JPH0726547A - Improvement work for weak ground - Google Patents

Abstract

PURPOSE:To obtain ground of stable bearing power for a long period by creating and swelling property piles made of a powder of a cement solidifying agent between sand piles made of sand, ballast, crushed stone and the like. CONSTITUTION:A plurality of sand piles 11 are created in the weak ground WG by means of, for example, sand compaction pile construction. At the same time or thereafter, swelling property piles 12 made of a solidifying agent in the length much shorter than that of sand piles 11 are created between sand piles 11. These swelling property piles 12 are casused to absorb water in the gab between soil particles in the surrounding ground and swell. The surrounding ground is made compact and the ground strength increased by this swelling. Because swell piles 12 once swollen becomes itself a hard body, stable bearing capacity of the ground can be maintained for a long period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving soft ground.

[0002]

2. Description of the Related Art Ground improvement methods can be broadly classified into those that mainly include physical treatment such as sand drain method and sand compaction pile method, and chemical treatment such as deep layer mixing method and chemical solution injection method. There are mainly construction methods, but when comparing the two, the latter chemical treatment construction method is very costly and the effect is often inferior in reliability, so the former physical treatment construction method is common. Has been adopted.

FIG. 4 shows a sand drain method as the physical treatment method, in which the casing is driven to a predetermined depth in the soft ground WG and the casing is pulled out while sand, gravel and the like are put therein. Thus, the sand pile 1 is formed in the ground WG at required intervals. In this case, since the soft ground WG has a high water content ratio, drainage is not promoted only by creating the sand pile 1 in the ground WG. Therefore, the loading soil P is applied on the soft ground WG on which the sand pile 1 is created, The vertically downward load of the loaded soil P removes pore water between the ground soil particles to the sand pile 1 side,
Water is discharged to the ground through the sand pile 1 and further discharged to a predetermined place through the sand mat M. By such a drainage action, the ground is consolidated and strengthened.

The consolidation of the ground by the sand drain method means that the volume of the ground is reduced by promoting drainage as described above, and the ground is inevitably subsided.
Then, the settlement due to the promotion of drainage is called consolidation settlement, but this consolidation settlement occurs as the drainage progresses in the soft ground WG, and becomes stable when the final settlement amount is reached. In Figure 4,
The state in which the consolidation settlement is finally stable is indicated by S in the phantom line. In this stable state, even if a load equal to or less than the load of the loading soil P that has caused the consolidation subsidence acts on the ground, the ground does not cause subsidence, and thus the ground has a permanent utility value. .

The above-mentioned sand drain method is mainly intended to promote drainage, and the sand compaction pile method is intended to increase the drainage action and to bear the supporting force of the sand pile. This method involves driving the casing into the soft ground to a predetermined depth, pulling up the casing while pressing the sand, gravel, etc., which have been put into the casing with a hammer or rod, and pushing out the sand, etc. from the tip of the casing. The hardened sand pile is created in soft ground. According to this sand compaction pile method, sufficient supporting force for soft ground can be obtained.

[0006] Fig. 5 shows a deep layer mixing treatment method mainly for chemical treatment, in which a swelling pile 2 made of powder of quicklime-based or cement-based solidifying agent is formed in a soft ground WG. It is a construction method. According to this construction method,
The swellable pile 2 absorbs interstitial water between soil particles to reduce the water content ratio immediately after its construction, and when it absorbs water, it expands by reacting with water (an expanded pile is indicated by 2 ').
The surrounding ground is compacted to immediately cause a consolidation subsidence S as shown by the phantom line, and the strength of the surrounding ground is further increased by the hardening action, and the pile itself becomes the hardened body 2 ', and the stable bearing force is obtained. Can be maintained.

[0007]

By the way, in the sand drain method of the physical treatment method described above, the increasing stress in the vertical direction due to the loading soil P promotes the drainage of the soft ground WG,
Since it causes consolidation settlement, it takes a very long time until this consolidation settlement reaches the final settlement amount (which can be calculated by calculation), and it is generally necessary to obtain consolidation settlement that can bear the load of the structure. Requires a leaving period of 90 days to 200 days. However, there is no time to spare for ground improvement work,
When the construction work of the building is awaiting immediately after the improvement work, it is necessary to rely on the costly foundation pile method (for foundation construction) and the chemical treatment method.

Further, in the sand compaction pile method, although the sand pile can sufficiently support the soft ground WG, since the drainage action is weak, the bearing capacity of the surrounding ground is lowered, and so-called subsidence occurs after the completion of construction. However, there is a problem that the ground is not stable. Further, in the above-mentioned deep layer mixing processing method, the material cost of the solidifying agent for forming the swelling pile is significantly higher than the material cost of the sand or the like of the sand pile, so that the construction cost is very high.

In view of the above-mentioned problems of the conventional construction method, the present invention makes it possible to significantly shorten the construction period and significantly reduce the construction cost, and to obtain a sufficient supporting force over the entire construction range of the soft foundation. The purpose is to provide an improved construction method.

[0010]

[Means for Solving the Problems] The soft ground improvement method of the present invention for achieving the above-mentioned object is provided in a soft ground WG.
It is characterized in that sand piles 11 made of sand, gravel, crushed stone, etc. are formed at required intervals, and swelling piles 12 made of cement-based solidifying agent powder 5 are formed between the sand piles.

[0011]

EXAMPLES Examples will be described with reference to the drawings.
As shown in FIGS. 1 and 2, in the soft ground WG, a plurality of sand piles 1 made of sand, gravel, crushed stone, slag, etc.
1 is formed at required intervals, and a swellable pile 12 made of a cement-based solidifying agent that is sufficiently shorter than the sand pile 12 is formed between the sand piles 11. In this case, the sand pile 11 and the swelling pile 12 may be simultaneously formed, or the swelling pile 12 may be formed after the sand pile 11 is formed. Of course, the sand pile 11 may be formed after the swellable pile 12 is formed. However, since the swellable pile 12 acts immediately as described below, after the formation of the swellable pile 12, it does not take much time. It is necessary to create the sand pile 11.

Each of the sand piles 11 has a length of, for example, 20 m (corresponding to the depth from the upper surface of the soft ground WG to the good quality ground T) and has an outer diameter of, for example, 500 mm, and each swellable pile 12 has a length thereof. Is about half of the sand pile 11,
For example, it is set to 10 m, and the outer diameter is set to 700 mm, for example. Further, the arrangement relationship between the sand pile 11 and the swelling pile 12 is, as shown in FIG.
It is surrounded by four sand piles 11, and the distance between the sand piles 11 and the swelling pile 12 is 1
It is good to set it to about 2 m.

Each of the sand piles 11 is constructed by, for example, a sand compaction pile method, and a cylindrical casing is driven into the soft ground WG to a depth close to the good ground T such as rock, and the sand is put into the casing. While the sand or the like is crushed by, for example, a rod that reciprocates vertically, the casing is pulled up, and the sand or the like is pushed out from the tip of the casing, whereby the entire pile is sufficiently compacted and the lower end portion of the good quality soil T The sand pile 11 supported by the above is formed.

In order to form the swellable pile 12, for example, as shown in FIG. 3, the casing 4 with the bottom lid 3 is rotated in one direction while penetrating into the soft ground WG, and when the required depth is reached. Then, the powder 5 of the cement-based solidifying agent is put into the casing 4. Thereafter, the inside of the casing 4 is pressurized with pressurized air, and the casing 4 is pulled out while rotating in the opposite direction, thereby pushing out the powder 5 from the open bottom lid 3 at the lower end of the casing 4 into the dug portion, The swellable pile 12 is formed by casting. Backfill of earth and sand is performed on the blanking section 6 of the pile 12. The cement-based solidifying agent powder 5 used for forming the swellable pile 12 contains calcium oxide, silicon dioxide, aluminum oxide, sulfur trioxide, etc. as main components.

According to the soft ground improvement method as described above, the sand piles 11 are formed in the soft ground WG, and the swellable pile 12 made of the powder 5 of the cement-based solidifying agent is provided between the sand piles 11. By forming the swellable piles 12, each swellable pile 12 absorbs the pore water between the soil particles in the surrounding ground to reduce the water content ratio immediately after the formation, and at the time of this water absorption, the swellable piles 12 react with water to expand and the volume thereof is increased. Increase 30-60% at the time of construction. 1 and 2
The expanded swellable pile is shown at 12 '.

When the swellable pile 12 expands in this manner, the ground surrounding the swellable pile 12 is consolidated, and the soil strength is enhanced by this consolidation, and the surplus gap between the soil particles that has not yet been absorbed by the swellable pile 12 is increased. Water is absorbed and removed by each sand pile 11. As a result, the density of the ground significantly increases, and the settlement S as shown by the phantom line on the upper side of FIG.
Cause. And the swelling pile 1 which has once expanded
No. 2 does not shrink, that is, does not reduce its volume because it becomes a hardened body by its hardening action. Therefore, this swellable pile 12 remains suspended in the ground as shown in FIG. The strength is further increased, and the sand pile 11 is integrally connected via the surrounding ground. For this reason, there is no risk of subsidence after a certain time, and the entire ground within the created range of the sand pile 11 and the swelling pile 12 can maintain a stable bearing force for a long period of time.

The above-mentioned subsidence begins to occur immediately after the swellable pile 12 is formed, and stabilizes within 2 to 3 days. Therefore,
The ground improvement work can be completed in a very short period of time,
The construction cost can be significantly reduced. Further, the amount of the solidifying agent used for forming the swelling pile 12 is about 1/6 of the amount of sand or the like used in volume.

In the above-mentioned embodiments, the sand pile is formed by the sand compaction pile method, but this sand pile can be formed by utilizing the sand drain method, the auger compaction pile method, and other methods. Further, the positional relationship between the sand pile and the swelling pile, or the length and outer diameter dimension can be set appropriately.

[0019]

According to the method of the present invention, sand piles made of sand or the like are formed in soft ground at required intervals, and swelling piles made of cement-based solidifying agent are formed between these sand piles. By doing so, the swellable pile absorbs interstitial water between soil particles in the surrounding ground to reduce the water content ratio immediately after formation, and expands by reacting with water during this water absorption. When the swellable pile expands,
The surrounding ground is consolidated, and this consolidation enhances the ground strength, and the excess pore water between the soil particles that has not yet been absorbed by the swelling pile is absorbed and removed by each sand pile. As a result, the ground becomes significantly denser, causing subsidence.

The swellable pile, which has once expanded, does not shrink because it becomes a cured product by itself by the curing action.
Therefore, the swellable pile further increases the shear strength of the surrounding ground by the wedge effect, and is in a state of being integrally connected with the sand pile through the surrounding ground. For this reason, there is no risk of subsidence after a while, and the entire ground within the area where the sand pile and swelling pile have been created can maintain stable bearing capacity for a long period of time and reliably prevent slipping damage to the ground. can do.

The above-mentioned subsidence begins to occur immediately after the formation of the swellable pile and stabilizes within a few days, so that the construction period can be greatly shortened. Further, the number of swellable piles formed may be a fraction of the number of sand piles, and the length of the swellable pile does not have to be equal to that of the sand piles.
For example, even if it is formed in a state of being suspended in the ground with a length of about one half of the sand pile, it can be integrally connected to the surrounding ground and the sand pile by the expansion and curing action as described above, The amount of the solidifying agent used for forming the swellable pile is much smaller than the amount of sand used for forming the sand pile, and therefore the conventional deep layer mixing using only the swellable pile is required. Compared with the processing method, the construction cost can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a soft ground improvement method according to the present invention.

FIG. 2 is a vertical sectional view of the above.

FIG. 3 is an explanatory cross-sectional view showing a process of forming a swellable pile.

FIG. 4 is an explanatory sectional view showing a sand drain method as a conventional example.

FIG. 5 is a cross-sectional explanatory view showing a conventional deep layer mixing processing method.

[Explanation of symbols]

 4 Casing 5 Powder of solidifying agent 11 Sand pile 12 Swellable pile 12 'Swellable pile in expanded state WG Soft ground T Good quality ground

Front page continued (72) Inventor Nakatomi, 6-7-15 Himejima, Nishiyodogawa-ku, Osaka-shi (72) Masafumi Kurimoto 6-7-15, Himejima, Nishiyodogawa-ku, Osaka

Claims (1)

[Claims] 1. A sand pile made of sand, gravel, crushed stone, etc. is formed at a required interval in soft ground, and a swelling pile made of a powder of a cement-based solidifying agent is formed between these sand piles. An improved construction method for soft ground, which is characterized in that