Research On Uneven Settlement And Control Technology Of Soft Soil In Reclamation Area

The uneven settlement of the foundation is one of the main causes of civil and construction engineering accidents.Especially in soft soil areas such as Shanghai and Tianjin,it is more likely to cause uneven settlement.The Tianjin LNG pipeline reclamation section is located in Nangang Industrial Park,Dagang District,Tianjin near Bohai Bay.The entire area was originally a sea surface and the original landform was an underwater bank slope geomorphological area in the shallow sea area of the Duliujian estuary of Dagang District.It is now formed by land reclamation.Due to some negative factors like the differences in reclamation time in the research area,the softness of surface soil,the high water content,moreover the short duration of consolidation drainage,the research area is prone to uneven settlement,threatening the normal use of the pipeline and the safety of human life and property.This paper selects Tianjin LNG pipeline reclamation as a research case for the uneven settlement and control technology in soft soil areas.Relying on detailed geological surveys and laboratory tests,the distribution characteristics of the strata along the pipeline and the characteristics of differential settlement deformation were systematically studied.In combination with numerical simulation analysis methods,the automatic monitoring data of settlement was compared and the solidification agent was used to study the soft soil engineering characteristics of the high salinity degree through laboratory tests.A comprehensive and systematic study has been made on the uneven settlement and the control technology of soft soil in the reclamation area.The main research results of this paper are as follows:(1)Through the collection of geological environment data of the research area,in-depth investigation of the distribution characteristics of the foundation soil on the basis of detailed understanding of the geological environment in the area,through systematic analysis of the bearing characteristics and settlement characteristics of the soft soil foundation along the pipeline,the preliminary division of the research area is the east-west section A,the north-south-B area,and the east-west section C area.At the same time,the on-site in-situ test and laboratory test results reveal that the soil layer above 6 m in the existing ground is an over-consolidation soil,and the filling below 6 m is under-consolidation soil.The uneven settlement is mainly caused by the additional stress generated by the filling soil on the original seabed.(2)Through the stratified summation method and CPT in-situ measurement algorithm to calculate the settlement of the entire pipeline,and in this process,the difference among the laboratory test,on-site results in situ and the different settlement calculation methods are analyzed and discussed,finally select the most Excellent calculation method.The calculation results shows that the settlement of foundations in the north-south pipeline is larger than the east-west section,and the settlement in the middle-eastern section is larger than the east-west and west-west section.The largest uneven settlement in the region is located in the middle of the north and south section,next the boundary of the cofferdam in each section.Settlement completed 70%within the first year,and consolidation was basically completed by the 5th year.(3)Using Flac3d software to build three-dimensional modeling of representative sections in different areas of the site,and verifying the accuracy of the theoretical calculation results through numerical simulation analysis methods.In the later period,automatic monitoring methods are used to monitor the sections of the uneven settlement,analyzing the safety of pipeline operations at the current stage.Combined with the relevant design parameters of pipeline,the pipeline safety operation threshold was proposed:when the monitoring data reaches 208mm,a yellow alarm is triggered;when the monitoring data reaches 249.6mm,a red alarm is triggered.Through comparative analysis of the four groups of monitoring data,it is shown that the monitoring values of the four equipments are below the yellow warning threshold and the settlement rate is in line with the expected calculation.The analysis of the numerical simulation results of the site representative paragraphs shows that the overall simulated data is similar to the laboratory estimate.And so on,laboratory estimates are also accurate and valid for other areas of the site.(4)Analysis of deviations between indoor calculation data,numerical simulation analysis data,and on-site monitoring data shows that:when the ps?1.3 MPa,the correction coefficient of the estimation equation of the compressive modulus of cohesive soil or soft soil is 0.907.When the ps>1.3 MPa,the correction coefficient of this equation is 0.878.A more accurate formula is obtained for estimating the compressive modulus of soft soil similar to research area:(1)Es=3.75ps^0.687(ps?1.3 MPa)(2)Es=1.88ps+1.91(ps>1.3 MPa)(5)Control techniques for uneven settlement in the research area combined with the engineering characteristics of the high salinity degree of soft soil on the site,Chengdu University of Technology independently developed a new type of salt-swelling and solidifying material SD as a curing agent for laboratory trials of artificially configured coastal high-alkalinity soft soil.The test results show that:The new solidifying agent can significantly enhance the strength of soft clay with high salinity,and can effectively control the uneven settlement caused by practical engineering.At the same time,it can significantly suppress the salting phenomenon of high salinity soft soil.The new curing agent has a high use value.