Cast-in-place concrete piles and their construction methods

Abstract

To provide a cast-in-place concrete pile with a pile head that can reliably secure the design diameter of the pile head even when the soil water pressure exceeds the lateral pressure of the concrete, and a method for constructing the same. [Solution] This cast-in-place concrete pile 2 is equipped with a diameter reduction prevention wall 6 extending from the ground surface to a predetermined depth around the pile body 5. The diameter reduction prevention wall 6 is formed by a low-strength material 6a that is cast into an outer casing 9 located outside the casing 7. The low-strength material 6a has sufficient adhesion strength to break away from the casing 7 and outer casing 9 with a predetermined force, and is able to maintain its shape even when subjected to the soil water pressure of the ground 1 and the pressure of the concrete 5a cast into the casing 7, and also possesses compressive strength that can withstand its own weight.

Description

[Technical Field]

[0001] The present invention relates to a cast-in-place concrete pile constructed by the so-called all-casing method and a method for constructing the same. [Background technology]

[0002] Conventionally, the so-called all-casing method is widely known as a construction method for cast-in-place concrete piles used in the foundations of buildings, etc. (see, for example, Patent Document 1).

[0003] This all-casing method first involves driving the casing into the ground to a predetermined depth while rotating or oscillating it, and then using a hammer grab to excavate and remove the soil inside the casing to form a pile hole.

[0004] Next, once the pile holes of the predetermined depth have been formed, the necessary bottom treatments are carried out, and reinforcing cages are installed inside the pile holes.

[0005] Then, while the casing is withdrawn, concrete is poured into the pile hole using a tremie pipe or the like, thereby constructing the reinforced concrete pile body in the ground.

[0006] In this process, the design outer diameter of the pile body (hereinafter referred to as the design diameter) is based on the outer diameter of the casing, and the internal pressure of the casing is controlled to be greater than the soil water pressure, so that fresh concrete flows up to the outer diameter of the casing. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2008-156864 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, with the conventional technology described above, the pressure exerted by the fresh concrete placed on the inner surface of the pile hole (hereinafter referred to as lateral pressure) is affected by the weight of the fresh concrete, and the lateral pressure is greater at the bottom of the pile hole and decreases towards the top.

[0009] Therefore, in this type of cast-in-place concrete pile, the lateral pressure due to the fresh concrete decreases at the pile head where the influence of the weight of the fresh concrete is smaller, and the pressure difference between the inside and outside of the casing becomes smaller, which could lead to a problem where the pile head becomes smaller than the design diameter.

[0010] In particular, in soft ground, the soil pressure in the ground becomes greater than the lateral pressure on the fresh concrete that has been poured, which poses a problem as the pile diameter at the pile head tends to become smaller than the design pile diameter.

[0011] On the other hand, conventional measures to address these challenges have included methods such as pouring extra concrete to a height higher than the design height of the pile head to increase the lateral pressure of the concrete, or placing weights on the pile head after concrete pouring to increase the lateral pressure of the concrete with the load of the weights. However, these methods have the problem of lacking reliability.

[0012] Therefore, in view of these conventional problems, the present invention aims to provide a cast-in-place concrete pile with a pile head that can reliably secure the design diameter of the pile head even when the earth pressure exceeds the lateral pressure of the concrete, and a method for constructing the same. [Means for solving the problem]

[0013] The invention described in claim 1, which solves the conventional problems described above, is a cast-in-place concrete pile in which the pile body is formed by concrete driven into a pile hole obtained by excavating the inside of a casing that has penetrated into the ground, while the casing is withdrawn, wherein the pile body is provided with a diameter reduction prevention wall extending from the ground surface to a predetermined depth, the diameter reduction prevention wall is formed of a low-strength material driven into an outer casing placed outside the casing, the low-strength material has an adhesion strength such that it can be separated from the casing and the outer casing by a predetermined force, and is able to maintain its shape even when subjected to the soil water pressure of the ground and the pressure of the concrete driven into the casing, and has compressive strength that can withstand its own weight.

[0014] The feature of the invention described in claim 2 is that, in addition to the configuration of claim 1, the thickness of the diameter reduction prevention wall is 10% or more and 30% or less of the pile diameter of the pile body.

[0015] The features of the invention described in claim 3 are as follows: In a method for constructing a cast-in-place concrete pile, in which a pile hole is formed by excavating the inside of a casing that has penetrated the ground, and concrete is poured into the pile hole while the casing is withdrawn, the method involves: driving an outer casing with a larger diameter than the casing into the ground, and repeatedly excavating and removing soil from inside the outer casing to a predetermined depth from the ground surface to form an outer pile hole; erecting the casing concentrically with the outer casing in the outer pile hole; driving the casing to a position slightly deeper than the bottom surface of the outer pile hole; then pouring a low-strength material into the gap between the casing and the outer casing to form a diameter reduction prevention wall; and thereafter, separating the casing from the diameter reduction prevention wall, and repeatedly driving the casing in, and excavating and removing soil from inside the casing to a predetermined depth in the ground to form the pile hole; and then pouring concrete into the pile hole while the casing is withdrawn to form the pile body.

[0016] The feature of the invention according to claim 4 is that, in addition to the configuration of claim 3, the low-strength material has an adhesion strength such that it can be cut off from the casing and the outer casing with a predetermined force, and can maintain its shape even when subjected to the earth pressure of the ground and the pressure of the concrete placed in the casing, and has a compressive strength capable of withstanding its own weight.

[0017] The feature of the invention according to claim 5 is that, in addition to the configuration of claim 3 or 4, the diameter reduction prevention wall is formed, and the outer casing is pulled out before the casing is cut off from the diameter reduction prevention wall.

[0018] The feature of the invention according to claim 6 is that, in addition to the configuration of claim 3 or 4, the casing is penetrated to a predetermined depth of the ground while being rotated.

[0019] The feature of the invention according to claim 7 is that, in addition to the configuration of claim 3 or 4, a peeling material is provided on the outer peripheral surface of the casing and / or the inner peripheral surface of the outer casing.

[0020] The feature of the invention according to claim 8 is that, in addition to the configuration of claim 7, the peeling material is composed of a sealing material, and the sealing material is provided only on the portion of the outer peripheral surface of the casing and / or the inner peripheral surface of the outer casing that does not penetrate into the ground.

[0021] The feature of the invention according to claim 9 is that, in addition to the configuration of claim 3 or 4, the pipe diameter ratio between the casing and the outer casing is 1.2 or more and 1.6 or less.

Advantages of the Invention

[0022] The in-situ concrete pile according to the present invention, by having the configuration according to claim 1, blocks the surrounding earth pressure by the diameter reduction prevention wall, prevents the concrete at the pile head from receiving the earth pressure, and can surely secure the designed diameter at the pile head of the pile body.

[0023] In addition, in the present invention, by providing the configuration described in claim 2, it is possible to cut off the edge between the casing and the outer casing, and a diameter reduction prevention wall with sufficient strength can be formed.

[0024] By providing the configuration described in claim 3, the construction method of the cast-in-place concrete pile according to the present invention can block the surrounding earth pressure by the diameter reduction prevention wall, prevent the concrete at the head of the cast-in-place concrete pile from receiving the earth pressure, and reliably ensure the designed diameter at the pile head of the pile body.

[0025] In addition, in the present invention, by providing the configuration described in claim 4, it is possible to cut off the edge between the casing and the outer casing, and a diameter reduction prevention wall with sufficient strength can be formed.

[0026] Furthermore, in the present invention, by providing the configuration described in claim 5, the outside of the diameter reduction prevention wall can be integrated with the ground before cutting off the edge of the casing. Also, the outer casing can be reused.

[0027] Furthermore, in the present invention, by providing the configuration described in claim 6, the concentricity between the casing and the outer casing can be enhanced.

[0028] In the present invention, by providing the configuration described in claims 7 to 8, the cutting off of the edge between the diameter reduction prevention wall and the casing and the outer casing can be facilitated.

[0029] In the present invention, by providing the configuration described in claim 9, the pile diameter ratio between the pile body and the diameter reduction prevention wall can be made appropriate.

Brief Description of the Drawings

[0030] [Figure 1] It is a longitudinal sectional view showing an example of the cast-in-place concrete pile according to the present invention. [Figure 2] There is an enlarged cross-sectional view of the pile head portion of the same pile. [Figure 3]This is a schematic enlarged longitudinal cross-sectional view showing the state of each step in the construction method of a cast-in-place concrete pile according to the present invention, where (a) shows the state in which the outer casing is erected on the ground surface, (b) shows the state in which the outer casing is driven in, (c) shows the state in which the casing is erected in the outer pile hole and the tip is driven in to a predetermined depth, and (d) shows the state in which the low-strength material is driven in. [Figure 4] Figure 3(d) is an enlarged cross-sectional view showing the casing and outer casing installed. [Figure 5] The above diagram shows a schematic enlarged vertical cross-sectional view illustrating the state of each process, where (e) shows the state when the outer casing is being withdrawn, (f) shows the state when the casing has been driven to a predetermined depth, (g) shows the state when concrete is being poured while the casing is being withdrawn, and (h) shows the state when the cast-in-place concrete pile has been constructed. [Modes for carrying out the invention]

[0031] Next, embodiments of the cast-in-place concrete pile according to the present invention will be described based on the examples shown in Figures 1 and 2. In the figures, reference numeral 1 denotes the ground and reference numeral 2 denotes the cast-in-place concrete pile.

[0032] In this embodiment, as shown in Figure 1, we will explain using a ground 1 as an example, in which a certain depth of soft ground 4 (cohesive soil: N value ≤ 2, sandy soil: N value ≤ 6) is laid on top of ordinary ground 3.

[0033] As shown in Figures 1 and 2, this cast-in-place concrete pile 2 comprises a reinforced concrete pile body 5 extending to a predetermined depth in the ground 1, and a diameter reduction prevention wall 6 surrounding the pile body 5, extending from the ground surface to a predetermined depth. The diameter reduction prevention wall 6 prevents the soil pressure of the ground 1 (soft ground 4) from directly acting on the pile head of the pile body 5, thus preventing it from affecting the lateral pressure of the concrete.

[0034] The pile body 5 is formed by concrete 5a that is poured into a pile hole 8, which is created by excavating the inside of the casing 7 that has penetrated the ground 1, while simultaneously withdrawing the casing 7.

[0035] Although not specifically shown in the diagram, a reinforcing cage is installed inside the pile hole 8, and the pile body 5 is made of reinforced concrete.

[0036] The diameter reduction prevention wall 6 is formed by driving a low-strength material 6a into an outer casing 9 located outside the casing 7, and the inner diameter of the low-strength material 6a is formed into a cylindrical shape that is the same as the outer diameter (design diameter D) of the pile body 5.

[0037] The thickness of the diameter reduction prevention wall 6 is formed to be between 10% and 30% of the pile diameter of the pile body 5.

[0038] Furthermore, this diameter reduction prevention wall 6 is formed to a height (depth) that can cover the pile head of the pile body 5, where the lateral pressure of the concrete decreases and the pressure difference between the inside and outside of the casing 7 becomes smaller. In particular, it is desirable that the height (depth) extends over the entire area of ​​the soft ground 4 (cohesive soil: N≦2, sandy soil: N≦6).

[0039] Furthermore, caution is necessary if the daily fluctuation of the groundwater level in the ground 1 where the cast-in-place concrete pile 2 is manufactured exceeds 1 meter, if the soil layer has large gaps such as a rubble layer, or if the construction range (depth) of the diameter reduction prevention wall 6 exceeds GL-10 m, as this may cause problems with the diameter reduction prevention wall 6.

[0040] The low-strength material 6a is constructed to have sufficient adhesion strength to break away from the casing 7 and outer casing 9 with a predetermined force, while also being able to maintain its shape even when subjected to the soil water pressure of the ground 1 and the pressure of the concrete poured into the casing 7, and possessing compressive strength that can withstand its own weight.

[0041] The specific conditions for the low-strength material 6a are as follows:

[0042] (1) In order for the outer casing 9 to have sufficient adhesion strength to detach from the diameter reduction prevention wall 6 with a predetermined force, f2 ≤ (Ta - f1 × A1) / A2 The following conditions must be met: Ta: Force that pulls apart the surface due to friction (kN) Ta=Ma / ra Ma: Rotational force (rotational torque) (kNm) that rotates the outer casing 9 ra: Radius of outer casing 9 (m) f1: Frictional force between the ground 1 and the outer casing 9 (kN / m 2 ) A1: Contact area between the ground 1 and the outer casing 9 (m²) 2 ) f2: Adhesion strength of low-strength material 6a (kN / m 2 ) A2: Contact area between low-strength material 6a and outer casing 9 (m²) 2 )

[0043] (2) In order for the casing 7 to have sufficient adhesion strength to detach from the diameter reduction prevention wall 6 with a predetermined force, f2 ≤ (Tb - f1 × A1) / A2 The following conditions must be met: Tb: Force that pulls apart surface friction (kN) Tb = Mb / rb ... (5) Mb: Rotational force (rotational torque) (kNm) that rotates casing 7 rb: Radius of casing 7 (m) f1: Frictional force between ground 1 and casing 7 (kN / m 2 ) A1: Contact area between ground 1 and casing 7 (m²) 2 ) f2: Adhesion strength of low-strength material 6a (kN / m2) A2: Contact area between low-strength material 6a and casing 7 (m²) 2 ) That is the case.

[0044] (3) In order to maintain the shape even when subjected to the soil water pressure of the ground 1 and the pressure of the concrete poured into the casing 7, M / z+N / A≦σca The following conditions must be met: M: Bending moment (kNm) N: Axial force (N) σca: Compressive strength of diameter reduction prevention wall 6 (low-strength material 6a) z: Section modulus of the diameter reduction prevention wall 6 (low-strength material 6a) A: Cross-sectional area of the diameter reduction prevention wall 6 (low-strength material 6a) (m 2 ) is as follows.

[0045] (4) In order to have a compressive strength that can withstand its own weight, σca ≧ W × H needs to satisfy the condition, W: Unit volume weight of the low-strength material 6a (kN / m 3 ) H: Driving height of the diameter reduction prevention wall 6 (low-strength material 6a) (m) is as follows.

[0046] Therefore, the low-strength material 6a is set to satisfy all the above conditions (1) to (4). Note that since the strength of the low-strength material 6a tends to increase with time, it is desirable to conduct a laboratory test in advance to grasp the strength change and determine the timing for performing the extraction work of the outer casing 9 or the casing 7.

[0047] As this low-strength material 6a, for example, low-strength mortar, fluidized treated soil, low-strength grout, etc. can be used.

[0048] Next, the construction method of the in-situ concrete pile 2 as described above will be described based on the embodiments shown in FIGS. 3 to 5. Note that the same components as those in the above embodiments will be denoted by the same reference numerals for description.

[0049] To construct this in-situ concrete pile 2, first, as shown in FIG. 3(a), the outer casing 9 is built into the upper surface of the ground 1, and as shown in FIG. 3(b), while repeating the penetration of this outer casing 9 from the ground surface and the excavation inside the outer casing 9 using a hammer grab or the like, the soil is discharged from the outer casing 9 to the ground, and it is penetrated to a predetermined depth of the ground 1.

[0050] At that time, it is desirable to previously provide a release material made of a sealing material or paint on the inner surface of the outer casing 9.

[0051] Furthermore, when using a release agent made of sealant, it is preferable to apply the sealant only to the portion of the inner circumferential surface of the outer casing 9 that does not penetrate into the ground. Specifically, the release agent should not be applied to the first few meters of the outer casing 9, and only the portion without the release agent should be penetrated into the ground. When using a release agent made of paint, the release agent may not be applied to the first few meters of the outer casing 9, and only the portion without the release agent may be penetrated into the ground, or the release agent may be applied to the entire surface.

[0052] The outer casing 9 is made of a steel pipe pile or the like equipped with a drilling blade (not shown) at its lower end, and has a larger diameter than the casing 7 that forms the pile body 5, with the pipe diameter ratio between the casing 7 and the outer casing 9 being 1.2 or more and 1.6 or less.

[0053] The following are examples of common casing 7mm diameter and outer casing 9mm diameter combinations.

[0054] [Table 1]

[0055] The means by which the outer casing 9 is driven into the ground 1 are not particularly limited, and it may be driven in by a vibro-hammer or the like, or a rotary or oscillating casing driving device may be used.

[0056] Furthermore, during the penetration of the outer casing 9, the position is adjusted using surveying equipment, etc., to ensure that it is concentric with the pile body 5, based on the design value of the pile body 5, while being driven in.

[0057] Furthermore, the predetermined depth to which the outer casing 9 penetrates is preferably a depth that extends to a position deeper than the lower end of the soft ground 4 if soft ground 4 exists near the ground surface.

[0058] Then, the outer casing 9 is driven in to a predetermined depth, and excavation inside the outer casing 9 using a hammer grab or the like, and the removal of soil from the outer casing 9 to the ground are repeated to form the outer pile hole 10.

[0059] Next, as shown in Figure 3(c), the casing 7 is erected concentrically with the outer casing 9 within the formed outer pile hole 10, and the casing 7 is driven in to a position y1 slightly deeper than the bottom surface of the outer pile hole 10. It is desirable to apply a release agent, such as a sealant or paint, to the outer surface of the casing 7 in advance.

[0060] The method for penetrating the casing 7 is not particularly limited, similar to that for the outer casing 9. It may be driven in using a vibro-hammer or the like, or a rotary or oscillating casing penetration device may be used. However, it is preferable to drive the casing 7 to a predetermined depth in the ground 1 while rotating it to ensure concentricity with the outer casing 9.

[0061] Preferably, the penetration depth of the casing 7 is at a position y1 slightly deeper than the bottom surface of the outer pile hole 10, penetrating the soft ground 4 and reaching the upper layer of the normal ground 3.

[0062] Then, as shown in Figure 4, once the casing 7 and the outer casing 9 are installed in a double-pipe configuration, a low-strength material 6a is cast into the gap between the outer surface of the casing 7 and the inner surface of the outer casing 9 to form a diameter reduction prevention wall 6.

[0063] Then, as shown in Figure 5(e), after the low-strength material 6a is poured, the outer casing 9 is withdrawn after about 3 to 4 hours. The withdrawal process is carried out while cutting off the adhesion with the low-strength material 6a using a rotary casing penetration device. It is also desirable to determine the timing of the withdrawal of the outer casing 9 based on the results of laboratory tests conducted in advance.

[0064] In this case, the adhesive strength of the outer casing 9 is such that it can be easily removed by applying a predetermined force. Furthermore, by providing a release agent on the inner surface of the outer casing 9, it can be removed even more easily.

[0065] Then, after the low-strength material 6a is poured, as shown in Figure 5(f), the casing 7 is separated from the diameter reduction prevention wall 6 after about one day and penetrated to a predetermined depth y2 in the ground 1. It is also desirable to determine the timing of the separation of the casing 7 based on the results of laboratory tests conducted in advance.

[0066] At this point, the low-strength material 6a has sufficient adhesion strength to separate the casing 7 from the diameter-reducing wall 6, and also exhibits sufficient compressive strength to prevent the shape of the diameter-reducing wall 6 from collapsing. Therefore, the casing 7 can be easily separated from the diameter-reducing wall 6 and penetrated into the ground 1.

[0067] Furthermore, while there are no particular limitations on the method of penetrating the casing 7, it is preferable to penetrate it while rotating it in order to smoothly separate it from the diameter reduction prevention wall 6.

[0068] Then, the process of driving the casing 7 in and excavating inside the casing 7 using a hammer grab, etc., is repeated, and the soil inside the casing 7 is removed to the surface, driving the casing 7 to a predetermined depth and forming the pile hole 8.

[0069] Once the pile hole 8 is formed, a bucket (not shown) is used to perform bottom treatment such as removing slime from the pile hole 8, and a reinforcing cage (not shown), which is made of reinforcing bars assembled into a cage shape, is installed in the pile hole 8 after this bottom treatment is completed.

[0070] Next, as shown in Figure 5(g), after a predetermined number of days (approximately 3 days) have elapsed since the placement of the low-strength material 6a, and the diameter reduction prevention wall 6 has achieved the predetermined strength, a tremie pipe (not shown) is inserted into the pile hole 8, and concrete 5a is poured into the pile hole 8 while the casing 7 is withdrawn. It is desirable to determine the timing of the withdrawal of the casing 7 based on the results of laboratory tests conducted in advance.

[0071] Then, as the casing 7 is withdrawn and the concrete pouring continues, the lower end of the casing 7 is withdrawn to the depth of the diameter reduction prevention wall 6, and the height of the concrete pouring also reaches the area enclosed by the diameter reduction prevention wall 6.

[0072] At that time, the lateral pressure on the concrete decreases at the concrete placement height, i.e., the upper part of the placed concrete, because the weight of the concrete is lighter. However, the earth pressure received from outside the diameter reduction prevention wall 6 is blocked by the diameter reduction prevention wall 6, and the placed concrete flows to the outer diameter portion of the casing 7 after the casing 7 is withdrawn, i.e., to the inner circumferential surface portion of the diameter reduction prevention wall 6, forming a pile head that is approximately the same as the design diameter D.

[0073] Furthermore, in order to increase the lateral pressure of the concrete and allow it to flow to the inner surface of the diameter reduction prevention wall 6, extra concrete may be poured (reinforced) to a position higher than the design height of the pile head, or a weight may be placed on top of the pile head after the concrete has been poured.

[0074] Then, the casing 7 is completely withdrawn from the pile hole 8, and as shown in Figure 5(h), the pile body 5 is formed inside the pile hole 8, with the pile head surrounded by the diameter reduction prevention wall 6. [Explanation of symbols]

[0075] 1 ground 1 2. Cast-in-place concrete piles 3 Normal ground 4 Soft ground 5. Main body of the pile 6 Diameter reduction prevention wall 7 Casing 8 pile holes 9. Outer casing 10 External pile holes

Claims

1. In a cast-in-place concrete pile, the pile body is formed by concrete being poured into a pile hole, which is created by excavating the inside of a casing that has penetrated the ground, while simultaneously withdrawing the casing. The pile body is provided with a diameter reduction prevention wall extending from the ground surface to a predetermined depth, The diameter reduction prevention wall is formed by a low-strength material cast into an outer casing located outside the casing. The low-strength material is characterized by having sufficient adhesion strength to break off from the casing and the outer casing with a predetermined force, being able to maintain its shape even when subjected to soil water pressure from the ground and pressure from the concrete poured into the casing, and possessing compressive strength that can withstand its own weight.

2. The cast-in-place concrete pile according to claim 1, wherein the thickness of the diameter reduction prevention wall is 10% or more and 30% or less of the pile diameter of the pile body.

3. In a method for constructing a cast-in-place concrete pile, in which a pile hole is formed by excavating the inside of a casing that has penetrated the ground, and concrete is poured into the pile hole while the casing is withdrawn to form the pile body, The process involves driving a larger diameter outer casing into the ground, excavating inside the outer casing, and removing the soil, repeating these steps to a predetermined depth from the ground surface to form an outer pile hole. The casing is then erected within the outer pile hole concentrically with the outer casing, and after the casing has been driven in to a position slightly deeper than the bottom of the outer pile hole, A low-strength material is cast into the gap between the casing and the outer casing to form a diameter reduction prevention wall. Thereafter, the casing is separated from the diameter reduction prevention wall, and the process of inserting the casing, excavating inside the casing, and removing the soil is repeated until a predetermined depth is reached in the ground to form the pile hole. A method for constructing a cast-in-place concrete pile, characterized by forming the pile body by pouring concrete into the pile hole while withdrawing the casing.

4. The method for constructing a cast-in-place concrete pile according to claim 3, wherein the low-strength material has sufficient adhesion strength to break off from the casing and the outer casing with a predetermined force, and is able to maintain its shape even when subjected to the soil water pressure of the ground and the pressure of the concrete poured into the casing, and has compressive strength that can withstand its own weight.

5. A method for constructing a cast-in-place concrete pile according to claim 3 or 4, wherein the diameter reduction prevention wall is formed, and the outer casing is withdrawn before the casing is separated from the diameter reduction prevention wall.

6. A method for constructing a cast-in-place concrete pile according to claim 3 or 4, wherein the casing is driven into the ground to a predetermined depth while being rotated.

7. A method for constructing a cast-in-place concrete pile according to claim 3 or 4, wherein a release agent is provided on the outer circumferential surface of the casing and / or on the inner circumferential surface of the outer casing.

8. The method for constructing a cast-in-place concrete pile according to claim 7, wherein the release agent is composed of a sealing material, and the sealing material is provided only on the outer circumferential surface of the casing and / or the inner circumferential surface of the outer casing in portions that do not penetrate the ground.

9. A method for constructing a cast-in-place concrete pile according to claim 3 or 4, wherein the pipe diameter ratio between the casing and the outer casing is 1.2 or more and 1.6 or less.

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