The Experimental Study On Mechanical Properties Of Fiber Reinforced Sands

There are many soft soil subgrade in the highway,railway subgrade construction projects.Geotextiles and geogrids are commonly used for soft soil roadbed reinforcement in order to improve its bearing capacity.Because there is a weak surface between the reinforced material and the soil,as a result the traffic lane has a large settlement under the action of traffic load.Geotechnical fibers with high tensile strength,good stability can effectively strengthen the soil according to a certain percentage added to the soil.Research on the mechanical properties of fiber reinforced soil has been carried out for many years,but there is still a lack of systematic,especially on the dynamic characteristics of fiber reinforced soil.In this paper,we will study the static and dynamic characteristics of fiber reinforced sands,the main research work is as follows:1 Statics test and theoretical analysis of fiber reinforced sands.A large number of consolidated-drained triaxial tests were conducted to systematically investigate the influences of parameters such as fiber content,fiber length,relative density and confining pressure on strength characteristics of fiber reinforced sands.The experimental results show that the strength of fiber reinforced sands increases with the increase of fiber content,fiber length,relative density and confining pressure.The stress-strain curves of the fiber reinforced sands are always in the hardening stage within the range of the applied load.When confining pressure and relative density are constant,the increase in shear strength of fiber reinforced sands have a good linear relationship with fiber content and fiber length.The strength calculation results show that the fiber reinforced sands not only has the friction strength,but also has a higher cohesion strength.The strength results obtained by experiment were compared with the predicted strength values calculated by the strength models of fiber reinforced sands,which are Zornberg Model and Michalowski Model.Deviation of predicted values calculated by Zornberg Model and measured results is much larger.Predicted values by Michalowski Model are in good agreement with the measured results when the fiber content is relatively low.The theoretical models assume that the cohesive strength of the fiber reinforced sands is zero,but the test results show that the fiber sand has a significant cohesive strength.There is a significant enhancement effect caused by fiber stretching and interaction between fibers and sands in the shearing process of fiber reinforced sands,which greatly improves its cohesive strength.2、Experimental and theoretical study on dynamic characteristics of fiber reinforced sands.The dynamic characteristics of fiber reinforced sands were studied by dynamic triaxial test.The waveform of the dynamic load is sinusoidal and the frequency is 0.1Hz.Under the conditions of D_r=0.5 andσ₃=100kPa,the dynamic characteristics of fiber reinforced sands were studied by changing the fiber content（ξ=0.2%,0.4%）,fiber length（l_f=7,13mm）and cyclic stress ratio（γ_d=0.22,0.24,0.26）.The results show that the fibers have significant effect on the dynamic characteristics of sands.Under the condition of constant fiber length,when the fiber content is large,the accumulation rate of excess pore water pressure is slow,the number of vibrations when liquefied is increased and the dynamic strength increases obviously.When the fiber content is large,the G_N/G_max decays slowly with the increase of the number of vibration.Under the same condition of fiber content,the effects of fiber length on the dynamic characteristics of fiber reinforced sands has similar laws with that of fiber content...