JP7525828B2 - Quay or revetment structure - Google Patents

Description

The present invention relates to the structure of a quay or revetment in which a water area is separated from land by a wall. The quays and revetments covered by the present invention include upright quays such as sheet pile quays, gravity quays, and cellular quays, as well as retaining walls and inclined revetments placed on the land side of a pier.

In the design of a quay or revetment that separates land from water, reducing the earth pressure acting on the wall from the land side can make the structure more economical. One method for reducing earth pressure is to inject lightweight geomaterials with small unit mass on the land side of the wall to reduce the overburden pressure. In addition, during an earthquake, the ground on the land side liquefies, which puts a very large earth pressure on the wall, so it is important to construct a geomaterial on the land side that is less likely to liquefy.
On the other hand, effective use of the soft soil and sand generated during dredging and construction work is being considered from the perspective of recycling. One method is to mix it with a modifier to enhance its strength and use it as the ground on the land side of the wall.

Patent Document 1 and Non-Patent Document 1 show a technique for obtaining solidified soil that is lighter than the original soil and sand by mixing water, cement-based solidification materials, thickeners, foaming agents, etc. with clayey dredged soil and soil generated from construction. This technique makes it possible to reuse dredged soil and soil generated from construction, while effectively using them as lightweight, liquefy-resistant ground materials for the structural components of quays and revetments, enabling quays and revetments to be constructed economically.
On the other hand, Patent Document 2 and Non-Patent Document 2 show a technique for increasing the strength of mud generated during dredging and construction work by mixing steelmaking slag as a modifier, which is useful as a technique for recycling by-products of steel production in addition to recycling soft soil. Since steelmaking slag contains iron and has a high soil particle density, solidified soil mixed with steelmaking slag has the characteristic of having a larger unit volume mass than the original soil and sand.

Japanese Patent Application Publication No. 5-106224 Patent No. 5014961

"Coastal Technology Library No. 31 Technical Manual for Lightweight Mixed Treated Soil Construction in Ports and Airports (Revised Edition)", Coastal Technology Research Center, July 2008, pp. 4-9 "Coastal Technology Library No. 47: Technical Manual for Using Calcium-Improved Soil in Ports, Airports, Coasts, etc.", Coastal Technology Research Center, February 2017, pp. 9-1 to 9-7

The use of lightweight solidified treated soil is effective under normal circumstances as a method for reducing the earth pressure on walls. However, during an earthquake, unlike granular ground materials, horizontal inertial forces act on solidified treated soil, which causes it to move as a unit, so the earth pressure on walls during an earthquake does not necessarily decrease if lightweight solidified treated soil is used. In particular, in areas deeper than the groundwater level, as shown in Figure 17, horizontal inertial forces act on the total weight of the solidified treated soil, while the frictional force that acts as a resistance is determined by the submerged weight of the solidified treated soil and the friction coefficient, so when the scale of earthquake motion is large, being lightweight can be a disadvantage. In such cases, conversely, a larger unit volume mass can be more stable during an earthquake.

The lightweight solidification-treated soil described in Patent Document 1 and Non-Patent Document 1 is not an all-purpose solution for reducing earth pressure for the reasons mentioned above. Conversely, the solidification-treated soil described in Patent Document 2 has the characteristic of having a larger unit mass per unit volume than the original soil and sand, but this characteristic may also work in the direction of increasing the earth pressure on the wall in some cases. In addition, the modifier described in Patent Document 2 is less likely to develop strength than cement-based solidification agents, so if the amount mixed is small, it may not be strong enough to be used as a material that is less likely to liquefy.

The object of the present invention is therefore to solve the problems of the prior art as described above, and to provide a structure of a wharf or revetment in which solidified soil, made of raw soil such as dredged soil mixed with a modifier, is placed on the land side of the wall, which can reliably reduce the earth pressure acting on the wall during an earthquake, and which can be constructed economically without requiring special construction work.

As a result of extensive research into solving the above problems, the inventors have come to the conclusion that, as a structure for a quay or revetment, (i) raw soil such as dredged soil is mixed with a modifier (e.g., steelmaking slag) that has a larger unit volume mass than the raw soil and causes a hydration reaction in the raw soil to produce solidified treated soil, and (ii) in the layer height direction of the solidified treated soil layer A located on the land side of the wall body 1, a large amount of "solidified treated soil with a large mixing ratio of modifier and a large unit volume mass" is placed deeper than the groundwater level, and a large amount of "solidified treated soil with a large mixing ratio of modifier and a large unit volume mass" is placed shallower than the groundwater level in the layer height direction of the solidified treated soil layer A located on the land side of the wall body 1. (iii) preferably, the distance in the layer height direction between the boundary surface a of the upper layer A1, which has a small unit mass of solidified treated soil and a small mixture ratio of modifier, and the lower layer A2, which has a large unit mass of solidified treated soil and a large mixture ratio of modifier, and the groundwater level is set to within 30% of the layer thickness of the upper layer A1, in the solidified treated soil layer A. In addition, since such a quay or revetment structure requires only changing the mixture ratio of modifier in the layer height direction of the solidified treated soil layer A, no special effort is required for construction and it can be constructed economically.

The present invention has been made based on these findings, and has the following gist.
[1] A quay or revetment structure in which a water area is separated from a land area by a wall (1), and a solidification-treated soil layer (A) is provided on the land area side so that the groundwater level is located midway in the layer height direction,
The solidified treated soil layer (A) is composed of solidified treated soil in which dredged soil and/or soil and sand are mixed with a modifier having a unit volume mass larger than that of the dredged soil and/or soil and causing a hydration reaction in the dredged soil and/or soil,
A quay or revetment structure characterized in that the solidification-treated soil layer (A) consists of an upper layer (A1) and a lower layer (A2), and the mixing ratio of the modifier and the unit volume mass of the solidification-treated soil are such that the upper layer (A1) is smaller than the lower layer (A2).
[2] A structure of a seawall or revetment as described in [1] above, characterized in that the distance in the layer height direction between the boundary surface (a) between the upper layer (A1) and the lower layer (A2) (however, if there is an intermediate layer between the upper layer (A1) and the lower layer (A2) where the solidified treated soil of both layers is mixed, the center position in the layer thickness direction of the intermediate layer shall be regarded as the "boundary surface (a)") and the groundwater level is within 30% of the layer thickness of the upper layer (A1).

[3] A structure of a seawall or revetment as described in [2] above, characterized in that in the layer height direction of the solidified treated soil layer (A), the boundary surface (a) between the upper layer (A1) and the lower layer (A2) is located at the groundwater level or below the groundwater level.
[4] A structure of a quay or revetment according to any one of the above [1] to [3], characterized in that it has a backfill soil layer (5) behind the solidification-treated soil layer (A), and at the interface between the solidification-treated soil layer (A) and the backfill soil layer (5), a part of the backfill soil layer (5) rests on the slope of the solidification-treated soil layer (A).
[5] A structure of a quay or revetment according to any one of the above [1] to [4], characterized in that the unit volume mass in air of the solidified treated soil constituting the lower layer (A2) is 20 kN/ ^m3 or more, and the unit volume mass in air of the solidified treated soil constituting the upper layer (A1) is 2 kN/ ^m3 or more smaller than the unit volume mass in air of the solidified treated soil constituting the lower layer (A2).

[6] A structure of a quay or revetment according to any one of the above [1] to [5], characterized in that the modifier is steelmaking slag.
[7] A structure of a quay or revetment according to any one of the above [1] to [6], characterized in that the solidification-treated soil constituting the upper layer (A1) is mixed with an auxiliary additive that promotes the strength development of the solidification-treated soil by the modifier.
[8] A structure of a quay or revetment according to the above [7], characterized in that the auxiliary additive is one or more selected from ground granulated blast furnace slag, granulated blast furnace slag other than ground granulated blast furnace slag, and cement.
[9] A structure of a quay or revetment according to any one of the above [1] to [8], characterized in that no backfill stones are provided behind the wall body (1).
[10] A structure of a quay or revetment, characterized in that the wall (1) in the structure of any one of the above [1] to [9] is a wall or embankment made of concrete and/or steel.

The structure of the quay or revetment of the present invention can reliably reduce the earth pressure acting on the wall during an earthquake in a quay or revetment structure in which solidified soil, which is a mixture of raw soil such as dredged soil and a modifier, is placed on the land side of the wall. Moreover, this quay or revetment structure can be constructed economically without any special effort in construction, since it is only necessary to change the mixture ratio of the modifier in the layer height direction of the solidified soil layer.
In addition, solidified treated soil placed below the groundwater level, where there is a risk of liquefaction, contains a large amount of modifying material, which not only gives it a large unit volume mass but also makes it easy to develop strength, making it easier to ensure sufficient strength as a material that is resistant to liquefaction, thereby reducing the risk of liquefaction.

FIG. 1 is an explanatory diagram showing a schematic longitudinal section of an embodiment of a quay wall structure according to the present invention; 2(a) and 2(b) are explanatory views each showing a schematic longitudinal section of another embodiment of the quay wall structure of the present invention. FIG. 1 is a schematic diagram showing a longitudinal section of a best embodiment of a quay wall structure according to the present invention; FIG. 4 is an explanatory diagram showing a schematic longitudinal section of an embodiment of a conventional quay wall structure for comparison with the quay wall structure shown in FIG. FIG. 4 is an explanatory diagram showing a schematic longitudinal section of another embodiment of a conventional quay wall structure for comparison with the quay wall structure of FIG. 3. An explanatory diagram showing a schematic example of the destruction mode of the ground during an earthquake in a past (conventional) quay wall structure. An explanatory diagram showing another example of the ground destruction mode during an earthquake in a past (conventional) quay wall structure. An explanatory diagram showing another example of the ground destruction mode during an earthquake in a past (conventional) quay wall structure. An explanatory diagram showing another example of the ground destruction mode during an earthquake in a past (conventional) quay wall structure. A schematic diagram showing the points of action of earth pressure during an earthquake and the movement of the wall (caisson) due to earth pressure during an earthquake in a past (conventional) quay wall structure. FIG. 1 is an explanatory diagram showing the action points of earth pressure during an earthquake and the movement of a wall (caisson) due to earth pressure during an earthquake in the quay wall structure of the present invention. This is an explanatory diagram showing an example of a construction method for a quay structure of the present invention, which is a schematic diagram showing a construction example in which a backhoe mixing method and a grab throwing method are combined. 13(a) and 13(b) are explanatory diagrams each showing a schematic longitudinal section of the wharf structure of the first embodiment. 14(a) and 14(b) are explanatory diagrams each showing a schematic longitudinal section of a wharf structure according to the second embodiment. 15(a) and 15(b) are explanatory diagrams each showing a schematic longitudinal section of a wharf structure according to a third embodiment. FIG. 13 is an explanatory diagram showing a schematic longitudinal section of the wharf structure of the fourth embodiment. An explanatory diagram showing the magnitude of horizontal inertial force and resistance force acting during an earthquake for solidified treated soil with a large unit mass placed below the groundwater level and solidified treated soil with a small unit mass.

The basis of the structure of the quay or revetment of the present invention is that (i) it is a quay or revetment structure in which a water area is separated from a land area by a wall 1 (hereinafter, for convenience of explanation, referred to as the "quay structure"), and a solidified treated soil layer A is formed on the land area side separated by the wall 1, (ii) the solidified treated soil (modified soil) constituting the solidified treated soil layer A is a mixture of dredged soil and/or sand (hereinafter, for convenience of explanation, referred to as the "raw soil") and a modifier (e.g., steelmaking slag) that has a larger unit volume mass than the raw soil and causes a hydration reaction in the raw soil, and (iii) in the layer height direction of the solidified treated soil layer A, a large amount of "solidified treated soil with a large unit volume mass and a high mixture ratio of modifier" is placed deeper than the groundwater level, and a large amount of "solidified treated soil with a small unit volume mass and a low mixture ratio of modifier" is placed shallower than the groundwater level. This type of structure can reduce deformation of the wall 1 during an earthquake, which will be described in more detail later with reference to Figures 3 to 11.

FIG. 1 is an explanatory diagram showing a vertical cross-section of one embodiment of a quay wall structure of the present invention (a gravity-type quay wall).
In the drawing, reference numeral 1 denotes a wall separating a water area from a land area, which in this embodiment is made up of a caisson 100. This caisson 100 is placed on the original ground 2 via a foundation rubble 3.
On the land side of the wall 1, a solidification-treated soil layer A is formed so that the groundwater level w is located (exists) midway in the layer height direction. In this embodiment, backfill stones 4 are installed behind the wall 1, and the solidification-treated soil layer A is formed so as to cover the backfill stones 4. 5 is a backfill soil layer, and the solidification-treated soil layer A is formed so as to be sandwiched between the wall 1 (or the wall 1 and the backfill stones 4) and the backfill soil layer 5.
In technical standards for port facilities, the groundwater level w is generally set to the height of the mean low tide plus 1/3 to 2/3 of the tidal range. In particular, in the case of a gravity-type wharf, it is generally considered acceptable to add 1/3 to the height, so in this invention, the groundwater level w is also defined as the height of the mean low tide plus 1/3 of the tidal range.

The solidification-treated soil (modified soil) constituting the solidification-treated soil layer A is obtained by mixing raw soil such as dredged soil with a modifier that has a larger unit mass per unit volume than the raw soil and causes a hydration reaction in the raw soil. The dredged soil may be previously dried (for example, dried in the sun) or dehydrated (a method of adding a chemical to flocculate the soil, then dehydrated and reduced in volume). The soil and sand may be construction waste soil (mud).
The modifier is mixed with the raw soil in order to (i) solidify the raw soil by the hydration reaction of the free lime contained therein, and (ii) increase the unit mass of the raw soil (solidified soil). Therefore, the modifier may be of any type as long as it has a larger unit mass than the raw soil and causes a hydration reaction in the raw soil, for example, one or more of steelmaking slag, concrete waste, etc. can be used, but among them, steelmaking slag, which has a large soil particle density and latent hydraulic properties, is preferred. Examples of steelmaking slag include slags generated in processes such as hot metal pretreatment, converter decarburization refining, casting, and electric furnace refining, such as hot metal pretreatment slags such as dephosphorization slag, desulfurization slag, and desiliconization slag, decarburization slag, casting slag, and electric furnace slag, and one or more of these can be used. Among these slags, decarburization slag (converter slag) and dephosphorization slag are particularly suitable. In order to obtain a sufficient effect, it is preferable to use slag in a powdered form.

The solidified treated soil layer A is composed of an upper layer A1 and a lower layer A2, and the mixing ratio of the modifier in the solidified treated soil and the unit volume mass of the solidified treated soil (unit volume mass in air) are set as upper layer A1 < lower layer A2. Here, since the groundwater level w is located (exists) halfway through the solidified treated soil layer A in the layer height direction, the solidified treated soil layer deeper than the groundwater level in the solidified treated soil layer A has a larger mixing ratio of modifier (average) and unit volume mass (average) of the solidified treated soil than the solidified treated soil layer shallower than the groundwater level. In other words, the structure is such that more "solidified treated soil with a higher mixing ratio of modifier and a larger unit volume mass" is placed deeper than the groundwater level, and more "solidified treated soil with a lower mixing ratio of modifier and a smaller unit volume mass" is placed shallower than the groundwater level.

In order to enhance the effect of the present invention, it is preferable that the distance d in the layer height direction between the interface a between the upper layer A1 and the lower layer A2 and the groundwater level w is as small as possible, and in particular, it is preferable that the distance d in the layer height direction is within 30% of the layer thickness of the upper layer A1. In addition, in order to further enhance the effect of the present invention, it is preferable that the upper layer A1 is below the groundwater level w, and therefore, in the layer height direction of the solidification-treated soil layer A, it is preferable that the interface a between the upper layer A1 and the lower layer A2 is located at the groundwater level w or below the groundwater level w.
Here, as an embodiment of the present invention, it is possible that an intermediate layer is generated or formed between the upper layer A1 and the lower layer A2, where the solidified treated soil of both layers is mixed, and in such a case, the center position in the thickness direction of the intermediate layer is the "interface a" between the upper layer A1 and the lower layer A2. Therefore, the upper part of the center position (interface a) in the thickness direction of the intermediate layer is the upper layer A1, and the lower part is the lower layer A2.
The thickness (layer height) of the solidification-treated soil layer A is usually about 5 to 18 m, depending on the size of the quay or revetment and the location conditions. The thickness of the upper layer A1 is often 2 to 4 m, depending on the height of the groundwater level w. The width of the solidification-treated soil layer A (the width of the top end in the direction perpendicular to the longitudinal direction of the wall 1) is usually about 22 to 80 m.

In the present invention, it is sufficient that the mixing ratio of the modifier in the solidified treated soil and the unit volume mass of the solidified treated soil are upper layer A1 < lower layer A2, and there are no special restrictions on the mixing ratio of the modifier in the solidified treated soils constituting the upper layer A1 and lower layer A2, and the unit volume mass of the solidified treated soils; however, in order to enhance the effects of the invention, it is preferable that the unit volume mass in air of the solidified treated soil constituting the lower layer A2 is 20 kN/ ^m3 or more, and that the unit volume mass in air of the solidified treated soil constituting the upper layer A1 is 2 kN/ ^m3 or more less than the unit volume mass in air of the solidified treated soil constituting the lower layer A2, and it is preferable to adjust the mixing ratio of the modifier in the solidified treated soils constituting the upper layer A1 and lower layer A2 so as to obtain this condition.
The mixing ratio of the modifier in the solidified treated soil is usually about 15 to 25 volume % in the upper layer A1 and about 35 to 45 volume % in the lower layer A2.
In addition, each of the upper layer A1 and the lower layer A2 may be composed of multiple layers in which the mixing ratio of the modifier or the unit volume mass of the solidified treated soil changes in the layer height direction, or in which the mixing ratio of the modifier or the unit volume mass of the solidified treated soil is different.

The solidified soil constituting the upper layer A1 has a lower mixing ratio of modifier than the solidified soil constituting the lower layer A2, so in order to ensure strength, auxiliary additives that promote the development of strength by the modifier may be mixed into the solidified soil constituting the upper layer A1. Examples of such auxiliary additives include ground granulated blast furnace slag that acts as an alkaline stimulant, granulated blast furnace slag other than ground granulated blast furnace slag, cement (Portland cement, blast furnace cement), etc., and one or more of these can be used. When this auxiliary additive is mixed, the mixing ratio of the auxiliary additive in the solidified soil is preferably 1% by mass or more, and the upper limit is preferably about 10% by mass.

Types of wall 1 include, but are not limited to, concrete walls such as the caisson in the embodiment of Figure 1, steel walls such as steel sheet piles and steel pipe sheet piles, composite walls combining concrete and steel, and embankments made of piled up blocks or large broken granite stones.
The quays and revetments that are the subject of the present invention include upright quays such as sheet pile quays, gravity quays, and cellular quays, as well as retaining walls and inclined revetments that are placed on the land side of a pier.
In the embodiment of Figure 1, a backfill stone 4 is placed behind the wall 1 (the back surface opposite the water area), but in the present invention, the effect of reducing the amount of deformation of the wall 1 during an earthquake can be obtained even without a backfill stone, so it is also possible to have a structure without a backfill stone.

2(a) and 2(b) are explanatory views each showing a schematic longitudinal section of a quay wall structure according to another embodiment of the present invention.
These embodiments show a gravity type quay wall using a caisson 100 as the wall body 1, in which backfill stones are not placed behind the wall body 1.
In the embodiment of Fig. 2(a), the cross-sectional shape of the solidified treated soil layer A is trapezoidal, and at the interface between the solidified treated soil layer A and the backfill soil layer 5, a part of the backfill soil layer 5 is placed on the side surface (slope) of the solidified treated soil layer A. In contrast, in the embodiment of Fig. 2(b), the cross-sectional shape of the solidified treated soil layer A is an inverted trapezoid, and at the interface between the solidified treated soil layer A and the backfill soil layer 5, a part of the solidified treated soil layer A5 is placed on the side surface (slope) of the backfill soil layer 5.
Since other configurations are similar to those in the embodiment shown in FIG. 1, the same reference numerals are used and detailed description is omitted.
In both of the embodiments of Figures 2(a) and (b), the effect of reducing the earth pressure acting on the wall body 1 during an earthquake can be obtained. In particular, in the case of the structure of Figure 2(a), if the strength of the solidified treated soil below the groundwater level is high, it will be difficult for a ground fracture line to pass through the solidified treated soil layer A, so it is expected that the earth pressure acting on the wall body 1 (caisson 100) during an earthquake will be greatly reduced.

Next, the effect of the quay wall structure of the present invention (the effect of reducing the deformation of the wall during an earthquake) will be described.
Fig. 3 shows a schematic vertical cross-section of an example of the wharf structure of the present invention. In this wharf structure, the boundary surface a between the upper layer A1 and the lower layer A2 is located at the groundwater level w, which is the optimal form for the present invention. For comparison, Fig. 4 and Fig. 5 show examples of past (conventional) wharf structures (each of which is an explanatory diagram showing a vertical cross-section of the wharf structure). Fig. 6 to Fig. 9 are explanatory diagrams showing the destruction mode of the ground during an earthquake in the past (conventional) wharf structure, Fig. 10 is an explanatory diagram showing the action point of earth pressure during an earthquake and the movement of the wall (caisson) due to earth pressure during an earthquake in the past (conventional) wharf structure, and Fig. 11 is an explanatory diagram showing the action point of earth pressure during an earthquake and the movement of the wall (caisson) due to earth pressure during an earthquake in the wharf structure of the present invention.

If the strength (adhesion) of the solidified soil is above a certain level, then as shown in Figures 6 and 7, a ground fracture line will occur during an earthquake that avoids the solidified soil layer. Figure 6 shows the case where the inside of the backfill soil layer below the solidified soil layer is fractured, and Figure 7 shows the case where slippage occurs at the boundary between the solidified soil layer and the backfill soil layer. The earth pressure acting on the caisson, which is a wall, during an earthquake is determined by the balance between the horizontal inertial force acting on the total weight of the soil mass above the fracture line and the frictional resistance force at the fracture line, but in such a case, if the underwater weight of the soil mass above the fracture line becomes lighter, the frictional resistance force will become smaller, as calculated in Figure 17. Therefore, depending on the magnitude of the earthquake, the solidified soil will become lighter, and the earth pressure acting on the caisson during an earthquake will increase.

On the other hand, if the strength of the solidified soil is insufficient, a ground fracture line will occur that passes through the inside of the solidified soil layer, as shown in Figures 8 and 9. Figure 8 shows a case where fracture occurs penetrating the backfill stone and the solidified soil layer, while Figure 9 shows a case where fracture occurs due to cracks caused by tensile stress in the solidified soil layer. In such a case, the inclination angle of the fracture line will be relatively steep, so resistance to horizontal inertial forces will be small, and earth pressure during an earthquake will tend to be greater than in Figures 6 and 7.
In the existing structure in Figure 4, the strength of the dredged soil is realized by adding a relatively small amount of cement, so the failure modes shown in Figures 8 and 9 are unlikely to occur. On the other hand, in the failure modes shown in Figures 6 and 7, the light unit mass acts to increase the earth pressure during an earthquake, as mentioned above.

The existing structure in Figure 5 has a smaller manifestation strength but a larger unit mass compared to cement-based solidified soil. In this structure, if the failure modes in Figures 6 and 7 occur, the earthquake earth pressure can be reduced compared to the structure in Figure 4, but the unit mass is larger below the groundwater level, so the center of gravity of the entire solidified soil layer is higher than that of the structure in Figure 3. Therefore, as shown in Figure 10, the point of action of the earthquake earth pressure on the caisson is also higher, so the caisson slides toward the water area and moves in a manner that makes it overturn, and the amount of movement of the top of the quay toward the water area is large. In addition, since the adhesion strength below the groundwater level is smaller than that of cement-based solidified soil, it may not be strong enough to be a material that is resistant to liquefaction. In such a case, the strength of the ground below the groundwater level during an earthquake is reduced, leading to failure modes such as those in Figures 8 and 9, which lead to increased earthquake earth pressure acting on the caisson.

In contrast, in the structure of the present invention shown in Fig. 3, solidified treated soil with a large unit mass and large adhesive force containing a large amount of modifier is placed below the groundwater level, and solidified treated soil with a small unit mass containing less modifier is placed below the groundwater level, so that when the failure modes shown in Figs. 6 and 7 occur, the earth pressure during an earthquake can be reduced compared to the structure shown in Fig. 4. In addition, compared to the structure shown in Fig. 5, the center of gravity of the solidified treated soil layer is lowered due to the small unit mass below the groundwater level, and as shown in Fig. 11, the point of action of the earth pressure during an earthquake on the caisson is also lower, so the caisson's overturning movement is reduced and the amount of movement of the top of the quay toward the water body is reduced. Furthermore, since the solidified treated soil below the groundwater level contains a large amount of modifier, the strength it exerts is also greater, which has the effect of making it easier to prevent the failure modes shown in Figs. 8 and 9 from being induced due to a decrease in ground strength during an earthquake. In addition, unlike solidification-treated soil applied underwater (deeper than the groundwater level), solidification-treated soil applied in the air (shallower than the groundwater level) develops strength without excess water being mixed in during application, so the average strength tends to be greater and the variation smaller than that of soil applied underwater. Therefore, even with a small amount of modifier mixed, a relatively high strength can be expected.
In addition, this effect is more easily obtained when the distance d in the layer height direction between the boundary surface a between the upper layer A1 and the lower layer A2 and the groundwater level w is as small as possible, and is strongest when the boundary surface a between the upper layer A1 and the lower layer A2 is located at the groundwater level w as shown in Figure 3. However, this effect can also be obtained, although to a lesser extent, even if the distance d in the layer height direction between the boundary surface a between the upper layer A1 and the lower layer A2 and the groundwater level w is large.

Due to the above-mentioned mechanism of effect, the larger the unit volume mass of the solidified treated soil below the groundwater level (the solidified treated soil in the lower layer A2 in the embodiment of Figures 1 to 3), the more advantageous it is; however, it is desirable for the unit volume mass in water to be at least 10 kN/ ^m3 (unit volume mass in air is 20 kN/ ^m3 ), and it is desirable to set the upper limit at around 13 kN/ ^m3 . This is assumed to be equal to or greater than the unit volume mass in water of general sandy soil. Furthermore, from the viewpoint of ensuring resistance against liquefaction, it is desirable for the adhesive strength of the solidified treated soil below the groundwater level (the solidified treated soil in the lower layer A2 in the embodiment of Figures 1 to 3) to be 125 kN/ ^m2 (uniaxial compressive strength 250 kN/ ^m2 ) or more.

The smaller the unit mass of the solidified treated soil below the groundwater level (the solidified treated soil of the upper layer A1 in the embodiment of Figs. 1 to 3), the more advantageous it is. Therefore, the unit mass in air is preferably 18 kN/ ^m3 or less, and the lower limit is preferably about ¹⁵ kN/m3. This is assumed to be less than the wet unit mass of general sandy soil. The strength of the solidified treated soil below the groundwater level (the solidified treated soil of the upper layer A1 in the embodiment of Figs. 1 to 3) is sufficient if it has an adhesive strength that does not cause the failure modes of Figs. 7 and 8. The necessary strength varies depending on the adhesive strength of the solidified treated soil below the groundwater level and the structural conditions, but the adhesive strength is preferably 25 kN/ ^m2 (uniaxial compressive strength 50 kN/ ^m2 ) or more.

Furthermore, as described above, in order to enhance the effect of the present invention, it is desirable to make the unit volume mass in the air of the solidified treated soil shallower than the groundwater level (the solidified treated soil in the upper layer A1 in the embodiment of Figures 1 to 3) 2 kN/m3 or more smaller than the unit volume mass in the air of the solidified treated soil deeper than the groundwater level (the solidified treated soil in the lower layer A2 in the embodiment of Figures 1 ^{to 3} ).
The above-mentioned uniaxial compressive strength is the uniaxial compressive strength after 28 days of curing, measured using the uniaxial compression test method for soil (JIS A1216:2009) for solidification-treated soil mixed indoors using a hand mixer or the like, and the above-mentioned adhesion strength is equivalent to 1/2 of that uniaxial compressive strength.

Since the strength of the solidified treated soil varies depending on the properties of the raw soil and the modifier, the strength of the solidified treated soil varies even if the mixing ratio of the modifier is the same. In the structure of the present invention, if the strength of the solidified treated soil is significantly low, especially below the groundwater level, the risk of the failure mode shown in Figures 8 and 9 being induced may increase. In addition, if it is assumed that heavy vehicles will run on the land area after backfilling, the solidified treated soil is required to have the necessary strength as a roadbed or road subgrade, and it is expected that the design strength will be insufficient. In such a case, it is possible to ensure the necessary strength by mixing an auxiliary additive that promotes the strength development by the modifier into the solidified treated soil below the groundwater level (the solidified treated soil of the upper layer A1 in the embodiment of Figures 1 to 3).
In addition, since the amount of this auxiliary additive is often small compared to the amount of the modifier, the mixing method and subsequent pouring method when mixing the auxiliary additive can be the same as when using the modifier alone. Therefore, by using the auxiliary additive, the construction process does not become complicated by being divided into two parts, one below the groundwater level and the other below the groundwater level.

The construction method for constructing the quay structure of the present invention can directly apply the mixing method and injection method of mud and modifier described in, for example, Non-Patent Document 2. In other words, construction can be carried out by appropriately combining the mixing process and injection process as shown below.
・Type of mixing process Continuous mixer mixing method Pipe mixing method Backhoe mixing method Drop mixing method ・Type of input process Direct input method (bottom open barge input)
Tremie pump installation method Grab insertion method

As an example, Figure 12 shows a construction example where the backhoe mixing method and the grab injection method are combined. In the backhoe mixing method, the modifier is injected into the raw soil inside a soil transport barge, and the soil is stirred and mixed for about 2 to 3 hours with a backhoe. There are two ways to do this: the soil transport barge is docked at a quay and mixing is done from land with a backhoe, or the soil transport barge is docked to the side of a barge equipped with a backhoe and mixing is done at sea. Figure 12 shows the former example. In the grab injection method, the mixture of raw soil and modifier is transported to the construction site by a soil transport barge, and then injected into the sea with a grab bucket attached to a grab dredger.

The volumes of the soil mixture with a lot of modifier (solidified soil) and the soil mixture with little modifier (solidified soil) are determined in advance in the construction drawings, etc., so if the volume of the soil mixture produced in the mixing process is continuously monitored, two types of soil mixtures can be constructed without changing the construction labor by changing the amount of modifier mixed during the process. In addition, the soil mixture begins to harden due to the hydration reaction 2 to 3 days after the modifier is mixed into the raw soil, and since it is in a soft state during construction, the added soil mixture naturally spreads almost horizontally. Therefore, the boundary between the soil mixture with a lot of modifier and the soil mixture with little modifier naturally becomes close to horizontal, and takes the shape shown in the embodiments of Figures 1 to 3.

[Example 1]
13(a) and (b) show an embodiment in which the quay wall structure of the present invention is applied to a gravity type quay wall using a caisson 100 as the wall body 1, and no backfill stones are used.
When backfill stones are not used, the cross-sectional shape of the solidified treated soil layer A may be trapezoidal as shown in Figure 13(a) (where a part of the backfill soil layer 5 rests on the side (slope) of the solidified treated soil layer A at the interface between the solidified treated soil layer A and the backfill soil layer 5), or may be inverted trapezoidal as shown in Figure 13(b) (where a part of the solidified treated soil layer A rests on the side (slope) of the backfill soil layer 5 at the interface between the solidified treated soil layer A and the backfill soil layer 5). Of these, when the cross-sectional shape is trapezoidal as shown in Figure 13(a), if the strength of the solidified treated soil below the groundwater level is high, it is difficult for the ground fracture line to pass through the solidified treated soil layer A, and it is expected that the earth pressure applied to the wall 1 (caisson 100) during an earthquake will be greatly reduced.
The construction procedure for the quay wall in the case of Fig. 13(a) is as follows: installation of foundation riprap 3, installation of wall body 1 (caisson 100), pouring of solidified treated soil for the lower layer A1, pouring of solidified treated soil for the upper layer A2, and pouring of backfill soil for the backfill soil layer 5. In the case of Fig. 13(b), the order is as follows: installation of foundation riprap 3, installation of wall body 1 (caisson 100), pouring of backfill soil for the backfill soil layer 5, pouring of solidified treated soil for the lower layer A1, and pouring of solidified treated soil for the upper layer A2.

[Example 2]
14(a) and (b) show an embodiment in which the wharf structure of the present invention is applied to a sheet pile type wharf using steel sheet piles 101 as the wall body 1, and no backfill stones are used.
In the figure, reference numeral 6 denotes a retaining work to be driven into the backfill soil layer 5, reference numeral 7 denotes a superstructure provided at the upper end of a steel sheet pile 101, and reference numeral 8 denotes a tie material connecting the upper end of the retaining work 6 to the superstructure 7.
In this case, the cross-sectional shape of the solidification treated soil layer A may be a trapezoid as shown in Fig. 14(a) or an inverted trapezoid as shown in Fig. 14(b). The effect of lowering the point of action of earth pressure during an earthquake is also effective for embedded wall structures 1 such as steel sheet piles. By moving the point of action closer to the embedded part, the restraining effect of the ground works more effectively, and the maximum bending moment generated in the sheet piles can be reduced.
The construction procedure for the quay wall in the case of Fig. 14(a) is as follows: installation of wall body 1 (casting of steel sheet piles 101), pouring of solidified treated soil for the lower layer A1, pouring of backfill soil for the backfill soil layer 5, pouring of retaining works 6, installation of tie material 8, installation of superstructure 7, and pouring of solidified treated soil for the upper layer A2. In the case of Fig. 14(b), the order is as follows: installation of wall body 1 (casting of steel sheet piles 101), pouring of backfill soil for the backfill soil layer 5, pouring of retaining works 6, pouring of solidified treated soil for the lower layer A1, installation of tie material 8, installation of superstructure 7, and pouring of solidified treated soil for the upper layer A2.

[Example 3]
15(a) and (b) show an example in which the wharf structure of the present invention is applied to a pier integrated with an earth retaining wall using steel pipe sheet piles 102 as the wall body 1, and no backfill stones are used.
In the figure, 9 is riprap, 10 is the superstructure that constitutes the pier, and 11 is a steel pipe pile that supports the superstructure 10.
In this case, the cross-sectional shape of the solidified soil layer A may be a trapezoid as shown in Fig. 15(a) or an inverted trapezoid as shown in Fig. 15(b). As in the case of a sheet pile wharf, the maximum bending moment generated in the steel pipe piles of the pier is reduced by reducing the earth pressure during an earthquake and lowering the point of action, resulting in a more economical cross-section.
The construction procedure for the pier in the case of Figure 15(a) is as follows: installation of the wall body 1 (driving the steel pipe sheet piles 102), driving of the steel pipe piles 11, pouring of riprap 9, construction of the superstructure 10, pouring of solidification treated soil for the lower layer A1, pouring of solidification treated soil for the upper layer A2, and pouring of backfill soil for the backfill soil layer 5. In the case of Figure 15(b) the construction procedure is as follows: installation of the wall body 1 (driving the steel pipe sheet piles 102), driving of the steel pipe piles 11, pouring of riprap 9, construction of the superstructure 10, pouring of backfill soil for the backfill soil layer 5, pouring of solidification treated soil for the lower layer A1, and pouring of solidification treated soil for the upper layer A2.

[Example 4]
16 shows an embodiment in which the structure of the present invention is applied to an inclined revetment using a bank body 103 as the wall body 1. The bank body 103 is constructed by piling up large broken granite stones.
In the figure, reference numeral 12 denotes a slope covering which covers the slope of the embankment 103, 13 denotes a wave breaker provided on the upper part of the slope covering, 14 denotes the foundation which supports the slope covering 12, 15 denotes a footing stone provided on the water side of the embankment 103 via the slope covering 12, 16 denotes a wave dissipating block, and 17 denotes a top covering which covers the top of the embankment 103 and part of the top of the solidified treated soil layer A.
In this case, by reducing the earth pressure during an earthquake, it is possible to prevent the top of the revetment from sinking, and in the event of a tsunami, the presence of the solidified treated soil is expected to have the effect of suppressing scouring of the back of the revetment.
The construction procedure for the revetment is as follows: construction of the foundation 14, installation of the wall 1 (construction of the embankment body 103), construction of the slope covering 12 and wave breaker 13, dumping backfill soil for the backfill soil layer 5, dumping solidification treated soil for the lower layer A1, dumping solidification treated soil for the upper layer A2, construction of the top covering 17, dumping the foot reinforcement stones 15, and installation of the wave dissipating blocks 16.

REFERENCE SIGNS LIST 1 wall body 2 original ground 3 foundation rubble 4 backfill stone 5 backfill soil layer 6 bracing work 7 superstructure 8 tie material 9 rubble 10 superstructure 11 steel pipe pile 12 slope cover 13 wave breaker 14 foundation 15 foot protection stone 16 wave dissipating block 17 top cover 100 caisson 101 steel sheet pile 102 steel pipe sheet pile 103 embankment body A solidified soil layer A1 upper layer A2 lower layer a boundary surface w groundwater level

Claims (10)

A seawall or revetment structure in which a water area and a land area are separated by a wall (1), and a solidification-treated soil layer (A) is provided on the land area side so that the groundwater level is located midway in the layer height direction,
The solidified treated soil layer (A) is composed of solidified treated soil in which dredged soil and/or soil and sand are mixed with a modifier having a unit volume mass larger than that of the dredged soil and/or soil and causing a hydration reaction in the dredged soil and/or soil,
A quay or revetment structure characterized in that the solidification-treated soil layer (A) consists of an upper layer (A1) and a lower layer (A2), and the mixing ratio of the modifier and the unit volume mass of the solidification-treated soil are such that the upper layer (A1) is smaller than the lower layer (A2). The structure of a quay or revetment as described in claim 1, characterized in that the distance in the layer height direction between the boundary surface (a) between the upper layer (A1) and the lower layer (A2) (however, if there is an intermediate layer between the upper layer (A1) and the lower layer (A2) where the solidified treated soil of both layers is mixed, the center position in the layer thickness direction of the intermediate layer is regarded as the "boundary surface (a)") and the groundwater level is within 30% of the layer thickness of the upper layer (A1). The structure of a quay or revetment according to claim 2, characterized in that in the layer height direction of the solidified treated soil layer (A), the boundary surface (a) between the upper layer (A1) and the lower layer (A2) is located at the groundwater level or below the groundwater level. The structure of a quay or revetment according to any one of claims 1 to 3, characterized in that a backfill soil layer (5) is provided behind the solidified soil layer (A), and at the interface between the solidified soil layer (A) and the backfill soil layer (5), a part of the backfill soil layer (5) rests on the slope of the solidified soil layer (A). A quay or revetment structure as described in any one of claims 1 to 4, characterized in that the unit volume mass in air of the solidified treated soil constituting the lower layer (A2) is 20 kN/ ^m3 or more, and the unit volume mass in air of the solidified treated soil constituting the upper layer (A1) is 2 kN/ ^m3 or more smaller than the unit volume mass in air of the solidified treated soil constituting the lower layer (A2). The structure of a quay or revetment according to any one of claims 1 to 5, characterized in that the modifier is steelmaking slag. The structure of a quay or revetment according to any one of claims 1 to 6, characterized in that the solidified treated soil constituting the upper layer (A1) is mixed with an auxiliary additive that promotes the development of strength in the solidified treated soil by the modifier. The structure of a quay or revetment according to claim 7, characterized in that the auxiliary additive is one or more selected from ground granulated blast furnace slag, granulated blast furnace slag other than ground granulated blast furnace slag, and cement. A quay or revetment structure according to any one of claims 1 to 8, characterized in that no backfill stones are provided behind the wall body (1). The structure of a quay or revetment according to any one of claims 1 to 9, characterized in that the wall (1) is either a concrete or/and steel wall or embankment.