Experimental Study on Interface Characteristics of Geogrid and Saturated Fine Sand
Abstract: The interface characteristics of reinforced soil is an important technical index for the design of reinforced soil structure, and it is the key to reveal the reinforcement mechanism of geosynthetic materials. The effects of shear rate, vertical stress and mesh size on the interface characteristics of uniaxial plastic geogrid for sale and saturated fine sand were studied by GDS interface shear. The test results show that the shear rate has little effect on the shear strength of the interface when the shear rate is small (≤1.0mm/min); the shear rate is in the range of 1.0～10mm/min, and the shear rate increases. The shear strength of the interface increases first and then decreases. The shear strength of the interface increases with the increase of vertical stress. The vertical stress enhances the interlocking effect of high quality uniaxial plastic geogrid on soil particles and limits the shearing of soil particles. Move, thereby improving the shear strength of the soil; when the shear rate is 1.0mm/min and the vertical stress is small (50-100kPa), the uniaxial plastic geogrid manufacturers reinforcement effect of the small mesh size is more obvious; the shear rate is 0.1mm/min, when the vertical stress is large (200～300kPa), the large mesh size uniaxial plastic geogrid factory price reinforcement effect is more obvious. The research results have reference value for the application of uniaxial plastic geogrid factory price in reinforced soil.
Keywords: uniaxial plastic geogrid factory price; saturated fine sand; interface characteristics; interface shear test; shear rate; mesh size
Research background
In the early 1960s, the French engineer Vidal first proposed the concept and principle of reinforced soil according to the results of the triaxial test. The geotechnical reinforcement technology was gradually applied in the construction of major projects such as roads, railways, airports, and ports. As a new type of material in the field of geotechnical engineering, geosynthetics are all kinds of products made of synthetic fiber, synthetic plastic, and synthetic rubber. They are light in weight, small in size and soft in adaptability to buildings and foundations. Large deformation, with the role of strengthening the soil. Geosynthetic materials were introduced into China in the 1970s and 1980s and were widely used in embankments, retaining walls, slopes, and other structures. The interface characteristics of reinforced soil (such as interface friction characteristics) as an important technical index of structural design will directly affect the stability of the structure. At present, the indoor tests for determining the interface characteristics of reinforced soil mainly include direct shear test and pull test. The reinforced body is a uniaxial plastic geogrid for sale, a geotextile, a geomembrane, and the like. The filler of reinforced soil is sand and cohesive soil.
Some scholars at home and abroad have studied the characteristics of the interface of the soil and have achieved certain results. Zhou et al. studied the interfacial properties of uniaxial plastic geogrid for sale and sand by drawing test. It was found that the shear band thickness increased with the increase of vertical stress, and the interfacial shear strength was related to the mesh size. Arulrajah et al. studied the static characteristics of high quality uniaxial plastic geogrid-soil interface based on the large direct shear test and pointed out that uniaxial plastic geogrid manufacturers significantly increased the shear strength of the soil. Liu Feijun et al. studied the effects of different shear rates on the shear behavior of sand and uniaxial plastic geogrid factory price by using large-scale direct shears. The results show that the shear rate has no effect on the shear behavior of the interface at the reinforced soil under monotonic shear. Large, the impact on the direct shear characteristics of the reinforced soil interface after cyclic shearing is obvious. Wu Hai et al. discussed the influence of different kinds of reinforced materials on the direct shear behavior of Sandwich-type reinforced soil under different vertical stresses through a large direct shear test. It is believed that the shear strength of the reinforced soil interface increases with the increase of vertical stress. And the uniaxial plastic geogrid manufacturers have the best reinforcement effect. Zhao Zhanjun studied the influence of vertical load on uniaxial plastic geogrid factory price reinforced soil by drawing test. It is considered that the greater the vertical stress, the smaller the influence of high quality uniaxial plastic geogrid drawing displacement on the dilatancy, and the uniaxial plastic geogrid manufacturers is in the drawing process. The smaller the increase in the dilatancy force.
Geosynthetics reinforced soil has good shear strength and excellent seismic properties. However, the above research results are obtained by the direct shear test and pull test. These two test methods have certain limitations on the study of the interface properties of the reinforced soil. For example, during the direct shear test, the shear plane is limited to the upper and lower shear. Shear damage between the boxes, not along the thinnest weak surface of the soil sample; in the drawing test, the reinforced body inevitably deforms in the soil during the preparation of the sample. The GDS interface shearing instrument can directly perform the interface shear test between the reinforced body and the soil, and the reinforced body does not undergo uneven deformation during the test, which overcomes the shortcomings of the above two test methods. Therefore, through a series of interfacial shear tests, the effects of shear rate, vertical stress and mesh size on the interface characteristics of uniaxial plastic geogrid for sale and saturated fine sands are studied in order to obtain conclusions with a reference value.
2. Test equipment and material selection
2.1 Test equipment
The instrument used in the test was an interface shear produced by GDS of the United Kingdom, as shown in Figure 1. The instrument can perform the shear test of uniaxial plastic geogrid for sale and saturated fine sand interface. The shear area can be kept constant during the test. The torque, axial stress and shear rate can be increased linearly or jumpy. Torque, shear displacement and shear can be performed. Cutting rate control, the infinitely rotating platform can achieve large enough shear displacement and can carry out large deformation analysis. Therefore, the GDS interface shearing instrument overcomes the limitations of the direct shear test and drawing test to some extent. The reinforced soil interface characteristics have great advantages. The interface cutter ring cutter has a diameter of 70 mm, a height of 22 mm, and a shearing area of 38.48 cm 2. The applied torsional and axial stresses are controlled by precision motors with a torsional moment of up to 200 N·m and axial stresses of up to 5 kN. The test process is controlled by a computer to control the operation of the precision motor, and the test data such as test time, torsion force, axial force, and axial deformation are automatically recorded.
2.2 Test materials
The sand used in the test was taken from the golden sand beach of the Yellow Sea in Qingdao. The sand analysis was carried out by sieve analysis. The particle gradation curve of the sand was as shown in Figure 2. The physical properties are shown in Table 1. The geosynthetic material used in the test is a glass fiber uniaxial plastic geogrid for sale. The specific style is shown in Figure 3. The relevant technical indicators are shown in Table 2.
3. Theoretical analysis principle and test plan
3.1 theoretical analysis principle
Using the principle of definite integral, the torque and shear angular displacement directly obtained by the interface shear test are converted into shear stress and horizontal displacement, respectively. The radius of the circular shear plane is R, and a small ring is taken from the center r, and the width is dr, and the area of the ring is dS=2πrdr. Because the shear stress is evenly distributed, the shear force acting on the ring is dF=2πrτdr, and the torque dM=2πr2τdr, then the shear stress is
Where: M is the torque (N·m); R is the radius of the circular shear plane of the axial stress rod (mm).
Where: rave is the average radius (mm); v is the shear angular velocity (deg/s); t is the shear time (s); R = 34 mm.
The shear strength characteristics of the interface under different test conditions were compared by the internal friction angle and cohesive force, and the interface friction coefficient f was introduced to describe the difference of interface friction characteristics.
Where: τ is the shear stress (kPa); σ is the vertical stress (kPa).
It can be known from equation (4) that the friction coefficient f is a variable and is related to the interface shear stress and the vertical stress.
3.2 Test plan
In order to study the effects of different shear rates, vertical stresses and mesh sizes on the interface characteristics of uniaxial plastic geogrid for sale and saturated fine sands, six shear rates were preset during the test (0.1, 0.5, 1.0, 2.0, 5.0, 10.0). Mm/min), 4 vertical stresses (50, 100, 200, 300 kPa) and 2 mesh sizes (5 mm x 5 mm, 10 mm x 10 mm). In order to prevent the sand sample from overflowing during the test, the height of the sample was taken as 20 mm, the dry density was 1.56 g/cm3, and 120 g of the sand sample was weighted according to the sample volume. In order to ensure that each sample has the same compactness, the interference of the sample compactness on the test results is reduced. The sand sample is filled in 4 layers by layer filling method during the loading process, each layer is 5mm thick, and each control is controlled. The layers are loaded with the same quality sand sample to a predetermined height of 20 mm. The axial stress rod has a bottom surface diameter of 68 mm and a height of 128 mm. The glass fiber high quality uniaxial plastic geogrid is bonded to the bottom surface of the axial stress rod by liquid glue, as shown in FIG. The shear test was carried out at a constant rate, and the shear was stopped when the shear displacement reached 8 mm. The sand interface after shearing was as shown in FIG.
Figure 6 is a plot of shear stress versus shear displacement (horizontal displacement) at the shear rate of the uniaxial plastic geogrid for sale and saturated fine sand at 0.1, 0.5, 1.0, 2.0, 5.0, and 10.0 mm/min, respectively. As can be seen from Figure 6:
(1) The shear stress-shear displacement curves of the interface of the reinforced soil under different shear rates all show a similar law, that is, the shear stress increases with the increase of shear displacement, and the shear stress decreases after reaching the peak. After a certain value, it tends to be stable.
(2) Under any vertical stress, when the shear rate increases from 0.1mm/min to 1.0mm/min, the peak shear stress of the interface shear stress fluctuates by 3%, and the sheer intensity corresponding to the peak intensity is within 1mm. The shear rate has little effect on the shear strength of high quality uniaxial plastic geogrid and saturated fine sand interface.
(3) When the shear rate increases from 1.0mm/min to 2.0mm/min, the vertical shear stress corresponding to the vertical stress of 50, 100, 150, 200kPa is increased by 16%, 9%, 4%, 8%, respectively; When the 2.0mm/min is increased to 5.0mm/min, the peak shear stress of the interface is increased by 11%, 20%, 16%, and 19%, respectively.
(4) When the shear rate increases from 5.0mm/min to 10mm/min, the vertical shear stress corresponding to the vertical stress of 50, 100, 150, 200kPa is reduced by 46%, 51%, 46%, 40%, ie, the interfacial shear stress peak The strength decreases with the increase of the shear rate, and the shear displacement corresponding to the peak intensity increases correspondingly, and the increased range is in the range of 1 to 2 mm. This is due to the fact that the shear rate is too fast and the soil particles fail to adjust in time to cause the shear strength to decrease.
Figure 7 is the shear strength curve of uniaxial plastic geogrid for sale and saturated fine sand at different shear rates. This curve is a linear regression fit between the peak strength and vertical stress of interfacial shear stress, that is, using the Mohr-Coulomb formula τ = σtan φ + c describes, where c, φ are the interfacial cohesion and internal friction angle obtained after linear regression fitting, respectively.
The interface shear strength indexes at different shear rates are shown in Table 3. Combined with Table 3, it was found that the high quality uniaxial plastic geogrid was implanted with saturated sand, and the interface produced a certain cohesion. When the shear rate increases from 0.1 mm/min to 10.0 mm/min, the cohesive force decreases first, then increases and then decreases, while the internal friction angle increases first, then decreases and then increases. This is because the shear rate is too fast, the sand particles cannot be fully embedded in the pores of the ribs, the interlocking occlusion effect is weakened, and the cohesive force is rapidly lost. The large shear rate makes the sand aligning time insufficient, and the pore water pressure is too late. Dissipation, the friction effect is enhanced, and the internal friction angle is increased.
4.2 Influence of vertical stress on shear strength of reinforced soil interface
Fig. 8 is a graph showing the relationship between shear stress and shear displacement of high quality uniaxial plastic geogrid and saturated fine sand under vertical stress of 50, 100, 200, 300 kPa. It can be seen from Fig. 8 that the peak shear stress at the same shear rate increases with the increase of vertical stress. When the vertical stress increases from 100 kPa to 200 kPa, the peak shear stress of the interface is 0.1. 1.0, 10.0mm / min shear rate increased by 13%, 16%, 36%. This is because as the vertical stress increases, the frictional resistance between the soil particles increases, which limits the mutual adjustment of the soil particles, the bite cooperation is strengthened, and the peak strength of the interface shear stress increases.
Table 4 shows the friction coefficient between high quality uniaxial plastic geogrid and saturated fine sand under different vertical stresses. It can be concluded from Table 4 that at the same shear rate, the interfacial friction coefficient decreases with the increase of vertical stress, and the greater the vertical stress, the smaller the friction coefficient reduction rate.
Since the area of the shear plane remains constant during the test, the variation of the vertical displacement of the shear plane is consistent with the shear law of the shear plane. In this paper, the shear plane changes to positive expansion and compression. negative. Figure 9 shows that with the increase of vertical stress at the same shear rate, the vertical displacement of the reinforced soil interface increases correspondingly. When the shear rate is 0.1mm/min, the law is most significant.
4.3 Influence of mesh size on shear strength of reinforced soil interface
Under the conditions of shear rate of 0.1,1.0mm/min and vertical stress of 50,100,200,300kPa, respectively, the effects of different mesh sizes on the shear strength of the interface were obtained and the different mesh sizes were obtained. The lower interface shear stress-shear displacement relationship curve is shown in Figure 10.
It can be seen from Fig. 10 that when the shear rate is 1.0 mm/min and the vertical stress is 50 kPa and 100 kPa, the peak strength of the interface shear stress of the small mesh size is significantly higher than the peak strength of the interface shear stress of the large mesh size, and the peak intensity is respectively Increased by 15% and 14%, indicating that the vertical mesh stress is smaller (50 ~ 100kPa), the small mesh size high quality uniaxial plastic geogrid reinforcement effect is more obvious; the shear rate is 0.1mm / min, the vertical stress is 200kPa and 300kPa When the large mesh size interface shear stress peak strength is significantly higher than the small mesh size interface shear stress peak intensity, and its peak intensity is increased by 12% and 20%, respectively, indicating that the vertical stress is large (200 ~ 300kPa), Large mesh size uniaxial plastic geogrid manufacturers reinforcement effect is more obvious.
Figure 11 shows the interface shear strength curves for different mesh sizes. It can be seen from the interface shear strength parameters of different mesh sizes in Table 5. When the shear rate is in the range of 0.1-1.0 mm/min, the small mesh size interface The cohesive force is higher than that of the large mesh size interface, while the internal friction angle is opposite, indicating that the large mesh size uniaxial plastic geogrid manufacturers have a more pronounced interlocking effect on the sand particles, which hinders the rearrangement of the sand particles.
5. Conclusion
(1) The interface characteristics of uniaxial plastic geogrid manufacturers and saturated fine sand are affected by the shear rate. When the shear rate is small (≤1.0mm/min), the shear strength of the interface is not affected. When the shear rate is in the range of 1.0-5.0mm/min, the shear strength of the interface increases with the shear rate. Increase; when the shear rate is large (>5.0mm/min and ≤10.0mm/min), the interfacial shear strength decreases with increasing shear rate.
(2) The shear rate is in the range of 0.1～10.0mm/min, and the shear strength of the interface increases with the increase of vertical stress. Especially when the vertical stress increases from 100kPa to 200kPa, the interface shear strength is 3 kinds. The shear rate was increased by 13%, 16%, and 36%, respectively. At the same shear rate, the interfacial friction coefficient decreases with the increase of vertical stress, and the greater the vertical stress, the smaller the friction coefficient reduction rate.
(3) Under different test conditions, the mesh size has different effects on the friction stir reinforcement effect of uniaxial plastic geogrid manufacturers. When the shear rate is 1.0mm/min and the vertical stress is small (50-100kPa), the uniaxial plastic geogrid factory price reinforcement effect of small mesh size is more obvious; the shear rate is 0.1mm/min, and the vertical stress is larger (200). At ~300 kPa), the large mesh size uniaxial plastic geogrid factory price reinforcement effect is more obvious. When the shear rate is in the range of 0.1-1.0 mm/min, the interfacial cohesion of the small mesh size is higher than that of the large mesh size, and the internal friction angle is opposite.
(4) Using the GDS interface shear to study the interface characteristics between uniaxial plastic geogrid manufacturers and saturated fine sand, compared with the traditional direct shear test, the vertical stress and shear stress on the shear plane during the shear test. The assumption of uniform distribution makes the test results more accurate and reliable and has important engineering significance. It further shows that the GDS interface shearing instrument has great advantages for analyzing and studying the interface characteristics of reinforced soil.