JPH0830331B2 - Soft ground improvement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Object of the Invention <Industrial field of application> The present invention relates to a method for manufacturing a sand pile for improving soft ground by controlling pile diameter.

<Prior art> Conventionally, in designing soft ground improvement work, based on the results of soil surveys at multiple points in the improved area, for example, an average design ground strength is designed and assumed. The ground strength target value corresponding to the weight and shape of the superstructure was indexed, and the diameter of the constructed sand pile and its construction pitch were determined so that the target strength could be obtained after ground improvement.

However, it is unavoidable that there is a variation in the strength of the wide area ground that cannot be grasped only by the results of preliminary soil surveys at a limited number of points.Therefore, the ground strength after improvement by the above method is However, there was a problem that the unevenness of the ground appeared as it was and that the ground was not always improved uniformly.

Therefore, in order to solve the above-mentioned problems, prior to the creation of each sand pile, the soil quality of the original ground at the site of construction was detected, and the diameter of the sand pile and A construction method has been proposed in which each sand pile is constructed by changing one or both of the strength and the strength (see Japanese Patent Publication No. 61-25859).

By the way, a sand discharging and compacting member is provided at the lower end of the intermediate pipe penetrating into the ground, and the member is forcibly moved up and down while pulling out the pipe, and discharging the sand previously filled in the hollow pipe into the ground, Moreover, in the compaction sand pile construction method in which it is pressed to perform compaction, the pressing force of the sand discharge and compaction member; F original ground strength; C _S construction sand pile diameter; A _S (typical in area Constructed sand pile strength; B (Φ, expressed by internal friction angle, non-dimensional), the following relational expression holds between them.

F = K ₁ · A _S · B · C _S …… (1) where K ₁ is a coefficient related to geology.

If the ground strength after improvement is to be made uniform, the F value in the above equation (1) should be regarded as a comprehensive index for construction management, and F = A _S or B with respect to C _S so as to keep it constant, or It can be seen that the purpose can be achieved by managing and constructing both sizes.

As a specific example using this relational expression, a sand discharge and compaction member, a voltage corresponding to the hydraulic pressure immediately before the stroke end of a hydraulic (hydraulic pressure cylinder) mechanism for operating up and down, and a hydraulic cylinder stored in advance Based on the data of the effective cylinder area of the device, the F value is then detected. The detected F value and the set (target) F ₀ value are compared, and if the two values do not match, a signal is sent to the control device, and a control signal issued from this causes an element related to the diameter of the constructed sand pile, such as a hollow. The sand pile construction method of pulling out the hollow pipe while making the detected F value match the set F ₀ value by controlling the winding speed of the winding winch for pulling out the pipe (JP-A-58- 1648
No. 14) is also being developed.

<Problems to be Solved by the Invention> In the above construction method, it is necessary to control the size of A or B or both of them so that F = constant.
As shown in the first diagram, a relatively low substitution rate a _S (= A _S / A ₀ = 10 to 3)
Ground improvement of around 0%, A ₀ ; shared area per sand pile), assuming a case where the construction pitch of sand piles is relatively large compared to the diameter of sand piles Therefore, the sand pile strength B may be considered to be a constant value in practical use.
F / A _S = K ₂ · C _S …… (2) By modifying equation (1), K ₂ is a coefficient different from K _1, and therefore this ground strength C _S (= K · F / A By instructing and managing a new sand pile diameter A to _S ), the above-mentioned uniform ground improvement can be realized.

The construction method of the present invention is intended to provide a pile diameter instruction management construction method for ground improvement based on the above-mentioned low substitution rate sand pile construction.

However, K = 1 / K ₂ (b) Configuration of the Invention <Means for Solving Problems> The method of the present invention has the following constituent features in order to achieve the above object.

(1) When creating a sand pile while forcibly moving up and down the sand discharge and compaction mechanism provided at the lower end of the hollow pile forming hollow pipe, when creating a sand pile, the cross-sectional area / allocation of each sand pile Area is 10 to 30%
In the process of constructing sand piles by continuously pulling out hollow tubes and compacting them while detecting the ground soil strength during the sand pile construction by the low substitution rate improvement method before and after, From the correspondence, calculate the sand pile diameter that satisfies the improvement target value in light of the detected ground foundation strength, and create a compacted sand pile while controlling to form the calculated and instructed sand pile diameter. A soft ground improvement method characterized by:

<Operation> (1) A sand pile hollow tube with a sand discharging and compacting mechanism at the lower end and an exciter at the upper end is suspended by a wire and erected on soft ground, and then vibration is generated. While operating the vessel, gradually loosen the hanging wire to penetrate the hollow tube into the ground.

(2) Inserting and filling sand material into the pipe until the intermediate pipe penetrates to a predetermined depth of the soft ground or until it penetrates, and pulls out the hollow pipe and at the same time activates the sand discharge and compaction mechanism The sand material is discharged and left in the ground, and the discharged sand material is compacted.

Based on the material prepared logically or empirically in advance for the strength C _{S of the} original ground obtained at this time, the instruction of the sand pile diameter that satisfies the improvement target value is received, and the diameter of the compacted sand pile is changed to the indicated diameter. Control until it becomes equal to.

In that case, change the length of the upper and lower strokes or the cycle of the hydraulic device that forcibly moves the compaction mechanism up and down, or adjust the drawing speed of the hollow pipe to adjust the sand pile diameter. Various means are provided for controlling the size.

(3) While confirming that the diameter of the created sand pile has reached the desired diameter, the hollow tube is continuously drawn out, and if necessary, the drawing is stopped and the sand material is replenished into the tube, and the strength of the depth is increased. The sand pile diameter that satisfies the improvement target value for C _{S is} calculated each time, and the process described in (2) above is repeated.

(4) By repeating the steps described in (2) and (3) above, one compacted sand pile that is continuous from the predetermined depth of the original ground to the surface of the ground is created.

When the hollow pipe described in (1) above is penetrated, (i) the reaction force of the ground against the sand discharging and compaction mechanism is measured via hydraulic pressure, and the original ground C _S and its change amount with respect to the depth gauge are measured. To measure.

(Ii) Alternatively, a cone tester provided at the lower end of the hollow tube is used to convert the penetration resistance of the hollow tube into an electronic signal, and the strength C _S with respect to the depth of the ground and its change are measured.

Is added, the ground strength C _S of the depth becomes known in the process of forming the compacted sand pile described in the above (2), (3) and (4), so this known strength C _S Can also be used to perform the steps described in (2), (3) and (4).

<Example> (No. 1) FIG. 2 shows the case of clay ground (stable measure against slippage failure), and (a) is a schematic cross-sectional view when embankment is applied to the ground improvement area. Sometimes the complete rate F _S for slip failure is determined in order to inspect whether the embankment can be completely constructed.

If the height, shape, and soil quality of the embankment are fixed, this F _S can be obtained from the strength C _{S of the} clay ground and the substitution rate a _S , and this relationship is shown in (b) above. (if fixing the a ₀ and a _S and a _S synonymous) C _S ~F _S ~A is a relationship diagram.

In the (b) Figure, C _S in the x-axis, F in the positive direction of the y-axis _S, take the A _S in a negative direction, now in C _S, for example F against _{S S} =
It is assumed that a constant A _S (s) that satisfies 1.2 is calculated.

Here, when C _S changes variously, for example, like the normal distribution curve shown in FIG. 7B, if A _S = constant value ( _S ) (m ′ line in the figure), then F as the calculation result is obtained. _S is smaller than F _S = 1.2 when C _S is small, and is larger than 1.2 when C _S is large (see the l ′ line).

On the other hand, when C _S changes, F _S = 1.2 (l
To satisfy the condition (line), the relationship between C _S and A _S is (b)
It must be on line m in the figure.

(I) For each construction site, the m line corresponding to the l line in the relationship diagram of FIG. 2 (b) is obtained and stored in advance.

In addition, from equation (2), C _S = K ₃ · F / A _S …… (3) In equation (3), the coefficient K ₃ is set by pre-test construction or empirical verification from construction results.

(Ii) At the start of the formation of the sand pile (at the deepest part), first the standard _AS (eg
_S ) is performed, and at the same time, the value of the pressing force F ₁ of the sand discharging and compacting member is obtained. Using this A _S and F ₁ , formula (3) is used to calculate the original ground strength C _S1 near the construction depth.

A _S1 corresponding to the above C _S1 is read from the m line in the C _S 〜 F _S 〜 A relationship diagram, and the next sand discharge and compaction member is driven to
_{Install S1} . At that time, a new pressing force F ₂ is obtained at the same time, a new C _S2 is calculated again by the equation (3), a new A _S2 is found from the m line of the C _S 〜F _S 〜A relationship diagram, and the next Realize new A _{S2 in} driving.

After this, this procedure is repeated a great number of times, and each time, the renewed As sand pile is continuously realized, and the construction of one sand pile is completed.

(Iii) In the above, as a means for changing A _S , for example, (a) adjustment of the drawing speed of the hollow tube, that is, adjustment of the winch winding speed of the hollow tube, (b) sand discharge and compaction Examples of such methods include adjusting the operation stroke of the member, or (c) adjusting the operation cycle of the sand discharging and compacting member.

(Part 2) Fig. 3 shows the case of sand ground (liquefaction prevention measures),
The relationship diagram for obtaining the pile cross-sectional area A that satisfies the improvement target when the original ground strength N _S varies is theoretically or empirically obtained and created in advance.

The figure shows the original ground strength N ₀ (= C _S ) on the x-axis and the improved ground strength N ₁ on the y-axis, and the N ₀ at the time of constructing a specific sand pile diameter.
The relationship with N ₁ is displayed. In the figure, the curve indicated by φ600 shows the relationship between the ground improvement strength and the ground improvement strength when a 60 cm diameter sand pile is constructed. The same applies to the curves indicated by φ700 and φ800.

The line N ₂ = 15 parallel to the x-axis shows the improvement target in this case, the intersection of the line and each sand pile diameter curve, N ₃ , N ₄ and N ₅
For the ground improvement target N ₂ , respectively, a sand pile of φ80 cm when the original ground strength is N ₃ and a sand pile of φ70 cm when N ₄ is used,
In addition, in case of N ₅ , it shows that it is possible to achieve the ground improvement target by constructing sand piles of φ60 cm.

Therefore, (i) when the hollow pipe penetrates into the ground, the pressing force F of the sand discharging / compacting member with respect to the depth is measured to measure the strength N ₀ (= C _S ) of the original ground with respect to the depth, and Measure the amount of change.

(Ii) Calculate the pile diameter (cross-sectional area A _S ) that can satisfy the improvement target at N ₀ based on the already-obtained third diagrammatic relational diagram.

(Iii) Create a sand pile diameter calculated for each soil strength corresponding to the depth of the improved soil.

(C) Effect of the Invention According to the method of the present invention, a low substitution rate a _S (= about 10 to 30%)
In the case of the soft ground improvement technology based on the sand pile construction of, by theoretically or empirically obtaining a relational diagram for obtaining the sand pile diameter A _S that satisfies the improvement target for the original ground strength C _{S in} advance, During the formation of sand piles, it is possible to construct and provide the ground with unevenness in strength to the required uniform improved ground simply by managing and constructing the diameter of the sand piles indicated in the above relationship diagram. it can.

[Brief description of drawings]

Figure 1 is a diagram depicting the replacement rate, the second figure shows C _S to F _S to A relationship diagram in the case of clay soil, the (a) the relationship between cross-sectional view of a soil improvement areas and fill, the (b) the C _S to F _S to a relationship diagram, FIG. 3 shows a N ₀ to N ₁ to a relationship diagram in the case of sand.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Norio Katsuhara 1-2-1 Taito, Taito-ku, Tokyo Within Fudo Construction Co., Ltd. (72) Kenji Kawamoto 1-2-1 Taito, Taito-ku, Tokyo Fudo Construction Co., Ltd. (72) Inventor Takeshi Kawata 1-2-1 Taito, Taito-ku, Tokyo Fudo Construction Co., Ltd. (72) Inventor Hideki Okamoto 1-2-1 Taito, Taito-ku, Tokyo Fudo Construction (56) References JP-A-58-113415 (JP, A) JP-A-59-173416 (JP, A)

Claims (1)

[Claims] 1. When a sand pile is formed while forcibly moving up and down a sand discharge and compaction mechanism provided at the lower end of a hollow tube for sand pile formation, the cross-sectional area of each sand pile is / Shared area is 10 ~
By the low displacement rate improvement method of around 30%, the hollow pipe is continuously drawn out during the construction of sand piles while the hollow pipes are continuously extracted to compact the sand piles. From the correspondence relationship with, the sand pile diameter that satisfies the improvement target value is calculated in light of the detected original ground strength, and the compacted sand pile is controlled while controlling to form the calculated and instructed sand pile diameter. A soft ground improvement method characterized by creating