JPS6156729B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the friction cut construction method for cast-in-place test piles for carrying out loading tests, etc., and a mortar seal device used therein.

Generally, in loading tests to investigate the bearing capacity of foundation piles, etc., cast-in-place piles with so-called friction cuts are often used. Figures 1 and 2 show a typical example of the friction cut method. First, a desired outer diameter, for example an outer diameter of 800 mmφ to 1600 mmφ, is
Insert the outer tube 1. Next, the inner tube 2, which has approximately the same length as the outer tube 1 and an outer diameter of 600 mmφ to 1400 mmφ, is inserted into the outer tube 1, and the ring packing 3 protruding from the inner surface of the outer tube 1 and the outer surface of the inner tube 2 are inserted into the outer tube 1. The friction cut spaces G at the lower ends of the inner and outer tubes are sealed by bringing the ring packings 4 protruding toward the sides into close contact. after that,
A support layer S under the underground excavation surface H is excavated to a predetermined depth with approximately the same outer diameter as the inner pipe 2, reinforcing bars are inserted and assembled into the excavated space P from above the inner pipe 2, and cement mortar is injected. , forming a so-called cast-in-place test pile B.

However, in the above construction method, since the friction cut space G is sealed by bringing the ring packings 3 and 4 into close contact,
As shown in Fig. 2, it is necessary to control the mutual positional relationship between the outer tube 1 and the inner tube 2, especially the vertical gap T, quite strictly, and even if the outer tube 1 sinks even slightly, the mortar will leak. Arise, friction cut space G
The disadvantage is that the lower part of the wall is filled with cement mortar.

Furthermore, when a load is applied to the inner pipe 2 in a loading test, the load stress is also transmitted to the outer pipe 1 via the packing rings 3 and 4, which increases the accuracy of the supporting force of the pile B, that is, the support layer. It is not possible to measure the bearing capacity of pile B only at S. In particular, if the distance T between the inner tube 2 and outer tube 1 is close enough to deform the packing rings 3 and 4, the supporting force due to the outer tube 1 will be considerably large and included in the measured value. Therefore, there is a problem that the regulation error of the interval T has a large adverse effect on the measurement accuracy of the pile bearing capacity.

In order to avoid the above-mentioned difficulties, methods have been developed and used in which the lower ends of the inner and outer tubes are filled with foamed urethane or a cloth or the like impregnated with a sealing material. However, even with these methods, leakage of mortar during filling with mortar cannot be completely prevented, and especially when the underground excavation surface H is considerably deep and has a large diameter pipe, mortar leakage cannot be completely prevented. The disadvantage is that leakage accidents often occur.

The present invention aims to solve the above-mentioned problems in the friction cut construction method of this type of cast-in-place test pile. Even in the case of large-diameter test piles as large as 2000mmφ, the friction cut space G can be easily and reliably sealed, and there is no risk of measurement errors during loading tests.
The object of the present invention is to provide a friction cutting method for cast-in-place test piles that enables extremely high-precision measurement of pile bearing capacity, and a mortar seal device used therein.

Hereinafter, the details will be explained based on one implementation of the present invention shown in FIGS. 3 to 5.

FIG. 3 is a cross-sectional view of a mortar seal device used in carrying out the method of the present invention. In the figure, 5 is a packer support frame, 6 is a packer, and 7 is an inlet for inflating gas. The packer support frame 5 has a brim-shaped upper support plate 5a and a lower support plate 5b, each having a diameter slightly smaller than the inner diameter of the outer tube 1, which are attached and fixed to the lower end of the inner tube 2 in parallel with an appropriate interval L. The upper support plate 5a is provided with an extraction hole 5c for the gas pressure inlet 7.

The packer 6 is formed into a circular tube shape from an elastic material such as rubber, and is inserted between the upper and lower support plates of the support frame 5. Also, the police car 6
A gas inlet 7 for pressurizing inflation gas is attached to the inlet 7, and the tip thereof passes through the outlet hole 5c of the upper support plate 5a and projects upward. The gas inlet 7 has a similar structure to the air inlet of a bicycle tube, and when the pressure from the hose (not shown) is stopped, the inlet is automatically closed by the internal pressure of the car. .

When pressurized fluid such as compressed air or compressed nitrogen gas is injected through the gas inlet 7, the packer 6 expands outward, and its outer surface expands by about 20 to 50 mm from the edges of the upper and lower support plates 5a and 5b. It is then brought out and tightly pressed against the inner circumferential surface of the outer tube 1.

In FIG. 3, the brim-shaped upper and lower support plates 5a and 5b are fixed directly to the lower end of the inner tube 2, but as shown in FIG. Upper and lower support plates 5a and 5b are fixed to both ends of a short pipe 8 that can be inserted, and the packer support frame 5 is constructed as a separate body.
Of course, this may be fixed to the lower end of the inner tube 2.

Next, a friction cut construction method for cast-in-place test piles using the mortar seal device will be explained.

Referring to FIG. 5, first, a steel outer pipe 1 of a required size is inserted up to the underground excavation surface H determined according to the thickness of the embankment or alluvial layer C, and the earth and sand inside it is discharged. It goes without saying that the outer tube 1 may be inserted by any method.

Next, the packer support frame 5 is attached to the tip of the inner tube 2 of a predetermined outer diameter to be inserted into the outer pipe 1 by welding or the like, and the packer 6 is inserted between the upper and lower support plates 5a and 5b. At the same time, a gas supply hose 9 is connected to the gas inlet 7. After that, the inner tube 2 is inserted into the outer tube 1, the central axis is positioned, and the upper end of the inner tube 2 is fixed to a support provided separately on the ground by an appropriate method. .

Next, the support layer S below the underground excavation surface H is excavated to an appropriate depth via the inner pipe 2, and after forming an excavated space P for the cast-in-place pile from which sand and gravel are discharged,
Predetermined reinforcing bars are inserted and assembled into the inner pipe 2 and the excavation space P.

When preparations for cement mortar injection are completed, pressurized fluid source 10 such as a cylinder or compressor is
Nitrogen, air, etc. are supplied from the tank through the hose 9 to inflate the pack car 6. The expanded pack car 6 has its outer peripheral edge bulging outward from the support plates 5a and 5b,
By coming into close contact with the inner wall surface of the outer tube 1, the friction cut space G is sealed.

After sealing the space G, cement mortar is poured from above the inner pipe 2 to complete the cast-in-place pile for testing.

When the cement mortar dries, a relief valve (not shown) is opened by an appropriate method to release the pressurized gas in the packer 6 and remove the support of the inner pipe 2 on the ground. As a result, the cast-in-place pile has been completely friction cut through the space G, and a loading test will be subsequently carried out.

In the above embodiment, the packer 6 is expanded immediately before filling with cement mortar, but after inserting the inner pipe 2, the packer 6 is expanded, and then the support layer S is excavated and the reinforcing steel is The cast-in-place pile may be formed in the order of assembling the concrete and pouring the mortar.

As described above, the present invention can easily and reliably seal the friction cut space G by simply attaching the mortar seal device A to the outer periphery of the lower end of the inner tube 2 and sending air, etc. to the gas packer 6, thereby improving work efficiency. This greatly improves the performance and eliminates any friction cut failures due to mortar leakage.

In addition, by removing the expanding gas in the gas packer 6, the inner tube 2, that is, the cast-in-place pile B, is completely friction cut, and a part of the load is transferred to the outer tube 1 during the loading test, and the pile support There is no possibility that the force measurements will be inaccurate.

Furthermore, the mortar seal device A has a structure in which a ring-shaped gas packer 6 is inserted into the support space formed by the upper and lower support plates 5a and 5b. It bulges out almost uniformly in the direction, and adheres extremely tightly to the inner circumferential surface of the outer tube, demonstrating high sealing performance. In particular, for large-diameter pipes in which the outer pipe 1 has an inner diameter of 1500 mmφ to 2000 mmφ or more, its sealing effect is far superior compared to other construction methods, and it prevents mortar leakage and prevents complete friction cuts. There is not a single example of a test in which it was not possible.

Moreover, even if there is some misalignment between the axes of the outer tube 1 and the inner tube 2, the gas packer 6 will be in complete contact with the inner circumferential surface of the outer tube 1 due to its expansion and deformation, leaving a partial gap. There is no possibility that this will cause mortar leakage.

As mentioned above, the present invention has excellent practical utility.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a cast-in-place pile using the conventional friction cut construction method, and FIG. 2 is a partially enlarged view of section A in FIG. 1. FIG. 3 is a sectional view showing a first embodiment of the mortar seal device according to the present invention, and FIG. 4 is a sectional view showing a second embodiment of the mortar seal device. FIG. 5 is a longitudinal sectional view of a cast-in-place pile using the construction method according to the present invention. 1...Outer pipe, 2...Inner pipe, 5...Patzker support frame, 5a...Upper support frame, 5b...Lower support frame,
6... Gas packer, 7... Inlet, 8... Short pipe, 9... Hose, 10... Pressurized fluid source, A...
Mortar seal device, H... Underground excavation surface, G...
Friction cut space, S... support layer, P...
Excavation space, B...cast-in-place test pile, C...embankment and alluvium.

Claims (1)

[Claims] 1. An outer pipe 1 is inserted to an underground excavation surface H of a certain depth, and then a mortar tool device A having a gas packer 6 at its lower end is attached inside the outer pipe 1. After inserting the tube 2 and injecting pressurized fluid into the gas packer 6 to expand it in the radial direction and sealing the friction cut space G formed between the outer tube 1 and the inner tube 2. A friction cutting method for a cast-in-place test pile, characterized in that cement mortar is filled from above the inner pipe 2 into the excavated space P formed in the support layer S below it and into the inner pipe 2. 2. A packer support frame 5 consisting of an upper support plate 5a and a lower support plate 5b, which are arranged and fixed in parallel with each other at a constant interval L, directly or indirectly to the outer peripheral surface of the lower end of the inner tube 2; 5. A mortar seal device comprising a ring-shaped gas packer 6 made of an elastic material that is inserted into a mortar seal 5 and expands when pressurized fluid is injected from a ground-based pressurized fluid source 10 through a hose 9.