JPH0441209B2 - - Google Patents

Description

[Detailed description of the invention] (a) Object of the invention Industrial application field The present invention relates to piles made of permeable sand, crushed stone, etc. used in soft ground improvement work, and a ground improvement method using the piles. .

Prior Art It is known that one of the soft ground improvement methods is the sand drain pile construction method. According to this method, a hollow casing is penetrated into the soft ground to a predetermined depth and placed inside the casing. The supplied sand is pulled out while applying vibration to the casing to create a sand pile, or the casing is partially pulled out and the sand is discharged into the ground to form a sand pile. , by re-penetrating the casing and repeating the process of compacting and expanding the diameter of the sand pile several times to continuously create a compacted sand pile, or by making the inside of the casing airtight and letting in compressed air during the process of pulling out the casing. Measures have been taken to create compacted sand piles vertically in the ground by feeding, compressing the sand surface, or applying pressure higher than the passive earth pressure at the bottom opening of the casing through the sand material. ing. The sand piles constructed in this manner were all made of a single material up to the bottom end.

Figures 2 and 3 are schematic cross-sectional views of the ground improvement area created by the above-mentioned construction method, and in Figure 2, based on the load and shape of the upper structure W,
The virtual sliding failure surface (line)
Then, a large number of sand piles s of length l are constructed between the ground improvement width rB, and an embankment B' is applied to the surface.
A superstructure W is constructed. Here, the ground improvement range B is the overall mass, for example (l×rB)
It is understood that it is represented by In addition, since the sand pile s is constructed on the virtual sliding failure surface x, the composite shear stress of the shear stress F (ψ) of the original ground and the shear stress G (φ) of the sand pile is applied to the superstructure W. , preventing slippage and damage.

However, ψ: strength of the original ground, adhesion force φ: internal friction angle of sand Referring to Figure 4, it is a schematic diagram of the above-mentioned ground strength, and assuming that the upper part shows the ground surface,
The strength ψ of the original ground itself is generally smaller in shallower parts and increases as it gets deeper, and the strength due to the sand piles s is almost evenly added to the original ground strength.

Since the virtual slip wave failure surface x passes through a shallow portion of the ground, the original ground strength ψ does not work relatively effectively to strengthen the slip failure surface.

Therefore, as shown in Figure 4, even if the driving pitch p is the same, the driving width of the sand pile s of length l is
rA, sand piles s of length l ₁ (l>l ₁ ) are driven on both sides of rA, each having a width r′C, and the total ground improvement width rC (rC=
rA + 2r′C) with embankment C′ placed on top of it,
In other words, an inverted convex shape ground improvement area C was proposed.
In this case, for example, if l ₁ = 1/2l and rB = rA + r'C, the ground improvement range C will be equal to range B, and the total amount of sand required for sand pile construction will be the same as that shown in the second diagram. Despite this, the number of sand piles driven in shallow ground increases, so the resistance of the improved ground to sliding failure increases in proportion to the number of sand piles built in the ground improvement r′C. . In other words, safety against sliding damage is improved.

Referring to Figure 4, the figure shows a sand pile s of length l ₁ .
This is a schematic diagram of the ground strengthened by sand piles.The increase in strength against sliding failure by sand piles is effective only in shallow parts of the ground, so at least the bottom of the sand piles is
As long as it extends to a position deeper than the depth of the virtual sliding failure surface passing through the ground, the desired effect can be expected.

However, in this case, the amount of sand in embankment C′ and the number of sand piles will increase slightly, and the lower part (unimproved part) of the sand pile driving part of short length l ₁ will be affected by other improvements. There may be cases where the area sinks compared to the area.

Problems to be Solved by the Invention In view of the above-mentioned problems, the present invention aims to develop a sand pile made of a novel composite material for this type of ground improvement, and to construct and create it. , which aims to provide a method for improving soft ground that reduces the area of ground improvement, thereby reducing the amount of improvement materials and number of times of construction, is safer against sliding failure, and is free from the risk of uneven settlement. It is.

(b) Means for solving the structural problems of the invention In order to achieve the above object, the soft ground improvement pile and improved construction method made of the composite material of the invention are comprised of the following requirements.

1. For sand piles, etc. that are constructed vertically continuously in the ground for the improvement of soft ground, at least until the point from the ground surface where the hypothetical sliding failure surface exceeds the depth where the sand piles, etc. cross, Compared to sand,
A ground improvement pile made of a composite material characterized by being filled with granular filler having a larger internal friction angle.

2. A soil improvement pile made of a composite material according to item 1 above, wherein crushed stone or gravel is used as the granular filler having a large internal friction angle.

3 Penetrate the hollow casing to a predetermined depth in the ground,
In a soft ground improvement method in which the sand supplied into the casing is discharged into the ground while pulling out the casing to create a sand pile, etc., the capacity of the sand supplied into the casing is determined by the sand pile created thereby. The upper end limits the pile to an amount that does not reach the point where the virtual sliding failure plane crosses, while subsequently supplying into the casing a granular filler with a larger internal friction angle than sand. A ground improvement method characterized by constructing continuous ground improvement piles made of composite materials.

Effect Piles made of the composite material of the present invention can be constructed on improved ground where the reinforcement of the hypothetical sliding failure surface is not sufficient despite the ground improvement range being sufficient to support the load of the superstructure. For example, the material of the pile in the shallow part of the ground where the hypothetical sliding failure surface passes is a granular filler with a larger internal friction angle than sand, so the shear stress is sufficiently larger than that of sand piles, and sand piles Compared to ground improvement using only soil, it is possible to improve safety against sliding failure.

In addition, since the pile components are not all made of granular filler with a large internal friction angle, it can be constructed relatively economically, and if sliding failure can be prevented, it can be relatively ground improvement. Since the width can be narrowed, the area of ground improvement as a whole can be reduced, resulting in economic advantages such as the reduction in the number of times of driving materials, embankment materials, and sand piles. Furthermore, since all the piles are constructed to have a uniform depth, there is no risk of uneven settlement as explained in the case of the pile shown in Figure 4.

Example Figure 1 is a schematic cross-sectional view of a soil improvement pile made of the composite material of the present invention and the area of soil improvement using the same pile. The plane x and the ground improvement range A are determined, and in accordance with the conditions, a large number of composite piles of length l are constructed at the specified driving pitch between the ground improvement width rA (rC>rB>rA), Embankment A' is applied to the surface of the embankment, and superstructure W is constructed on top of it. x is a virtual sliding failure surface that passes through a shallow part of the ground. t
is a pile made of crushed stone, gravel, etc., which has a larger internal friction angle than the sand pile s, and the depth l ₁ from the ground surface is filled with crushed stones instead of sand, and the virtual sliding failure surface x is , All of these crushed stone (gravel) piles are crossed to prevent sliding damage.
In the case of the Composer method (a type of compacted sand pile construction method), the internal friction angle related to the sand pile strength φ≒
It is about 30°. Referring to FIG. 4, the composite pile of the present invention uses sand piles as described above in the deep part to reduce costs and prevent the occurrence of uneven settlement, and then in the shallow part, i.e. In areas where the original ground strength is low, crushed stone piles with an internal friction angle of approximately 35° are used to reinforce the piles and improve the ability to prevent slipping and failure.

The construction method for the above-mentioned composite piles simply involves paying attention to the calculation and measurement of the volume of sand to be supplied into the hollow casing and the timing of switching the supply material to crushed stone or gravel; other construction methods are the same as those of conventional methods. There's no big difference.

(c) Effects of the invention As described above, if the composite pile of the present invention is used to improve soft ground, the overall area of ground improvement can be small, so pile materials, embankment materials, and piles can be Since the number of times of pouring is reduced, it is possible to save money in terms of cost and length of construction period. In addition, there is no risk of uneven settlement, and special effects and effects can be expected, such as an increased safety factor against sliding failure.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view of soil improvement piles made of the composite material of the present invention and the soil improvement area created using the same piles, and Figures 2 and 3 are respectively the soil improvement areas created using conventional construction methods. Schematic sectional view of 4th
The figures show schematic diagrams of the respective ground strengths. W...superstructure, A, B and C...ground improvement range, l and l ₁ ...pile length, A', B' and C'...embankment, rA, rB and rC...ground improvement width, x...virtual Sliding failure surface (line), s...sand pile, t...crushed stone pile, m...strength of the ground.

Claims (1)

[Scope of Claims] 1. In sand piles, etc. that are continuously constructed vertically in the ground for improving soft ground, at least the virtual sliding failure surface from the ground surface exceeds the depth at which the sand piles, etc. cross. A ground improvement pile made of a composite material that is filled with granular filler that has a larger internal friction angle than sand material. 2. A ground improvement pile made of a composite material according to claim 1, wherein crushed stone or gravel is used as the granular filler having a large internal friction angle. 3 Penetrate the hollow casing to a predetermined depth in the ground,
In a soft ground improvement method in which the sand supplied into the casing is discharged into the ground while pulling out the casing to create a sand pile, etc., the capacity of the sand supplied into the casing is determined by the sand pile created thereby. The upper end limits the pile to an amount that does not reach the point where the virtual sliding failure plane crosses, while subsequently supplying into the casing a granular filler with a larger internal friction angle than sand. A ground improvement method characterized by constructing continuous ground improvement piles made of composite materials.