Research On Dynamic Compaction Test And Numerical Calculation Of Collapsible Loess Foundation

Collapsible loess is widely distributed in China,which has potential harm to existing buildings.dynamic compaction is more widely applied to treat collapsible loess than many other methods,for its advantage of simple devices,economical and applicability.More effort is needed to research mechanism of dynamic consolidation in unsaturated collapsible loess, because of its complexity.In this paper,deformation characteristics,dynamic property and dynamic compaction effect factors are studied,through theoretical analysis,flooding- dynamic compaction test on site and numerical calculation.( 1) Analyzes consolidation mechanism of collapsible loess foundation, reinforcement process of soil deformation mainly due to relative displacement of particles, gas in soil is extruded.Principle of vibration model and hammer body dynamic equilibrium equation are established based on completely elastic collision by solving hammer body dynamic balance equations,hammer body displacement, velocity and acceleration in process of change over time formula are obtained which can solve out maximum displacement and maximum velocity and maximum acceleration and its corresponding time.(2)A set of relatively complete filed test schemes are designed based on principles of flooding- dynamic compaction.In process of flooding area, tamping energy decay faster, pass smaller depth which is only 4 m or so,which are obtained through dynamic compaction test field flooded area and non-flooded area.After flooding effect, effective reinforced depth of dynamic consolidation is about 7 m,whose elimination effect is obvious.Flooding effect led to more close-grained, dynamic compaction soil before settlement of dynamic compaction is lesser, energy transfer more down and tamping can main consumption on vertical compressive deformation of soils, but also part of energy with level of Rayleigh wave propagation, lead to surrounding soil lateral extrusion.Two test areas tamper hole radius are 2.7 m and 2.3 m respectively, after soaking treatment,soil compaction on punching shear damage effect is more apparent.Three pilots bearing capacity are 240 kPa, 180 kPa, 160 kPa,respectively,pilot for 1 # water content is low, dynamic consolidation compaction effect is obvious, therefore bearing capacity is higher, 2 #, 3 # pilot are in flooded areas, higher water content, nearly saturated state, dynamic consolidation can’t be better obtained.(3)This paper has calculated and analysis the dynamic compaction characteristics, with ABAQUS calculation software, the Mohr Coulomb model, rigid body impact load, first-order four node element, no reflection boundary condition and ALE adaptive technology. The results show that, the largest amount of uplift the surrounding the crater is 3m along distance axis, and calculating crater radius is about 2.5~3m. With the increase of the dynamic compaction energy, the crater depth and uplift are linear increasing. When the elastic modulus of soil is larger than 10 MPa, the crater depth and the elastic modulus present the approximate linear relationship. With the increase of the number of dynamic compaction, the plastic deformation area gradually expanded, when it more than 7 times, and the plastic deformation zone is similar to the shape of the apple shape.(4)Vertical peak stress decreases with the increase of the depth, vertical velocity decreases along time growth, sustained vibration to 0.55 s. Vibration velocity spread outward along the ground surface. The time of peak velocity increase with the increase of distance along the axis under the hammer, and peak velocity decreases. With the increase of the compaction energy, the peak value of the vertical stress increases gradually. Acceleration spreed downward along time increases with a certain angle, the angle of acceleration downward diffusion increase with number of dynamic compaction increases, between 40~45°. In the construction process, we can select a reasonable compaction spacing according to the point of view of the energy spreed downward, ensure rammed soil reinforcement effect is good.The research results of this paper have important theoretical and practical significance for the research and engineering practice of the collapsible loess foundation with dynamic consolidation.