JPH08134893A - Stabilization of soft ground - Google Patents

Abstract

PURPOSE: To greatly reduce the material and manufacturing cost. CONSTITUTION: After a cylindrical casing 2 and a tremie pipe have been buried in a specified depth of the ground as a unit, the casing 2 is left in the ground and a cement solidifying material M is fed from the front end of tremie pipe 3 in the soil in the casing 2 while pulling off the tremie pipe 3. A vibro-float 16 is inserted in the soil in the casing while vibrating it. Thereafter, the mixed granular material S in the casing is discharged in the ground while mixing the solid in the casing 2 with the cement solidifying material M by vibrating the vibro-float and vertically moving it and also pulling off the casing 2. In this way, the mixed granular material S discharged in the ground absorbs the water in the ground and forms soil improvement piles P.

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, and in particular, it is used in the field of improving soft ground by placing ground improvement piles on the soft ground.

[0002]

2. Description of the Related Art The mainstream ground improvement method is
This is the so-called sand compaction pile method.

In this method, the casing is driven into a soft ground to a predetermined depth, the earth and sand inside the casing are discharged to the ground, and then the sand, gravel and the like put into the casing are crushed by a vibrator or rod. By pulling sand or the like from the tip of the casing while pulling it up, compacted piles, that is, compacted piles are formed in the soft ground. According to this sand compaction pile method, sufficient supporting force for soft ground can be obtained.

[0004]

However, the most difficult point of the above sand compaction pile method is that the material sand or gravel is very expensive and almost impossible to procure in Japan, and most of them are procuring from foreign countries. It is the current situation. Even foreign-made ones are quite expensive.

Further, there has been a problem that the sand compaction pile is divided in the middle of the ground due to the flow pressure in the deep ground, especially in the deep ground, and the supporting force is lost for a long period of time.

An object of the present invention is to solve the above problems.

[0007]

In order to solve the above-mentioned problems, according to claim 1 of the present invention, a tubular casing 2 and a tremie tube 3 inserted therein are integrated by an auger machine 1. After burying the casing 2 to a predetermined depth in the ground, the casing 2 is separated from the auger machine 1 and left in the ground, and while the tremie pipe 3 is pulled out, the cement-based solidifying material M or cement powder is extracted from the tip of the casing 2 in the soil in the casing 2. And then attached to the tip of rod 17 and vertically movable by vertical moving means.
Is vibrated and inserted into the soil in the casing 2 to the bottom thereof, and then the vibro flot 16 is vibrated and moved up and down to mix and stir the soil in the casing 2 and the cement-based solidifying material M or cement powder. Then, the casing 2 is pulled out together with the rod 17 while forming the mixed powder and granules of the both, and the mixed powder and granules S in the casing 2 are removed.
Is discharged into the ground, and the mixed powder particles S discharged into the ground absorb moisture in the ground to form the ground improvement pile P.

According to a second aspect of the present invention, the vibroflot 16 is vibrated and moved up and down even when the vibroflot 16 is inserted into the soil inside the casing 2.

According to a third aspect of the present invention, a butterfly-shaped opening / closing plate 22 is provided at a lower portion of the vibro flot 16 so as to be laterally expanded by earth pressure and closed by being folded downward by its own weight. The butterfly-shaped opening / closing plate 22 is opened / closed as the vibro flot 16 is moved up and down by the moving means.

According to the fourth aspect, the hydraulic cylinder 18 is used as the vertical moving means.

In the fifth aspect, the cement-based solidifying material M contains calcium oxide, silicon dioxide, aluminum oxide and sulfur trioxide as main components.

[0012]

According to the method of claim 1 of the present invention, the casing 2 is embedded by the auger machine 1 to a predetermined depth in the soft ground, and the soil inside the casing 2 is used as it is as a soil material for pile formation. Therefore, it becomes extremely economical and the construction cost can be significantly reduced.

Further, in the method of the present invention, after the tremie pipe 3 is embedded in the ground integrally with the casing 2, the casing 2 is separated and left in the ground while the auger machine 1 pulls out the tremie pipe 3. Cement-based solidifying material M or cement powder from the tip of the casing 2
Since it is put into the soil inside, when the cement-based solidifying material M or cement powder is put in, there is a possibility that moisture or sand may enter from the surrounding soft ground or the soil pressure of the surrounding ground may affect it. There is no, thereby cement-based solidifying material M
Or the cement powder no longer reacts unexpectedly,
A high-quality mixed powder S can be formed. Also, the tremie tube 3
No special equipment and work is required for inserting and withdrawing.

During the drawing process of the casing 2, the casing 2 is vibrated by the vibration of the vibro flot 16 and the vertical movement of the vibro flot 16 by the hydraulic cylinder 18.
The soil inside and the cement-based solidifying material or the cement powder are stirred and mixed to form the mixed powder S, and the discharge of the mixed powder S from the lower end of the casing 2 is promoted.
Further, when the discharged mixed powder S is hardened in the ground, the ground improvement pile P can exert a sufficient load-bearing support force, thereby increasing the axial compressive strength.

Further, according to the present invention, the mixed powder and granules S discharged into the ground absorb moisture in the ground to form the ground improvement pile P, so that it is included in the soft ground. The density of the soft ground is increased by absorbing the moisture in the mixed powder S, and the mixed powder S absorbs the moisture in the ground to be hardened to swell the soft ground. Is consolidated, which can effectively achieve the consolidation of soft ground.

According to the method of the second aspect of the present invention, the vibro flot 16 is vibrated and moved up and down even when it is inserted into the soil inside the casing 2. Therefore, the vibro flot 16 is vibrated into the soil inside the casing 2. It becomes easy to insert the Loflot 16, and the soil inside the casing 2 is disturbed and loosened, and the soil and the cement-based solidifying material or cement powder are premixed and stirred. Therefore, the vibroflot at the time of extraction Mixing and stirring by 16 is enabled.

According to the construction method of the third aspect, the butterfly-shaped opening / closing plate 22 mounted on the lower portion of the vibro flot 16 is opened laterally by the pressure of earth and sand when the vibro flot 16 is moved downward, and this is opened. In this state, it moves downward to push the earth and sand and the like, and when it moves upward, it closes downward due to its own weight, so that it can smoothly move up without receiving the resistance of the earth and sand and the like.
By opening and closing the butterfly-shaped opening / closing plate 22 in accordance with the vertical movement of the vibro flot 16, it is possible to effectively mix and stir the soil inside the casing 2 and the cement-based solidifying material M or cement powder. Further, the discharge of the mixed powder or granules S from the lower end of the casing 2 is further promoted, and a pressing force is exerted on the discharged mixed powder or granules S to form a sufficiently consolidated pile P. it can.

According to the construction method of the fourth aspect, by using the hydraulic cylinder 18 as the vertically moving means, a sufficient driving force can be obtained, and the structure is compact and the mounting is easy.

According to the method of claim 5, when the cement-based solidifying material containing calcium oxide, silicon dioxide, aluminum oxide and sulfur trioxide as the main components is used, the result of the experiment shows that ordinary cement powder is used. The uniaxial compressive strength when 240 kg / m ³ was added was 2 kgf / cm ² , whereas the uniaxial compressive strength when 240 kg / m ³ was added was 6.4 kgf / It has been found that at cm ² , it exhibits about three times the strength of cement powder. Therefore,
According to this cement-based solidifying material, a very good supporting force as a pile can be exhibited.

[0020]

EXAMPLES Examples will be described with reference to the drawings.
1 (A) and 1 (B) show a pile forming apparatus used for carrying out the construction method according to the present invention. First, Fig. 1
In (A), reference numeral 1 is an auger machine equipped with a cylindrical casing 2 and a tremie tube 3 inserted therein, which drives the casing 2 to rotate, and is supported by a reader (not shown) so as to be able to move up and down. It is adapted to be suspended from the top of the reader by a lifting wire (not shown). This auger machine 1 includes a prime mover 5 with a speed reducer in a machine frame 4, a hollow shaft body 6 for rotatably driving a casing, a gear 7 fixed to an output shaft 5a of the prime mover 5, and the hollow shaft. The rotation of the output shaft 5 a is transmitted to the hollow shaft body 6 by the gear 8 fixed to the body 6.

The hollow shaft body 6 for driving the casing has a lower end portion protruding downward from the lower surface of the machine frame 4 by an appropriate length.
The upper end portion 2a of the casing 2 is externally fitted to the downward protruding end portion, and a plurality of through holes or screw holes provided between the upper end portion 2a of the casing 2 and the hollow shaft body 6 side are respectively attached / detached pins or The bolt 9 is inserted or screwed into the casing 2 so as to be integrally rotatable with the casing 2.

The tremie tube 3 is usually the casing 2
Has a diameter about 1/3 of that of the tremie tube 3 and is concentrically arranged in the casing 2 and its upper end 3a is fixed in the machine frame 4. ,
A hopper 11 for supplying a cement-based solidifying material or cement powder is continuously provided via a large-diameter cylindrical portion 10. As shown in FIG. 1 (A), the large-diameter cylindrical portion 10 is opened by its own weight as shown by a solid line, and the air pressure injected from an air nozzle 12 provided in the cylindrical portion 10 is shown by a phantom line. It is equipped with an on-off valve 13 that closes. Then
After the required amount of cement-based solidifying material or cement powder is supplied from the hopper 11 into the tremie pipe 3, the on-off valve 13 is closed by injecting air from the air nozzle 12, and the tremie is supplied by the air. The internal pressure of the pipe 3 is increased so that the cement-based solidifying material or cement powder is extruded from the lower end of the tremie pipe 3.

When using the tremie tube 3, as shown in FIG.
As shown in (C), the bottom lid 14 is attached to the lower end of the tremie tube with an adhesive tape 15, for example.

In FIG. 1B, 19 is equipped with a hydraulic cylinder 18 (vertical moving means) connected to the tip of a hollow rod 17 having a vibro flot 16 at the lower end, and is equipped with a leader or a crane. A casing mounting pipe body 20 for detachably mounting the casing 2 at a lower portion of the elevating body 19 is protruded from the lower surface of the elevating body 19 by an appropriate length and the hydraulic cylinder 1
It is provided so as to surround 8. The casing mounting pipe 20 is similar to the casing driving hollow shaft body 6, and the casing 20 has an upper end portion 2 of the casing 2.
a is fitted outside, and the upper end portion 2a of the casing 2 and the tubular body 2
The casing 2 is integrally mounted by inserting or screwing the attachment / detachment pin or the bolt 9 into a through hole or a screw hole (not shown) provided over the 0 side. It should be noted that an air spring or the like that can move up and down by a predetermined stroke may be used instead of the hydraulic cylinder 18 as the vertical moving means, but the hydraulic cylinder 18 has a more compact structure and is easier to install.

FIG. 2 shows a vibroflot 16 mounted on the lower end portion of the rod 17. This vibroflot 16 is well known, and although not shown, an eccentric shaft is rotated by an electric motor. It is designed to generate horizontal vibration. The power supply cable for the electric motor is inserted into the hollow portion of the rod 17, and is extended from the upper end of the rod 17 to the outside.
Reference numeral 21 is shown in (B). The cable 21 is in the form of a coil that can expand and contract so as to correspond to the vertical movement of the rod 17 by the hydraulic cylinder 18.

Also, at the bottom of the vibro flot 16,
As shown in FIG. 1 (B) and FIG. 2, there is provided a butterfly-shaped opening / closing plate 22 which opens so as to be laterally expanded by earth pressure and closes so as to be folded downward by its own weight. That is, a short tubular support pipe 23 having a large diameter is attached to the vibro flot 16 through a plurality of attachment pieces 24, and a horizontal support shaft 25 is fixed in the lower end portion of the support pipe 23 in the diametrical direction. A butterfly-shaped opening / closing plate 22 composed of a pair of semi-circular plates 22a, 22a is pivotally attached to a shaft 25.
Is normally closed by folding downward by its own weight as shown by the solid line in FIG. 1 (B), and by receiving earth pressure from below, it rotates upwards as shown by the phantom line in FIG. It is expanded and abutted and supported by the lower end of the support tube 23 at the expanded position.

In order to connect the casing 2 to the casing driving hollow shaft body 6 of the auger machine 1, as described above, the plurality of pin holes provided in the upper end portion 2a of the casing 2 and the lower end portion of the hollow shaft body 6 are connected. The detachable pin or the bolt 9 may be inserted into the pin hole or the screw hole provided at the position corresponding to the pin hole.
Instead of the connection method according to, a one-touch connection method as shown in FIG. 3 may be adopted. That is, a pair of engaging projections 26 are provided on the outer peripheral surface of the lower end portion of the hollow shaft body 6, and the upper opening 27a is narrowed on the inner peripheral surface of the upper end portion of the casing 2 and the lower opening thereof is enlarged in one horizontal direction. A pair of L-shaped recessed grooves 27 formed in the stopper 27b are formed, and, for example, the auger machine 1
And the engaging protrusions 26 of the hollow shaft body 6 are fitted into the openings 27a of the L-shaped recessed grooves 27 of the casing 2 to move the hollow shaft body 6 in the arrow direction (ground penetration) of FIG. When the casing 2 is rotated in a rotating direction), the engaging protrusions 26 move toward the locking portions 27b and are locked, whereby the casing 2 is connected to the hollow shaft body 6.

Next, the construction method of the present invention using the pile forming apparatus having the above-described structure will be described with reference to FIG. 4 and other drawings as needed. Incidentally, in FIG.
Indicates the order of construction.

First, as shown in FIG. 4, while rotating the casing 2 in the direction of the arrow by the auger machine 1, the casing 2 is embedded in the soft ground together with the tremie pipe 3 inserted into the casing 2. During this filling, a required amount of cement-based solidifying material is filled and supplied into the tremie pipe 3.
During the embedding of the tremie pipe 3, the lower end of the tremie pipe 3 is the bottom lid 14.
Since it is blocked by, the earth and sand and water do not enter the cement-based solidifying material inside from the lower end of the tremie pipe 3.

If the casing 2 and the tremie pipe 3 are embedded to a predetermined depth in the ground as shown in FIG.
As shown in (A), the detachable pin or bolt 9 connecting the casing driving hollow shaft body 6 of the auger machine 1 and the casing 2 is removed, and the casing 2 is removed from the auger machine 1 as shown in FIG. The auger machine 1 is pulled up and the tremie pipe 3 is pulled out from the soil inside the casing 2 while being separated and left in the ground.

As the tremie pipe 3 is pulled out, the adhesive tape 15 fixing the bottom lid 14 is peeled off by the self-weight of the cement-based solidifying material supplied into the tremie pipe 3, and the bottom lid 14 is removed. After falling off, as shown in FIG. 4, the cement-based solidifying material M inside is injected from the lower end of the tremie pipe 3 into the soil inside the casing 2 (the hollow portion of the soil after the tremie pipe 3 is removed). At this time,
As shown in (A), while supplying air from the air nozzle 12 and closing the on-off valve 13, the internal pressure on the upper side of the tremie pipe 3 is increased, and the cement-based solidifying material M is pumped downward by the air pressure. Then, it is discharged from the lower end of the tremie tube 3.

When the tremie pipe 3 is completely removed from the soil inside the casing 2 as shown in FIG. 4, the elevating body 19 instead of the auger machine 1 is directly above the casing 2 embedded in the ground. Then, as shown in (1) of FIG.
While vibrating and vertically moving the vibroflot 16 at the tip of the rod 17 that is continuously hung down via the hydraulic cylinder 18, it is inserted into the soil inside the casing 2. By vibrating and vertically moving the vibroflot 16 during this insertion, the soil inside the casing 2 is agitated and loosened, and the soil and the cement-based solidifying material put therein are effectively agitated. Will be mixed.

Further, in this case, the butterfly-shaped opening / closing plate 20 provided at the bottom of the vibroflot 16 is
6 When moving downward, it opens laterally due to the pressure of the soil, moves downward in this open state to push the soil, and when moving upward, it closes downward by its own weight, smoothly without receiving the resistance of the soil It is possible to move upward, and by such opening and closing action of the butterfly-shaped opening and closing plate 22, the internal soil of the casing 2 and the cement-based solidifying material M can be stirred and mixed. In addition, vibro flot 1 to the soil inside the casing 2
At the time of inserting 6, the vibro flot 16 may stop vertical movement by the hydraulic cylinder 18 and only vibrate.

By the time the vibro flot 16 reaches the bottom of the soil inside the casing 2, the casing mounting pipe 20 of the elevating body 19 will enter the upper end of the casing 2 protruding from the ground, In this state, the operations of the vibro flot 16 and the hydraulic cylinder 18 are temporarily stopped, and the upper end portion 2a of the casing 2 and the casing mounting pipe body 20 protruding into the inside are connected by the attachment / detachment pin or the bolt 9. After connecting the casing 2 to the elevating / lowering body 19 in this manner, the vibrating flot 16 is again vibrated and moved up and down by a predetermined stroke.
The inside of the casing 2 is pulled out by pulling up the casing 2 together with the vibro flot 16 and the rod 17 by raising and lowering the elevating body 19 while mixing and stirring the soil inside and the cement-based solidifying material M to form a mixed powder S of both. The mixed powder and granules S are discharged from the lower end to form the ground improvement pile P in the ground (see and in FIG. 4).

During the process of pulling out the casing 2 as described above, the vibration of the vibro flot 16 and the hydraulic cylinder 1
The vertical movement of the vibroflot 16 by 8 causes the soil inside the casing 2 and the cement-based solidifying material M to be agitated and mixed to form the mixed powder S, and the casing 2 of the mixed powder S The discharge from the lower end is promoted, and the powder mixture S is compacted and compacted.
Moreover, since the vibro flot 16 is equipped with the butterfly-shaped opening / closing plate 22 at its lower part,
Is laterally opened by the earth pressure, that is, the pressure of the mixed powder S when the vibro flot 16 is moving downward, and is moved downward in this open state to push the mixed powder S and move it upward. At times, it can be closed downward by its own weight and smoothly move up without receiving the resistance of the powder mixture S. In this way, the butterfly-shaped opening / closing plate 22 opens and closes in accordance with the up-and-down movement of the vibro flot 16, thereby effectively stirring and mixing the soil inside the casing 2 and the cement-based solidifying material M, and
The discharge of the mixed powder or granules S from the lower end of the casing 2 is further promoted, and the pressing force is applied to the discharged mixed powder or granules S, whereby a sufficiently compacted pile P is formed.

On the other hand, the mixed powder S discharged into the ground
Immediately after its formation (hardening begins after about 3 hours), it absorbs the interstitial water between soil particles in the surrounding ground to reduce the water content and reacts with water during this water absorption. It expands and its volume is 30 ~
Increase by 60%. In this way, when the ground improvement pile P expands, the surrounding ground is consolidated, and the ground strength is enhanced by this consolidation, and the once expanded ground improvement pile P becomes a hardened body itself by the hardening action. There is no contraction, that is, no reduction in volume, so that this ground improvement pile P will consolidate the surrounding ground and further increase its strength while being suspended in the ground.

In the method of the present invention, the material to be introduced into the soil inside the casing 2 by the tremie pipe 3 may be the above cement-based solidifying material or cement powder, but when the cement-based solidifying material is used. Is preferably calcium oxide, silicon dioxide, aluminum oxide, and sulfur trioxide as the main components. Specifically, the following compounding ratios are suitable.

Silicon dioxide 18.6 to 20.2% Aluminum oxide 6.2 to 4.6% Ferric oxide 1.8 to 2.5% Calcium oxide
59.6-63.1% Magnesium oxide About 1.8% Sulfur trioxide 7.
7 to 6.7% Insoluble balance 0.1 to 0.2%

Further, as a commercially available cement-based solidifying material,
The product name Heart Keep P-430 (manufactured by Tokuyama Corporation) or the product name Aso Solid Ace (manufactured by Aso Cement Co., Ltd.) is preferable.

[0040]

According to the construction method of claim 1 of the present invention,
The casing and the tremie pipe are embedded in the soft ground to a predetermined depth by an auger machine, and the soil inside the casing is used as it is as earth and sand material for pile formation without excavation. The cost can be significantly reduced.

After the tremie pipe was embedded in the soft ground together with the casing by the auger machine, the casing was cut off and left in the ground, and the tremie pipe was pulled out by the auger machine while the cement-based solidifying material M or the cement was removed from the tip. Since the powder is put into the soil inside the casing, it is possible to prevent the infiltration of moisture and earth and sand from the surrounding soft ground by the casing while the cement-based solidifying material or cement powder is being put in. Alternatively, the cement powder does not react unexpectedly, and it becomes possible to form high-quality mixed powder granules, and further, special equipment and work are not required for inserting and pulling out the tremie tube.

During extraction of the casing, the vibroflot vibrates and the vertical movement thereof causes the soil inside the casing and the cement-based solidifying material or cement powder to be effectively agitated and mixed, whereby a more homogeneous mixed powder or granular material is obtained. And the discharge of the mixed powder and granules from the lower end of the casing is promoted, so that a good soil improvement pile can be efficiently constructed.

Further, according to the method of the present invention, since the mixed powder and granules discharged into the ground absorb the water in the ground to form the ground improvement ill, the water contained in the soft ground is absorbed. With increasing the density of the soft ground by being absorbed by the mixed powder, the mixed powder absorbs the moisture in the ground and hardens to consolidate the soft ground by swelling the powder, This can effectively achieve the consolidation of soft ground.

According to the method of claim 2, the vibro flot can be easily inserted into the soil inside the casing, and the soil inside the casing and the cement-based solidifying material or cement powder can be mixed and stirred in advance. Thus, the mixing and stirring by the vibro flot at the time of drawing can be effectively performed.

According to the construction method of claim 3, the butterfly-shaped opening / closing plate opens and closes in accordance with the up-and-down movement of the vibro flot, thereby effectively mixing and stirring the soil inside the casing and the cement-based solidifying material or cement powder. Can be done automatically,
Further, the discharge of the mixed powder or granules from the lower end of the casing can be further promoted, and a pressing force can be applied to the discharged mixed powder or granules to form a sufficiently compacted pile.

Further, according to the construction method of the fourth aspect, by using the hydraulic cylinder as the vertically moving means, a sufficient driving force can be obtained, and the structure is compact and the mounting is easy.

Further, according to the construction method of the fifth aspect, it is possible to obtain a ground improvement pile having a semi-permanently strong supporting force.

[Brief description of drawings]

FIG. 1 (A) is a partial cross-sectional side view showing an auger machine for carrying out the construction method of the present invention, a casing and a tremie pipe equipped with the auger machine, and FIG. 1 (B) shows a lifting body through a hydraulic cylinder. 4C is a partial cross-sectional side view showing a state in which the rod is attached, and FIG. 6C is a partially enlarged side view of the lower end of the tremie tube.

FIG. 2 is a perspective view showing a vibro flot.

FIG. 3 is a perspective view showing another example of connecting a casing to a casing driving hollow shaft of an auger machine.

FIG. 4 is an explanatory diagram showing a construction sequence of the method of the present invention.

[Explanation of symbols]

 1 auger machine 2 casing 3 tremie pipe 5 prime mover 6 casing driving hollow shaft body 9 detachable pin or bolt 11 hopper 16 vibro flot 17 rod 18 hydraulic cylinder (vertical moving means) 19 lifting body 22 butterfly-shaped open / close plate S mixed powder Granule P Ground improvement pile

Claims (5)

[Claims] 1. A tubular casing and a tremie pipe inserted therein are integrally embedded by an auger machine to a predetermined depth in the ground, and then the casing is separated from the auger machine and left in the ground, and the tremie pipe is pulled out. While
A cement-based solidifying material or cement powder is put into the soil in the casing from its tip, and then a vibroflot attached to the tip of the rod and movable up and down by a vertically moving means is vibrated in the soil in the casing. While vibrating the vibro flot and then moving it up and down, the soil in the casing and the cement-based solidifying material or cement powder are mixed and stirred to form a mixed powder and granules of the both, while While pulling out with the rod, the mixed powder and granules in this casing are discharged into the ground, and the mixed powder and granules discharged into the ground absorb moisture in the ground to form a ground improvement pile. Improvement method for soft ground. 2. The method for improving soft ground according to claim 1, wherein the vibro flot is vibrated and moved up and down even when the vibro flot is inserted into the soil inside the casing. 3. A bottom portion of the vibroflot is equipped with a butterfly-shaped opening / closing plate that opens laterally by earth pressure and closes downwardly by its own weight, and the vibroflot upper and lower parts are vertically moved by the vertical moving means. The method for improving soft ground according to claim 1 or 2, wherein the butterfly-shaped opening / closing plate is opened / closed according to the movement. 4. The method for improving soft ground according to claim 1, wherein a hydraulic cylinder is used as the vertical movement means. 5. The method for improving soft ground according to claim 1, wherein the cement-based solidifying material contains calcium oxide, silicon dioxide, aluminum oxide and sulfur trioxide as main components.