JP2010065525A - Sand pile preparation method and improved ground in floating-type sand compaction pile construction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems of lacking in a sand quantity corresponding to a sinking-into quantity and lacking in an expanding diameter of a sand pile, since a bulbous shape is formed when the sand pile is deformed sideways and downward, when strength of weak viscous earth is small, in a sand pile preparation method in a conventional floating-type sand compaction pile construction method, on the sand pile preparation method in the floating-type sand compaction pile construction method. <P>SOLUTION: In this sand pile preparation method in the floating-type sand compaction pile construction method for preparing a sand pile only in an upper layer part of a weak viscous earth layer, a casing 11 is penetrated into the weak ground, and when preparing the sand pile of a first cycle after filling sand in the casing, the sand quantity for forming a desired bulbous body 13b is inputted by increasing a quantity to a standard sand quantity when preparing the sand pile of the first cycle of an ordinary sand compaction pile construction method performed penetratingly up to a sea bottom surface from a lower surface boundary of a weak ground viscous earth layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sand pile formation method in a floating SCP method among sand compaction pile methods (hereinafter referred to as an SCP method), and an improved ground using a sand pile formed by the method. The SCP method is a typical ground improvement method for increasing the strength of the ground by creating a compacted sand pile in a soft viscous soil layer. Sand piles are generally formed by penetrating from the lower boundary of the soft-viscous soil layer to the bottom of the sea, but in some cases, sand piles are created only in the upper layer of the soft-viscous soil layer. This is called “type SCP method”.

  The sand pile creation method in the above floating SCP method is driven compaction method (vibrocomposer method), tip vibration compaction method (strong sandpile method), tip diameter expansion compaction method (mechatronic consolidation system), etc. For example, the so-called “return method” of the driving compaction method, as shown in FIG. 2, the casing 11 filled with the sand 10 is once pulled up in the soft ground 12 and the same as the casing 11. After the sand pile 13 having a diameter is formed, the sand pile 13 is expanded and simultaneously compacted by pushing the casing 11 back, thereby forming a predetermined compacted sand pile 13 (see Patent Document 1). In FIG. 3, casing diameter: Dc, pulling height: h, retraction amount: s, and finished diameter: Ds are design matters. However, looking at the past construction results of the SCP method, it can be seen that Dc = 1.175 m, h = 3 m, s = 2 m, and Ds = 2 m are the most frequently used combinations. Among them, Dc is a restriction of construction machines, and Ds is determined by design and cannot be changed at the time of construction. However, h and s can be adjusted according to construction conditions.

Japanese Patent Laid-Open No. 58-50216

The creation of the sand pile by the reversal method is that a sufficient reaction force is exerted at the lower end of the sand pile with respect to the pushing force, which is a reliable condition for sand pile creation with expansion and compaction. If it is a normal penetration type SCP method, a sufficient reaction force can be obtained from the foundation ground having a high bearing force existing under the soft viscous soil layer.
However, it is difficult to expect a sufficient reaction force on the soft and viscous soil in the sand pile construction method in the floating SCP method, and the indentation phenomenon occurs due to the lack of supporting force, and there is a concern about insufficient diameter expansion and compaction. . In particular, when the strength of the soft and viscous soil is small in the first-cycle reversal process, which is the initial stage of sand pile formation, the sand pile is deformed laterally and downwardly, resulting in a bulbous shape 13a. Is expected to form. The part located below the planned bottom level of the sand pile is the indented part, and in the area where sand pile creation is planned, the amount of sand corresponding to the amount of indentation is insufficient, so the diameter of the sand pile is insufficient. Become.
The sand pile creation method and the improved ground in the floating SCP method according to the present invention are to create a compacted sand pile reliably in such a floating SCP method, and to realize the improved ground by this, the conventional problem is solved. It has been proposed to solve.

  The gist for solving the above-mentioned problems of the sand pile formation method in the floating sand compaction pile method according to the present invention is to create a sand pile pile only in the upper layer part of the soft viscous soil layer. In the sand pile formation method in the construction method, the amount of the sand for forming a desired bulbous body at the time of sand pile formation in the first cycle after the casing is penetrated into soft ground and the sand is filled in the casing Is added to the standard sand amount at the time of sand pile creation in the first cycle of the normal sand compaction pile method that penetrates from the lower boundary of the soft soil cohesive soil layer to the bottom of the sea.

Moreover, 1.25 ≦ Ds / Dc ≦ 2. As the casing diameter: Dc, the finished diameter of the sand pile: Ds, the casing lifting height: h, the casing retraction amount: s, h * = h−s. By adjusting h / h * for the Ds / Dc value of 25, the input sand is increased to a maximum of 2.0 times the standard sand volume, and the sand pile is created by the backlash method. .
Further, in order to increase the amount of the input sand to be increased to α times the standard sand amount, after the casing is filled with sand, the casing is pulled up to a height that is α times the lifting height in the conventional method. This includes building sand piles by increasing the amount of strike back as much as increasing the height.

  The improved ground according to the present invention is improved by the sand pile formed by the sand pile forming method of the floating sand compaction pile method according to the present invention.

  According to the sand pile creation method and the soft ground in the floating SCP method of the present invention, when sand piles are created only in the upper layer portion of the soft viscous soil layer, the sand to be introduced into the casing in the first cycle is the standard sand amount. The shortage of the diameter expansion at the lower end of the sand pile is eliminated by increasing the amount to form a large-sized bulbous body. Further, when the sand pile is continuously formed on the bulbous body, the bulbous body contributes to the reaction force supply against the pushing force. Thereby, there exists an outstanding effect that the reliable creation of a compacted sand pile is attained.

It is explanatory drawing which shows the result of the FEM (finite element method Finite Element Method, the same hereafter) ground deformation analysis which concerns on the bulb-shaped body 13b constructed in the sand pile construction method in the floating SCP method according to the present invention. It is explanatory drawing which shows the Example of the driving | operation compaction method in the SCP method concerning a prior art example in a procedure. It is explanatory drawing which shows a mode that a sand pile is formed in height h * = (h-s) by drawing and pushing in with the casing of the 1st cycle in sand pile formation. It is explanatory drawing which shows the mode of creation of the bulbous body 13a which is the sand pile of the 1st cycle by the SCP method in the soft ground in a prior art example by FEM ground deformation analysis. It is explanatory drawing which shows the application range of this invention while explaining the relationship between h / h * which implement | achieves standard sand amount with respect to various Ds / Dc value, and the rate of increase of input sand amount and h / h * .

  In the floating SCP method according to the present invention, as shown in FIG. 1, the sand pile for the first cycle is formed into a bulb-like body 13b that exhibits a firm reaction force. The amount of sand to be charged / filled is increased with respect to the standard sand amount. In the present invention, the soft ground is intended for viscous soil layers having an N value of 7 or less that exist on the sea and on land.

In FIG. 3, the input sand amount V0 = (π / 4) · Dc2 · h.
If the sand pile volume after reversal is V1, the volume change rate due to compaction is m,
V1 = m · V0.
On the other hand, the sand pile volume assumed in the design is V2 = (π / 4) · Ds2 · h *, and therefore, the sand input rate α is as follows.
α = m (h / h *) / (Ds / Dc) 2:
Calculation formula: From α = (V1 / V2) = (mV0 / V2) = m (h · Dc2 / h * · Ds2).

Ds / Dc is the finished diameter of the sand pile made dimensionless with the casing diameter, and can take various values every time the ground improvement work is carried out. By adjusting h / h *, α = 1.0 can do. This is the conventional method, and the amount of sand input at this time is the standard sand amount.
On the other hand, by adjusting h / h * so that 1.0 <α ≦ 2.0, the input sand is increased to a maximum of 2.0 times the standard sand amount, and the sand is returned by the backlash method. Create a pile. Furthermore, the raising and driving of the casing at the time of the sand pile construction in the first cycle can be performed in several times.

Here, the charging rate α indicating the degree of increase in sand needs to be larger as the strength of the soft and viscous soil to be improved is smaller, but the N value ≈ 0 such that α> 2.0. This ultra-soft clay soil is outside the scope of the present invention. Also, if the N value of the cohesive soil layer is greater than 7, the sand pile can be reliably created by the conventional method of α = 1, so this is also out of scope. That is, the N value of the soft and viscous soil targeted in the present invention is about 0 to 7, and an α value of 1.0 <α ≦ 2.0 is set correspondingly.
As for the Ds / Dc value, the range of 1.25 ≦ Ds / Dc ≦ 2.25, in which the floating SCP method is considered effective, is targeted. (Hatch range in FIG. 5)

  An example of sand pile increase is as follows: Ds = 2m, Dc = 1.175m (Ds / Dc = 1.70), m = 0.966 (typical value according to construction results), h = 3m, h * = 1m , Α = 1.0 is standard construction by the conventional method. On the other hand, when h = 3.9m and h * = 1m, α = 1.3, which is 1.3 times the amount of standard sand. The sand pile will be constructed by increasing the amount. (Position of ○ in Figure 5)

  In Example 1, the sand 11 for forming a desired bulbous body 13b is formed when a sand pile is formed in the first cycle after the casing 11 is inserted into the soft ground and the sand 10 is filled into the casing 11. The amount of sand when pulling up the casing 11 having a diameter Dc = 1.175 m by 3 m and returning it 2 m to create a sand pile 13 having a height of 1 m and a diameter Ds = 2 m (hereinafter referred to as standard sand amount) ) To 1.3 times, and put into the casing.

  Thus, in order to make the amount of sand thrown into the casing 11 1.3 times the amount of standard sand, after the casing 11 is filled with the sand 10, the lifting height h of the casing 11 is set to 3.9 m. This is achieved by pulling up and setting back the amount of return s = 2.9 m and forming the sand pile 13b.

  The reason why the height h of the casing 11 is set to 3.9 m is 3 m × 1.3 times = 3.9 m because the height h of the casing 11 is 3 m. Since h * = h−s = 1 m is set, the amount of strike back s = 2.9 m.

  In this way, as shown in FIG. 1 as a result of the FEM ground deformation analysis, a bulbous body 13b having a finished diameter Ds = 2 m is formed. Despite the increased size of the bulbs formed and indentation, there is no shortage of diameter expansion.

  During the sand pile construction in the first cycle, the casing 11 can be pulled up and driven in multiple times. For example, the lifting height h1 = 2 m and the return amount s1 = 1.5 m can be followed by the lifting height h2 = 1.9 m and the return amount s2 = 1.4 m.

  In this way, the large-sized bulbous body 13b can be formed, thereby eliminating the insufficient diameter expansion at the lower end of the sand pile. When the sand pile is continuously formed on the bulbous body 13b, the bulbous body 13b contributes to the supply of the reaction force against the pushing force, and the formation of the compacted sand pile is ensured.

  Moreover, in this Example 1, the sand thrown in in the first cycle was set to 1.3 times the standard sand amount. Of course, if the strength of the target soft viscous soil is different, the desired sand pile diameter to be created is set. The required increase in the amount of input sand to achieve will also vary. In the present invention, in the case of the floating SCP method, the amount of sand to be introduced in the first cycle is appropriately compared to the standard sand amount so that a bulbous body 13b that acts in the same manner as in Example 1 can be formed. Is to increase the amount.

  The improved ground according to the present invention is improved by the sand pile formed by the sand pile construction method of the floating SCP method.

  The floating SCP method according to the present invention is described with the case where there is a soft viscous soil layer to be ground improved under the sea floor, but the soft viscous soil layer present under the ground surface is improved. Even in this case, it can be applied without problems.

10 sand,
11 casing,
12 Soft ground,
13 Sand pile,
13a, 13b Bulboid.

Claims (5)

In the sand pile construction method in the floating sand compaction pile method, which creates a sand pile only in the upper part of the soft viscous soil layer,
When the sand pile is built in the first cycle after the casing is inserted into the soft ground and the sand is filled in the casing,
Standard sand at the time of sand pile construction in the first cycle of the normal sand compaction pile method in which the amount of sand to form the desired bulbous body is penetrated from the lower boundary of the soft soil cohesive soil layer to the bottom of the sea To increase the amount of input,
A sand pile construction method for floating sand compaction pile construction. Casing diameter: Dc, finished diameter of sand pile: Ds, lifting height of casing: h,
Casing reversal amount: s, h * = h−s, 1.25 ≦ Ds / Dc ≦ 2.25 Ds / Dc value is adjusted by adjusting h / h * to obtain standard sand amount To increase the amount of sand input up to 2.0 times the maximum, and create a sand pile by the backlash method,
The sand pile creation method of the floating sand compaction pile method according to claim 1. To make the sand amount α times the standard sand amount, after the casing is filled with sand, the casing is pulled up to a height that is α times the lifting height in the conventional method, and this is the same as the increase in the lifting height. Just create a sand pile with an increased amount of backlash,
The sand pile creation method of the floating sand compaction pile method according to claim 2. The lifting and driving of the casing during sand pile construction in the first cycle is performed in multiple times.
The sand pile creation method of the floating sand compaction pile method according to claim 3. The ground was improved by the sand pile formed by the sand pile forming method of the floating sand compaction pile method according to claim 1,
Improved ground characterized by

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