Field Test And Applied Research On The Improvement Of Miscellaneous Fill Foundation By Vibratory Probe Compaction Method

Vibratory probe compaction is a new treatment method for foundations developed in the 1960 s.It fixes the vibratory probe under the vibrator,and sinks into the soil in the form of vertical vibration,then adjusts frequency of the vibrator to reaches the resonance frequency of the vibrator-probe-soil system,and the vibration amplification effect during the resonance is used to cause the surrounding soil to vibrate violently,so as to the optimal transfer of vibration energy from the vibratory probe to the surrounding soil,through which soils can be significantly compacted.Because of the advantages such as convenient construction,economical and practical,green and environmental protection,it has been successfully applied in liquefiable silt and collapsible loess foundations in recent years.However,there is few reports on the relevant application research and case studies of the vibratory probe compaction method in the treatment of miscellaneous fill foundations.Through soil disturbance test,vibration test,inspection of reinforcement effect and calculations analysis,combined with engineering case,this paper studies the treatment effect and construction parameters of miscellaneous fill foundations by vibratory probe compaction method,to verify the feasibility of vibratory probe reinforcing miscellaneous fill,and provides a new technical means for the treatment of miscellaneous fill foundation.The main research contents and results are as follows:(1)Through surface vibration test during the construction process,the vibration response of the soil under different working conditions and different vibration frequencies were analyzed to determine the frequency parameters of each process stage,and the pattern of vibration transmission and energy attenuation were studied as well.The surface vibration test results show that the resonance frequency of the vibratory probe compaction method to reinforce the miscellaneous fill foundation is about 16 Hz.When sinking at a high frequency,the soil vibrates mainly in the vertical direction.The vibration of soils at a low frequency is mainly in horizontal directions,and the horizontal vibration component will even be greater than the vertical vibration component.During the construction process,the maximum vibration velocity decreases with the increase of the distance from the vibration point,and most energy generated by the vibration is absorbed by the soil near the vibration point while the safe distance of H-probes is less than 2 m.(2)The variation of horizontal displacement and layered settlement of soil were monitored to analyze the reinforcement mechanism and the impact of vibratory probe vibration on the surrounding soil before and after reinforcement,and discussed the construction technology of vibration at the bottom.The results of soil disturbance test show that the peak value of soil horizontal displacement and layered settlement decreases along with the increase of the distance from the vibration point,and increases with the increase of the construction depth,and the influence range of single vibration point reaches 1.5m.The soil around the vibration point is significantly affected by lateral compaction,and the soil particles are rearranged by repeated violent vibration,resulting in the loose miscellaneous fill to be compacted.The reinforcement range of the vibratory probe in deep soil is larger than that in shallow soil,and the reinforcement effect in the deep soil is better than that in the shallow soil.The prolonged vibration cannot expand the reinforcement range,but the compaction effect of shallow soil can be improved.For miscellaneous fill foundations,the best treatment effect can be achieved if the load time is more than one minute,and the excess load time does not significantly improve the compactness.(3)The treatment effect was evaluated by in-situ tests,and the influence of vibration point spacing and vibration superposition on the reinforcement effect was analyzed.The results show that whether it is a triangular or square arrangement,the strength of the centroid point after reinforcement is greater than that of the center of two points,and the strength of the center of two points is greater than the vibration point.The reinforcement effect is the best with small compaction point spacing,and reducing the distance between vibration points can improve the reinforcement effect.After reinforcement,the void ratio of the soil is reduced,and the Rayleigh wave velocity,the bearing capacity and the density of the foundation have been improved.The influence range exceeds the designed reinforcement depth,and the soil density within 1m below the construction surface is greatly improved.The above shows that the vibratory probe compaction method can be used for the treatment of deep miscellaneous fill foundations.(4)Compared and analyzed the design standards and research data of the deep vibratory compaction method both domestically and globally,gave the suggestions for the determination method of the vibration frequency,compaction point spacing,and vibration time.(5)Aiming at the problem of poor compaction effect in the shallow soil,a treatment scheme of deep vibration probe compaction combined with shallow grouting is proposed,which solves the problem of the poor compaction effect of shallow soil caused by too large spacing and too small overburden stress in a project.Moreover,compared with the conventional grouting treatment method,the technical and economic benefits are significant,which can provide a reference for similar projects.