JP2733558B2 - Construction method of underground diaphragm wall - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for constructing an underground continuous wall constructed in the ground, and more particularly to a method for constructing an underground continuous wall with less occurrence of cracks.

[Conventional technology] The underground continuous wall forms the foundation of structures such as earth retaining walls, water blocking walls, artificial islands, etc., or the underground structures such as underground tanks such as LNG and LPG. The following are widely implemented in general.

After dividing the underground continuous wall to be constructed into a plurality of elements, first, every other element is excavated by an excavator (hereinafter, these elements are referred to as preceding elements), and concrete is placed in the excavated deep trench. And then excavating the remaining elements (hereinafter referred to as following elements) with an excavator and placing concrete to connect the concrete walls of the preceding element and the following element, Therefore, a construction method of constructing an integrated underground continuous wall in the ground is used.

[Problems to be Solved by the Invention] In general, concrete generates stress due to heat generated during hardening. Therefore, when concrete is cast on a succeeding element after the construction of the preceding element, the concrete is constructed by the restraint of the preceding element. There was an inconvenience that cracks occurred due to stress in the underground continuous wall.

In order to deal with such a problem, a method of reducing this temperature crack has been used in the past by taking into account the mixing surface of the concrete to be poured, but a high degree of water stopping effect such as an underground tank is required. In particular, it is necessary to greatly reduce the occurrence of this thermal crack in the underground continuous wall, and there is a problem that a sufficient effect cannot be obtained by taking measures only for the concrete mixing surface.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and reduces the stress generated when constructing a succeeding element, thereby greatly reducing the rate of occurrence of cracks in underground continuous walls. The purpose of the present invention is to provide a method for constructing a middle continuous wall.

[Means for Solving the Problems] In the method of constructing an underground continuous wall of the present invention, the following element is cast by concrete pre-cooled.

[Operation] Since the succeeding element is cast with pre-cooled concrete, even if it generates heat when it hardens, the temperature difference from the previously constructed preceding element becomes small, so that the stress between the elements is reduced. The occurrence can be minimized, and as a result, the occurrence of temperature cracks can be reduced.

 Hereinafter, the present invention will be described in detail.

FIG. 1 shows an example of an underground continuous wall constructed by the underground continuous wall construction method of the present invention. This underground continuous wall 1 is divided into a plurality of elements along its length direction, and these elements are preliminarily constructed as every other preceding element 2. The following elements 3 are constructed so as to be connected. The succeeding elements 3 are cast by pre-cooled concrete.

As a concrete pre-cooling method for constructing the succeeding elements 3, in addition to using cold water and ice as the concrete mixing water, a method using a cooled aggregate can be used. It is preferable to use a method of cooling the sand or the like with liquid nitrogen since a large pre-cooling can be performed. In winter, when the concrete temperature of the pre-constructed preceding elements 2 is low and large pre-cooling cannot be performed, a hotbed line or the like is buried in the vicinity of the preceding elements 2. By increasing the relative temperature difference between the already constructed preceding element 2 and the concrete for constructing the succeeding element 3... By increasing the concrete temperature of the pre-cooling element 2. be able to.

As described above, the cracks in the underground continuous wall 1 constructed by increasing the relative temperature difference between the concrete temperature of the previously constructed preceding element 2 and the concrete placing temperature of the succeeding element 3. The occurrence can be reduced for the following reasons.

FIG. 2 shows the changes over time in the temperature of the concrete forming the preceding elements 2 and the temperature of the concrete forming the following elements 3. In the figure, the broken line indicates the concrete temperature of the pre-constructed element 2 ..., the solid line indicates the concrete temperature of the succeeding element 3 without pre-cooling, and the alternate long and short dash line indicates the concrete temperature after pre-cooling. This shows the concrete temperatures of the row elements 3.
The stress σ generated between the preceding element 2 and the following element 3 can be roughly calculated by the following equation (1).

σ = R (ΔT ₂ −ΔT ₁ ) αEcB (1) where R is the degree of external constraint, α is the coefficient of thermal expansion of concrete, Ec is the Young's modulus of concrete, and B is the stress relaxation rate. The [Delta] T ₁ is for showing the difference between the preceding element 2 ... temperature and the stable temperature T ₀ of the droplet設時concrete building a trailing element 3 ..., [Delta] T ₂ constructs a trailing element 3 ... and the maximum temperature Tmax which the concrete has reached during the curing, shows the difference between the steady-state temperature T _0.

(1) In the formula, R, α and Ec are all constants.
To reduce the generated stress σ may be reduced [Delta] T _2, in FIG. 2, to reduce the [Delta] T ₂ by precooling the concrete to construct the trailing elements 3 ... a as indicated by the dashed line Can be. When the temperature of the concrete forming the succeeding element 3 is low in winter, the concrete of the preceding element 2 is heated in advance to increase ΔT ₁ ,
It is possible to temporarily reduce ΔT ₂ −ΔT ₁ to reduce the generated stress σ.

By reducing the generated stress σ, cracks generated in the underground continuous wall can be reduced.

[Example] The results of an underground continuous wall constructed by a conventional construction method for use as an underground tank are referred to as construction example 1, and the results of an underground continuous wall constructed by the construction method of the present invention are constructed example 2. And as a construction example 3, by comparing these with each other, the reduction rate of cracks by the construction method of the present invention was examined.

(Construction Example 1) After the preceding element was constructed, concrete maintained at the outside temperature (22.3 ° C) was cast to construct the succeeding element, which was used as an underground continuous wall.

(Construction Example 2) After constructing the preceding element, the pre-cooling amount Δ
At Tp = 10 ° C., concrete kept at 12.3 ° C. was cast to construct a subsequent element, which was used as an underground continuous wall.

(Construction Example 3) After constructing the preceding element, the pre-cooling amount Δ
At Tp = 15 ° C., concrete maintained at 7.3 ° C. was cast to construct a subsequent element, which was used as an underground continuous wall.

The effect of reducing cracks according to the present invention was confirmed by the following procedure. The time-dependent change in the temperature of each concrete placed as a subsequent element in the above-mentioned construction examples 1 to 3 is shown in the third example.
Shown in the figure. In FIG. 3, the solid line is that of Construction Example 1,
The dashed line indicates that of the construction example 2, and the dashed line indicates that of the construction example 3. From Fig. 3, the casting temperature Tp of each concrete
, The pre-cooling amount ΔTp, and the maximum temperature Tmax reached during curing are as shown in Table 1 below.

Further, a temperature crack index ET was calculated based on a temporal change of the temperature of the concrete forming the succeeding element, and the crack occurrence probability P was obtained. The results are shown in FIG.
As a result, in the case of the construction example 1 using concrete not subjected to pre-cooling, the crack occurrence probability P is 60%, and in the construction example 2 with ΔTp = 10 ° C., 43%, and in the construction example 3 with ΔTp = 15 ° C. It was found that the cracking probability was reduced to about half by the pre-cooling amount at 15 ° C.

Further, the crack indices of the construction examples 1 to 3 were determined and are shown in Table 2.

The results in Tables 1 and 2 both support the above observation results, and the use of the construction method of the present invention can greatly reduce the probability of occurrence of temperature cracks.

[Effects of the Invention] As described above, the method of constructing an underground continuous wall according to the present invention is to cast the succeeding element with pre-cooled concrete. Can be reduced, and as a result, the probability of occurrence of cracks in the constructed underground continuous wall can be greatly reduced.

Therefore, if this construction method is used, the waterproofness and durability of the underground continuous wall can be improved.
It can be suitably used for construction of underground tanks such as PG.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an example of an underground continuous wall constructed by the method of constructing an underground continuous wall according to the present invention, and FIG. 2 shows a temporal change of the temperature of concrete forming a subsequent element. FIG. 3 is a graph comparing the time-dependent changes in the temperature of concrete with and without pre-cooling, and FIG. 4 is a graph showing the relationship between the probability of occurrence of temperature cracks and the crack index. . 1 ... Underground continuous wall, 2 ... Leading element, 3 ... Trailing element.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Katsumi Kondo 2-16-1, Kyobashi, Chuo-ku, Tokyo Shimizu Construction Co., Ltd. (72) Inventor Masamitsu Edo 2-2-1-1, Kyobashi, Chuo-ku, Tokyo Shimizu Construction Inside the corporation

Claims (1)

(57) [Claims] 1. An underground continuous wall to be constructed is divided into a plurality of elements along its length, and these elements are constructed as alternate elements every other element, and then connected to each other by connecting the preceding elements. A method for constructing an underground continuous wall in a ground by constructing a line element and constructing an underground continuous wall in the ground, wherein the following element is cast by pre-cooled concrete. How to build a wall