JP2006348466A - Improved ground concurrently using different types of sand compaction piles (scp) - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide low-replacement improved ground using steel slag. <P>SOLUTION: In a ground improving structure using the steel slag, a pile 1 made of an unhardenable material such as natural sand, and a steel slag pile 3 are concurrently used in a juxtaposed manner. In the improved ground concurrently using different types of SCP (sand compaction piles), an upper layer section 7 of the improved ground 6 is the improved ground 6 using the piles 1 and 3, and a lower layer section 8 thereof is the improved ground 6 using the pile 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an improved ground by a sand compaction pile method (hereinafter also referred to as an SCP method), and in particular, steel slag piles using steel slag by the SCP method and different types of SCP piles of the sand pile of the SCP method are used in combination. Regarding improved ground.

  Conventionally, as a ground improvement construction method, (1) a sand compaction pile construction method (hereinafter also referred to as an SCP construction method) in which a sand pile 1 as shown in FIG. 7 is placed on a soft clay ground 2 is known.

  The above-mentioned SCP method uses sand to forcibly place a solid large-diameter sand pile into the ground to be improved. In the case of loose sand ground, liquefaction prevention due to compaction is weak. This is a ground improvement method for the purpose of strengthening strength or preventing consolidation settlement by forcibly replacing the clay ground.

  In particular, the SCP method for clay ground has high replacement improvement (improvement rate ≧ 60 to 70%) and low replacement improvement (improvement rate ≦ 30%). Among them, the low replacement SCP method is the high replacement SCP method. Compared to the construction method, the number of piles is small and economical.

  On the other hand, sand piles used in the SCP method have been used for high quality natural sand. However, sand piles have been used in many places mainly in port construction in recent years. Effective utilization of recycled materials such as slag is promoted.

  For example, when the high replacement SCP method is applied to clay ground, (1) The improvement effect as a composite ground consisting of SCP pile and clay ground by forced partial replacement with SCP pile is expected. The performance required for this is a point on strength, and it is possible to use steel slag piles instead of sand piles.

  On the other hand, when the low replacement SCP method is applied to the clay ground, in addition to (1) the improvement effect as a composite ground composed of the SCP pile and the clay ground by the forced partial replacement by the SCP pile, (2 ) There is a point which aims at the effect of the strength increase by consolidation of the soft clay ground by the drain effect of the SCP pile. When a steel slag pile of the same length as the sand pile is constructed in the sand pile of such a low replacement SCP method, the steel slag, for example, steelmaking slag is hardened due to the latent hydraulic property and the water permeability is significantly reduced. Since the effect of (2) is hindered, there is a problem that there is a limitation in use such as difficulty in applicability of the steel slag pile to the SCP method with improved low replacement. In addition, with low displacement improvement using steel slag piles, stress concentration on steelmaking slag piles due to hardening of steelmaking slag occurs and it becomes impossible to function as a drain material due to reduced water permeability. It is also known that this is not possible (see Non-Patent Document 1, for example).

Moreover, in the clay ground, instead of the sand pile in the low substitution SCP method, as shown in FIG. 6, when the low substitution improvement of only the steelmaking slag pile 3 is made, the steelmaking slag pile 3 is significantly hardened and permeable. The low replacement improvement method using only the steel-making slag pile 3 is difficult because it causes a decrease in the consolidation promoting function of the soft clay ground 2 due to the decrease in the properties. Moreover, when doing in this way, the problem also arises that (2) a decrease in yield strength and an increase in horizontal displacement accompanying the transition to the overturning failure mode of the ground improvement part due to the concentration of the horizontal force on the steel slag pile 3 (for example, Non-patent document 2).
Issuance of Coastal Development Technology Center, Steelmaking Slag Use Handbook for Port Construction P19-P20, 2000.3 Naoki Kitazume et al., Destruction behavior P1-P28 of fixed-type pile-shaped deep-mixed ground, Report from the Port Engineering Laboratory, 1998.

  As described above, even though the steelmaking slag pile 3 can be used for the high replacement SCP method, there is a problem that it cannot be used for the low replacement SCP method.

  It is an object of the present invention to provide an improved ground using different types of SCP piles that can advantageously solve the above-mentioned problems in the low replacement SCP method in the ground improvement.

  In order to advantageously solve the above-described problems, the improved ground using the different types of SCP piles of the present invention uses two types of SCP piles, an SCP pile using steel slag and an SCP pile using natural sand. In the improved ground, the length of the SCP pile using steel slag is shorter than the length of the SCP pile using natural sand or the like. As a result, steel slag piles and non-hardening material piles are formed on the upper part of the improved ground, and the lower part of the improved ground is made of only non-hardening material piles such as natural sand having a consolidation effect.

The present invention has the following effects.
(1) Since the portion of the pile made of non-hardening material such as natural sand exhibits the action of the drain material, there is a consolidation effect of the ground.
(2) Since the upper layer portion of the improved ground has a higher displacement improvement than the lower layer portion, the resistance to overturning damage due to horizontal force is improved.
(3) Since the improved upper layer is a higher displacement improvement than the lower layer, the consolidated subsidence becomes a part of the lower layer, and the amount of subsidence is reduced, and the consolidation of the entire improved ground is expected Compared with the SCP pile method, the settlement period is shortened, so the construction period can be shortened.
(4) Compared with the low replacement method using only steel slag piles, the bearing force can be increased by the improved ground by expanding (increasing depth) the arc slip line that gives the minimum safety factor.
(5) Compared to the case where the entire improved ground is a high replacement improved ground, the construction is easy and economical.

    Next, the present invention will be described in detail based on the illustrated embodiment.

  1 to 3 show an embodiment of the present invention, in which a non-hardening material 4 such as natural sand by an SCP method is placed on a submarine clay ground 2 to form a long non-hardening material. A large number (required number) of piles 5 are formed at intervals in the front-rear direction and the left-right direction of the ground improvement area. Moreover, the short steel slag pile 3 using the steel slag by the SCP method is formed. That is, the non-hardening material pile group by many long non-hardening material piles 5 and the steel slag pile group by many short steel-making slag piles 3 formed between these become a revetment structure. It is formed in a mixed manner along.

  As shown in the figure, it is an improved ground 6 in which a long non-hardening material pile 5 and a short steel slag pile 3 are used in parallel on a clay ground 2, and the placement dimensions of the steel slag pile 3 are shown in the figure. In this form, it is about ½ of the placement dimension of the pile 5 made of non-hardening material such as natural sand, but it can be appropriately set depending on the design.

  In the improved ground 6 constructed as described above, the upper layer portion 7 in which the non-hardening material pile 5 and the steel slag pile 3 are mixed becomes a high replacement improved ground compared to the lower layer improved ground, and the lower layer portion 8 Becomes a low replacement improved ground of only the pile 54 made of non-hardening material such as natural sand.

As described above, the improved ground 6 of the present invention using the short steel slag pile 3 by the SCP method and the long non-hardening material pile 5 by the SCP method has the following advantages.
(1) Since the function as a drain material can be exhibited by a pile 5 made of non-hardening material such as natural sand placed in parallel with the steel slag pile 3, consolidation by hardening the steel slag SCP pile 3 There is no reduction in cure.
(2) In the improved upper layer portion 7, since the replacement is improved higher than the lower layer portion, the resistance to overturning damage due to horizontal force is improved.
(3) Since the upper layer portion 7 is an improved layer in which two types of piles are mixed and has high strength, it is not particularly necessary to improve consolidation, so that the consolidation period can be shortened and the amount of settlement can be suppressed.
(4) Compared with the low replacement method using only steel slag piles, the bearing capacity can be increased by the improved ground by expanding (increasing depth) the arc slip line that gives the minimum safety factor.
(5) The construction is easier and more economical than the case where the entire improved ground is a high replacement improved ground.

The steel slag mentioned above means blast furnace slag (blast furnace decooling slag, blast furnace granulated slag) and steelmaking slag.
The steelmaking slag is a stone-like by-product mainly composed of limestone that is produced in the steelmaking process by removing unnecessary components from hard and brittle pig iron produced in a blast furnace and making it tough and workable steel, Converter slag, hot metal pretreatment slag, electric furnace slag, and the like can be used.

  Moreover, as said non-hardening material, copper granulated slag, ferronickel slag, coal ash granulated material, concrete waste etc. can also be used besides natural sand.

  In the illustrated embodiment, a discarded stone mound 9 is formed on the improved ground, and a caisson 10 is sequentially deposited and settled in series on the discarded stone mound 9, and a filler such as waste is appropriately filled in the caisson. Then, the concrete floor slab 11 and the superstructure 12 are provided, and the backfill soil 13 is filled in the back of the caisson 10 to form a caisson revetment structure 14.

As described above, the present invention can provide the following effects.
(1) Since the action of the drain material is shared by the non-hardening material pile such as sand having a long casting length, there is a consolidation effect of the ground.
(2) Since the upper layer portion of the improved ground has a higher displacement improvement than the lower layer portion, the resistance to overturning damage due to horizontal force is improved.
(3) Since the improved upper layer is a higher displacement improvement than the lower layer, the consolidated subsidence becomes a part of the lower layer, and the amount of subsidence is reduced, and the consolidation of the entire improved ground is expected. Compared with the conventional SCP pile construction method, the construction period can be shortened because the settlement period is remarkably shortened, for example, by half.
(4) Compared with the arc slip line r (see Fig. 5) of the low displacement improved ground 6 using only steel slag piles, the arc slip line R that gives the minimum safety factor is expanded (deepening), so that the steel slag piles Compared with only the low replacement improved ground, the supporting force can be further increased.
(5) Compared to the case where the entire improved ground is a high replacement improved ground, the construction is easy and economical.

Here, with reference to FIG. 4, the arrangement | positioning form and improvement rate of the non-hardening material pile 5 are demonstrated, and the shape which connects the non-hardening material pile 5 center like FIG. When the diameter is 2 m (cross-sectional area As = 3.14 m ² ) and the non-hardening material pile 5 is driven at an interval of x = 2.1 m, the improvement rate is = 0.71. Similarly, when the regular triangle of (b) is used, the improvement rate as = 0.82. Similarly, in the rectangular arrangement of (c), the improvement rate is 0.36 when x1 = 4.2 and x2 = 2.1. It becomes. By appropriately setting the diameter and arrangement of the non-curable material pile 5 and the arrangement interval, the improvement rate can be appropriately set to about 30% to about 80%.

  As shown on the left of FIG. 4 (d), after a number of non-hardening material piles 5 made by the SCP method are pre-constructed on the ground 2 such as clay ground at intervals, the same pile construction device is used on the right. As shown, when the steel slag pile 3 is constructed between the non-hardening material piles 5 by the SCP method, it can be efficiently constructed using the same pile construction apparatus. Moreover, after constructing many steel slag piles 3 in advance, non-hardening material piles 5 may be constructed between the steel slag piles 3. The length of the steel-making slag pile 3 relative to the length of the non-hardening material pile 5 is appropriately set depending on the design.

The use of the ground improvement range and improvement rate by the SCP method is generally determined by a stability analysis assuming an arc slip under normal load action conditions as shown in FIG.
In other words, impetus causing arc slip, as a moment around the center of the arc point O point is given by _{M R = ΣF R · L R} . When considering the slip clockwise Here, the center of gravity of F _R is the weight of the soil-structure to the right of the vertical line passing through the arc center point, L _R is soil-structure from a vertical line that passes through the arc center point It is the distance to. On the other hand, the moment M as a resistance to the arc slip, and the moment M _{L =} ΣF _{L · L L} around point O in the left part of the vertical line, moments about point O by the resistance of the ground of the arc sliding surface M _S = Sum of Στ · R. Here, τ is the shear strength of the ground, and R is the radius of the arc.
Ensuring safety for ground breaking against arcuate slip safety factor Fs represented by the ratio of the resistance moment M for starting moment M _R is performed by confirming that the desired value.

For the ground improved by the SCP method, the shear resistance of the above ground is the following formula considering the improvement rate by the SCP pile, the shear strength of the SCP pile, the shear strength of the original ground, and the strength increase due to the consolidation of the original ground ( The shear strength as the composite ground represented by 1) is used.
τ = (1−a _S ) (c ₀ + c / p · (σ _c · z + μ _c · σ _z −P _C ) · U) +
(Γ _s z · μ _s · σ _z ) a _s · tan φ _s · cos ² θ (1)

Here, in the formula (1),
τ: Shear resistance of improved ground a _s : Substitution rate c ₀ : Adhesive force of cohesive soil σ _z : Increased stress due to loading μ _c = 1 / [1+ (n−1) a _s ]
μ _s = n / [1+ (n−1) a _s ]
n: Stress sharing ratio U: Pressure density c / p: Adhesion rate increase coefficient γ _s : Unit volume weight of sand in water Weight [= (1-a _S ) γ ′ _c + a _S γ ′ _s ]
μ _s , μ _c : Stress concentration (reduction) coefficient P _c : Preliminary consolidation stress z: Depth of earth covering θ: Angle formed by sliding surface and horizontal plane

From the above formula (1), the c / p · (σ _c · z + μ _c · σ _z −P _C ) · U term on the right side of the above equation is ignored in the high substitution method, but an increase in the consolidation strength of the clay is expected. In the low replacement method, the shear resistance of the improved ground is greatly influenced by this term. That is, in the low-substituted non-curable material pile 1, in accordance with the consolidation degree U increases, increased adhesive force due to compaction (upper right-hand side of equation _{c / p · (σ c ·} z + μ c · σ z -P C) · U ) And the shear resistance is increased.
The term (γ _s z · μ _s · σ _z ) a _s · tan φ _s · cos ² θ means the shear strength of the sand pile.

  In the above embodiment, the case where the present invention is applied to the lower ground of the revetment structure has been described. However, when the present invention is implemented, the present invention may be applied to soft ground other than the clay ground.

BRIEF DESCRIPTION OF THE DRAWINGS It is a longitudinal front view which shows the state which built the improved ground which applied the ground improvement construction method using the steel slag of this invention, and the caisson revetment on the improved ground. It is a cross-sectional plan view of the upper layer part of FIG. It is a cross-sectional plan view of the lower layer part of FIG. (A) (b) (c) is a top view which shows the arrangement | positioning form of a sand pile, respectively, (d) is a top view which shows an example of the construction form which forms a steel slag pile after forming a sand pile. It is explanatory drawing for demonstrating that an arc slip line expands in the case of the improved ground which implemented this invention. It is a vertical front view which shows the state which built the improvement ground only of the steel slag pile, and the caisson revetment on the improvement ground. It is explanatory drawing for demonstrating the destruction of a ground, and the ground support force improvement mechanism by a SCP method.

Explanation of symbols

1 Pile made of non-hardening material such as sand pile 2 Clay ground 3 Steel slag pile 6 Improved ground 7 Upper layer 8 Lower layer 9 Discarded stone mound 10 Caisson 11 Concrete slab 12 Upper work 13 Backfill soil 14 Caisson revetment structure

Claims (1)

  In SCP improved ground consisting of SCP pile using steel slag and SCP pile using natural sand etc., the length of SCP pile using steel slag is shorter than the length of SCP pile using natural sand etc. Improved ground using different types of SCP piles.

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