular, the filling liquid at the periphery of the pile is a liquid containing ordinary Portland cement and a cement-based solidifying material as a main component, to which an appropriate amount of bentonite is added. For example, ordinary Portland cement, especially for sandy soil, and cement-based solidifying material, for cohesive soil, respectively, exhibit soil improvement effects, thereby increasing the ground strength in each step (No. 000
9).

[0003] All of the above-mentioned conventional ones are intended to improve the ground by forming a columnar body in the ground by using a large amount of solidifying material such as lime or cement, thereby increasing the material cost. There is also concern about the impact on the environment due to the use of solidified materials. Further, since only the excavated portion is formed into a strong columnar portion, there is a surface that is inferior in the compaction effect around the excavated portion.

[0004] Therefore, an object of the present invention is to provide a ground improvement method which has excellent adaptability to the environment and can effectively consolidate the periphery of an excavation hole.

[0005]

Means for Solving the Problems The present inventor studied the difference between the compaction in the vertical direction and the compaction in the horizontal direction, and applied the conventional method by applying a pressure near the static earth pressure coefficient in the horizontal direction. It has been found that consolidation proceeds more quickly. For example, in a simple manner, in draining water such as tofu, water is drained in a relatively short time by applying an appropriate load, and it takes more time than necessary to drain the water if the load is too large. And it may collapse.

The inventor of the present invention has conducted intensive studies to enable effective consolidation by pressing the earth auger at a low speed of 25 rotations per minute or less, preferably about 20 rotations per minute when pressurizing after excavation. In addition, since it is difficult to control the pressing force with only the large aggregate, the aggregate having a good particle mixture such as mountain sand is used. Furthermore, mixing of quicklime and the like was effective for the ground and the like composed of fine particles in the extremely soft ground.

According to the first aspect of the present invention, an excavation hole having a predetermined depth is formed while rotating the earth auger, and thereafter,
Ground that reversely rotates the earth auger at a low speed, applies a vertical axial force, and applies a horizontal force to the aggregate introduced from the surface by the earth auger to consolidate around and inside the excavation hole; This is an improved construction method.

According to the first aspect of the present invention, the ground around the excavation hole can be effectively compacted by reversely rotating the earth auger at a low speed while applying an axial force in the excavation direction.

A second aspect of the present invention is a ground improvement method in which the reverse rotation of the earth auger is 25 rotations per minute or less.

According to the structure of the second aspect, by rotating the auger at a relatively low speed, it is possible to apply an appropriate pressing force close to the static earth pressure coefficient to the aggregate by the rotation of the auger.

Further, the invention of claim 3 is a ground improvement method in which an aggregate of 6 to 10% is added to the improved ground volume.

According to the structure of the third aspect, appropriate compaction can be performed without the ground being collapsed.

[0013]

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

Next, the procedure of the ground improvement method of the present invention will be described. First, in the ground surface part 3 that performs ground improvement,
Boring, taking samples from underground, and conducting prescribed tests. Thereby, various data described later is calculated. First, as shown in FIGS. 1 and 2, the earth auger 5 is rotated in the excavation direction to form the excavation hole 11 having a predetermined depth. Thereafter, the earth auger 5 is reversely rotated at a low speed, and the aggregate 12 is charged from the surface. In this case, as shown in FIG. 3, the axial force which is the vertical load W applied to the earth auger 5 is 2
The earth auger 5 is set to 25 rpm or less, preferably about 20 rpm. As the aggregate 12, excavated earth and sand 13 excavated by the excavation of the earth auger 5 can be used, and in this case, about 6% to less than 10%, preferably 6% of the improved ground volume. About 7% of aggregate 12 is introduced. In other words, if the aggregate 12 of about 6% to about 10% of the improved ground volume is added and all the excavated soil is returned to the excavation hole 11,
It is preferable that 13 is about 6% to about 7% of the ground improvement capacity. The improved ground volume is obtained by multiplying the area of the site where the ground is to be improved by the digging depth of the digging hole 11,
Specifically, referring to FIG. 4, the surrounding circle 5, circle 4, circle 9, circle 13, circle 17, circle 21, circle 22, circle 23, circle 24, circle 20, circle 1
The part surrounded by the center line of the excavation hole 11 shown by 6, 12, 12, 3, 8, 7 (indicated by a dashed line in the figure) is the improved ground area of the ground surface part 3, and this area 2 multiplied by the depth of the excavation hole 11 shown in FIG. Then, about 6% to less than 10%, preferably about 6% to about 7% of the ground improvement volume is added to the aggregate 12, and the total amount added to each drill hole 11 is the number of the drill holes 11. An amount of aggregate 12 approximately equivalent to the divided amount is added. Furthermore, in soft ground, the aggregate 12 may include quicklime 14. quicklime
When using 14, the quicklime 14 and the sand 13 can be mixed and then put into the drilling hole 11, or the quicklime 14 can be first charged into the drilling hole 11 and then the sand 13 can be charged. By setting the vertical load W and the number of rotations applied to the earth auger 5 in this manner, the force in which the aggregate 12 moves in the horizontal direction can be effectively obtained, and the ground around the excavation hole 11 can be effectively formed. Can be compacted. If the combined weight of the earth auger 5 and the rotating means 4 is about 2 to 3 tons, in this example, the vertical load W can be obtained without providing a separate weight or the like. When the vertical load W is set to be large, a weight (not shown) is provided on the rotating means 4, or a wire (not shown) is connected to the rotating means 4 and the wire is wound. What is necessary is just to add a downward load.

The action will be described in detail here. When the viscous soil is agitated, it becomes liquid soft, and when left in this state, it loses the liquid property or becomes rigid.
When the stirring is pressurized with a random and nearly static stress (a condition close to the static earth pressure coefficient), the structural arrangement changes from the incompletely oriented structure to the above-mentioned one close to the oriented structure. This phenomenon is called the thixotropy phenomenon and has been recognized for a long time.

On the other hand, in embankment tests on expressways and the like, a difference is found between the actual displacement value and the theoretical value up to now, 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 value of the effective earth covering pressure and the value of the lateral restraining pressure are usually different. Therefore, distortion in the ground occurs only in the vertical (vertical) direction, and no distortion occurs in the horizontal direction. Therefore, such a consolidation test adapted to the conditions of stress and strain in the ground is currently called a K0 test. The value of the static earth pressure coefficient K0 approximates 0.95-sin Φ '(Φ' is the internal friction angle in the soil).

Considering the static earth pressure coefficient K0 from the undrained shear test of an anisotropically consolidated normally consolidated viscous soil by Skempton et al. 1) If the water content is equal,
Those subjected to K0 consolidation have greater undrained shear strength. 2) There is a possibility of having a thixotropic factor due to a difference in time required for shearing. 3) If the stress history is different, the skeleton structure of the clay is different.

Further, considering the change in water content caused by forcibly applying a vertical load to the shaft, the total load 機械 (2 to 3 tons in the embodiment) serving as a mechanical reaction force is determined in advance in the soil. Has a simple linear relationship between the water content δ (initial water content) and the radius of influence R due to the use of the earth auger 5. Here, the influence radius R was set to 1.6 m (meter).

C = ξ * A (ε / δ * 1.6) The above equation gives the mechanical additional speed C, which is related to the rotation speed of the earth auger 5. still,
In the above equation, ε is a moisture content coefficient, which is determined by the moisture content of the ground to be improved as shown in Table 1 below.

[0020]

[Table 1]

From these, the ground strength after improvement can be expressed by the following equation.

[0022]

(Equation 1)

In the above, A is the pore pressure coefficient in soil, N
Is the strength coefficient in soil (standard penetration test value + 1).

[0024] By applying a pressure near the static earth pressure coefficient and applying a pressure close to the horizontal while slowly applying pressure, the minimum stress increase 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. Pressurization that greatly exceeds the static earth pressure coefficient causes destruction of the entire ground. Then, by adjusting the quick lime 14 by mixing with the quick lime 14, the adjustment is made by the heat generation and the water absorption expansion of the quick lime 14. The input amount of the aggregate 12 is about 6% to less than 10%, preferably about 6% to 7% of the improved ground volume, that is, the pile sand of the aggregate 12 added to the excavated soil. 13
By setting 6% to 7% of the ground improvement volume, stable construction without ground destruction becomes possible. If the aggregate input amount exceeds 10% of the ground improvement volume, the possibility of ground failure increases.

FIG. 4 is a plan view showing a construction procedure. By performing ground improvement at 11 excavation holes in the order of numerical values described in circles, ground improvement over a wide range can be efficiently performed. Then, as shown in FIG. 4, the adjacent excavation holes 11 and 11 are arranged at the intersections of the cells, the interval between them is 2 m, and the interval H between the diagonal positions is approximately 2.83 m. Since the radius of influence R is set to be equal to or less than twice the radius of influence R (1.6 m), the radius of influence R overlaps at the position of the adjacent excavation hole 11, and the ground improvement can be reliably performed.

As described above, in the present embodiment, the drilling hole 11 having a predetermined depth is formed while rotating the earth auger 5 in the forward direction, and thereafter, the earth auger 5 is reversely rotated at a low speed. At the same time, the ground improvement method is to apply an axial force in the excavation direction and apply a horizontal force to the aggregate 12 introduced from the ground surface portion 3 by the earth auger 5 to consolidate the periphery of the excavation hole 11 and the inside of the excavation hole 11. When the earth auger 5 is reversely rotated at a low speed while applying an axial force in the excavation direction,
The ground improvement can be performed by effectively compacting the surrounding ground. Also, when quicklime 14 or the like is added, the amount of use can be reduced.

As described above, according to the present embodiment, claim 2
Corresponding to the reverse rotation of the earth auger, 25
Because it is less than rotation, by rotating at a relatively low speed,
By the rotation of the auger 5, an appropriate pressing force close to the static earth pressure coefficient K0 can be applied to the aggregate 12.

As described above, according to the present embodiment, claim 3
Accordingly, an aggregate of 6 to 10% is added to the improved ground volume, so that appropriate consolidation can be performed without the ground being collapsed.

Further, as an effect on the embodiment, before the improvement, a survey was conducted by drilling, and at least a water content ratio was obtained by a laboratory soil test of the collected sample, and a value of a consolidation test result was obtained. The static earth pressure coefficient K0 based on the angle Φ ', the initial water content δ, the pore pressure coefficient A,
By calculating the strength coefficient N and the water content coefficient ε, it is possible to set a suitable vertical load W and a rotation speed of the earth auger 5 based on the mechanical additional speed C and the total additional load 適 し of the machine suitable for the site. it can. Further, since what is added to the aggregate 12 is quicklime 14, it is safe and suitable for the natural environment.

The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention. For example, various earth augers can be used.

[0031]

According to the first aspect of the present invention, an excavation hole having a predetermined depth is formed while rotating the earth auger forward, and thereafter, the earth auger is reversely rotated at a low speed and a vertical axial force is applied. This is a ground improvement method in which a horizontal force is applied to the aggregate supplied from the ground surface by the earth auger to consolidate the surroundings of the excavation hole and the inside of the excavation hole. A ground improvement method capable of effectively consolidating can be provided.

[0032] The invention of claim 2 is a ground improvement method in which the reverse rotation of the earth auger is 25 rotations per minute or less, which is excellent in environmental compatibility and effectively consolidates the periphery of the excavation hole. A ground improvement method that can be performed can be provided.

[0033] The invention of claim 3 is a ground improvement method in which 6 to 10% of aggregate is added to the improved ground volume, which is excellent in environmental compatibility and effective in surrounding the excavation hole. And a ground improvement method capable of compacting the ground.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention at the beginning of excavation.

FIG. 2 is a cross-sectional view showing a state in which an excavation hole is formed according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a state in which the earth auger according to the embodiment of the present invention is rotated in the reverse direction to perform a compacting operation.

FIG. 4 is a plan view of a ground surface portion for performing ground improvement showing one embodiment of the present invention.

[Explanation of symbols]

 3 Ground surface part 5 Earth auger 11 Drilling hole 12 Aggregate 13 Mountain sand 14 Quicklime

Claims (3)

[Claims] An excavation hole having a predetermined depth is formed while rotating the earth auger, and thereafter, the earth auger is reversely rotated at a low speed, and a vertical axial force is applied. A ground improvement method characterized in that a horizontal force is applied to the aggregate supplied from above to consolidate around and inside the excavation hole. 2. A reverse rotation of the earth auger is performed at a rate of 2 / min.
The ground improvement method according to claim 1, wherein the rotation speed is 5 rotations or less. 3. The ground improvement method according to claim 1, wherein an aggregate of 6 to 10% is added to the improved ground volume.