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Technical code for ground treatment of steel tanks
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GB/T 50756-2012
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Standard similar to GB/T 50756-2012 GB/T 51033 GB/T 50856 GB/T 50082 Basic data | Standard ID | GB/T 50756-2012 (GB/T50756-2012) | | Description (Translated English) | Technical code for ground treatment of steel tanks | | Sector / Industry | National Standard (Recommended) | | Word Count Estimation | 126,123 | | Quoted Standard | GB 50007; GB 50011; GB 50021; GB 50025; GB 50046; GB 50290; GB 50473; GB/T 17689; JGJ 94; SH/T 3123; JT/T 521 | | Regulation (derived from) | Bulletin of the Ministry of Housing and Urban No. 1361 | | Issuing agency(ies) | Ministry of Housing and Urban-Rural Development of the People's Republic of China; General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China | | Summary | This standard applies to storage of crude oil, petrochemical products and other similar liquid liquid vertical cylindrical steel storage tank foundation treatment (hereinafter referred to as " the tank foundation treatment ") the design, construction and | GB/T 50756-2012: Technical code for ground treatment of steel tanks---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
1 General
1.0.1 This specification is formulated in order to make the design and construction of steel storage tank foundation treatment safe and applicable, advanced in technology, economical and reasonable, ensure quality, and protect the environment.
1.0.2 This code is applicable to the design, construction and quality inspection of vertical cylindrical steel storage tank foundation treatment for storing crude oil, petrochemical liquid products and other similar liquids (hereinafter referred to as "storage tank foundation treatment").
1.0.3 In addition to meeting the engineering design requirements, the foundation treatment of storage tanks should also be adapted to local conditions, local materials, environmental protection and resource conservation.
1.0.4 The foundation treatment of storage tanks shall not only comply with this code, but also comply with the current relevant national standards.
2 Terms and symbols
2.1 Terminology
2.1.1 composite foundation
Part of the soil is reinforced or replaced to form a reinforced body, and the reinforced body and the surrounding foundation soil jointly bear the load.
2.1.2 Cushion replacement method
The foundation treatment method is to excavate the shallow soft soil layer or uneven soil layer on the surface, backfill with hard and coarse-grained materials, and compact or tamp to form a dense cushion.
2.1.3 hydrostatic preloading
In the stage of water filling and pressure testing of the storage tank, the foundation treatment method is used to preload the foundation with the water filling load of the storage tank to consolidate and compact the foundation.
2.1.4 Dynamic compaction, dynamic consolidation
Repeatedly lift the rammer to a high place to let it fall freely, give impact and vibration energy to the foundation soil, and compact the foundation soil.
2.1.5 Dynamic replacement by dynamic compaction
Use the dynamic compaction method to fill in gravel while tamping to form a gravel pier in the foundation. The ground treatment method of the composite foundation composed of crushed stone pier, soil between the pier and upper crushed stone cushion.
2.1.6 vibroflotation, vibro-replacement
Under the combined action of the horizontal vibration of the vibrator and high-pressure water, the loose sandy soil layer is vibrated and dense, or holes are formed in the soft soil layer, and then coarse grain materials such as gravel are backfilled to form piles, which are combined with the original foundation soil. Foundation treatment methods.
2.1.7 Sand-gravel column method
Vibration, impact or water flushing is used to form holes in the foundation, and crushed stones, sand or gravel are squeezed into the holes to form dense piles of sand and gravel, which are combined with the soil between the original piles to form a composite foundation.
2.1.8 cement flyash gravel pile method cement-flyash-gravel pile
The pile body is formed by mixing cement, fly ash, crushed stone, stone chips or sand with water, and the composite foundation is composed of piles and soil between piles.
2.1.9 cement-solid deep mixing pile method
Using cement as the main material of the curing agent, the curing agent and the foundation soil are forcibly stirred by a deep mixing machine to form a pile body with integrity, water stability and certain strength, and form a composite foundation with the soil between the piles and the filler layer ground treatment method.
2.1.10 lime-soil compaction column
The equipment is used to squeeze the hole horizontally, so that the soil between the piles can be compacted. The foundation treatment method is to fill the pile hole with lime soil and tamp it layer by layer to form a lime soil pile, and form a composite foundation with the soil between the piles.
2.1.11 reinforced-concrete pile composite foundation reinforced-concrete pile composite foundation
Reinforced concrete piles are used as vertical reinforcements, and the composite foundation is composed of piles and soil between piles.
2.2 Symbols
2.2.1 Action and action effect.
pcz—the self-weight pressure value of the soil at the bottom of the cushion;
pz—additional pressure value at the bottom of the cushion;
Pk—corresponding to the standard combination of load effects, the average pressure value at the bottom of the tank foundation;
Ut—the average consolidation degree of the foundation at the consolidation time t;
St——sedimentation rate at time t;
Sc—calculate the consolidation settlement by layered sum method.
2.2.2 Resistance and material properties.
az—the characteristic value of the foundation bearing capacity of the soil layer at the bottom of the cushion layer after depth correction;
ak—the characteristic value of the bearing capacity of the natural foundation at the bottom of the foundation;
sk - characteristic value of soil bearing capacity between piles after treatment;
spk — characteristic value of bearing capacity of vibro-pile composite foundation;
qsi - characteristic value of lateral frictional resistance of the i-th layer soil pile;
qp——the characteristic value of pile tip soil bearing capacity;
Ra—the characteristic value of the vertical bearing capacity of a single pile;
Tr—the tensile strength of the reinforced body corresponding to the strain of 5%;
Es—compression modulus of soil between piles;
Esp—compression modulus of composite soil layer;
ρd——dry density;
ωop—optimum water content.
2.2.3 Geometric parameters.
Ap - pile body cross-sectional area or pile cap area;
b——width of plastic drainage strip;
d - the diameter of the pile and the diameter of the pile hole;
de——Equivalent circle diameter of treated foundation area shared by single pile, effective drainage diameter of drainage body;
dp——the equivalent conversion diameter of the plastic drainage belt;
H—thickness of filler layer in ring wall of tank foundation;
s—clean distance between piles, distance between pile holes;
δ——thickness of plastic drainage belt;
θ——pressure diffusion angle.
2.2.4 Calculation coefficient and others.
m—area replacement rate;
n - pile-soil stress ratio, well diameter ratio;
λc - compaction coefficient.
3 Basic Regulations
3.0.1 Before selecting the foundation treatment plan for the storage tank, the following tasks should be completed.
1 Study and master the detailed site, geotechnical engineering conditions and the requirements of the storage tank for the foundation, etc.;
2 Clarify the purpose of foundation treatment, the scope of treatment, and various technical and economic indicators required to be achieved after treatment;
3 Combined with the actual situation of the project, understand the local foundation treatment experience, construction conditions, supply of building materials, and the foundation treatment experience and usage of similar storage tank projects on similar sites in other regions;
4 The environmental conditions of the construction site should be mastered, including the conditions of adjacent buildings and structures, underground engineering and related underground pipelines.
3.0.2 When selecting a storage tank foundation treatment scheme, it is advisable to choose a scheme that works together between the storage tank foundation and the foundation.
3.0.3 For sites with liquefied soil layers, an appropriate storage tank foundation treatment plan should be selected according to the seismic fortification category of the storage tank foundation, the liquefaction level of the foundation, and the specific situation. The selected plan should comply with the current national standard "Code for Seismic Design of Buildings "Relevant provisions of GB 50011.
3.0.4 When selecting a storage tank foundation treatment plan, the suitability of the selected plan should be determined according to the corrosive grade of groundwater and foundation soil, and the current national standard "Code for Anti-corrosion Design of Industrial Buildings" GB 50046, and the anti-corrosion measures to be taken should be determined.
3.0.5 When the storage tank foundation is constructed on a site that needs to be backfilled or blown fill, the tank foundation treatment plan should be determined together with the site backfill or blown fill scheme, and specific requirements for the site backfill and blown fill should be put forward.
3.0.6 When choosing a foundation treatment plan, attention should be paid to the impact of construction noise, vibration, soil compaction, mud, etc. on the environment, and the adopted plan should meet the national and local environmental protection requirements.
3.0.7 The determination of the tank foundation treatment method should be carried out according to the following steps.
1 According to the requirements of the storage tank on the foundation, combined with geotechnical engineering conditions, environmental conditions and the impact on adjacent buildings and structures and other factors, conduct a comprehensive analysis, and preliminarily select several feasible foundation treatment schemes, including choosing two or more foundation treatments A comprehensive treatment plan composed of methods;
2 For the various foundation treatment schemes initially selected, conduct technical and economic analysis and comparison in terms of reinforcement principles, scope of application, expected treatment effects, materials consumed, construction machinery, construction period requirements and impact on the environment, etc., and choose the best foundation treatment method;
3 For the selected foundation treatment method, it is advisable to carry out corresponding field tests or experimental construction on representative sites according to the design level of the foundation of the storage tank and the complexity of the site, so as to test the design parameters and treatment effect. When the design requirements are not met, the reasons shall be found out, and the design parameters shall be modified or the ground treatment method shall be adjusted.
3.0.8 For the treated foundation, the foundation bearing capacity of the foundation width and depth shall not be corrected; when there is still a weak underlying layer within the range of the stressed layer, the foundation bearing capacity of the underlying layer shall be checked and calculated.
3.0.9 When the storage tank foundation is built on the treated foundation, foundation deformation check calculation should be carried out.
3.0.10 The foundation stability checking calculation shall comply with the relevant provisions of the current national standard "Code for Design of Steel Storage Tank Foundation" GB 50473.
3.0.11 Construction technicians should understand the foundation treatment purpose of the project undertaken, be familiar with foundation reinforcement principles, technical requirements and quality standards, etc. Special personnel should be responsible for quality control and monitoring during construction, and construction records should be kept well. When any abnormal situation occurs, it should be properly resolved with relevant departments in a timely manner. Quality supervision should be carried out during the construction process, and project quality inspection and acceptance should be carried out in accordance with relevant national regulations after construction.
3.0.12 Composite foundation load test shall comply with the provisions of Appendix A of this code.
3.0.13 The foundation of the storage tank built on the treated foundation shall be observed for settlement until the settlement is stable.
4 Replacement cushion method
4.1 General provisions
4.1.1 The replacement cushion method is suitable for foundation treatment of shallow soft or uneven soil layers such as silt, silty soil, collapsible loess, plain fill, miscellaneous fill, hidden ditches, and dark ponds.
4.1.2 A comprehensive analysis should be carried out based on the characteristics of the tank foundation, geotechnical engineering conditions, construction machinery and equipment, and the nature and source of the filler, so as to design the replacement cushion and select the construction method.
4.1.3 When the cushion layer is partially replaced, the foundation bearing capacity and deformation modulus of the compacted cushion layer should be similar to the undisturbed soil layer at other parts under the same foundation.
4.1.4 When the bearing layer under the cushion is bedrock with a slope greater than 10%, and the slope direction is not conducive to the stability of the tank foundation, the surface of the bedrock should be made into a stepped shape.
4.2 Design
4.2.1 The thickness of the cushion layer shall be determined according to the depth of the weak soil layer to be replaced or the bearing capacity of the soil layer at the bottom of the cushion layer. When determined according to the bearing capacity of the soil layer at the bottom of the cushion, it shall meet the requirements of the following formula.
pz＋pcz≤az (4.2.1)
In the formula. pz—corresponding to the standard combination of load effects, the additional pressure value (kPa) at the bottom of the cushion layer, the value is determined according to the relevant provisions of the current national standard "Code for Design of Building Foundations" GB 50007;
pcz——the self-weight pressure value of the soil at the bottom of the cushion layer (kPa);
az—the characteristic value of foundation bearing capacity of the soil layer at the bottom of the cushion layer after depth correction (kPa).
4.2.2 The thickness of the replacement cushion should meet the deformation requirements of the tank foundation, and the thickness of the cushion should not be less than 0.5m, and should not be greater than 3m.
4.2.3 The width of the bottom surface of the cushion layer shall meet the requirements of the stress diffusion on the bottom surface of the foundation, which may be determined from the outer edge of the tank foundation downwards at an expansion angle of 45°. The top surface of the cushion should not be less than 500mm beyond the outer edge of the foundation.
5.2 Design
5.2.1 The design of the water-filled preloading scheme should be carried out according to the following steps.
1.Preliminarily formulate a water-filled preloading scheme according to the engineering geological conditions of the site, the base pressure of the storage tank foundation and the expected degree of consolidation;
2 Carry out detailed consolidation degree and overall and local stability check calculation according to the preliminarily formulated water-filled preloading scheme. When the checking calculation result does not meet the safety and construction period requirements, the water filling and preloading scheme should be adjusted, and then the checking calculation should be re-checked;
3 After the water-filled preloading scheme is determined, settlement calculation and settlement rate calculation are still required.
5.2.2 When a vertical drainage body is required, the design of the vertical drainage body shall meet the following requirements.
1 The vertical drainage body can adopt ordinary sand wells, bagged sand wells and plastic drainage belts. The diameter of ordinary sand wells can be 300mm-500mm, and the diameter of bagged sand wells can be 70mm-120mm. The equivalent conversion diameter of the plastic drainage belt can be calculated as follows.
In the formula. dp - plastic drainage belt equivalent conversion diameter (mm);
b——Width of plastic drainage belt (mm);
δ——thickness of plastic drainage belt (mm).
2 The plane layout of the vertical drainage bodies can be arranged in an equilateral triangle or a square, and the layout range should be extended by 3 rows at the outer edge of the foundation. The relationship between the effective drainage diameter and spacing of the drainage body is.
Arrangement of equilateral triangles de = 1.05l;
Square arrangement de = 1.13l.
3 The spacing of vertical drainage bodies may be determined according to the consolidation characteristics of the foundation soil and the required consolidation degree within a predetermined time. During design, the spacing of the drainage body can be selected according to the well diameter ratio n, where n is the ratio of the effective drainage diameter of the drainage body to the shaft diameter or the equivalent conversion diameter. The spacing of plastic drainage belts or bagged sand wells can be selected according to n=15-22, and the spacing of ordinary sand wells can be selected according to n=6-8.
4 The depth of the vertical drainage body shall be determined according to the distribution of the soil layer, the requirements of the storage tank for foundation stability and deformation. For storage tanks controlled by foundation stability, the depth of the vertical drainage body shall exceed the most dangerous sliding surface by 2m; for storage tanks controlled by foundation deformation, the depth of the vertical drainage body shall be based on the Deformation is determined. When the thickness of the compressed layer is not large, the vertical drainage body should penetrate the compressed soil layer.
5.2.3 The water-filled preloading method should adopt the method of graded constant-velocity loading, and the loading series should be determined according to the calculation of the growth of the foundation strength.
5.2.4 The settlement rate of the foundation can be calculated according to the following formula.
Settling rate during the loading process of stage i.
Settling rate during I-stage shelving.
In the formula. St——sedimentation rate at time t;
qi——the loading rate of the i-th stage (kPa/d);
qn——the loading rate of the nth level load (kPa/d);
β—consolidation attenuation coefficient, generally obtained by back calculation from actual measurement, if there is no empirical value, it can be calculated according to Table 5.2.4;
r——calculation coefficient, which is the ratio of the average additional stress above and below within the scope of the compressed layer of foundation soil;
α——calculation coefficient, adopted according to Table 5.2.4 according to drainage consolidation conditions;
mi—empirical coefficient considering the lateral deformation of the foundation and other influences, which may be 1.1~1.4;
Tn－1, Tn—the start and end time of loading and stopping stages;
t——the time between the i-th loading segment;
Sc—consolidation settlement, calculated by layered sum method;
P0 - the total amount of loading;
e - the base of the natural logarithm.
Table 5.2.4 α and β values under different drainage consolidation conditions
Note. 1, n is diameter ratio.
2 H1 is the depth of the sand well (m); H2 is the thickness of the compressed soil layer below the sand well (m).
3 Uz is the average degree of consolidation of the vertical drainage of the foundation (%).
4 ch is the radial consolidation coefficient of foundation soil (cm2/s).
5 cv is the vertical consolidation coefficient of foundation soil (cm2/s).
6 H is the shortest vertical drainage distance of the foundation (cm).
5.2.5 Under the condition of one or more stages of constant-velocity loading, the average degree of consolidation of the foundation can be calculated as follows.
In the formula. Ut—the average degree of consolidation of the foundation at the consolidation time t (%);
∑△p——accumulated value of load at all levels (kPa);
t——preloading time (d);
Tn－1——the start time (d) of nth level load loading;
Tn——the termination time of the nth level load, when calculating the degree of consolidation at time t during the nth level load, Tn is changed to t(d).
5.2.6 The shear strength of a point in the saturated cohesive soil foundation under the action of preload when the consolidation time is t can be calculated according to the following formula.
τft=η(τf0+△τfc) (5.2.6-1)
In normal consolidation state.
In the over-consolidated state.
In the formula. τft——the shear strength of a point in the foundation when the consolidation time is t (kPa);
τf0——The natural shear strength of the soil at this point before loading, determined by the cross plate shear test, unconfined compression test or triaxial consolidation undrained...
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