The Study of Large-Scale Triaxial Texts on Metamorphic Soft Rock Embankment Filler

Transcription

1 1 st International Conference on Transportation Infrastructure and Materials (ICTIM 2016) ISBN: The Study of Large-Scale Triaxial Texts on Metamorphic Soft Rock Embankment Filler Yanyan Du School of Highay, Chang an University, Xi an, , China ABSTRACT: In order to study the etting deformation characteristics of the metamorphic soft rock embankment filler, large-scale triaxial tests are conducted ith double lines method respectively. Variation of etting strains (i.e., the differences beteen strains of dry and saturated states under the same vertical deviator stress) is analyzed. Results sho that, under different confining pressures, the etting strain 1 13 is increased ith the increase of vertical deviator stress, the curve present eak strain hardening. the curve have turning points under different confining pressures, the turning points position are located in about 70% of the maximum deviator stress. The position of the turning points gradually move back ith the increase of confining pressures, sho that confining pressure is not only influence the magnitude of etting deformation, also influence its change rules. There are to development stages of filler etting strain curves. The size of the critical etting strains are closely related to the ratio of vertical deviator stress and confining pressure. In contrast ith the metamorphic soft rock embankment the value of and u under the condition of actual ork, the development la of the etting deformation after the ater is analyzed. INTRODUCTION Engineering practices sho that the metamorphic soft rock after flooding ill case etting deformation and make the embankment produce settlement. It also ill affect driving safety and bring serious effects on the project. But for metamorphic soft rock used for highay embankment packing research is not much, its engineering properties and etting deformation rules of research data are lacking. Therefore, it is important to research some ork hich is related to soft rock embankment filler. Wetting deformation refers to the packing of flooding under a certain stress state, particles in mineral ater immersion to soften and by ater lubrication beteen particles cause mutual sliding beteen particles, crushing and rearranged, these make the packing part of etting deformation and cause the phenomenon of stress redistribution. The deformation is mainly produced by the soil material from dry to et on the basis of the stress state. Abroad, Nobari and Duncan (1973) for the first time in the calculation of deformation and stress of the earth and rockfill dam considered the coarse aggregate of etting deformation. Nobari put forard a full amount of the initial stress method; Marsal, Nolezalova and Leihter etc. got the empirical formula of calculation of etting strain on the basis of a large number of consolidation test and apply this method specific to finite element method. In the domestic, Zhujiang Shen, etc. got et model and improved this model on the basis of *Corresponding author. Tel.: @163.com. 875

2 "single line method"; according to the no tensile stress numerical calculation model, Junxian Zou obtained the etting deformation under the different impacted parameters. But in general, the researching of taking the soft rock filler as the subgrade filler are far from mature. Studying for the la of development of etting deformation is less. This paper has carried on the large-scale triaxial compression experiments in vie of the metamorphic soft packing. The double line method as adopted, etting deformation characteristics of dry and saturated state metamorphic soft packing ere studied under different confining pressures. THE STRUCTURE AND BASIC PROPERTIES OF METAMORPHIC SOFT ROCK Through the analysis of the grinding electron microscopy metamorphic rock test named the rock accurately and analyzed the rock mineral composition and content. The rock is composed of 60% ~ 70% sericite and crystallite biotite and 30% ~ 40% felsic minerals, and contain 1% ~ 3% a small amount of tourmaline, sphene and so on. The size of the platy mineral particles is less than or equal to 0.1mm. It is mainly composed of feldspar, quartz, a small amount of tourmaline accessory mineral, etc. So the rocks entitled thousand pieces of mylonite, referred to Qian-mi rock. Using the highay engineering specification for rock test and through the particle density, collapse resistance index, ater absorption and the uniaxial compressive strength test, got the basic physical and mechanical properties of metamorphic rocks. As shon in the table 1. Table 1. Metamorphic soft rock physical and mechanical properties. Uniaxial compressive strength /MPa Sample Particle proportion Collapse resistance dry saturation Softening coefficient Qin-mi rock Metamorphic soft rock physical and mechanical properties data sho that the Qian-mi rock collapse resistance index is not high, Such metamorphic rock in only high durability and easy disintegrate in the long-term ind or sunshine; the bibulous rate of metamorphic soft rock is lo, also prove that the rock is not easy to sell; but at the same time, rock softening coefficient is small, sho that the rock after flooding under the action of external force is easy to damage. The influence of ater is obvious. In this area according to the classification indexes of rock strength, Qian-mi rock saturated uniaxial compressive strength is less than 30 MPa, belong to the soft rock. LARGE-SCALE TRIAXIAL COMPRESSION EXPERIMENTS OF METAMORPHIC SOFT ROCK In order to make the grading of the soil close to the actual situation as far as possible, test determine the test packing similar gradation based on the method of similar grading. As shon in the table

3 (σ 1 -σ 3 ) 10 2 /kpa Table 2. Metamorphic soft packing grading table. The original grading of packing The testing grading of packing Particle diameter D(mm) Percentage of test gradation(%) Particle diameter D(mm) Percentage of test gradation(%) 200~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Relationship beteen stress and strain The Qin-mi metamorphic soft rock filler as selected as the test sample. With a diameter of 30cm, 60cm high, the maximum size of particles are not more than 6cm for triaxial test, select the density is 2.2 g/cm 3, respectively in the confining pressures for the 200kpa, 300kpa, 400kpa, 600kpa, the samples of the dry and saturated ith double line method is studied. The shear rate of the test is 0.1mm/min, tests ould stop hen the shear is the axial strain of 15%. Under the four kinds of confining pressure (200kpa, 300kpa, 400kpa, 600kpa), dry sample s stress-strain curve are shon in figure 1 belo. Under the four kinds of confining pressure (200kpa, 300kpa, 400kpa, 600kpa), saturated sample s stress-strain curve are shon in figure 2 belo kpa 300kpa 400kpa 600kpa /% Figure 1. Relationship beteen stress and strain under different confining pressure for dry metamorphic soft rock. As is shon in figure 1, the strain of the sample under different confining pressures increase ith the increase of the vertical deviator stress ( 13), and under the dry state, the metamorphic soft rock filler s curve of stress-strain relationship is softening, hich has a peak, after the peak, the strain shos a trend of decline ith the increase 877

4 (σ 1 -σ 3 ) 10 2 /kpa of the vertical deviator stress, and the loer the confining pressure is, the earlier the peak appears, suggests that the confining pressure has certain influence to the peak; under the saturation state, the metamorphic soft rock filler s curve of stress-strain relationship behaves hardening type and there is no peak, the strain increases ith the increasing of vertical deviator stress sloly. No matter hat the sample is dry or saturated, the vertical deviator stress increase ith the increase of confining pressure hen the strain is same, and there is less vertical deviator stress hen the strain is small. It implies that confining pressure can affect the mechanical properties of the filler. In addition, the filler s elastic modulus increases ith the increase of confining pressure, and the drying condition of initial elastic modulus is generally greater than the saturation state of elastic modulus, the drying condition of the fillers sho the characteristics that plastic first then elastic kpa 300kpa 400kpa 600kpa ε 1 /% Figure 2. Relationship beteen stress and strain under different confining pressure for saturated metamorphic soft rock. The figure 3 shos the relationship of the filler beteen the vertical deviator stress and the strain hen the confining pressure is respectively 200kpa, 300kpa, 400kpa, 600kpa. In figure (a),hen the confining pressure is 200kpa, the deformation caused by the saturation is greater than the dry state ith the same axial deviator stress, and the deformation caused by the etting increases gradually ith the increasing of the axial deviator stress ( ); Under the dry condition, a turning point of axial 1 3 deviation stress appears hen the strain is from 2% to 4%, at this point, it has the biggest differences from the deviator stress of saturated state, and the gap increases ith the increasing of confining pressure gradually, hich is respectively 4.21x10 2 kpa, 4.25x10 2 kpa, 8.07x10 2 kpa, 11.68x10 2 kpa. The dry state deviator stress decreases after the peak point, the vertical deviator stress of saturated state increases gradually after the strain is from 3% - 6%, hat can be seen from figure 3 is hen the strain reaches 15%, the deviator stress of saturated and dry state has little difference. Also, hen the confining pressure is 300kpa, 400kpa, 600kpa, e can get the similar regularity of stress and strain, as is shon in figure 3 (b), (c), (d). Accordingly, hen the sample as saturated by ater, due to the mineral particles immersed softening and the 878

5 (σ 1 -σ 3 ) 10 2 /kpa function of lubrication, it shos slip, broken and rearranged beteen the particles. Making a part of etting deformation, and the intensity is reduced. Analysis of etting settlement of the soft metamorphic rock Under the condition of same confining pressure and the same deviator stress, the differences strain beteen of the saturated state and dry metamorphic soft rock are defined as the et strain 1. (2.1) d d Where 1 is the strain of the specimen in the saturated state (%), 1 is the strain of the specimen in the dry state (%) confing pressure 200kpa confing pressure 300kpa confing pressure 400kpa confing pressure 600kpa /% Figure 3. Relationship beteen vertical deviator stress and etting strain under different confining pressures. In figure 3, hen the etting strain is constant, the deviator stress increases ith the increase of the confining pressure, hich shos that confining pressure affect the amount of etting settlement of metamorphic soft rock filler in a certain extent. Wetting strain are increased ith the increase of deviator stress under different confining pressures, the curves deformation sho the strain hardening type. In the beginning, the slope of the curve is larger, and the slope is gradually decreased, after the deviation stress exceeds a certain value, the strain amplitude increases greatly. curve under different confining pressures. The turning point is located at about 70% of the maximum deviator stress. The rate of increase of etting strain is smaller before turning point and is increased after turning point, ith the increase of confining pressure, the turning points on the curve move backard. At loer confining pressures (200kPa, 300kPa), the turning point is more obvious, at the higher confining pressures (400kPa, 600kpa), the radian of transition is larger. In the late stage, the slope of the curve decrease gradually, the turning point is not obvious. So, the confining pressure not only affects the size of the etting deformation, but also affects the rules of the change. In order to analyze the influence of confining pressure on the et deposition, the corresponding strain of the turning point is defined as the critical etting strain, hich There are turning points on the is expressed by 1, u, the corresponding deviator stress is expressed by ( 13) u. 879

6 In figure 4, hen the confining pressures are 200kpa, 300kpa, 400kpa, 600kpa, the critical etting strain are 1.57%, 1.97%, 2.51%, 2.82%, and the corresponding values of deviator stress are 651.2kpa, 898.6kpa, kpa, kpa. The ratio of the axial deviator stress to the corresponding confining pressure is expressed by, hich is ( ) 1 3 (2.2) confining pressure 200kpa confining pressure 300kpa confining pressure 400kpa confining pressure 600kpa 9 Figure 4. Relationship beteen and etting strain under the different confining pressures. In the figure 4, under different confining pressures, the etting strain increases ith the increase of confining pressures. The curve starts ith a small slope, and the slope increases after the turning point, it suggests that the etting settlement is not apparent before the turning point. The settlement caused by et alays occurs after the turning point, and the greater the confining pressure is, the greater the etting settlement is. Under larger confining pressure, the broken rate of soft rock particles increases, the particles ould rearrangement, so that the bond strength beteen particles reduced significantly, hich produce a large et deposition. The critical etting strain corresponding to is expressed by u. When the confining pressure is 200kpa, 300kpa, 400kpa, 600kpa, the corresponding values of u are 3.24, 3.3, 2.84, 3.3, and it can be seen that the values of u near the turning point ranges from 2.8 to 3.3. When u, the amplitude of the etting strain 1 that increases ith becomes small, it means that the filler s settlement caused by etting is not the bigger hen the embankment as saturated and the upper load doesn t reach the critical value. When u, the slope of the etting strain 1 increases greatly, the increment of is smaller and then tend to be stable. When the filler is saturated and upper embankment load or additional load is greater than the critical state, the settlement caused by etting increases rapidly and has certain influence on the settlement of the embankment. Contrast and u at the actual orking condition of the soft rock embankment, then e can analyze the regularity of development of the etting deformation. 880

7 CONCLUSIONS (1) The strain of the metamorphic soft rock filler under different confining pressures increases ith the increase of the vertical deviator stress. There is a peak hen the filler is under the dry state, the curve of stress-strain is softening. When it is under the saturated state, the curve of stress-strain behaves hardening type and there is no peak. The filler s elastic modulus increases ith the increase of the confining pressures. The dry condition of the filler shos the characteristics of elasticity at the first and plasticity after. It implies that confining pressures can affect the mechanical properties of the filler. (2) When the confining pressure is 200kpa, the deformation caused by the saturated state is greater than the dry state ith the same axial deviator stress. It shos that the strength and the bite force beteen the particles are reduced, the grain softening and the load carrying capacity decrease hen the filler is saturated ith ater. The deformation caused by the etting increases gradually ith the increasing of the axial deviator stress ( 13). Under the dry state, a turning point of axial deviator stress appears hen the strain is from 2% to 4%, at this point, it has the biggest differences from the deviator stress of saturated state, and the gap increase ith the increase of confining pressure gradually. Similarly, confining pressures for 300kpa, 400kpa, 600kpa, can get a similar la. (3) The etting strain 1 increases ith the increase of the deviator stress 1 3 under the different confining pressures, and the curve behaves eak hardening. There alays is a turning point under the different confining pressures, the turning point is located at about 70% of the maximum deviator stress. The etting strain increases sloly before the turning point, but becomes faster after the turning point, and the position of the turning point pushed back ith the increase of the confining pressures. It implies that the confining pressure not only affects the size of the etting deformation, but also affects the change of the la. (4) The values of u range from 2.8 to 3.3. When u, the amplitude of the etting strain becomes small ith the increased, it means that the filler s settlement caused by etting is not the bigger hen the embankment as saturated and the upper load doesn t reach the critical value. When increases greatly, the increment of u, the slope of the etting strain is smaller and then tend to be stable. When the filler is saturated and upper embankment load or additional load is greater than the critical state, the settlement caused by etting increases rapidly and has certain influence on the settlement of the embankment. Contrasting and u at the actual 881

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