Study On Deformation Of Waterproof Supporting Structure And Seepage Characteristics For Excavations Of Riprap Field In Coastal Areas

Deep layers of silt often exist in coastal areas,which forms permanently retained land though jackstone treatment.The volume of riprap is relatively large,forming a gap between each other,and they are highly permeable.The groundwater in the excavations located in riprap stratum is completely connected with the surrounding seawater,so it is a great difficulty to form a good curtain for cutting off drains.The overall stability,deformation control and groundwater seepage of the excavations are the keys to the success of the project,and determine that the conventional design and construction methods are not suitable for the excavations in coastal areas.Therefore,it is of great significance to choose the appropriate support and waterproof scheme.Based on the excavations project of SheKou cruise center in ShenZhen,this paper summarized the geological features of the riprap site near the sea according to the geotechnical investigation report.The retaining and protection structure was designed and calculated based on a variety of support schemes.The final scheme suitable for the excavations was determined according to the typical test results.The deformation law of excavations and retaining and protection structure was obtained by summing up the monitoring data.The numerical model was established by using the geotechnical analysis software Midas GTS NX;the stress-seepage coupling analysis method was applied to visually reflect the deformation and seepage field characteristics of the excavations after excavation,and the numerical calculation results were verified with the actual data.The main work of this paper is as follows:(1)Combined with geotechnical investigation report,the excavations support structure was designed and calculated with the help of qimstar FRWS 9.0 software.It is concluded that the put slope excavation should be carried out in the open field with put slope setting conditions,and the cantilevered punched cast-in-row piles should be used to support those without put slope setting conditions.(2)Through seepage test curtain for cutting off drains with a variety of schemes,it is concluded that high pressure jet grouting pile and grout between pile to curtain for cutting off drains cannot be achieved the requirements of the hydraulic conductivity,and only "reinforced concrete pile + concrete pile" of waterproof solution can meet the design requirements,thus adopt the secant piles in row scheme on the east and south sides of the excavations.(3)The secant pile wall is equivalent to the diaphragm wall of a certain thickness according to the principle of equivalent stiffness.The displacement of excavations,the deformation of retaining and protection structure and the seepage field distribution after excavation were analyzed through set up no curtain for cutting off drains,different depth curtain for cutting off drains conditions.The total head distribution cloud map,seepage velocity distribution cloud map and vector diagram were calculated.The analysis shows that the setting of the curtain for cutting off drains effectively blocks the seepage of groundwater,but the seepage velocity is still very large when it does not cross the riprap stratum.Therefore,the depth of the curtain for cutting off drains must be set below the riprap stratum in high-permeability riprap reclamation site.(4)Based on the optimization of the retaining and protection for excavations scheme,it is concluded that on the premise of the success of the retaining and protection for excavations and control construction accuracy,the project cost can be saved through reduce the overlap of secant piles in row.