JPS6254925B2 - - Google Patents

Description

[Detailed description of the invention]

This invention provides a method for easily determining the apparent CBR value by comparing the results of a penetration test conducted on sampled soil in a laboratory with the results of a penetration test conducted at the soil sampling site, which is conventionally known as a CBR test for soil. This paper relates to a simple test method for soil bearing capacity ratio and a soil penetration tester. Land must satisfy certain conditions depending on its intended use, and when preparing the land, compaction tests, penetration tests, soil constant measurements, etc. are conducted on the soil sampled on the land, and if necessary, other land,
In order to use the soil collected at sites B, C, etc. on the target land, work is carried out to improve the soil quality to suit the purpose of use, either alone or in combination. Conventionally, the CBR test has been generally performed as a test method for the above-mentioned soil quality, and is specified in the Japanese Industrial Standards (JIS Standard A1211). The origin of the CBR test and other matters are detailed in the book "Soil Testing Methods" published by the Japan Society of Soil Engineering and are well known, but only some of the matters are listed here for reference. (1) Origin of the CBR test So-called deflection pavement is generally constructed by stacking layers called the subgrade, base layer, and surface layer on top of the subgrade. The traffic load transmitted to the base layer via the surface layer is dispersed in the base layer and transmitted to the roadbed, and further dispersed in the roadbed and transmitted to the roadbed. Therefore, the traffic load must be reduced in the base layer to below the allowable bearing capacity of the roadbed, and furthermore, the traffic load must be distributed in the subgrade to be below the allowable bearing capacity of the subgrade. Therefore, it can be said that the bearing capacity of the subgrade is the basic condition for the design of the subgrade, base layer, and surface layer stacked on it, and the bearing capacity of the subgrade is the basic condition for the design of the base layer and surface layer stacked on it. Methods for determining the bearing capacity of a subgrade or roadbed include shear tests, flat plate loading tests, and penetration tests, but the method specified in JIS A 1211 involves inserting a standard-sized penetration piston into the soil. This test measures the load strength required to penetrate the soil and determines the strength of the soil and therefore its bearing capacity, and is called a CBR test. From 1928 to the following year, California in the United States
When OJPorter investigated the failure of deflection pavements in the state, we used CBR (California
He devised a measure called Bearing Ratio. As a standard measure for comparison, a large number of CBR
The test was repeated and the average value was determined as CBR100%. Subsequently, Porter et al. investigated the CBR of subgrades and roadbeds, and in 1942 created a design curve to calculate the thickness of deflecting pavement from CBR. In 1940, the US Corps of Engineers, A. Casagrande, T.A.
As a result, the CBR method was adopted, and in June 1942, with some modifications to the California method, the current tamping test method was established. Regarding the design curve, the results of field experiments,
It has also been confirmed that there is no need to make any essential changes. A major advantage of the CBR test is that it is widely applicable and can be used on almost any soil, from clay to clay. In addition, CBR is also available in various countries.
This test, or a test method similar to this, was defined and adopted as a JIS standard in Japan. (2) Overview of the JIS standard CBR test method 1 Scope of application This standard applies the intrusive method to soil specimens prepared by compacting in a mold, undisturbed soil specimens collected in a mold, and field soil. The test method for determining the subgrade soil bearing capacity ratio (hereinafter referred to as CBR) is specified. 2 Definition of terms CBR is the ratio of the test load strength at a certain penetration amount to the standard load strength at that penetration amount, and is expressed as a percentage. CBR refers to the value at a normal penetration depth of 2.5mm. 3. Indoor testing of disturbed soil specimens Indoor testing of disturbed soil specimens is divided into the following two methods, depending on the maximum allowable particle size of the soil particles in the sample: 19.1 mm or 38.1 mm. 3.1 19.1 mm method (for soil particles with a maximum allowable particle size of 19.1 mm) 3.1.1 Test equipment (1) Mold, collar, and perforated bottom plate The mold conforms to JIS A 1210 (Soil compaction test method by compaction) 2.1 The 15cm mold specified in (2) shall be capable of attaching a collar approximately 50mm in height and fastening it to the perforated bottom plate (see Figure 1 (No. 10).
(see figure). The diameter of the hole in the bottom plate is
It should be 2mm or less. (2) Spacer disk The spacer disk shall be a metal cylinder with a diameter of 148 mm and a height of 50 mm. (3) Rammer Rammer is JIS A 1210
(Soil compaction test method by compaction)
It shall be a 4.5Kg rammer as specified in 2.2. (4) Penetration piston The penetration piston has a diameter of 50
It shall be a steel cylinder with a length of 200 mm and a circular edge surface of mm. (5) Loading device, (6) Power meter, (7) Penetration measuring device, and other tools listed in (17) are omitted. Sections 3.1.2 Sample preparation, 3.1.3 Specimen preparation, and 3.1.4 Water absorption expansion test are omitted. 3.1.5 Penetration test (1) Place a load plate with the same weight as in 3.1.4(2) on top of the specimen. (2) Attach the specimen and the penetration piston to the loading device as shown in Figure 7 (see Figure 10). Place the penetrating piston precisely in the center of the specimen and bring it into close contact with the specimen, but in this case the load should be 5 kg or less,
This is the zero load for the test. (3) Record the reading of the force meter on the loading device;
Or set it to zero. Place the dial gauge to measure the amount of penetration on the edge of the mold and set it to zero. (4) Apply a load smoothly so that the piston penetrates the specimen at a speed of 1 mm per minute, and measure the penetration depth of 0.5 mm, 1.0 mm, 1.5 mm,
2.0mm, 2.5mm, 3.0mm, 4.0mm, 5.0mm,
Record the force meter readings for each of 7.5 mm, 10.0 mm, and 12.5 mm ⁽⁶⁾ . If the force meter reading reaches the maximum value before the penetration amount reaches 12.5 mm,
Record the load strength and penetration amount at that time. Note (6) The force meter readings for penetration depths of 10.0 mm and 12.5 mm may be omitted. (5) After recording the reading at the final penetration depth, remove the load and remove the specimen from the loading device. (6) While extruding soil from the mold using a sample extruder, remove 0.5 m from the surface of the specimen.
If the maximum particle size of soil particles is approximately 5 mm, take a sample of 100 g or more in the range of ~3.0 cm, or 250 g or more in other cases, and measure the water content. 3.1.6 Calculation of CBR (1) Divide the load obtained from the penetration test results by the cross-sectional area of the penetrating piston, express it as load strength (Kg/cm ² ), and draw a load strength-penetration amount curve ^{(7 )} (see Figure 8). curve 2
When the load strength-penetration curve curves upward as shown in Figure 8, draw a tangent at the inflection point of the load strength-penetration curve and find the intersection of the tangent with the horizontal axis. Modify the load strength-penetration amount curve as the origin of the penetration point. Note (7) Penetrating load strength may be expressed in load (Kg). In this case, it becomes a load-penetration curve. (2) Read the load strength at penetration depths of 2.5 mm and 5.0 mm on the load strength-penetration curve obtained in (1), and calculate CBR using the following formula ⁽⁸⁾ . CBR=Load strength/Standard load strength x 100 (%) For the standard load strength, use the values in Table 1. Note (8) When the penetration load strength is expressed in load (Kg), read the load at the penetration depth of 2.5mm and 5.0mm on the load-penetration curve, and use the following formula.
CBR

Calculate [Table]. CBR = Load/Standard load x 100 (%) For the standard load, use the values in Table 1. (3) CBR usually takes the value at a penetration depth of 2.5mm. CBR at penetration depth 5.0mm is 2.5
If it is larger than mm, make a new specimen and conduct the test.
However, if you get the same result again, take the CBR at 5.0mm. 3.2 38.1mm method (when the maximum permissible soil particle size is 38.1mm)...(Omitted) 4. Indoor test of undisturbed soil specimen...(Omitted) 5. Field test 5.1 Test equipment (1) Load The load shall be a truck or other easily movable device that can act as a load on the loading device. (2) Loading device The loading device has a capacity of 500 to 5000 kg depending on the expected load strength, and consists of a screw jack or oil jack with a force meter with an accuracy of 1/100 or more, and a ball seat. The piston penetration speed can be adjusted to 1 mm per minute. (3) Penetration measurement device The penetration measurement device is
It shall consist of two diccal gauges as specified in 3.1.1(7), a fixture for attaching them to the penetrating piston, and a mount as shown in Figure 10.
(Figure 10 is omitted) (4) Penetration piston and load plate The penetration piston and load plate are the same as in 3.1.1 (4) and (9). (5) Others Prepare dry sand, shovels, hand towels, etc. 5.2 Test method (1) Finish the surface of the test area to a horizontal surface with a diameter of approximately 30 cm. In areas that cannot be finished flat, spread a thin layer of dry sand to create a flat surface. (2) Assemble the field test equipment as shown in Figure 10 (not shown). (3) Place the load plate in accordance with the provisions of 3.1.4(2). (4) Conduct a penetration test according to the method specified in 3.1.5. (5) After completing the penetration test, take the amount of samples shown in Table 2 from the test location and measure the water content. (6) Determine the density of the soil near the test location. 5.3 Calculation of CBR According to 3.1.6. As mentioned above, the CBR tests according to the JIS standard have the following drawbacks, except for the field test in section 5. (a) It is necessary to transport the sampled soil to the testing laboratory. (b) Testing usually takes 7 to 10 days due to various laboratory procedures. (c) Therefore, it takes a long time to determine whether the soil at the site can be used as a subgrade, and the workability of subgrade construction is extremely poor. Furthermore, the above-mentioned on-site test method 5 is not a method that can easily obtain accurate values. As mentioned above, the method of transporting sampled soil to a laboratory and testing it in order to determine the soil quality cannot achieve the speed required in on-site construction. A penetration testing machine is also used. As an example, the cylindrical body may include a spring, a handle may be provided to press the spring, and the needle associated with the spring may be manually pushed into the soil at a measurement point by hand, approximately per second, by grasping the handle. A type of machine (proctor) that penetrates at a speed of 1/2 inch was devised in the United States and has been used as a typical soil penetration test machine. It requires heat kneading, and there are large individual differences even among experienced testers, which inevitably leads to large deviations in the measured values, and the reliability of the penetration test results is low. There were flaws. The present invention aims to eliminate the drawbacks of such on-site soil penetration testing machines, provide a soil penetration testing machine that can obtain accurate test values, and use the testing machine to calculate the subgrade soil bearing capacity ratio. Apparent CBR on site
The purpose is to provide a simple test method that can be determined by values. The configuration of the present invention will be explained below with reference to the drawings. To explain the structure of the soil penetration tester 1, it has a rectangular upper substrate 2 and a lower substrate (table).
3 are joined at each corner by four guide rods 4, which extend below the lower substrate to form legs 5. Sliding tubes 8 and 9 at both ends of the upper slider 6 and lower slider 7 are fitted into the guide rod 4 between the upper substrate 2 and the lower substrate 3, and both sliders 6 and 7 are held so as to be able to move up and down. The lower surface of the upper slider 6 has a boss 10, and a hollow vertical frame 11 is fitted and supported in the hole of the boss so as to be parallel to the guide rod 4, and is tightened with a bolt 12. Inside the vertical frame 11, there is an upper spring receiving member 13 at the upper end and a coil spring 14 in the middle.
and a lower spring receiving member 15 that slides on the inner wall of the vertical frame 11 are fitted in order, one end 16 of the lower spring receiving member is fitted into the inner edge 18 of a window 17 formed in the vertical frame 11, It is brought into contact with the lower end portion 20 of an index 19 (diamond-shaped front surface) which is slidable and held by friction. A center hole 21 is provided at the lower end of the vertical frame 11.
An end plate 22 having a diameter is screwed therein, a screw hole 23 is screwed into the lower part of the upper spring receiving member 13 passing through the center hole 21, and a needle 24 is screwed into the screw hole. The needle 24 has a threaded part 26 at the upper end of an intermediate shaft part 25, and a fitting part 27 formed at the lower end with a constant diameter d and a constant length l, and the diameter d has a cross-sectional area of 1, 3/4, 1 /2, 1/3, 1/4, 1/5, 1/10, 1/2
Prepare 9 types of shapes A to I that are cut to 0.0 and 1/40 square inch. The shaft portion 25 passes through a boss 28 fixed to the lower slider 7, and is fixed by a fixing screw 29 provided on the boss. A screw shaft 31 is connected to the upper slider 6 via a rotary joint 30, and the screw shaft is screwed into a female threaded portion 32 connected to the upper substrate 2, and a handle 33 is fixed to the upper end. The rotating joint 30 has a thrust bearing 34 in contact with the upper surface of the upper spring receiving member 13, and a flange 36 of the connecting member 35 in contact with the upper surface of the bearing. It has a structure in which it is locked at a stepped portion 38, and the connecting member 35 is screwed to the screw shaft 31. When the handle 33 is rotated, the vertical frame 11 is guided by the guide rod 4 together with the upper slider 6 and can be moved up and down, and the penetration part 27 of the needle 24 is inserted into the soil sample 41 in the mold 40 placed on the lower substrate 3. You can force it. The indicator 19 moves upward depending on the amount of penetration of the needle 24. When a predetermined amount of penetration is reached, the handle 33 is rotated in the opposite direction to remove the needle 24.
to rise. The amount of displacement of the index 19 is read by the scale 39. Although not shown in the drawings, it would be more effective if, in addition to the handle, the threaded shaft 31 is connected with a speed reducer and a motor in order so that it can be driven both manually and mechanically. Next, a simple test method for subgrade soil bearing capacity ratio (CBR) of the present invention using the soil penetration tester 1 will be explained. (1) Test equipment (i) Soil penetration resistance tester (21.7Kg) 1 unit as explained above (ii) Rammer (4.84Kg) 2.5Kg, falling height 30cm
1 piece (iii) Perforated mold (2.03Kg) 40 diameter = 10cm,
Height = 125cm with holes (86 3.0mm holes spaced at 20mm intervals)
1 piece) (iv) Collar (1.19Kg) 1 piece (v) Bottom plate (1.68Kg) 1 piece (vi) Small butt (0.30Kg) 1 piece (vii) Spatula (0.20Kg) 1 piece (viii) Bucket ( 0.80Kg) 1 piece (ix) Water (5.00Kg) 5 Total weight 37.68Kg (2) Test procedure (i) First stage...Collect about 3Kg of soil generated on site into a vat. Add water and knead the soil in your palms to see if it becomes lumpy or not.
Determine the stage. If the soil becomes lumpy, it is considered poor soil and will not proceed to the next stage 2 test. (ii) Second stage...Put the above sample into a perforated mold 40 and use a 2.5Kg rammer to
Harden 3 layers at a time. The compacted sample is immersed in water for 20 minutes in a perforated mold 40. (iii) Third step: The needle 24 of the soil penetration tester 1 of the present invention is penetrated into the sample after being immersed in water, and the penetration resistance is measured. Penetration speed is 3
mm/sec. Depending on the soil quality, needles with cross-sectional areas A to I in Table 1 below are used.

[Table] H type is most suitable for sandy soil. (iv) 4th stage...needle 24 1.5 inches (38.1
mm) and read the maximum value of the needle resistance at that time. (v) Fifth step: From the above needle resistance value, calculate the needle index according to Figure 7. (vi) Step 6: Find out the apparent CBR value from the above needle index according to Figure 8. (3) Preliminary experiment (i) Effect of changing the shape (cross-sectional area) of the needle 24 When the penetration speed is constant at 13 mm/sec, 3 mm/sec, etc., the shape (cross-sectional area) of the needle
There were variations in the needle resistance value or needle index (the value obtained by dividing the needle resistance value by the cross-sectional area) when the needles were different, but the difference was not extreme, and this degree of difference was due to variation in measurements due to the shape of the same needle 24. It was moderately hot. (ii) Effect of change in penetration speed Even in the same sample, the needle resistance value varies depending on the penetration speed of the needle 24. In the case of a manual penetration tester, 13 mm/sec is normal, and in this case, there were variations in the needle resistance value, but with the penetration tester of the present invention, the needle resistance value was 3 mm/sec.
The measured values were stable in mm/sec. (iii) Effect of water immersion time The CBR test is conducted under the condition that water has penetrated onto the subgrade, so it is judged that there is no mechanical correlation without the water immersion condition. . In the simple test method of the present invention, it is necessary to shorten the immersion time in water as much as possible, and for this reason, holes were made in the mold to improve the circulation of water. The water immersion time was determined by measuring the saturation degree of the sample over time, and the time point when the saturation level reached a certain level and leveled off was considered to be the water immersion time. The relationship between the immersion time and the degree of saturation is shown in Figure 9, which shows that the degree of saturation remains constant after 20 minutes of immersion. As a result, the water immersion time was determined to be 20 minutes. (iv) Comparison of the method of the present invention and the conventional method The method of the present invention is expressed by the above-mentioned needle index, and the conventional method is expressed by the CBR value determined by the laboratory test specified in JIS standard A1211. was sampled and measured.
As an example, samples No. 1-1 to No. 15-2 are illustrated in Table 2. As a result of the test, it was proven that there is a correlation between the needle index and the CBR value, as shown in Figure 8.

【table】

【table】

[Table] (v) Physical test The ratio of gravel, sand, and fine particles in soil varies greatly depending on the sampling site, and this ratio greatly affects the CBR value. ),
Sand content (%), fine powder content (%), etc., specific gravity, liquid limit (%), plastic limit [test to know the boundary between semi-solid and plastic soil] (%), and water content ratio (%)
were investigated for the collected samples, and on the other hand, the particle size adjustment samples (fine particle content R = 15%, 22.5%, 30%, 45
%, 60%) of each sample. This result will be omitted from description since it is a useful result when applying the method of the present invention. (vi) Experiment to determine the number of tamping times In order to know the effect of tamping the sample on the CBR value, the amount of 74 μ passing (%) was 20, 15 and 10.
The γd (t/m ³ ), ω (%), and degree of compaction (%) were measured for the samples of 25, 20, and 15 times of tamping, and the results are useful when applying the method of the present invention. Since the results are useful for reference, their description is omitted. As mentioned above, when using the method of the present invention, the needle value can be measured immediately after collecting a sample on site, and the apparent CBR value can be calculated from this value, which saves a lot of time, effort, and cost for soil quality determination. The decision to reuse or dump soil can be made in a very short time at the construction site. Therefore, there is an excellent effect that the construction work can be carried out quickly, and the penetration testing machine has the excellent effect that it is easy to handle and can easily perform highly accurate measurements on site.

[Brief explanation of the drawing]

1 to 9 illustrate embodiments of the present invention, in which FIG. 1 is a front view of the soil penetration tester, FIG. 2 is a side view, FIG. 3 is a plan view, and FIG. FIG. 5 is an enlarged side view showing a part of the lower part of the vertical frame in cross section; FIG. 6 is a front view of the needle; Figure 7 is a comparison diagram of needle resistance value and needle index, and Figure 8 is a comparison diagram of the needle index of the present invention method and the conventional method.
A comparison diagram with the CBR value, Figure 9 is a diagram showing the relationship between sample water immersion time and saturation percentage, and Figure 10 is a diagram showing the relationship between the sample water immersion time and saturation percentage.
Fig. 11 is a front view illustrating the penetration test method of A1211 (corresponding to Fig. 7), and Fig. 11 is a diagram showing the same load strength and penetration curve. 1... Soil penetration tester, 2... Upper substrate, 3
... lower board, 4 ... guide rod, 5 ... leg, 6 ...
Upper slider, 7...Lower slider, 11...
... Vertical frame, 12 ... Bolt, 13 ... Upper spring receiving member, 14 ... Coil spring, 15 ... Lower spring receiving member, 17 ... Window, 18 ... Inner edge, 19 ... Index, 22 ... End Plate, 24... Needle, 27... Penetration part, 29... Fixing screw, 33
... Handle, 39 ... Scale, 40 ... Mold, 41 ... Soil sample.

Claims (1)

[Claims] 1. An upper substrate and a lower substrate are connected by a guide rod, and an upper slider and a lower slider are slidably fitted into the guide rod with a gap between them, and the upper slider A vertical frame is supported in parallel with the guide rod, and an upper spring receiving member, a coil spring, and a lower spring receiving member that slides on the inner wall of the vertical frame are fitted in order into the vertical frame, and one end of the lower spring receiving member is slidable on the vertical frame and abuts against the lower end of the index held by friction, and a needle is replaceably connected to the lower end of the lower spring receiving member, and the middle part of the needle is connected to the lower end of the lower spring receiving member. fixed to the slider,
The upper slider is connected to a screw shaft screwed to the upper substrate via a rotary joint to constitute a soil penetration tester, and on the other hand, soil is collected in a mold at the site and immersed together with the mold in water for a certain period of time. The soil sample that has been water-treated by pulling it up is placed on the lower base of the soil penetration testing machine together with the mold, and the needle is pulled into the soil sample by rotating the screw shaft and lowering the vertical frame. penetrate,
Read the amount of displacement of the index moved relative to the vertical frame,
On the other hand, the apparent CBR corresponding to the displacement amount of the above index is determined by a correlation diagram created by comparing the values obtained by the penetration test of the subgrade soil bearing capacity ratio (CBR) test method conducted in advance on the same soil in the laboratory. A simple test method for subgrade soil bearing capacity ratio to calculate the value. 2. The upper substrate and the lower substrate are connected by a guide rod, an upper slider and a lower slider are slidably fitted into the guide rod with a gap between them, and the upper slider is fitted in parallel with the guide rod. A vertical frame is fixed, and an upper spring receiving member, a coil spring, and a lower spring receiving member that slides on the inner wall of the vertical frame are fitted in order into the vertical frame, and one end of the lower spring receiving member is slid onto the vertical frame. a needle is removably connected to the lower end of the lower spring receiving member, and an intermediate portion of the needle is fixed to the lower slider; A soil penetration testing machine characterized in that the upper slider is connected to a screw shaft screwed onto the upper substrate via a rotating joint. 3. The soil penetration testing machine as set forth in claim 2, wherein the screw shaft is connected to a driving device for both manual and mechanical driving.