JPH0483012A - Ground improvement method to prevent liquefaction - Google Patents

Abstract

PURPOSE:To perform sufficient compaction of the whole ground by driving a number of piles by use of a mixture of quick lime having specified burning temperature and grain size, a water permeable material, water granulation, and plaster. CONSTITUTION:Limestone is burned at 1200-1500 deg.C to form a hard burnt quick lime having a grain size of 5mm or more. This quick lime is mixed with a water permeable material such as sand and crushed stone, material water granulation, and plaster to form a foundation improving material. A pile driver 1 is advanced into the ground, the improving material is discharged into a casing 2 from a side hopper 5, and this is pulled out to build a pile 7 in the ground. A number of piles 7 are similarly driven at desired intervals, and the earth is charged in the hole of the pile head part to prevent the float. The hydration reaction of the quick lime is gradually proceeded to sufficiently expand the quick lime. Thus, the sufficient compaction of the whole body is economically performed, and the ground can be improved into a highly rigid ground.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a ground improvement material and a ground improvement method for preventing liquefaction. Due to the slow hydration reaction due to water absorption, and the expansion and compression due to the pozzolanic reaction between the clay and sand in the ground and the water frame and plaster.

This article relates to soil improvement materials and soil improvement methods for improving the ground and preventing liquefaction of sandy soil.

(Prior Art) There is a concern that sandy soil deposited on the coasts of rivers and seashores may liquefy due to earthquakes, and countermeasures are urgently needed.

Generally, in order to compact loose sandy ground with a high groundwater level, the so-called quicklime pile method is known, which improves the ground by the reaction of quicklime, sand, crushed stone, gypsum, water frame, etc., which absorbs water, expands, and hardens the ground by compression. ing. In addition, there are methods in which permeable materials such as sand and crushed stone are placed in piles in the ground and compacted using a vibrating drive device (sand compaction pile method), and crushed stones placed on the ground surface are tamped with vibrating rods. The method used is to insert it into the ground and compact it. Furthermore, there is also the crushed stone drain method, which uses an auger to create piles of crushed stone in the ground without tamping, and uses it as a water channel to remove excess pore water pressure that occurs during earthquakes.

(Problem to be solved by the invention) In the quicklime pile construction method, in the case of permeable sandy ground with abundant groundwater, the hydration reaction of quicklime occurs instantaneously, and the residual pressure that compresses the ground around the pile is It is small and cannot be compacted sufficiently.

In addition, sand compaction pile construction methods may generate vibration and noise, which may cause pollution problems, which limits the scope of application of the construction method. Furthermore, with the crushed stone drain method, the effectiveness of the method is questionable due to clogging of the drain.

Another disadvantage is that the ground subsides after an earthquake.

The present inventors have conducted various studies on the properties of quicklime used in the above-mentioned soil improvement material. As a result, the quicklime conventionally used for ground improvement is light burnt quicklime obtained by burning limestone at a relatively high temperature, and the particle size is small. It was found that there was a problem in that the water use reaction of quicklime occurred quickly.

The present invention was made in view of the above-mentioned problems, and its purpose is to provide a ground improvement method that can compact the entire ground well, improve the ground to have high rigidity, and improve the ground to be less likely to cause liquefaction. The goal is to provide the following.

(II!Means and effects for solving the problem) According to the research conducted by the present inventors, since the underground water level is high in sandy ground where there is a risk of liquefaction, conventional light burnt quicklime is not suitable for ground improvement. could not be effective. Limestone first undergoes thermal decomposition at around 900°C to become quicklime, but the hydration rate of the resulting quicklime varies depending on various conditions during production. When limestone is heated, it gradually decomposes from the surface toward the center of the stone, while the already decomposed quicklime on the surface grows into quicklime particles by maintaining the heating temperature and time, and the rate of water use gradually slows down. .

That is, it has been found that hard calcined lime obtained by calcining limestone at a high temperature of 1,200 to 1,500 degrees Celsius brings about favorable results in improving sandy soil. It was also discovered that when the above-mentioned hard-burned quicklime particles have a particle size of 5 mm or more, the hydration rate of the quicklime is slow when mixed with water-containing sand, and the quicklime remains as quicklime for 10 to 15 minutes. Ta.

The present invention is based on these findings, and its gist is: ``Hard calcined lime obtained by calcining limestone at 1,200 to 1,500 °C, the particle size of which is 5+ m or more; A liquefaction prevention ground improvement method characterized by inserting a liquefaction prevention ground improvement material containing at least a permeable material, a water frame, and gypsum into the ground, compacting the ground, and hardening the ground. .

The quicklime used in the present invention is obtained by calcining raw stone with a particle size of 20 to 40 nm in a vertical furnace at about 1,200 to 1,500°C, and is called hard calcined lime. It is something. Therefore, it is completely new, unlike lightly calcined quicklime, which has been conventionally used in the chemical industry, steel manufacturing, and civil engineering and construction. The quality is determined by the test method based on the Japan Lime Association method, i.e., the amount of 4N'Hcl consumed when quicklime is sized to 1 to 5m, poured into water at a certain temperature, and then neutralized with 4NHal. The hard calcined lime used in the present invention has the above-mentioned Hcl consumption of 5 after the start of titration.
The minute value is 100 gloss and the 10 minute value is 150 oc or less.

Even if such hard-burned quicklime is mixed with wet sand and clay, water frame slag, gypsum, etc. attached to the sand, the
It is stable without hydration in its original state (5-35 cm of quicklime) for ~15 minutes.

In addition, the activity of the above-mentioned lightly calcined quicklime, which is generally used for chemical industry, etc., is a 5-minute value, and the consumption of 4NHCl is 200cc.
, 300 cc in 10 minutes, indicating an extremely fast hydration rate.

Next, it takes several minutes to mix the hard-burned quicklime and other hardened materials used in the present invention into the sand in the sandy soil bed in a water-containing state. However, as mentioned above, since the hydration rate of hard calcined lime is slow, the above-mentioned mixing operation ends before the hydration starts. Therefore, the hydration reaction starts after the mixed material is pushed into the ground in the form of a pile, and the expansion and compaction effects caused by the conversion of quicklime into slaked lime work effectively.

Quicklime becomes slaked lime in the ground and fills well between the sand particles in the ground, and the negative charge on the surface of the clay attached to the sand is replaced by calcium ions, causing agglomeration of the clay particles and preventing liquefaction. It can be effective. Furthermore, by using blast furnace water frames and gypsum together, the vitality of slaked lime causes a pozzolanic reaction, producing hydraulic compounds.
It can harden and reform the ground. In the conventional sand compaction method, ground improvement is performed by mechanically filling crushed stone, sand, etc. that approximates the local sand layer. This is due to the effect of weight.

Next, the hard calcined lime used in the present invention is not limited to limestone calcined at a high temperature, but dolomite raw stone calcined at a high temperature can also be used. In addition to the above-mentioned hard-calcined quicklime, the ground improvement material in the present invention includes water-permeable materials such as sand and crushed stone, solid water frames, natural gypsum, chemical gypsum, anhydrite, hemihydrate gypsum, and other gypsums. Mix and use. The mixing ratio is 20 to 5 parts of hard calcined lime.
Preferably, the amount of water permeable material is 0 parts by weight, the water permeable material is 30 to 70 parts by weight, and the visible water frame and plaster are 10 to 50 parts by weight.

Pile construction in the ground using the soil improvement material according to the present invention is carried out as follows. First, (a) shown in FIG.
The construction method of the present invention will be explained according to the order of (e).

(a) First, set the pile driver 1 vertically at the desired position.

With the shoe 3 at the tip of the circular fJ-shaped casing 2 closed, the casing 2 is rotated and gradually penetrated into the soil by the spiral blades 4.

(b) The tip of the casing 2 is at a predetermined depth. When it reaches this point, stop the rotation of casing 2, and open the upper side hopper 5.
From there, the ground improvement material mixed in advance is discharged into the casing 2 until the pile cap level reaches L□.

(c) Open the shoe 3, send compressed air from the compressor 6, pressurize the inside of the casing 2 to a predetermined pressure P□, and rotate the casing 2 to pull it out.

(d) Piles 7 of soil improvement material are constructed underground. In this way, piles 7 made of a ground improvement material whose main component is hard-burned quicklime are driven at predetermined intervals.

(e) Measures will be taken to prevent the ground surface from rising up to the pile cap level L1 of the piles of the ground improvement material that have been driven, such as by filling with soil from the site. The cast piles 7, which are a ground improvement material whose main component is hard-burned quicklime, absorb moisture in the surrounding soil, compress the spaces between the piles as they expand, and further harden, thereby improving the structure of the ground. A composite ground is formed of improved ground and hardened columnar bodies compared to the original ground.

In this way, this construction method can be constructed on sandy ground with low vibration and noise, compacts the ground between the piles, and also develops the strength of the piles, so it is possible to perform construction on sandy ground with low vibration and noise. A highly rigid ground is formed as a composite ground with the sand layer.

Therefore, the ground has high liquefaction resistance.

Next, a test to confirm the formulation and expansion rate of the soil improvement material of the present invention and a full-scale example will be explained, and the formulation and improvement effects will be specifically shown.

(Example 1) Confirmation test of mixing ratio and expansion rate The mixing ratio of the materials to be mixed with the soil improvement material assumes the sand compaction pile method among conventional construction methods, and the above-mentioned construction method is set as the method for inserting into the ground. did. In this case, in order to reduce the installation cost compared to the sand compaction pile construction method by the amount of non-compaction, and to make the total construction cost the same as the sand compaction pile construction method, 1. Find the weight-based unit price of the ground improvement material of the present invention, Based on this, the blending ratio of the materials to be mixed was determined.

When the unit price of the ground improvement material of the present invention, which is compatible with the sand compaction pile construction method, is 1, the unit prices of the materials to be mixed were set at the ratios shown in Table 2.

Table 1 The unit price A of the soil improvement material is calculated using the following formula % formula % using the compounding rate symbols in Table 1, where the compounding rate is defined on the inside weight basis. The blending ratio of each material was determined so that The improvement effect was determined from data on the expansion rate of the piles in the experimental soil tank and the penetration resistance of the ground between the piles.

According to the experimental data, although there were variations in the expansion rate, the expansion rate that reduces the voids in sandy soil and provides the necessary compaction strength is 1.3 times the pile diameter and 1 times the volumetric expansion rate.
．． It was set as 69. Then, the blending ratio of each material within the range of an expansion coefficient greater than this value and a pile material unit price of 1 or less was determined by a simple preliminary test.

The improvement effect depends on the pile diameter and the area ratio of the pile to the ground.
．． It was fixed at 1. The results of this test are plotted in the relationship between the expansion rate of the pile and the unit price ratio of the soil improvement material, as shown in Figure 2.

The test results were within the target range of an expansion rate of 1.69 or more and a material unit price standard value of 1 or less in all experimental soil tanks. Furthermore, the penetration resistance of the ground between the piles increased 2 to 3 times compared to the value before the pile reaction, indicating a compaction effect.

(Example 2) Based on the results of the laboratory test in Example 1, we determined the compounding ratio of materials as shown in Table 2 that matched the conventional construction method both economically and in terms of expansion rate, and conducted a full-scale test. - A concrete pit 4.6 m long, 3.7 m wide, and 5 m deep was built outdoors, and water was filled in it and sandy soil was poured into it to create an artificially loose saturated sandy ground. . On this artificial ground, piles were constructed using 400I casings each having a depth of 5 m and an equilateral triangular arrangement with a pitch of 1.2 m, according to the construction method described above.

Figure 3 shows the N value of the number of blows obtained by the Tetsuken type penetration test before and after soil improvement. Immediately after pile driving and 28 days later, the N value of the ground improved to t, so the improvement effect was recognized at each depth.

FIG. 4 is a diagram showing changes over time in the horizontal earth pressure and water pressure between the piles, measured by an earth pressure gauge and a water pressure gauge installed between the piles. From this result, the expansion pressure of the pile is approximately three times that of the effective soil, and because the soil is permeable and sandy, even if excess water pressure occurs, it quickly dissipates, indicating hydrostatic pressure. I understand.

The above-mentioned improvement effects are comparable to those of the conventional sand compaction method in terms of the relationship between the increase in N value and the pile area ratio. In addition, as shown in Figure 2, the pile material has a composition that is more economical than conventional construction methods.

Regarding the determination of liquefaction in this example, when we calculated the safety factor against liquefaction as indicated in the building foundation structure design guidelines, it became a value of 1 or more after the improvement, so liquefaction prevention It was confirmed that the measures were taken.

(Effects of the Invention) According to the ground improvement material and soil improvement method according to the present invention, the entire ground can be improved by creating piles of an economical soil improvement material containing hard calcined quicklime as the main reaction material in the ground. The ground can be improved to be compact and highly rigid, making it less prone to liquefaction. Therefore, its practical value is extremely great.

[Brief explanation of drawings]

FIGS. 1(a) to 1(e) are schematic sectional views showing the construction order of the ground improvement method according to the present invention. FIG. 2 is experimental data showing the relationship between the pile expansion rate and the pile material unit price ratio according to Example 1. FIG. 3 is an N value distribution diagram showing the improvement effect of Example 2, and FIG. 4 is a diagram showing temporal changes in horizontal earth pressure and water pressure between piles according to the same example. 1... Pile driver 2... Casing 3... Shoe 4... Spiral wing 5... Side hopper 6...
・Compressor 7... Pile patent applicant
Toda Construction Co., Ltd. Onoda Chemico Co., Ltd. (a) Figure i (d) Figure 2 Pile material sugar weight 1@

Claims (1)

[Claims] Liquefaction prevention ground made by mixing hard calcined lime obtained by calcining limestone at 1,200 to 1,500°C with a particle size of 5 mm or more, and at least a water permeable material, a water frame, and gypsum. A soil improvement method for preventing liquefaction that is characterized by inserting improvement materials into the ground, compacting the ground, and hardening the ground.