| Cement-soil mixing pile is one of the most extensive and effective treatment technologies on strengthening soft ground.In recent years,combined with intelligent technology,bidirectional DJM pile has been successfully applied in various projects,and its prospect is broad.However,there is little research on the field-laboratory compressive and shear strength characteristics of intelligent bidirectional DJM pile and the stability analysis of strengthening channel embankment,which is not conducive to guiding engineering practice and the application of this technology.Relying on the soft ground treatment project of Baishan junction,this paper mainly adopts the research methods of laboratory test,field monitoring and numerical simulation to clarify the strength change law between the unconfined compressive strength(UCS)and shear strength of cemented soils,systematically studies the stability of intelligent bidirectional DJM pile strengthening the approach channel embankment,and compares it with field monitoring results.The results can be used to guide site construction,and it has reference significance for the stability analysis of related intelligent bidirectional cement-soil mixing pile composite foundation.The main research contents and results are as follows:(1)Based on the prevenient research of bidirectional DJM pile,intelligent construction technology is studied aiming at the problems of poor pile quality,imperfect supervision and environmental pollution of conventional technologies.The intelligent operation of construction equipment is realized by adopting the integrated design of automatic feeding device,screw air compressor.Corresponding relationship between the control parameters of construction equipment and static cone penetration test indexes is established to realize the intelligent automatic discrimination of construction pile length.Cloud monitoring system realizes the real-time upload of construction data,online supervision and management of managers.Field coring test results show that the UCS at 28 days is more than 1.80 MPa,which is about 50% ～ 80% higher than that of conventional technologies.And the strength dispersion of intelligent bidirectional DJM piles is very low,which also indicate that the average strength error along the depth is controlled within 5%,and the actual piles’ lengths exceed the top surface of bearing stratum by 0.5～ 1.0m.(2)Typical soil samples in the muddy silty clay layer were selected to carry out laboratory UCS test and triaxial unconsolidated undrained test,so as to explore the change law of strength characteristics of cemented soil.The strengths of cylinder samples at 90 days are about 13% higher than those of cube samples.The UCS increases with the rise of age and cement ratio,which is nearly linear with the logarithm of age.The ratio of deformation modulus of cemented soil to UCS ranges from 55 to 97,and the age as well sample shape has a great influence on the ratio.The cohesion of cemented soil increases approximately linearly with the UCS;the internal friction angle is between 22° and 33°.The average strength of in-situ core samples is more than 70% of that of laboratory cemented soil.Intelligent bidirectional DJM pile technology plays a significant role in improving the mixing uniformity and enhancing the reinforcement effect.The fitting relationship between strength ratio and age logarithm can effectively make up for the strength difference between laboratory and in-situ cemented soil,and uniformly describe the strength change law of cemented soil.(3)Based on typical field reinforcement section,the tests were carried out,including pore water pressure monitoring,horizontal displacement monitoring and earth pressure monitoring.The monitoring data shows that current composite foundation is in good working condition.The excess pore water pressure tends to accumulate and dissipate with the progress and intermittence of filling,besides,the filling rate has a great influence on the accumulation of excess pore water pressure.With the application of fill load,horizontal displacement of soils increases rapidly,and the horizontal displacement of different soil layers varies significantly.The grid reinforcement can effectively reduce the lateral deformation and enhance the stability of composite foundation.The earth pressure at the top of the piles is greater than that locates in the soils.There is little difference in the earth pressure between two-piles and three-piles,which indicates the soil stress distribution between the piles is relatively uniform.With the increase of fill load,the earth pressure at the top of piles increases rapidly,and finally the pile-soil stress ratio is stable between 2 and 3.(4)Combined with field coring test and laboratory test results of intelligent bidirectional DJM piles,ABAQUS was used for numerical simulation,and the calculated results are in good agreement with field measured data.Based on shear strength reduction technique,the slope’s stability safety factor under different conditions such as untreated,conventional reinforcement,composite reinforcement and different water levels are calculated.It is found that the untreated slope is very likely to be unstable and damaged.The stability safety factor of composite reinforced slope meets stability requirements,and is 6.96% higher than that of conventional reinforcement.The stability safety factor increases with the rise of the approach channel’s water level,and the maximum horizontal displacement decreases.Under the premise of ensuring the normal navigation function of approach channel,maintaining a high water level is conducive to anti sliding stability of the embankment slope.The stability safety factor of the composite reinforced slope increases approximately linearly with the increase of piles’ cohesion.In addition,the safety factor of the slope treated by intelligent bidirectional DJM piles is about 32.9% higher than that of conventional technology,which means the effect of enhancing the anti sliding stability of the slope is remarkable. |
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