Experimental And Theoretical Study On Dynamic Characteristics Of Composite Silt With Different Reinforcements

Flexible pile composite foundation and lateral reinforced soil are widely used in geotechnique engineering. In many conditions, they may bear varied dynamic load, but the knowledge of their dynamic characters is far behind the need of engineering. Using the silt gathered in Taiyuan, dynamic triaxial experiments are conducted on composite samples with vertical reinforcement, such as cement–soil reinforcement, lime–soil reinforcement, or cement mortar reinforcement, and composite samples with horizontal reinforcement, such as fibers. By comparison with pure silt soil, the influences of vertical reinforcement or horizontal reinforcement are studied. The influence regularities of different factors on dynamic parameters, such as dynamic elastic modulus, etc., are discussed. The averaging curves, recommended values and empirical formulas of major dynamic parameters under different factors are presented. This is benefit to acknowledge the dynamic property of composite silt with different reinforcements. These data will be valuable to engineering practices in Taiyuan area. The main works and achievements are concluded as follows:1. For composite silt with cement–soil reinforcement, lime–soil reinforcement, or cement mortar reinforcement, the relationship of dynamic stressσd versus dynamic strainεd is nearly hyperbola. The relationship ofσd andεd depends on the level of dynamic strain. It needs more dynamic stress to get a certain dynamic strain when reinforcement rigidity, replacement ratio, confining pressure, or dry density has an increment, or moisture content has a decrement.2. The dynamic elastic modulus E d of 3 kinds of composite sample mentioned above decrease with dynamic strain increasing. At the same strain level, theEd increases as confining pressure, replacement ratio, or dry density increasing, and it decreases as moisture content decreasing. When dynamic strain is small, the influence of confining pressure, replacement ratio, dry density or moisture content on E d is more obviously.3. The maximum dynamic elastic modulusEdmax of composite silt are much higher than that of pure silt due to reinforcement. TheEdmax of 3 kinds of composite samples mentioned above is bigger when there is an increment of the reinforcement rigidity. To these four factors, reinforcement replacement, confining pressure, dry density, and moisture content, when the other three factors are in same level, the E dmax is becoming bigger when there is an increment of replacement ratio, confining pressure, dry density, or moisture content.4. For the composite silt with cement-soil reinforcement, the reinforcement rigidity proposes the greatest influence on E dmax among the influence factors. The influence of replacement ratio decreases as confining pressure increasing, and proposes the greatest influence upon the composite samples with cement–soil reinforcement but the smallest influence upon those with cement mortar reinforcement. The influence of confining pressure decreases as replacement ratio increasing, and the degree of such influence varies with different reinforcement at lower replacement ratio. However, with the increasing of replacement ratio, the influences of confining pressure upon different composite samples will drop down to a same level.5. The E d / Edmax -εd curves for all 3 kinds of composite samples mentioned above appear in order according reinforcement replacement ratio, and experimental points concentrate relatively within respective narrow areas. This phenomenon indicates that the dependence of Ed / Edmax on confining pressure, dry density, and moisture content decrease, but the influence of replacement ratio on Ed / Edmax is still significant. Moreover, curves of Ed / Edmax moving down with replacement ratio increasing shows that the plastic deformation capability and dynamic resistance capability of composite samples will improved with replacement ratio increasing.6. In view of the importance of E d / Edmax -εd curves (or Gd / Gdmax ~γd curves ) and E dmax( Gd max)in dynamic analysis, the averaging curves, recommended values and regressing formulas E d / Edmax -εd for the 3 kinds of composite samples mentioned above are put forward basing on a large number of experiment data. The empirical formulas of E dmax, for composite silt with different reinforcement under different replacement ratio, confining pressure, initial dry density, and initial moisture content, are also provided. These can be used as reference in the practice.7. The inference formulas of E dmax from pure silt to composite silt under different influence factors, such as replacement ratio, confining pressure, initial dry density, and initial moisture content, are set up. Then the experiment results of ordinary silts (pure soil) can be used to predict E dmax of composite silt with different reinforcements under various influence factors.8. For silt with fibers,σd ~εd curves, dynamic modulus E d, and the maximum dynamic elastic modulus E dmax are influenced by fiber material, numbers of fiber layer, confining pressure, and dry density. It will get the best effect only when these factors match well. The E d / Edmax -εd curves of silt with fibers concentrate relatively within a narrow areas, which indicates the dependence of Ed / Edmax on fiber material, numbers of fiber layer, confining pressure, and dry density decreases.9. Theλ~γd curves of 3 kinds of composite sample with vertical reinforcement mentioned above have three stages: gentle stage, steep rise stage, second gentle stage. The main distinction is that the steep rise stage appears at different dynamic shear strain for the 3 vertically reinforced composite soils. Theλ~γd curves of silt with fibers have not steep rise stage, the rise stage is slow.10. The dynamic ability of silt can be improved by vertical reinforcement or horizontal reinforcement. Under higher confining pressure, the effect of vertical reinforcement is more than horizontal reinforcement; under lower confining pressure, the effect of horizontal reinforcement is similar to the vertical reinforcement with low reinforcement replacement ratio.11. A dynamic constitutive relation of composite soil with vertical reinforcement is established based on Ranberg-Osgood model by experiment analysis.