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Technical code for building in expansive soil regions
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GB 50112-2013
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Basic data | Standard ID | GB 50112-2013 (GB50112-2013) | | Description (Translated English) | Technical code for building in expansive soil regions | | Sector / Industry | National Standard | | Classification of Chinese Standard | P13 | | Classification of International Standard | 93.020 | | Word Count Estimation | 130,154 | | Older Standard (superseded by this standard) | GBJ 112-1987 | | Quoted Standard | GB 50007; GB 50021; GB 50026; GB 50153; GB 50292; JGJ 8; JGJ 94 | | Regulation (derived from) | Bulletin of the Ministry of Housing and Urban-Rural Development 1587 | | 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 the expansion of land area construction survey, design, construction and maintenance management. | GB 50112-2013: Technical code for building in expansive soil regions---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 implement the national technical and economic policies in construction projects in expansive soil areas, to achieve safety and applicability, advanced technology, reasonable economy, and environmental protection.
1.0.2 This code is applicable to survey, design, construction and maintenance management of construction projects in expansive soil areas.
1.0.3 For engineering construction in expansive soil areas, according to the characteristics of expansive soil and engineering requirements, factors such as topographical conditions, climate characteristics, and changes in soil moisture should be considered comprehensively, local experience should be emphasized, and prevention and control measures should be taken according to local conditions.
1.0.4 The survey, design, construction and maintenance management of construction projects in expansive soil areas shall not only comply with this specification, but also comply with relevant current national standards.
2 Terms and symbols
2.1 Terminology
2.1.1 expansive soil
The clay component in the soil is mainly composed of hydrophilic minerals, and it is a cohesive soil that has two deformation characteristics of water absorption expansion and water loss shrinkage.
2.1.2 free swelling ratio
After the artificially prepared dry loose soil sample swells and stabilizes in water, the percentage of its volume increase to the original volume.
2.1.3 swelling potential
A measure of the expansion-contraction deformation, or expansion force, that an expansive soil may produce when environmental conditions change.
2.1.4 swelling ratio
The percentage of the ratio of the height increase value to the original height of the ring-knife soil sample in the consolidation instrument after it is soaked in water and swells under a certain pressure.
2.1.5 swelling force swelling force
The maximum internal stress produced by the water-soaked soil sample in the consolidation instrument when the volume remains constant.
2.1.6 value of swelling deformation
Under a certain pressure, the deformation amount of expansive soil after absorbing water and expanding and stabilizing.
2.1.7 linear shrinkage ratio
The ratio of the height reduction value to the original height of the ring knife soil sample under natural humidity after drying or air-drying.
2.1.8 coefficient of shrinkage coefficient of shrinkage
The vertical linear shrinkage rate of the ring knife soil sample when the water content decreases by 1% in the linear shrinkage stage.
2.1.9 value of shrinkage deformation
The amount of deformation of expansive soil after dehydration shrinkage is stabilized.
2.1.10 value of swelling-shrinkage deformation
The total deformation of expansive soil after water absorption and water loss shrinkage are stabilized.
2.1.11 grade of swelling-shrinkage
The foundation evaluation index of the influence degree of expansion and contraction deformation of expansive soil foundation on low-rise buildings.
2.1.12 Atmospheric influence depth climate influenced layer
Under the influence of natural climate, the effective depth of expansion and contraction deformation of foundation soil caused by factors such as precipitation, evaporation and temperature.
2.1.13 climate influenced markedly layer
Atmospheric effects are particularly pronounced at depth.
2.2 Symbols
2.2.1 Actions and action effects
Pe - expansive force of soil;
pk—corresponding to the standard combination of load effects, the average pressure value at the bottom of the foundation;
pkmax——the maximum pressure value at the edge of the bottom surface of the foundation when the standard combination of load effects is applied;
Qk—corresponding to the standard combination of load effects, the vertical force acting on the top of the pile under the most unfavorable working conditions;
sc——gradient deformation of foundation;
se - expansion and deformation of foundation soil;
ses - expansion and contraction deformation of foundation soil;
ss—shrinkage and deformation of foundation soil;
νe——Standard value of the maximum expansion and pullout force of the side soil of the pile in the layer with severe atmospheric influence.
2.2.2 Material properties and resistance
fa——modified characteristic value of foundation bearing capacity;
fak — characteristic value of foundation bearing capacity;
qsa - characteristic value of lateral resistance of the pile;
qpa——the end resistance characteristic value of the pile;
ω1——the natural water content of the soil at 1m below the surface;
ωp——the plastic limit water content of soil;
γm —weighted average weight of the soil above the bottom surface of the foundation;
δef ——free expansion rate of soil;
δep—expansion rate of expansive soil under a certain level of load;
δs—the vertical line shrinkage of the soil;
λs——soil shrinkage coefficient;
ψw—soil moisture coefficient.
2.2.3 Geometric parameters
AP - cross-sectional area of the pile end;
d - foundation embedding depth;
da——atmospheric influence depth;
hi - the calculated thickness of the i-th layer of soil;
h0 - the original height of the soil sample;
hw——the height of the soil sample after soaking in water and swelling under a certain level of load;
l - the distance between the centers of adjacent column foundations of the building;
la——the length of the pile tip entering the layer below the sharp atmospheric influence layer or in the non-expansive soil layer;
lp—horizontal distance from the outer edge of the foundation to the slope shoulder;
up - the circumference of the pile body;
ν0 - the original volume of the soil sample;
νw—the volume of the soil sample after swelling and stabilizing in water;
zi—calculated depth of the i-th layer of soil;
zen—calculation depth of expansion deformation;
zsn——shrink deformation calculation depth;
β——The angle of the design slope.
2.2.4 Design parameters and calculation coefficients
ψe—experiential coefficient for calculation of expansion and deformation;
ψes—experiential coefficient for calculation of expansion and contraction deformation;
ψs—experience coefficient for calculation of shrinkage deformation;
λ——uplift coefficient of pile side soil.
6 Investigate local construction experience, and conduct research and analysis on cracked and damaged buildings.
4.1.3 The preliminary investigation shall determine the expansion and contraction grade of the expansive soil, evaluate the stability and geological conditions of the site, and determine the general layout of the building, the foundation scheme and preventive measures of the main buildings, and the prevention and treatment of adverse geological effects. Provide information and suggestions, and should also include the following.
1 When the engineering geological conditions are complex and the existing data do not meet the design requirements, engineering geological surveying and mapping should be carried out, and the scale used should be 1/1000～1/5000;
2 Identify adverse geological effects such as landslides and ground fissures in the site, and evaluate the degree of harm;
3 Estimate the seasonal variation range of groundwater level and its impact on foundation soil expansion and contraction, strength and other properties;
4 Take undisturbed soil samples for indoor basic physical and mechanical properties test, shrinkage test, expansion force test and expansion rate test under 50kPa pressure to determine whether there is expansive soil and its expansion potential, and find out the physical and mechanical properties of expansive soil on site and the foundation Shrinkage level.
4.1.4 The detailed investigation should find out the distribution of the foundation soil layer of each building and its physical and mechanical properties and expansion and contraction performance, and provide detailed engineering geological information for foundation design, prevention and control measures, slope protection, and treatment of adverse geological effects. Information and suggestions should also include the following.
1 Take the undisturbed soil sample for indoor expansion rate test, shrinkage test and statistical analysis of the data under the pressure of 50kPa to determine the expansion and contraction level of the building foundation;
2 Carry out indoor expansion force, contraction and expansion rate tests under different pressures;
3 For buildings with special requirements in the foundation design grades of Class A and Class B, the on-site water immersion load test shall be carried out according to the provisions of Appendix C of this code;
4 Provide suggestions on foundation design and construction scheme, prevention and control measures of adverse geological effects, etc.
4.1.5 The layout of exploration points, hole depth and soil sample collection shall meet the following requirements.
1 The arrangement of exploration points and the control drilling depth shall be determined according to the terrain and geomorphic conditions and the design level of the foundation. The drilling depth shall not be less than the atmospheric influence depth, and the control 5m;
2 The exploration points for taking undisturbed soil samples shall be arranged according to the foundation design level, landform unit and foundation soil expansion and contraction level, and the number shall not be less than 1/2 of the total number of exploration points; in the detailed investigation stage, the foundation design level shall be Class A The buildings should not be less than 2/3 of the total number of exploration points, and should not be less than 3 exploration points;
3 The undisturbed soil samples should be taken from 1m below the surface, and one piece of soil sample should be taken every 1m from 1m below the surface to the atmospheric influence depth; where there are obvious changes in the soil layer, it is advisable to increase the number of soil samples; below the atmospheric influence depth, take soil The spacing may be 1.5m to 2.0m.
4.1.6 When drilling, do not inject water into the hole.
4.2 Engineering characteristic index
4.2.1 The free expansion rate test shall be carried out in accordance with the provisions in Appendix D of this code. The free expansion rate of expansive soil should be calculated according to the following formula.
(4.2.1)
In the formula. - free expansion rate of expansive soil (%);
——the volume of the soil sample after swelling and stabilizing in water (mL);
——The original volume of the soil sample (mL).
4.2.2 The expansion rate test shall be carried out in accordance with the provisions of Appendix E and Appendix F of this code. The expansion rate of expansive soil under a certain level of load should be calculated according to the following formula.
(4.2.2)
In the formula. ——expansion rate of expansive soil under a certain level of load (%);
——The height of the soil sample after swelling and stabilizing in water under a certain level of load (mm);
——The original height of the soil sample (mm).
4.2.3 The expansion force test shall be carried out in accordance with the provisions of Appendix F of this code.
4.2.4 The shrinkage coefficient test shall be carried out in accordance with the provisions of Appendix G of this code. The shrinkage coefficient of expansive soil should be calculated according to the following formula.
(4.2.4)
In the formula. - shrinkage coefficient of expansive soil;
——the difference in vertical line shrinkage corresponding to the difference between the linear change stage and the water content difference between two points during the shrinkage process (%);
——The difference of water content between two points in the linear change stage during the shrinkage process (%).
4.3 Site and foundation evaluation
4.3.1 Site evaluation should ascertain the distribution of expansive soil and topographic and geomorphic conditions, and comprehensively evaluate the construction site based on engineering geological characteristics, soil expansion potential and foundation expansion and contraction grades, and evaluate engineering geology and soil The expansion potential and foundation expansion and contraction grades are divided into divisions.
4.3.2 The classification of construction sites shall meet the following requirements.
1 The terrain slope is less than 5°, or the slope top area with a terrain slope of 5°-14° and a horizontal distance from the shoulder of the slope is greater than 10m, shall be a flat site;
2 A site with a terrain slope greater than or equal to 5°, or a site with a terrain slope of less than 5° and a local terrain height difference within the same building range greater than 1m, shall be a slope site.
4.3.3 The site has the following engineering geological characteristics and building damage patterns, and the cohesive soil whose free expansion rate is greater than or equal to 40% should be judged as expansive soil.
1 The cracks in the soil are developed, often with smooth surfaces and scratches, and some cracks are filled with grayish-white, gray-green and other variegated clay. Hard or hard plastic under natural conditions;
2 Most of them are exposed on terraces of second grade or above, piedmont and hilly areas at the edge of basins. The terrain is relatively gentle, without obvious natural steepness;
3 Shallow landslides and ground fissures are common. The newly excavated pit (trough) wall is prone to collapse and other phenomena;
4 Most of the buildings are "upside-down characters", "X" or horizontal cracks, which open and close with climate change.
4.3.4 The expansion potential of expansive soil shall be classified according to Table 4.3.4.
Table 4.3.4 Classification of expansion potential of expansive soil
4.3.5 The expansive soil foundation shall be evaluated according to the degree of influence of foundation expansion and contraction deformation on low-rise masonry buildings, and the expansion and contraction grade of the foundation may be graded according to Table 4.3.5 according to the graded deformation of the foundation.
Table 4.3.5 Expansion and shrinkage grades of expansive soil foundation
4.3.6 The graded deformation of the foundation should be determined according to the deformation characteristics of the expansive soil foundation, and can be calculated according to the formula (5.2.8), formula (5.2.9) and formula (5.2.14) of this code respectively, where the expansion rate of the soil It should be determined according to the test in Appendix E of this specification.
4.3.7 The characteristic value of foundation bearing capacity can be comprehensively determined by methods such as load test or other in-situ tests combined with engineering practice experience, and shall meet the following requirements.
1 The important buildings with heavy loads should be determined by field immersion load test in Appendix C of this code;
2 In areas where a large amount of test data and engineering experience are available, it can be determined according to local experience.
4.3.8 The horizontal swelling force of expansive soil can be determined according to test data or local experience.
5 designs
5.1 General provisions
5.1.1 The design of buildings on expansive soil foundations should follow the principles of prevention first and comprehensive management. When designing, it should be based on the engineering geological characteristics of the site, hydrometeorological conditions and the design level of the foundation, combined with local experience, pay attention to the general plane and vertical layout, and adopt measures to eliminate or reduce the expansion and contraction deformation of the foundation and adapt to the uneven deformation of the foundation. The architectural and structural measures; and the construction and maintenance management requirements should be specified in the design documents.
5.1.2 The foundation design of the building shall take corresponding measures according to the adaptability of the building structure to the uneven deformation of the foundation. Buildings with graded deformation of the foundation less than 15mm and built on low-lying sites with high groundwater levels all year round can be designed according to general foundations.
5.1.3 The earth pressure of the exterior wall of the basement shall take into account the effect of the horizontal expansion force at the same time.
5.1.4 For high-temperature structures such as chimneys, furnaces and kilns, and low-temperature buildings such as cold storage, heat insulation measures should be taken according to the degree of possible deformation damage.
5.1.5 In the seismic fortification area, the building and structural prevention and control measures shall meet the seismic structural requirements at the same time.
5.2 Foundation calculation
Ⅰ Embedded depth of foundation
5.2.1 The embedding depth of the building foundation on the expansive soil foundation shall be determined based on the following conditions.
1 venue type;
2 expansion and shrinkage grade of expansive soil foundation;
3 The atmosphere affects the depth of the sharp layer;
4 The structural type of the building;
5 The magnitude and nature of the load acting on the foundation;
6 The purpose of the building, whether there is a basement, equipment foundation and underground facilities, foundation form and structure;
7 Foundation buried depth of adjacent buildings;
8 The influence of groundwater level;
9 Foundation stability.
5.2.2 The embedding depth of the foundation of the building on the expansive soil foundation shall not be less than 1m
5.2.3 For multi-storey buildings on a flat site, when the foundation burial depth is taken as the main prevention and control measure, the minimum burial depth of the foundation should not be less than the depth of the layer affected by the atmosphere; for slope land, it can be determined according to Article 5.2.4 of this code; When the ground has special requirements on deformation, it should be determined through the calculation of foundation expansion and contraction deformation, and other measures should be taken if necessary.
5.2.4 When the slope angle of the slope is 5°~14°, and the horizontal distance from the outer edge of the foundation to the slope shoulder is 5m~10m, the buried depth of the foundation (Figure 5.2.4) can be determined according to the following formula.
d=0.45da (10－lp)tanβ 0.30 (5.2.4)
In the formula. d - foundation embedding depth (m);
da——atmospheric influence depth (m);
β——design slope angle (°);
lp—horizontal distance from the outer edge of the foundation to the slope shoulder (m).
Figure 5.2.4 Calculation diagram of buried depth of foundation on slope
Ⅱ Bearing capacity calculation
5.2.5 The pressure on the bottom surface of the foundation shall meet the following requirements.
1 When the axial load acts, the pressure on the bottom surface of the foundation shall meet the requirements of the following formula.
pk≤fa (5.2.5-1)
In the formula. pk—corresponding to the standard combination of load effects, the average pressure value at the bottom of the foundation (kPa);
fa—the corrected characteristic value of the bearing capacity of the foundation (kPa).
2 When the eccentric load acts, the pressure on the bottom surface of the foundation shall not only meet the requirements of the formula (5.2.5-1), but also meet the requirements of the following formula.
pkmax≤1.2fa (5.2.5-2)
In the formula. pkmax—corresponding to the standard combination of load effects, the maximum pressure value (kPa) at the edge of the bottom surface of the foundation.
5.2.6 The corrected characteristic value of the bearing capacity of the foundation shall be calculated according to the following formula.
fa=fak+γm(d－1.0) (5.2.6)
In the formula. fak - characteristic value of foundation bearing capacity (kPa), determined according to the provisions of Article 4.3.7 of this code;
γm——the weighted average weight of the soil above the foundation bottom, and the buoyant weight below the groundwater level.
Ⅲ Deformation Calculation
5.2.7 The deformation of expansive soil foundation can be calculated according to the following deformation characteristics.
1 The water content of the soil at 1m below the natural surface of the site is equal to or close to the minimum value or the ground is covered and has no possibility of evaporation, and the foundation that is often wetted by water during the use of the building can be calculated according to the amount of expansion and deformation;
2 The water content of the soil 1m below the natural surface of the site is greater than 1.2 times the water content of the plastic limit or the foundation directly affected by high temperature can be calculated according to the amount of shrinkage deformation;
3 In other cases, it can be calculated according to the expansion and contraction deformation.
5.2.8 The expansion and deformation of foundation soil shall be calculated according to the following formula.
(5.2.8)
In the formula. ——expansion and deformation of foundation soil (mm);
——The empirical coefficient for calculating the expansion and deformation should be determined according to the local experience. When there is no experience to rely on, 0.6 can be used for buildings with three floors or less;
——The expansion rate (in decimals) of the i-th layer of soil under the bottom surface of the foundation under the action of the sum of the average self-weight pressure and the average additional pressure corresponding to the quasi-permanent combination of the load effect, determined by indoor tests;
——calculated thickness of the i-th layer of soil (mm);
——The number of soil layers divided from the bottom surface of the foundation to the gauge depth, and the calculation depth zen of expansion deformation (Figure 5.2.8), shall be determined according to the depth of atmospheric influence, and may be determined according to the depth of influence of water immersion when there is a possibility of water immersion;
Figure 5.2.8 Calculation diagram of expansion and deformation of foundation soil
1 - self-weight pressure curve; 2 - additional pressure curve
5.2.9 The shrinkage and deformation of foundation soil shall be calculated according to the following formula.
(5.2.9)
In the formula. Ss—shrinkage and deformation of foundation soil (mm);
——The empirical coefficient for calculating the amount of shrinkage and deformation should be determined according to local experience. When there is no basis for experience, 0.8 can be used for buildings with three floors or less;
——The shrinkage coefficient of the i-th layer of soil under the bottom surface of the foundation, determined by the indoor test;
——In the process of foundation soil shrinkage, the average value of water content change (expressed in decimals) that may occur in the i-th layer of soil, calculated according to the formula (5.2.10-1) of this code;
——The number of soil layers divided from the bottom surface of the foundation to the calculation depth, and the calculation depth zsn of shrinkage deformation (Figure 5.2.9), shall be determined according to the depth of atmospheric influence; when there is heat source influence, it may be determined according to the depth of heat source influence; When there is a stable groundwater level inside, it can be calculated up to 3m above the water level.
Figure 5.2.9 Schematic diagram of water content change calculated by foundation soil shrinkage deformation
5.2.10 The water content change value of each soil layer within the calculation depth of shrinkage deformation (Fig. 5.2.9) shall be calculated according to the following formula. When there is impermeable bedrock at a depth of 4m below the surface, the change in water content can be assumed to be constant [Fig. 5.2.9(b)].
(5.2.10-1)
(5.2.10-2)
In the formula. —— the water content change value of the i-th layer of soil (expressed in decimals);
——The water content change value of the soil at 1m below the surface (expressed in decimals);
, - the natural water content and plastic limit of the soil at 1m below the surface (expressed in decimals);
——Soil moisture coefficient, under the influence of natural climate, the ratio of the minimum value of the moisture content of the soil layer 1m below the surface to its plastic limit.
5.2.11 The humidity coefficient of the soil should be determined according to the change of the local soil moisture content over 10 years. If there is no data, it can be calculated according to the following formula according to the relevant local meteorological data.
(5.2.11)
In the formula. ——the ratio of the sum of the local evaporative power from September to February of the following year to the annual evaporative power (months with monthly average temperature less than 0°C are not included in the statistics). The reference values of evapotranspiration and precipitation in some areas of my country can be taken according to Appendix H of this specification;
c——The sum of the difference between evaporation and precipitation in the month with the dryness greater than 1.0 and the monthly average temperature greater than 0°C (mm), where the dryness is the ratio of evaporation to precipitation.
5.2.12 Atmospheric influence depth should be measured by deep deformation observation or water content observation of soil in each climate zone...
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