Hangzhou Sansi Instrument Analysis K30 Foundation Coefficient Load Test
The foundation coefficient K30 is the magnitude of the compressibility of the surface of the soil generated by the plane pressure. It is a static load plate load test using a rigid load plate with a diameter of 300 mm. Take the load σs corresponding to 1.25 mm on the stress-displacement (σ-s) curve measured for the first time, according to K30=σs/ Calculated in 1.25, the unit is MPa/m.
1. Applicable conditions and requirements for the K30 foundation coefficient load test
There are many factors affecting the size of the test value of the flat load test. Including the nature of the filler, grading, compaction coefficient, water content, rolling process, maximum dry density, optimum water content, test operation methods and test surface flatness. In order to standardize the test process, the applicable conditions and requirements for the plate load test are proposed.
Second, the load board size
The K30 plate load test is applicable to all kinds of soil and earth and rock mixed fillers with a particle size not larger than 1/4 of the diameter of the load plate.
Because the load plate of K30 is only 300mm in diameter. Therefore, there is a certain limit on the particle size and gradation of the filled soil. Otherwise, the particle size is too large and the gradation is not uniform. The test result of K30 will bring a large error, which is difficult to truly reflect the pressure of the subgrade. Real situation. According to the experience of Qinshen Passenger Dedicated Line, K30 is suitable for the detection of foundation coefficient K30 of uniform foundation soil (such as coarse and fine grained soil). It is also suitable for testing the uniform graded crushed stone, but for the uneven distribution of particles. Stone soil, its K30 test is difficult to obtain accurate and reliable test results.
Third, the effective depth range
The K30 plate load test has an effective depth range of 400 to 500 mm.
Since the K30 plate load test results reflect the properties of the foundation soil within the depth range of about 1.5 times the platen diameter under the pressure plate, in order to truly and comprehensively reflect the situation of the deeper soil layer, it is necessary to carry out comprehensive evaluation in combination with other detection methods. .
Fourth, factors affecting the K30 test results
For homogenous sand with fast water volatilization, the surface is hard shell, softened, or soil disturbed by other factors, the plate load test shall be placed below the disturbance zone.
There are many factors affecting the K30 test results, but the change in water content is the main factor causing the accidental error of the K30 test results, which means that the K30 test results are time-sensitive. In general, the control is applied near the optimum water content, the roadbed compaction coefficient is high, the subgrade quality is good, the surface stiffness of the bed is large, and the K30 test result is high. However, due to the influence of seasonal and weather temperature changes, the degree of evaporation of water is different, and the water content is different, so the water content is a variable. Practice has proved that after the completion of rolling, when the water content of the subgrade is large, the K30 test result is small; when the water content is small, the K30 test result is high. Since the compacted soil is in an unsaturated state, the water content has a great influence on its mechanical properties. This causes the K30 test results to be highly discrete and poorly reproducible due to changes in water content. To this end, field testing should eliminate the effects of changes in soil water content.
Five, time
For coarse and fine homogeneous soil, it should be carried out within 2 to 4 hours after compaction.
During the K30 test, it was found that the K30 test results at different times were quite different, especially for graded gravel. This is due to the different detection time, the water content and the knot strength of the subgrade are different. If the K30 test is carried out 2 to 3 days after the completion of the rolling, the K30 test results are improved, and the design requirements of the K30 are satisfied. However, doing so will result in unmatched and unreliable K30 test results. Therefore, in order to test the quality of the roadbed filling, the K30 test is only meaningful if it is tested within a certain time limit after the completion of the rolling.
Six, test interface
The test surface must be a flat, pit-free floor. For rough surface or unevenness caused by coarse-grained soil or mixture, a layer of dry medium sand or gypsum putty of about 2~3mm should be laid. In addition, the test surface must be kept away from the source to maintain test accuracy.
Fine-grained soil (silt, clay) can be tested only under compacted conditions. In the case of uncertainty, the depth of the ground should be tested, the depth below the ground to d (d = carrier plate diameter).
Seven, weather factors
Rainy weather or weather with winds greater than 6 may not be tested.
Eight, K30 foundation coefficient load test equipment
Load plate: The load plate is a circular steel plate with a diameter of 30 cm and a plate thickness of 25 mm. There should be a level bubble on the load plate.
Loading device:
1) Hydraulic jack and manual oil pump, connected by high pressure oil hose. The top of the jack should be provided with a ball joint and equipped with an adjustable screw and an elongated rod to accommodate various reaction devices of different heights. The selected load should be greater than or equal to 50kN.
2) The length of the hydraulic oil hose is at least 2m, and the quick joints of the automatic opening and closing valves should be installed at both ends to prevent the hydraulic oil from leaking out.
3) The manual hydraulic pump should be equipped with an adjustable pressure reducing valve to accurately classify and load the load plate.
4) The gauge of the pressure gauge should reach 1.25 times of the maximum test load, and the accuracy is not less than 0.6.
5) When the load is directly measured using a dynamometer, the accuracy of the dynamometer should be 1%.
The carrying capacity of the reaction device shall be greater than the maximum test load of 10 kN.
The sinking measuring device consists of a bridge and a meter. The bridge is used to install the metering fixed bracket or as a measuring reference plane. It consists of a supporting raft and a supporting base with a length of more than 3 m. When the span is 4 m, the section coefficient should be greater than or equal to 8 cm. The meter should be equipped with 3 to 4 dial gauges or electronic digital dialects with an accuracy of 0.01 mm. The measuring range should be no less than 10 mm. Each meter should be equipped with an adjustable fixing bracket.
Others: iron shovel, steel ruler (length 400mm), brush, mason trowel, spatula, level, plumb, pleat, dry sand, gypsum, oil, sunshade and wind protection facilities.
IX. Calibration requirements for K30 foundation coefficient load test
When testing the foundation factor, the instrument should be tested and verified.
Within three months of the test of the new instrument, it should be calibrated once a month to make the corresponding error correction. When the three calibration errors are less than ± 5%, the instrument enters a stable period.
Each time the instrument is put into a new work site or it must be verified once a year.
X. K30 foundation coefficient load test test operation steps
The test surface of the site should be leveled and brushed with a brush to remove the loose soil. When on a slope, the load plate support surface should be made horizontal.
Place the flat load meter:
1) Place the load plate on the test floor. The load plate should be in good contact with the ground. If necessary, a thin layer of dry sand (2~3mm) or plaster putty can be laid. When using plaster putty as a cushion, apply a layer of oil film on the bottom surface of the load plate, then place the load plate on the plaster layer, turn the load plate left and right and gently hit the top surface to make it completely in contact with the ground. At the same time, the level can be adjusted by means of a leveling bubble or level on the load plate.
2) Place the load-bearing part of the reaction device above the load plate and brake it. The support point of the reaction device must be 1 m away from the outer edge of the load plate.
3) Place the jack on the load plate below the reaction device. The extension rod and the adjustment screw can be used to make the top end of the jack ball close to the bearing part of the reaction device. The jack should be kept vertical without tilting during assembly. .
4) Place the bridge, and the bridge support should be placed 1 m away from the outer edge of the load plate and the support point of the reaction device. The placement of the gauges must be symmetrical to each other and should be equidistant from the center of the load plate.
Loading test:
1) For a stable load plate, add 0.01MPa load in advance for about 30 seconds. After the load is stabilized, remove the load, adjust the dial gauge reading to zero or read the dial gauge reading as the starting reading of the sinking amount.
2) Load in stages in increments of 0.04 MPa. For each additional load, the load and sinking readings should be read after the sinking amount has stabilized.
3) The test may be terminated when the total sinking amount exceeds the specified reference value (1.25 mm), or the load strength exceeds the estimated actual maximum contact pressure at the site, or the yield point of the foundation is reached.
When there is an abnormality in the test process (such as the load plate is seriously inclined and the load plate is excessively sinking), the test point should be dug down to the depth corresponding to the diameter of the load plate and the test should be repeated. The occurrence of anomalies should be noted in the test record form.
XI. Calculation and drawing of K30 foundation coefficient load test test results
According to the test results, the relationship between load strength and sinking amount is plotted.
The load strength at the reference value of the sinking amount is obtained from the relationship between the load strength and the sinking amount, and the foundation coefficient is calculated as follows:
K30=σs/ss(1)
In the formula:
K30—Foundation coefficient (MPa/m) measured from a load plate with a diameter of 30 cm, calculated as an integer.
--- The load strength (MPa) corresponding to ss = 1.25'10m in the σ-S curve.
Ss - sinking reference value (= 1.25'10m).
Twelve, test record format
Table 1K30 flat load test record
Project Name Packing Type Test Number
Project location Filling thickness Test date
Construction unit
Load plate diameter inspection elevation test person in charge
load
order
Load
strength
σ(Mpa)
Oil pressure gauge
reading
P pressure (Mpa)
Sinking amount s (mm)
(percentage reading)
Load plate center sinking amount (mm)
Table 1 Table 2 Table 3 Average
Preload 0.01
Reset 0.00
1 0.04
2 0.08
3 0.12
4 0.16
5 0.20
6 0.24
1. Applicable conditions and requirements for the K30 foundation coefficient load test
There are many factors affecting the size of the test value of the flat load test. Including the nature of the filler, grading, compaction coefficient, water content, rolling process, maximum dry density, optimum water content, test operation methods and test surface flatness. In order to standardize the test process, the applicable conditions and requirements for the plate load test are proposed.
Second, the load board size
The K30 plate load test is applicable to all kinds of soil and earth and rock mixed fillers with a particle size not larger than 1/4 of the diameter of the load plate.
Because the load plate of K30 is only 300mm in diameter. Therefore, there is a certain limit on the particle size and gradation of the filled soil. Otherwise, the particle size is too large and the gradation is not uniform. The test result of K30 will bring a large error, which is difficult to truly reflect the pressure of the subgrade. Real situation. According to the experience of Qinshen Passenger Dedicated Line, K30 is suitable for the detection of foundation coefficient K30 of uniform foundation soil (such as coarse and fine grained soil). It is also suitable for testing the uniform graded crushed stone, but for the uneven distribution of particles. Stone soil, its K30 test is difficult to obtain accurate and reliable test results.
Third, the effective depth range
The K30 plate load test has an effective depth range of 400 to 500 mm.
Since the K30 plate load test results reflect the properties of the foundation soil within the depth range of about 1.5 times the platen diameter under the pressure plate, in order to truly and comprehensively reflect the situation of the deeper soil layer, it is necessary to carry out comprehensive evaluation in combination with other detection methods. .
Fourth, factors affecting the K30 test results
For homogenous sand with fast water volatilization, the surface is hard shell, softened, or soil disturbed by other factors, the plate load test shall be placed below the disturbance zone.
There are many factors affecting the K30 test results, but the change in water content is the main factor causing the accidental error of the K30 test results, which means that the K30 test results are time-sensitive. In general, the control is applied near the optimum water content, the roadbed compaction coefficient is high, the subgrade quality is good, the surface stiffness of the bed is large, and the K30 test result is high. However, due to the influence of seasonal and weather temperature changes, the degree of evaporation of water is different, and the water content is different, so the water content is a variable. Practice has proved that after the completion of rolling, when the water content of the subgrade is large, the K30 test result is small; when the water content is small, the K30 test result is high. Since the compacted soil is in an unsaturated state, the water content has a great influence on its mechanical properties. This causes the K30 test results to be highly discrete and poorly reproducible due to changes in water content. To this end, field testing should eliminate the effects of changes in soil water content.
Five, time
For coarse and fine homogeneous soil, it should be carried out within 2 to 4 hours after compaction.
During the K30 test, it was found that the K30 test results at different times were quite different, especially for graded gravel. This is due to the different detection time, the water content and the knot strength of the subgrade are different. If the K30 test is carried out 2 to 3 days after the completion of the rolling, the K30 test results are improved, and the design requirements of the K30 are satisfied. However, doing so will result in unmatched and unreliable K30 test results. Therefore, in order to test the quality of the roadbed filling, the K30 test is only meaningful if it is tested within a certain time limit after the completion of the rolling.
Six, test interface
The test surface must be a flat, pit-free floor. For rough surface or unevenness caused by coarse-grained soil or mixture, a layer of dry medium sand or gypsum putty of about 2~3mm should be laid. In addition, the test surface must be kept away from the source to maintain test accuracy.
Fine-grained soil (silt, clay) can be tested only under compacted conditions. In the case of uncertainty, the depth of the ground should be tested, the depth below the ground to d (d = carrier plate diameter).
Seven, weather factors
Rainy weather or weather with winds greater than 6 may not be tested.
Eight, K30 foundation coefficient load test equipment
Load plate: The load plate is a circular steel plate with a diameter of 30 cm and a plate thickness of 25 mm. There should be a level bubble on the load plate.
Loading device:
1) Hydraulic jack and manual oil pump, connected by high pressure oil hose. The top of the jack should be provided with a ball joint and equipped with an adjustable screw and an elongated rod to accommodate various reaction devices of different heights. The selected load should be greater than or equal to 50kN.
2) The length of the hydraulic oil hose is at least 2m, and the quick joints of the automatic opening and closing valves should be installed at both ends to prevent the hydraulic oil from leaking out.
3) The manual hydraulic pump should be equipped with an adjustable pressure reducing valve to accurately classify and load the load plate.
4) The gauge of the pressure gauge should reach 1.25 times of the maximum test load, and the accuracy is not less than 0.6.
5) When the load is directly measured using a dynamometer, the accuracy of the dynamometer should be 1%.
The carrying capacity of the reaction device shall be greater than the maximum test load of 10 kN.
The sinking measuring device consists of a bridge and a meter. The bridge is used to install the metering fixed bracket or as a measuring reference plane. It consists of a supporting raft and a supporting base with a length of more than 3 m. When the span is 4 m, the section coefficient should be greater than or equal to 8 cm. The meter should be equipped with 3 to 4 dial gauges or electronic digital dialects with an accuracy of 0.01 mm. The measuring range should be no less than 10 mm. Each meter should be equipped with an adjustable fixing bracket.
Others: iron shovel, steel ruler (length 400mm), brush, mason trowel, spatula, level, plumb, pleat, dry sand, gypsum, oil, sunshade and wind protection facilities.
IX. Calibration requirements for K30 foundation coefficient load test
When testing the foundation factor, the instrument should be tested and verified.
Within three months of the test of the new instrument, it should be calibrated once a month to make the corresponding error correction. When the three calibration errors are less than ± 5%, the instrument enters a stable period.
Each time the instrument is put into a new work site or it must be verified once a year.
X. K30 foundation coefficient load test test operation steps
The test surface of the site should be leveled and brushed with a brush to remove the loose soil. When on a slope, the load plate support surface should be made horizontal.
Place the flat load meter:
1) Place the load plate on the test floor. The load plate should be in good contact with the ground. If necessary, a thin layer of dry sand (2~3mm) or plaster putty can be laid. When using plaster putty as a cushion, apply a layer of oil film on the bottom surface of the load plate, then place the load plate on the plaster layer, turn the load plate left and right and gently hit the top surface to make it completely in contact with the ground. At the same time, the level can be adjusted by means of a leveling bubble or level on the load plate.
2) Place the load-bearing part of the reaction device above the load plate and brake it. The support point of the reaction device must be 1 m away from the outer edge of the load plate.
3) Place the jack on the load plate below the reaction device. The extension rod and the adjustment screw can be used to make the top end of the jack ball close to the bearing part of the reaction device. The jack should be kept vertical without tilting during assembly. .
4) Place the bridge, and the bridge support should be placed 1 m away from the outer edge of the load plate and the support point of the reaction device. The placement of the gauges must be symmetrical to each other and should be equidistant from the center of the load plate.
Loading test:
1) For a stable load plate, add 0.01MPa load in advance for about 30 seconds. After the load is stabilized, remove the load, adjust the dial gauge reading to zero or read the dial gauge reading as the starting reading of the sinking amount.
2) Load in stages in increments of 0.04 MPa. For each additional load, the load and sinking readings should be read after the sinking amount has stabilized.
3) The test may be terminated when the total sinking amount exceeds the specified reference value (1.25 mm), or the load strength exceeds the estimated actual maximum contact pressure at the site, or the yield point of the foundation is reached.
When there is an abnormality in the test process (such as the load plate is seriously inclined and the load plate is excessively sinking), the test point should be dug down to the depth corresponding to the diameter of the load plate and the test should be repeated. The occurrence of anomalies should be noted in the test record form.
XI. Calculation and drawing of K30 foundation coefficient load test test results
According to the test results, the relationship between load strength and sinking amount is plotted.
The load strength at the reference value of the sinking amount is obtained from the relationship between the load strength and the sinking amount, and the foundation coefficient is calculated as follows:
K30=σs/ss(1)
In the formula:
K30—Foundation coefficient (MPa/m) measured from a load plate with a diameter of 30 cm, calculated as an integer.
--- The load strength (MPa) corresponding to ss = 1.25'10m in the σ-S curve.
Ss - sinking reference value (= 1.25'10m).
Twelve, test record format
Table 1K30 flat load test record
Project Name Packing Type Test Number
Project location Filling thickness Test date
Construction unit
Load plate diameter inspection elevation test person in charge
load
order
Load
strength
σ(Mpa)
Oil pressure gauge
reading
P pressure (Mpa)
Sinking amount s (mm)
(percentage reading)
Load plate center sinking amount (mm)
Table 1 Table 2 Table 3 Average
Preload 0.01
Reset 0.00
1 0.04
2 0.08
3 0.12
4 0.16
5 0.20
6 0.24
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