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Abstract： In this paper，two 80，000 cubic meters oil storage tanks are located on the seaside of a petrochemical project.For the treatment of large area thick layer soft soil foundation of seashore，crushed stone pile is used to compound it，and then it is pre-pressed by stages and then the foundation treatment scheme is designed.
1.Engineering survey
A petrochemical project，located on the seaside，plans to build two 80，000 cubic meters of oil tanks，which，according to planning requirements，are being built at the same time.The diameter of the oil tank is 80 m，the height of the oil tank is 20 m， the distance between the two tanks is 120 m，the net distance between the two tanks is 40 m，the weight of the filling body is about 25 000 KPA，the corresponding base pressure is 72 KPA， the maximum height of oil storage is 16，and the maximum pressure of the tank base is 270 KPA.According to the deformation control requirements of the oil tank equipment for the foundation，the plane inclination （any direction） is not greater than 3/1000，the uneven settlement of the tank circumference is less than 25 mm per 10m， and the slope of the cone surface of the tank foundation is obtained.No less than 8/1000 and the settlement difference between the center and the edge of the tank is less than 280 mm.
2.Foundation treatment scheme optimization
The 80，000 m ?oil tank is 80 m in diameter and the maximum pressure of the base is 270 kpa，and the site is mainly composed of thick layer soft soil，the strength and deformation of which obviously cannot meet the requirements of 80 000 m ?large tank foundation，so the foundation treatment must be carried out.. According to the engineering geological conditions of the site，the third layer of sandy silty soil is judged to be moderate to severe liquefaction，so anti-liquefaction treatment must be carried out，and the liquefaction of the inland foundation soil in the pile length range can be eliminated by setting the gravel pile in the foundation.The influence depth of liquefaction of foundation soil during earthquake can be considered in the range of 15m below the ground，so the pile length of gravel pile can be taken 15m.After being treated with gravel pile，the bearing capacity of the composite foundation can reach 110 kpa， which still can not meet the requirements of 270kpa of 80 000 m ?oil tank foundation. Therefore， it is necessary to further strengthen the oil tank foundation by water filling preloading method.Table 1 It can be seen that the 52nd layer of the site is silty soil layer with a depth of about 25m.Therefore，the plastic drainage belt of 26m can enter 52 layers，using the horizontal permeability of this layer to play the role of two-way drainage.
After comprehensive consideration，it was decided that the combined treatment of 80 000 m ?oil tank foundation with compacted gravel pile composite foundation and plastic drainage zone water filling preloading method was adopted.The layout of gravel piles is shown in figure 1-1.
4.Conclusion
The design length of gravel pile is 15m，the design length of plastic drainage belt is 26m，so the calculation of foundation consolidation parameter is also divided into three sections，the first is the length of gravel pile，the second is the distance from the bottom of gravel pile to the bottom of plastic drainage belt，the second section is the distance from the bottom of gravel pile to the bottom of plastic drainage belt，and the calculation of foundation consolidation parameter is also carried out in three sections. The third section is the distance from the bottom of the plastic drainage belt to the bottom of the compression layer，26 m / 40 m.At the same time，bout 100mm distance was inserted from the grouting pipe to the bottom of the hole，and the grouting pipe was pulled out while grouting at the edge of the hole.When the orifice flowed out of the cement slurry，it stopped after 6 days and 8 days later. After 6 days，the cement slurry was finally condensed， and the sealing of the hole orifice was carried out again，and the secondary grouting was carried out until it was saturated.Grouting water The ash ratio is：0.4 to 0.45; bound to the 200 mm reinforced mesh of the 6@200mm;the C30 concrete is sprayed to the thickness of 100 mm，the spacing of the crushed stone piles is s = 1.5m，and the pile length is taken as L = 15 m in consideration of the requirements for liquefaction treatment of the foundation soil.
reference documentation
[1]Technical Code for Building Foundation treatment （JGJ79-2012）[S].Beijing：China Construction Industry Press， 2012
[2]Code for Design of concrete structures （GB50010-2010） [S].Beijing：China Construction Industry Press，2010
[3]Teng Yanjing，Wang Weidong，Kang Jingwen，Liu Jianguo，Li Jianmin.New advances in basic engineering technology[J].Journal of Civil Engineering，2016，20（04）：15/21
[4]Wang Wei，Yang Min，Yang Hua.Comparative analysis of short-short pile foundation and other types of foundation[J]. Journal of Architectural structures， 2006， 39 （01）： 34 / 40
1.Engineering survey
A petrochemical project，located on the seaside，plans to build two 80，000 cubic meters of oil tanks，which，according to planning requirements，are being built at the same time.The diameter of the oil tank is 80 m，the height of the oil tank is 20 m， the distance between the two tanks is 120 m，the net distance between the two tanks is 40 m，the weight of the filling body is about 25 000 KPA，the corresponding base pressure is 72 KPA， the maximum height of oil storage is 16，and the maximum pressure of the tank base is 270 KPA.According to the deformation control requirements of the oil tank equipment for the foundation，the plane inclination （any direction） is not greater than 3/1000，the uneven settlement of the tank circumference is less than 25 mm per 10m， and the slope of the cone surface of the tank foundation is obtained.No less than 8/1000 and the settlement difference between the center and the edge of the tank is less than 280 mm.
2.Foundation treatment scheme optimization
The 80，000 m ?oil tank is 80 m in diameter and the maximum pressure of the base is 270 kpa，and the site is mainly composed of thick layer soft soil，the strength and deformation of which obviously cannot meet the requirements of 80 000 m ?large tank foundation，so the foundation treatment must be carried out.. According to the engineering geological conditions of the site，the third layer of sandy silty soil is judged to be moderate to severe liquefaction，so anti-liquefaction treatment must be carried out，and the liquefaction of the inland foundation soil in the pile length range can be eliminated by setting the gravel pile in the foundation.The influence depth of liquefaction of foundation soil during earthquake can be considered in the range of 15m below the ground，so the pile length of gravel pile can be taken 15m.After being treated with gravel pile，the bearing capacity of the composite foundation can reach 110 kpa， which still can not meet the requirements of 270kpa of 80 000 m ?oil tank foundation. Therefore， it is necessary to further strengthen the oil tank foundation by water filling preloading method.Table 1 It can be seen that the 52nd layer of the site is silty soil layer with a depth of about 25m.Therefore，the plastic drainage belt of 26m can enter 52 layers，using the horizontal permeability of this layer to play the role of two-way drainage.
After comprehensive consideration，it was decided that the combined treatment of 80 000 m ?oil tank foundation with compacted gravel pile composite foundation and plastic drainage zone water filling preloading method was adopted.The layout of gravel piles is shown in figure 1-1.
4.Conclusion
The design length of gravel pile is 15m，the design length of plastic drainage belt is 26m，so the calculation of foundation consolidation parameter is also divided into three sections，the first is the length of gravel pile，the second is the distance from the bottom of gravel pile to the bottom of plastic drainage belt，the second section is the distance from the bottom of gravel pile to the bottom of plastic drainage belt，and the calculation of foundation consolidation parameter is also carried out in three sections. The third section is the distance from the bottom of the plastic drainage belt to the bottom of the compression layer，26 m / 40 m.At the same time，bout 100mm distance was inserted from the grouting pipe to the bottom of the hole，and the grouting pipe was pulled out while grouting at the edge of the hole.When the orifice flowed out of the cement slurry，it stopped after 6 days and 8 days later. After 6 days，the cement slurry was finally condensed， and the sealing of the hole orifice was carried out again，and the secondary grouting was carried out until it was saturated.Grouting water The ash ratio is：0.4 to 0.45; bound to the 200 mm reinforced mesh of the 6@200mm;the C30 concrete is sprayed to the thickness of 100 mm，the spacing of the crushed stone piles is s = 1.5m，and the pile length is taken as L = 15 m in consideration of the requirements for liquefaction treatment of the foundation soil.
reference documentation
[1]Technical Code for Building Foundation treatment （JGJ79-2012）[S].Beijing：China Construction Industry Press， 2012
[2]Code for Design of concrete structures （GB50010-2010） [S].Beijing：China Construction Industry Press，2010
[3]Teng Yanjing，Wang Weidong，Kang Jingwen，Liu Jianguo，Li Jianmin.New advances in basic engineering technology[J].Journal of Civil Engineering，2016，20（04）：15/21
[4]Wang Wei，Yang Min，Yang Hua.Comparative analysis of short-short pile foundation and other types of foundation[J]. Journal of Architectural structures， 2006， 39 （01）： 34 / 40