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Abstract: The analysis adopted the earthy conventional compaction test to determine the irrationality in maximum dry density of Aeolian sand. Dry vibrating method compacting test, counterweight-added dry vibrating method compacting test, and counterweight-added water-saturated vibrating method compacting test were respectively given to samples of Aeolian sand. With the analysis of test data, advantages, disadvantages and applicability of each test method were summarized. A conclusion was drawn that counterweight-added water-saturated vibrating method compacting test was applicable to determine maximum dry density of Aeolian sand.
Key words: roadbed construction; Aeolian sand; maximum dry density; vibration; water-saturated; counterweight-added
中圖分类号： U213.1 文献标识码： A 文章编号：
Vast deserts exist in Northwest China. With the development and construction of the West, road construction in desert regions has been in full swing. Road materials in desert regions are mainly Aeolian sand. There is no a complete set of standards facilitating the implementation for determination of maximum dry density of Aeolian sand in current specifications, so it becomes an issue puzzled the construction unit during the construction. Following are several test methods to determine maximum dry density of Aeolian sand. With reference to actual site construction conditions, a test method most suitable for use is selected.
1. Earthy standard compaction test not suitable for Aeolian sand
The standard compaction method is used to provide compaction test for the 3 groups of Aeolian sand samples. Fig. 1 shows test results.
Fig.1 Relation between Dry Density and Vibrating Time (Standard Compaction Method)
Much is obtained from analysis of above test results:
1) When water content increases, spraying sand results in waste of reactive power due to liquefaction of sand sample surface. Several tests demonstrate its compaction curve fails to meet quality requirements of fixed and even shape which increases with the increase of reactive power.
2) During repeated parallel tests, discreteness of test result is rather high. There is no a stable unit quality index.
3) During the change of water content, two peal values occur in density. Dry peak value is greater than the peak value of water content and is completely different from earthy peak value. This shows properties of sand and earth differ. It also shows sand density is not in close relation to water content. Thus, it fails to meet requirements of density standard which is used as the standard reference and complies with engineering requirements.
2. Dry vibrating compacting test
It is common sense in production and living of the public in desert regions that Aeolian sand compacts due to the vibration inside the vessel. According to documents of Yulin Road Administration Bureau, resonance frequency of Aeolian sand is 25-55 Hz. The frequency increases as the density increases. A 1m × 1m concrete vibrating table is used in the test. Amplitude of vibrating table is adjusted to 0.3mm; vibrating frequency is 47.7 Hz. The vessel is a big barrel for standard compaction test. Its volume is 3,085 cm3.
Three kinds of Aeolian sand samples with the particle size slightly different from each other are selected for dry density analysis test. Table 1 shows physical characteristics of samples.
Table 1 Composition of Grain for Test Sand Purpose %
As shown in Table 1, particle size composition of Aeolian sand is 0.6-0.074 mm. In earth classification, it belongs to the fine sand category. Less silt contained in it shows its low activity, non-cohesiveness, strong looseness and favorable water stability. Dry the three Aeolian sand samples above. Vibrating test is conducted on them at different moments on condition that water content is zero so as to determine its most favorable vibrating moment.
Fig. 2 shows test results.
Fig.2 Relation between Dry Density and Vibrating Time (Dry Vibrating Method)
The test shows density of Aeolian sand increases as vibrating time increases. When the time is 4-6 min, density reaches the peak value, while continuous vibration leads to decrease of the density. Initial analysis assumes: displacement occurs in sand due to the effect by gravity, inertial impaction force, friction and vibration force among particles during the vibration. Several small particles move to the gap of large particles, resulting in narrow interspace of sand. When the time is 4-6 min, interspace among sand becomes narrowest, while density at this time is the maximal. Inherent vibrating frequency of sand and that of the vibrating table are in the most favorable harmony and unity. When vibration continues, sand density changes, so its inherent vibrating frequency inevitably changes and density decreases. This also applies to actual construction of roadbed engineering. When vibration rolling machine vibrates and rolls for 4-6 times, according to field test, compactness of roadbed reaches the peak value. However, if the machine continues rolling, compactness will decrease to certain degree instead of increase. This coincides with properties of Aeolian sand. If vibrating frequency of the vibrating table is required to be the same with the changed vibrating frequency of sand at this time, a frequency vibrating table must be used to adjust the vibrating frequency. Only by this can a new harmonized and stable status be reached. Based on the three reasons below, the frequency vibrating table is not suitable for determination of maximum dry density of actual Aeolian sand:
1) The frequency vibrating table is very complex. As a result, it is not widely used in production practices;
2) Inherent vibrating frequency of Aeolian sand differs due to the different structure;
3) Equipment supporting adjustment of construction machines shall be compatible with it.
Problems above may complicate the study and test, and bring difficulty to the operations, resulting in much inconvenience in use. In conclusion, the maximum dry density of Aeolian sand determined by dry vibrating method complies with the law, but it is not ideal.
3. Counterweight-added dry vibrating method compacting test
The counterweight-added dry vibrating method is a test method which adds certain pressure on top of the sand from the outside on the base of dry vibrating method. The dry soil method in JTJ 051-1993 Test Methods for Soils of Highway Engineering standard is used. A 1m × 1m concrete vibrating table is used in the test. Amplitude of vibrating table is adjusted to 0.3mm; vibrating frequency is 47.7 Hz. The vessel is a big barrel for standard compaction test. Its volume is 3,085 cm3. Add 18 kPa weights; the area is 177 cm2. Fill in layers and compact it to determine its maximum dry density. Operational steps are: the compaction barrel is fixed on the vibrating table.Sand samples are added into the barrel. The barrel is filled in three layers. After filling each layer, vibrate the counterweight added for 10 min. After the vibration, height of test samples is measured within the barrel and the actual volume is calculated.Its maximum dry density is calculated after weighing. Table 2 shows test results.
Table 2 Result of Counterweight-added Dry Vibrating Method Test
Test result shows, the use of counterweight-added dry vibrating method test yields larger density than common dry vibrating method. Initial analysis assumes: in addition to the effect from gravity, inertial impaction force, friction and vibration force among particles, sand is also affected by external pressure. When sand is compressed, its volume will not change; the small gap among sand is fair smaller than that in common dry vibration. It is easily to be arranged to the best position by the effect from vibration. Compared to the common dry vibrating method, the similarity is, when sand density reaches certain degrees, its inherent frequency changes, and continuous vibration will not contribute to greater compactness. The difference is, with the existence of certain external pressure, after being moved to large particles, fine particles will not be moved out of large ones due to changes in frequency. Thus, sand compactness will not decrease. In several tests determining the maximum dry density of Aeolian sand, maximum dry density obtained by counterweight-added dry vibrating method reaches the peak value. However, in actual construction, road roller rolls for several times. It is hard to meet conditions that permanent counterweight is added to sand during the test under such circumstance. As a result, standard compacting test of counterweight-added is not suitable for test of Aeolian roadbed construction.
4. Counterweight-added water vibrating method compacting test
This method is derived from the experience of water-fall houses for the public in desert regions. The principle is that sand will be compacted if it is vibrated in water. A 1m × 1m concrete vibrating table is used in the test. Amplitude of vibrating table is adjusted to 0.3mm; vibrating frequency is 47.7 Hz. The vessel is a big barrel for standard compaction test. Its volume is 3,085 cm3. Three groups of sand samples are selected for the vibration test at different moments to determine the most favorable vibrating moment. Operational steps are: the compaction barrel is fixed on the vibrating table and is fully filled with sand samples. Then water is slowly added into the barrel until water leaks from barrel bottom and the barrel is vibrated. Its compactness tested according to time segmentation.Figure 3 shows test results.
Fig.3 Chart on Relationship between Maximum Dry Density and Time of Vibration
（with additional weight water vibration method）
Water vibrating test can obtain the dry density between these obtained from common dry vibrating method and counterweight-added dry vibrating method. Initial analysis assumes: in addition to the effect from gravity, inertial impaction force, friction and vibration force among particles in water, sand is also affected by water buoyancy and pore water pressure. When sand is under semi-suspended status, the friction among sand is extremely small. With the vibrating effect, it is easily arranged to the best position. As shown in the curve for which dry density changes with the time, when vibration begins under specified vibrating frequency and amplitude, the dry density at first increases as time increases. When the time reaches 4-6 min, sand density is the maximum. If vibration is continued, sand density will decrease. It shows there occurs over vibration. The best original arrangement method is damaged as the vibration continues, resulting in decrease of density. In construction of test road section, results from roadbed test with the maximum dry density obtained by such method show, after the roadbed is rolled for six times by road roller, the compactness can reach 94% of the requirements. This can be the basis of roadbed test.
Test results show sand under external pressure and vibrated in water can reach the maximum compactness. Value obtained from the test is greater than these from common vibrating method, counterweight-added dry vibrating method and standard compaction method. It complies with actual conditions in practical test and inspection for roadbed. This can be the evaluation standard for test.
5. Conclusion
Dry density determined by counterweight-added water vibrating method has greater advantages when comparison is made between it and other methods. Its compactness standard is rather high and satisfies the quality standard as required by the engineering. It is suitable for compaction process of the roadbed for sand road and shows wide application value.
Paper received on: June 2, 2013
About the author: Zhao Qingsong (1978- ) is a male engineer from Beijing who mainly undertakes road ＆ bridge construction and management of technology and quality.
About the translator: Ji Jingtao (1983- ) is a male class 1 construction engineer of Mongolian ethnicity and from Beijing who mainly undertakes site technology management and production organization in construction of highway and bridges.
Key words: roadbed construction; Aeolian sand; maximum dry density; vibration; water-saturated; counterweight-added
中圖分类号： U213.1 文献标识码： A 文章编号：
Vast deserts exist in Northwest China. With the development and construction of the West, road construction in desert regions has been in full swing. Road materials in desert regions are mainly Aeolian sand. There is no a complete set of standards facilitating the implementation for determination of maximum dry density of Aeolian sand in current specifications, so it becomes an issue puzzled the construction unit during the construction. Following are several test methods to determine maximum dry density of Aeolian sand. With reference to actual site construction conditions, a test method most suitable for use is selected.
1. Earthy standard compaction test not suitable for Aeolian sand
The standard compaction method is used to provide compaction test for the 3 groups of Aeolian sand samples. Fig. 1 shows test results.
Fig.1 Relation between Dry Density and Vibrating Time (Standard Compaction Method)
Much is obtained from analysis of above test results:
1) When water content increases, spraying sand results in waste of reactive power due to liquefaction of sand sample surface. Several tests demonstrate its compaction curve fails to meet quality requirements of fixed and even shape which increases with the increase of reactive power.
2) During repeated parallel tests, discreteness of test result is rather high. There is no a stable unit quality index.
3) During the change of water content, two peal values occur in density. Dry peak value is greater than the peak value of water content and is completely different from earthy peak value. This shows properties of sand and earth differ. It also shows sand density is not in close relation to water content. Thus, it fails to meet requirements of density standard which is used as the standard reference and complies with engineering requirements.
2. Dry vibrating compacting test
It is common sense in production and living of the public in desert regions that Aeolian sand compacts due to the vibration inside the vessel. According to documents of Yulin Road Administration Bureau, resonance frequency of Aeolian sand is 25-55 Hz. The frequency increases as the density increases. A 1m × 1m concrete vibrating table is used in the test. Amplitude of vibrating table is adjusted to 0.3mm; vibrating frequency is 47.7 Hz. The vessel is a big barrel for standard compaction test. Its volume is 3,085 cm3.
Three kinds of Aeolian sand samples with the particle size slightly different from each other are selected for dry density analysis test. Table 1 shows physical characteristics of samples.
Table 1 Composition of Grain for Test Sand Purpose %
As shown in Table 1, particle size composition of Aeolian sand is 0.6-0.074 mm. In earth classification, it belongs to the fine sand category. Less silt contained in it shows its low activity, non-cohesiveness, strong looseness and favorable water stability. Dry the three Aeolian sand samples above. Vibrating test is conducted on them at different moments on condition that water content is zero so as to determine its most favorable vibrating moment.
Fig. 2 shows test results.
Fig.2 Relation between Dry Density and Vibrating Time (Dry Vibrating Method)
The test shows density of Aeolian sand increases as vibrating time increases. When the time is 4-6 min, density reaches the peak value, while continuous vibration leads to decrease of the density. Initial analysis assumes: displacement occurs in sand due to the effect by gravity, inertial impaction force, friction and vibration force among particles during the vibration. Several small particles move to the gap of large particles, resulting in narrow interspace of sand. When the time is 4-6 min, interspace among sand becomes narrowest, while density at this time is the maximal. Inherent vibrating frequency of sand and that of the vibrating table are in the most favorable harmony and unity. When vibration continues, sand density changes, so its inherent vibrating frequency inevitably changes and density decreases. This also applies to actual construction of roadbed engineering. When vibration rolling machine vibrates and rolls for 4-6 times, according to field test, compactness of roadbed reaches the peak value. However, if the machine continues rolling, compactness will decrease to certain degree instead of increase. This coincides with properties of Aeolian sand. If vibrating frequency of the vibrating table is required to be the same with the changed vibrating frequency of sand at this time, a frequency vibrating table must be used to adjust the vibrating frequency. Only by this can a new harmonized and stable status be reached. Based on the three reasons below, the frequency vibrating table is not suitable for determination of maximum dry density of actual Aeolian sand:
1) The frequency vibrating table is very complex. As a result, it is not widely used in production practices;
2) Inherent vibrating frequency of Aeolian sand differs due to the different structure;
3) Equipment supporting adjustment of construction machines shall be compatible with it.
Problems above may complicate the study and test, and bring difficulty to the operations, resulting in much inconvenience in use. In conclusion, the maximum dry density of Aeolian sand determined by dry vibrating method complies with the law, but it is not ideal.
3. Counterweight-added dry vibrating method compacting test
The counterweight-added dry vibrating method is a test method which adds certain pressure on top of the sand from the outside on the base of dry vibrating method. The dry soil method in JTJ 051-1993 Test Methods for Soils of Highway Engineering standard is used. A 1m × 1m concrete vibrating table is used in the test. Amplitude of vibrating table is adjusted to 0.3mm; vibrating frequency is 47.7 Hz. The vessel is a big barrel for standard compaction test. Its volume is 3,085 cm3. Add 18 kPa weights; the area is 177 cm2. Fill in layers and compact it to determine its maximum dry density. Operational steps are: the compaction barrel is fixed on the vibrating table.Sand samples are added into the barrel. The barrel is filled in three layers. After filling each layer, vibrate the counterweight added for 10 min. After the vibration, height of test samples is measured within the barrel and the actual volume is calculated.Its maximum dry density is calculated after weighing. Table 2 shows test results.
Table 2 Result of Counterweight-added Dry Vibrating Method Test
Test result shows, the use of counterweight-added dry vibrating method test yields larger density than common dry vibrating method. Initial analysis assumes: in addition to the effect from gravity, inertial impaction force, friction and vibration force among particles, sand is also affected by external pressure. When sand is compressed, its volume will not change; the small gap among sand is fair smaller than that in common dry vibration. It is easily to be arranged to the best position by the effect from vibration. Compared to the common dry vibrating method, the similarity is, when sand density reaches certain degrees, its inherent frequency changes, and continuous vibration will not contribute to greater compactness. The difference is, with the existence of certain external pressure, after being moved to large particles, fine particles will not be moved out of large ones due to changes in frequency. Thus, sand compactness will not decrease. In several tests determining the maximum dry density of Aeolian sand, maximum dry density obtained by counterweight-added dry vibrating method reaches the peak value. However, in actual construction, road roller rolls for several times. It is hard to meet conditions that permanent counterweight is added to sand during the test under such circumstance. As a result, standard compacting test of counterweight-added is not suitable for test of Aeolian roadbed construction.
4. Counterweight-added water vibrating method compacting test
This method is derived from the experience of water-fall houses for the public in desert regions. The principle is that sand will be compacted if it is vibrated in water. A 1m × 1m concrete vibrating table is used in the test. Amplitude of vibrating table is adjusted to 0.3mm; vibrating frequency is 47.7 Hz. The vessel is a big barrel for standard compaction test. Its volume is 3,085 cm3. Three groups of sand samples are selected for the vibration test at different moments to determine the most favorable vibrating moment. Operational steps are: the compaction barrel is fixed on the vibrating table and is fully filled with sand samples. Then water is slowly added into the barrel until water leaks from barrel bottom and the barrel is vibrated. Its compactness tested according to time segmentation.Figure 3 shows test results.
Fig.3 Chart on Relationship between Maximum Dry Density and Time of Vibration
（with additional weight water vibration method）
Water vibrating test can obtain the dry density between these obtained from common dry vibrating method and counterweight-added dry vibrating method. Initial analysis assumes: in addition to the effect from gravity, inertial impaction force, friction and vibration force among particles in water, sand is also affected by water buoyancy and pore water pressure. When sand is under semi-suspended status, the friction among sand is extremely small. With the vibrating effect, it is easily arranged to the best position. As shown in the curve for which dry density changes with the time, when vibration begins under specified vibrating frequency and amplitude, the dry density at first increases as time increases. When the time reaches 4-6 min, sand density is the maximum. If vibration is continued, sand density will decrease. It shows there occurs over vibration. The best original arrangement method is damaged as the vibration continues, resulting in decrease of density. In construction of test road section, results from roadbed test with the maximum dry density obtained by such method show, after the roadbed is rolled for six times by road roller, the compactness can reach 94% of the requirements. This can be the basis of roadbed test.
Test results show sand under external pressure and vibrated in water can reach the maximum compactness. Value obtained from the test is greater than these from common vibrating method, counterweight-added dry vibrating method and standard compaction method. It complies with actual conditions in practical test and inspection for roadbed. This can be the evaluation standard for test.
5. Conclusion
Dry density determined by counterweight-added water vibrating method has greater advantages when comparison is made between it and other methods. Its compactness standard is rather high and satisfies the quality standard as required by the engineering. It is suitable for compaction process of the roadbed for sand road and shows wide application value.
Paper received on: June 2, 2013
About the author: Zhao Qingsong (1978- ) is a male engineer from Beijing who mainly undertakes road ＆ bridge construction and management of technology and quality.
About the translator: Ji Jingtao (1983- ) is a male class 1 construction engineer of Mongolian ethnicity and from Beijing who mainly undertakes site technology management and production organization in construction of highway and bridges.