JGJ 72-1990 Code for Geotechnical Engineering Investigation of High-Rise Buildings JGJ72-90
Some standard content:
Industry Standard of the People's Republic of China
Survey Regulation
JGJ72--90
Editor: Survey Institute of the Ministry of Machinery and Electronics Industry Approval Department: Ministry of Construction of the People's Republic of China Ministry of Machinery and Electronics Industry Effective Date: August 1, 1991
4--10-1
Notice on the Release of Industry Standard "Geotechnical Survey Regulation for High-Rise Buildings"
Construction Standard (1991] No. 87
According to the requirements of the 1986 document No. 86-1 of the former Ministry of Machinery Industry, the "Geotechnical Survey Regulation for High-Rise Buildings" edited by the Survey Institute of the Ministry of Machinery and Electronics Industry has been reviewed and approved as an industry standard, numbered JGJ72--90, and will be implemented on August 1, 1991.
This standard is under the unified management of the Ministry of Construction and is under the supervision of the Ministry of Machinery and Electronics Industry. The Ministry of Construction Survey and Research Institute is responsible for interpretation. This standard is published and distributed by the Standard and Quota Research Institute of the Ministry of Construction. Ministry of Construction of the People's Republic of China
Ministry of Machinery and Electronics Industry of the People's Republic of China December 30, 1990
Chapter 1
Chapter 2
Chapter 3
Section 1
Section 2
Chapter 4
Chapter 5
Chapter 6
Basic Provisions| |tt||Survey plan layoutbzxZ.net
Natural foundation
—10—4
4—10—4
4—10—5
4—10—5
4—10—6
In-situ testing and monitoring. 4—10-·
Indoor testing
·4—10—7
Geotechnical engineering evaluation and calculation4—10--7
..... 4107
Section 1 Site stability evaluation
Section 2
Natural foundation evaluation and calculation. 4—10—7Section 3 Pile foundation evaluation and calculation. 4—10—10 times
Chapter 7
Appendix 2
Appendix 3
Appendix 4
Appendix 5
Appendix 6
Appendix 7
Geotechnical engineering investigation report
.. 4--10-11
Ultimate bearing capacity N., Ng, N.
Coefficient table
Electric bearing capacity
Electric bearing capacity
....... 4--10--12
Average additional pressure coefficient…4--10-12
Press E. Coefficient for calculating settlement
Vertical bearing capacity table of precast piles
Vertical bearing capacity table of cast-in-place piles
Key points of deep well load test
Terms used in this regulation
Additional explanation
4—-10—14
.. 4--10-15
... 4--10—15
.... 4-1016
.. 4--10--16
4--10—16
4—10--3
Main symbols
Foundation bottom area,
Cross-sectional area of pile body;
Compression coefficient:
Foundation bottom surface width,
Cohesion
Compression index of soil,
Rebound index of soil;
Controlled exploration point depth:
General exploration point depth,
-foundation burial depth or pile body diameter;
Compression modulus of soil;
Deformation modulus of soil,
Aperture ratio!
Design value of foundation bearing capacity;
Basic value of foundation bearing capacity,
Standard value of foundation bearing capacity,
. ——The ultimate bearing capacity of the foundation calculated by the ultimate bearing capacity formula, -The design value of the foundation bearing capacity calculated by the control plastic zone formula; the friction resistance of the side wall of the double bridge static penetration probe f.
H,———The building height from the outdoor ground, -The length of the building;
Pile length. Segmented pile length or foundation length, p
The design value of the average pressure at the bottom of the foundation;
—The initial consolidation pressure of the soil,
The additional pressure at the bottom of the foundation,
The specific penetration resistance of the single bridge static penetration test
The deadweight pressure of the soil
The resistance of the double bridge static penetration probe,
The standard value of the bearing capacity of the soil at the pile end
The standard value of the friction of the soil around the pile
Single pile Standard value of vertical bearing capacity
settlement,
predominant period of site soil;
length of the perimeter of the pile body;
U,——shear wave velocity;
depth of the main bearing layer;
correction coefficient of pile end resistance;
adjustment coefficient, reduction coefficient or correction coefficient: -gravity density of soil
——internal reservoir core angle
——empirical coefficient of settlement calculation.
Chapter 1 General
Section 1.0.1 This code is specially formulated to implement relevant national technical and economic policies, improve the technical level of geotechnical engineering investigation of high-rise heritage buildings, unify the technical standards of investigation, and ensure the safety and normal use of building foundations. Article 1.0.2 This code is applicable to geotechnical investigation of high-rise buildings with less than 8 floors and less than 1:50 floors, important structures with a height of more than 5mm and less than 100m, and high-rise structures with a height of more than 100m and less than 300m. Article 1.0.3 When conducting geotechnical investigation of commercial buildings, it is necessary to attach importance to regional experience, collect data extensively, understand the design intent in detail, conduct careful investigation, and make reasonable evaluation to meet the requirements of geotechnical engineering design, and propose a foundation plan and geotechnical investigation report that is technologically advanced, economically reasonable, and feasible. Article 1.0.4 When adopting this code, it shall comply with the provisions of the current relevant national standards and specifications.
Chapter II Basic Provisions
Element 2.0.1 According to the safety classification principles of the Code for Design of Building Foundations, the classification of high-rise buildings shall be determined in accordance with Table 2.0.1: Standards for Classification of Safety Classes of High-Rise Buildings
Safety Class
Consequences of Alkali Damage
Severe Damage
Building Types
High-rise buildings of 20 floors and above, high-rise buildings of 14 floors and above with complex shapes: important structures of 75m and above, high-rise structures of 150m and above, high-rise buildings of 20 floors, high-rise buildings with complex shapes less than 14 floors, and buildings less than 75 m: high-rise buildings below 150m. When the site has insufficient survey data, and the safety grade of the high-rise building is level one or a high-rise building complex, its geotechnical engineering survey is divided into two stages: preliminary survey and detailed survey. The preliminary survey stage should evaluate the stability of the site and foundation, demonstrate and propose suggestions for the selection of foundation schemes, and the detailed survey stage should make a detailed review of the site engineering geological conditions, and provide economically reasonable schemes and required detailed information for foundation design and foundation treatment. When the site has sufficient data and it is a single level two high-rise building, the two stages can be combined into one stage, but the requirements of the two stages should be met at the same time. When the foundation of a high-rise building is constructed, the survey unit should participate in the construction inspection. For areas with complex site engineering geological conditions, in addition to participating in the construction inspection, construction surveys should also be carried out when necessary.
Section 2.0.3 Before conducting a rock survey for a high-rise building, the design intent must be understood in detail, and the following information should be obtained: a general plan of the building with the coordinates or outlines of the four corners of the building, the indoor and outdoor floor elevations, and the original terrain and features; second, the building structure type, characteristics, number of floors, total height, total load (load combination conditions should be provided when conditions permit), underground facilities, waterproof and moisture-proof requirements, etc.; third, the expected foundation type, plane size, burial depth, and other special foundation design and construction requirements.
Section 2.0.4 Before conducting a survey, the existing survey data, existing construction experience, earthquake geological data, and site environmental history data of the site and its adjacent areas should be collected and studied in detail.
Section 2.0.The main issues that should be addressed in geotechnical engineering investigations for high-rise buildings are:
, determine whether there are adverse geological phenomena in and around the construction site that may affect the stability of the project, such as determining the stability of new active faults, ground fissures, karst (caves, karst trenches, karst troughs, etc.), landslides and steep slopes, and investigate whether there are ancient river channels, dark ponds, artificial caves or other artificial underground facilities; in strong earthquake zones, it should be determined whether there are liquefiable strata and an evaluation should be made of the possibility of liquefaction, determine the site soil type and construction site category, and provide relevant data for seismic design; second, determine the stratum structure and uniformity of the construction site, especially the weak ground under the foundation. The distribution of layers and hard strata, as well as the physical and mechanical properties of each layer of rock and soil,
Third, find out the type of groundwater, burial conditions, permeability, corrosiveness and seasonal variation of groundwater level; judge the possibility of excavation of foundation pits to reduce groundwater and the impact on existing adjacent buildings, provide relevant information on lowering groundwater levels, and propose a dewatering plan when necessary,
Fourth, for high-rise buildings suitable for natural foundations such as Xiao-type foundations or box foundations, it is necessary to focus on finding out the distribution of soil layers in the bearing layer and main load-bearing layer, evaluate and predict their bearing capacity and deformation characteristics, provide the applicable bearing capacity and perform deformation calculations. Demonstrate and analyze the foundation design plan, propose an economically reasonable plan, and make suggestions on issues that should be paid attention to in the design and construction of the superstructure and foundation. When necessary, propose the slope and support scheme for deep foundation pit excavation.
5. For high-rise buildings suitable for the use of various types of piles and pier foundations, economically reasonable pile foundation types should be recommended according to site conditions and construction conditions, and reasonable pile tip bearing layers should be selected. The distribution of bearing layers and weak underlying layers should be investigated in detail. The friction around piles and the pile end bearing capacity of the bearing layers should be proposed in layers. The bearing capacity of single piles and the bearing capacity and settlement verification when pile groups are regarded as solid foundations should be estimated. For precast piles, the possibility of pile sinking and the impact on adjacent buildings should be determined, and suitable construction equipment should be recommended; suitable construction methods should be recommended for cast-in-place piles, and issues that should be paid attention to during construction should be proposed.
6. For first-level high-rise buildings, settlement observations must be carried out; for foundations with large buried depths or close to adjacent buildings and pipelines, monitoring of foundation pit rebound, deformation of foundation pit slopes, or uplift of the surrounding ground when driving (pressing) piles, and vibration effects should be carried out. If shallow and deep foundation treatments are used, comparative inspections of the foundations before and after treatment should be carried out.
The geotechnical engineering investigation work to solve the above problems can be carried out once or in stages according to the actual situation.
Article 2.0.6 When calculating the bearing capacity of the foundation, the load effect transmitted to the bottom surface of the foundation should be based on the basic combination; the self-weight of the soil is calculated according to the actual gravity density; when calculating the deformation of the foundation, the load transmitted to the bottom surface of the foundation should be combined according to the long-term effect, and the wind load and ground action should not be considered.
Chapter 3
Layout of Investigation Plan
Section 1 Natural Foundation
Article 3.1.1 The plane layout of the exploration points should take into account the distribution of the building body load, the stratum structure and uniformity, especially the stratum uniformity that should be satisfied to evaluate the lateral inclination of the building. The following provisions shall be met during layout: 1. For each single-unit first-level high-rise building, the number of exploration points shall not be less than 6, and for second-level high-rise buildings, the number shall not be less than 4. 2. When the plane of the building is rectangular, it is advisable to arrange it in double rows. When it is irregular, it is advisable to arrange it according to the corners and center points of the protruding parts. 3. In places where the number of floors, loads and building shapes vary greatly, an appropriate number of exploration points shall be arranged.
4. The spacing between exploration points is generally 15 to 35m. A smaller value may be taken for first-level high-rise buildings and a larger value may be taken for second-level high-rise buildings. In order to accurately identify abnormal zones such as culverts, ponds and streams, the spacing between exploration points may be appropriately increased. 5. In areas with developed karst, the number of exploration points shall be appropriately increased. If necessary, exploration points may be arranged under each column base. In areas with granite residual soil, the spacing between exploration points may take the smaller value of the four clauses of this article.
6. For the needs of precipitation design, special exploration points for identifying groundwater filtration rate, flow direction and testing of hydrogeological parameters shall be arranged as necessary.
VII. The number of control exploration points should be 1/2 of the total number of exploration points. Article 3.1.2 The depth of exploration points should comply with the following provisions: 1. The depth of control exploration points should be appropriately greater than the calculated depth of the foundation compression layer. For box foundations or raft foundations, it can be calculated and determined by the following formula: d, = d + ab
Where d is the depth of control exploration points (m); (3.1.2-1)
——The buried depth of box foundation or raft foundation (m): α. -——The empirical coefficient related to the compressibility of the soil, which is taken according to Table 3.1.2 based on the main soil layer under the foundation,
6—The width of box foundation or compound foundation, for circular foundation or ring plate foundation, it is considered according to the maximum diameter, and for irregular foundations, it is considered according to the width or diameter equivalent to the area of square, rectangle or circle (m).
The depth of the general exploration point should be appropriately greater than the depth of the main stress-bearing layer. For box foundation or Xiao-type foundation, it can be calculated and determined according to the following formula: dg =d+αgb
(3.1.2-2)
-The depth of the general exploration point (m);
where dg
is the empirical coefficient related to the compressibility of the soil, and the value is taken according to Table 3.1.2 based on the ag
main soil layer under the foundation.
Empirical coefficient α. ,α. Value
Gravel, soil and sand
0. 5~ 0.7 0. 7
0. 3 ~ 0. 4
Table 3.1.2
Clay soil
Including yellow soil)
~0.50.5 ~0.70. 6~ 0.9
Note: The range values in the table take the smaller value as the value for the same soil type that is old, dense or has a deep groundwater table, and take the larger value otherwise.
3. For extended foundations, the depth of the exploration point shall comply with the provisions of the detailed exploration stage of the current "Geotechnical Engineering Investigation Code"; 4. For general exploration points, when there is a relatively stable hard stratum (such as gravel soil) with a thickness of more than 3.0m within the predetermined depth range, it is sufficient to drill into the layer to an appropriate depth to correctly name and determine its nature. The weak stratum should be appropriately deepened or drilled through.
5. In areas with shallow karst development, when the thickness of the soil layer under the bottom of the foundation is less than the calculated depth of the foundation compression layer, general drilling holes should reach the complete bedrock surface, and controlled drilling holes or drilling holes specifically for identifying karst caves should be 3~5m deep into the complete bedrock or 3~5m deep into the complete bedrock at the bottom of the cave.
6. In granite residual soil areas, when it is a box foundation or a Xiao-type foundation, when calculating the depth of the exploration point, its α. and α coefficient, for residual gravelly clay and residual sandy clay, it can be determined according to the value of silt in Table 3.1.2, and for residual clay, it can be determined according to the value of clay in Table 3.1.2. When encountering bedrock within the predetermined depth, the control hole should be deep into the strong weathering zone (the number of hits measured in the standard penetration test is greater than 50) by not less than 1.0m, and the general exploration point can reach the strong weathering rock surface. VII. The depth of drilling holes that need to evaluate the collapsibility of loess, sand liquefaction, site excellence cycle, as well as to find out the permeability of groundwater, or other special purposes, shall be specially determined according to the requirements of relevant specifications. Article 3.1.3 The number of exploration points and the amount of soil taken for soil sampling and in-situ testing shall comply with the following provisions. 1. The number of exploration points for soil sampling and in-situ testing shall not be less than 2/3 of the total number of exploration points. When it is necessary to calculate the slope, there shall be soil sampling holes at the four corner points. 2. The number of soil samples taken for mechanical indicators in each main soil layer under each building and each test data shall meet the requirements specified in Table 3.1.3: 4-10-5. 3. For the calculation of the stability of the basement side wall and foundation pit slope or the design of anchor rods, no less than 6 pieces (groups) of soil samples shall be taken in the main soil layer above the basement.
Number of soil samples and in-situ tests for each main soil layer
Undisturbed soil bomb (number, groups)
In-situ test (times)
Within the bearing layer
Bottom of bearing capacity
Main bearing capacity
Table 3.1.3
Main bearing capacity below
Note: ①The depth of the main bearing layer (z.), calculated by z,=a,b③The in-situ measurement range in this table only refers to; cross plate shear test, transverse compression test or standard penetration test
②For shear test, the number of undisturbed soil samples is (groups)①The number in the table is taken for the first-level high-rise building, and for the second-level high-rise building. Section 2 Piles
Section 3.2.1 Pile foundations The pile foundations referred to in this section only include reinforced concrete precast piles commonly used in high-rise buildings and various types of concrete cast-in-place piles and piers. Section 3.2.2. The layout of exploration points in the plane should comply with the following provisions: 1. For end-bearing piles, piers or piles with end bearing as the main force, when the pile foundation is under the extended foundation, the exploration points should be arranged according to the column line, and the spacing should be controlled. Generally, it is 12 to 24 meters. When the slope of the bearing layer exposed by adjacent exploration points exceeds 10%, the exploration points should be increased.
2. For friction piles or piles with friction as the main force, and pile groups under raft foundations or box foundations, the spacing of exploration points can be considered as 20 to 35 meters, but when the slope of the soil layer exceeds 10% and the soil properties change greatly, the exploration points should be appropriately increased. 3. For large-diameter (diameter ≥ 800mm) piles or extended-bottom piers, when the geological conditions change greatly, it is advisable to arrange an exploration point at each (pier) position. 4. Among the total number of exploration points, more than 173 exploration points should be controlled exploration points.
Article 3.2.3 The depth of the exploration point shall comply with the following provisions: 1. For end-bearing piles or piles (piers) that are mainly end-bearing, the depth of the control exploration point shall be 3~5m below the expected pile tip plane or 6~10 times (the smaller value for large-diameter piles or piers, the larger value for small-diameter piles) the width or diameter of the pile body, and the general exploration point shall be 1~2m deep into the expected bearing layer. For the bedrock bearing layer, the depth of the control exploration point shall be 3~5m deep into the slightly weathered zone, and the general exploration point shall be 1~2m deep into the slightly weathered zone. If a fault fracture zone is encountered, it shall be drilled through and enter the relatively intact rock mass 3~5m.
2. For friction piles or piles dominated by friction, the depth of the control exploration point should exceed the expected pile length by 3~5m, and the general exploration point should exceed the expected pile length by 1~2m. When it is necessary to calculate the deformation of the pile group, the pile group can be regarded as an imaginary solid foundation. The depth of the control exploration point should exceed the depth of the compression layer calculated from the pile tip plane. The depth of the compression layer can be considered as (1~2)b (b is the width of the imaginary solid foundation), or it can be calculated as the ratio of additional pressure to soil self-weight pressure of 20%. When encountering incompressible hard strata within this depth, the exploration can be terminated. 3.2.4 For each main soil layer within the depth range of the pile foundation exploration, soil samples should be taken and in-situ tests such as static penetration test, standard man test, cross plate shear test, etc. should be carried out. The amount of soil taken and the number of tests under each standard building should meet the requirements of Table 3.2.1.
4—10—6
Number of samples and in-situ tests for each main soil layer
Undisturbed soil samples (pieces, groups)
In-situ tests (times)
Strength layer
Note: In this table, in-situ tests refer only to shear tests on slabs and standard penetration tests for transverse compression. (②For shear tests, the number of undisturbed soil samples is (groups). ③The number in the table takes the larger value for first-level high-rise buildings and the smaller value for second-level high-rise buildings. Chapter 4 In-situ testing and monitoring
Shear 4.0.1 Article 4.0.2 In order to determine the uniformity of the strata, measure the bearing capacity and deformation characteristics of the foundation soil, predict the bearing capacity of a single pile, and determine the possibility of pile sinking, single-bridge or double-bridge static penetration tests may be carried out in sandy soil or clay soil without gravel. Article 4.0.3 In order to determine the possibility of liquefaction of sandy soil or silt, a certain number of standard penetration tests may be carried out to measure the bearing capacity of sandy soil or silt, and a small number of boreholes should be selected to conduct penetration tests continuously from top to bottom at a certain interval. Heavy or super-heavy dynamic penetration tests may be carried out to measure the bearing capacity of silt, sandy soil and gravel soil.
Article 4.0.3 In order to measure the bearing capacity of soft soil foundation and the friction and end bearing capacity of piles, ten Shear test on a slab. Article 4.0.4 To measure the bearing capacity and deformation of clay, silt and sand, transverse compression tests can be carried out in layers. Article 4.0.5 To meet the needs of construction dewatering design or basement design, it is advisable to carry out pumping tests or water injection tests on appropriate wells and holes on site to measure the permeability coefficient of the stratum (if necessary, the horizontal and vertical permeability coefficients should be measured separately). When necessary, it is also necessary to measure the flow direction and velocity of groundwater. Article 4.0:6 To determine the site soil type, site category, excellent period and other parameters required for anti-exposure design for seismic design, velocity or ground micro-motion tests can be carried out.
Article 4.0.7 For first-class high-rise buildings, in order to determine The bearing capacity and deformation modulus of the fixed bearing layer or the main bearing layer can be determined by a flat plate load test. When the strong or moderately weathered bedrock is used as the bearing layer, it is impossible to take samples for the saturated uniaxial compressive strength test. A rock mass load test can be carried out to directly determine the rock mass bearing capacity. The test key points should comply with the provisions of the current "Code for Design of Building Foundations". Section 4.0.8 For one-story buildings, the single bearing capacity should be determined by on-site static shear load test, and the number of test piles should not be less than 3; when the horizontal load is large, a horizontal thrust load test should be carried out, and the number of test piles should not be less than 2. The end bearing capacity of the expanded base pier should be determined by a deep parallel load test. The test key points are shown in Appendix 6. For the first-level For high-rise buildings, if conditions permit, a prototype single pier bearing capacity test can be conducted.
Article 4.0.9 For non-destructive inspection of pile body quality, dynamic measurement method or other effective methods can be used. The number of piles to be tested should not be less than 10% of the total number of piles. Sufficient static load test comparison data must be available to determine the bearing capacity of a single pile by dynamic measurement method. Article 4.0.10 When the foundation pit is deep and the area is large, it is advisable to conduct foundation pit unloading rebound observation. For high-rise buildings, settlement observation should be conducted. The observation work should start from the completion of the foundation bottom surface construction until the settlement is stable. The instruments, observation methods and settlement stability standards used for settlement observation should meet the requirements of relevant special regulations.
Article 4.0.11 In order to consider the impact of foundation pit excavation, pile foundation construction or other foundation treatment construction on adjacent existing buildings, monitoring work should be carried out on slope displacement (or deformation), pore water pressure changes, and pile driving dynamic effects. Chapter 5 Indoor Tests
Article 5.0.1 This chapter only includes the test requirements of special indoor test items in the geotechnical engineering investigation of high-rise buildings. The test requirements of conventional test items shall still be carried out in accordance with the current relevant specifications and regulations. Article 5.0.2 The shear test required for calculating the bearing capacity of the foundation shall comply with the following provisions:
1. The soil samples taken should pay attention to maintaining the original structure of the soil. For first-level high-rise buildings, triaxial shear tests should be used when the stratum is cohesive soil. The test should adopt a variety of methods: For second-level high-rise buildings, direct shear can be used when the stratum is plastic cohesive soil and silt with a saturation of less than 0.5. The number should comply with the provisions of Table 3.1.3.
2. The method of shear test should be selected according to the calculation method adopted, the construction rate and the drainage conditions of the soil, so as to conform to the actual stress conditions of the building as much as possible. In general, unconsolidated undrained shears can be used for soils with fast construction speed and poor drainage conditions, and consolidated undrained shears can be used for soils with slow construction speed and good drainage conditions, but the degree of possible consolidation of the foundation under the building load and preload should be considered.
3. The results of the triaxial shear test should provide the Mohr circle and its strength envelope. Section 5.0.3 is a compressibility index for calculating foundation settlement. According to different calculation methods, the following test methods can be used: 1. When the compression modulus of the general uniaxial compression test is used to calculate the settlement according to the layered summation method, its maximum pressure value should exceed the expected sum of the soil self-weight pressure and the additional pressure. The compression coefficient should take the compression coefficient and corresponding compression modulus of the pressure section from the soil self-weight pressure to the sum of the soil self-weight pressure and the additional pressure. Its value is calculated according to the following formula:
a= 1000-1-e:
αCompression coefficient (MPa-),
F. 1. Compression modulus (MPa),
(5.0.2-1)
(5.0.2-2)
1. The soil self-weight pressure and the sum of the self-weight pressure and the additional pressure, respectively. The values are rounded up according to the soil depth (kPa); the porosity ratios corresponding to the natural state and pl, p2, respectively. Fo. ef. e2
When it is necessary to consider the situation of excavation unloading and reloading, a rebound and repulsion shrinkage test should be carried out. The vertical load should simulate the actual loading and unloading situation. The specific value is determined by the test design.
, When the consolidation settlement calculation considering the stress history is adopted, the maximum test pressure should meet the needs of drawing a complete e~logp curve. It should be increased until a long straight line segment appears. If necessary, it can be increased to 3000~5000kPa to obtain the initial consolidation pressure pe, compression index C. and rebound index C. The p. value can be determined by the card diagram method. The C. value may not be corrected. The rebound starting pressure of the C. value can be determined by rounding off the overlying deadweight pressure of the soil sample at different depths, and care should be taken not to affect the value of the p value. When the settlement rate needs to be considered, the consolidation coefficient Cvo should be measured.
Article 5.0.4 When the foundation pit excavation needs to use open ditches, well points or pipe wells to pump water to lower the groundwater level, the permeability test of the relevant soil layer should be carried out, and if necessary, the on-site pumping test should be carried out to meet the needs of the dewatering design. Article 5.0.5 For the shear test for verifying the stability of the slope and the support design of retaining walls, anchors, etc., it is advisable to use triaxial non-structured non-drained shear or direct shear.
Article 5.0.Article 6 When it is necessary to use strength indicators to estimate the bearing capacity of piles or to verify the deformation of pile groups, indoor tests should comply with the following provisions: 1. When it is necessary to estimate the ultimate friction resistance of the pile side, the triaxial unconsolidated undrained strength Cu and the median u value can be used,
2. When it is necessary to estimate the ultimate end bearing capacity of the pile, for clay soils, the consolidated undrained strength Cueu or the effective stress strength c' and Φ
can be measured in the pile tip bearing layer and the underlying layer. 3. When it is necessary to verify the deformation of pile groups, the compressibility indicators of the soil, namely the compression modulus, compression index, rebound index, etc., should be measured for the soil in the compression layer below the pile tip plane.
Chapter 6
Geotechnical Engineering Evaluation and Calculation,
Section 1
Market Site Stability Evaluation
Article 6.1.1 High-rise building sites should avoid shallowly buried (buried depth not exceeding 100m) new active faults. The avoidance distance should be determined based on the grade, scale and nature of the new active faults, basic earthquake intensity, thickness of the covering layer and engineering properties. High-rise buildings should also avoid areas where active ground fissures pass through. The avoidance distance and measures to be taken can be determined according to relevant regional regulations.
Article 6.1.2 The site stability of high-rise buildings located on slopes should be considered from the following points:
1. Buildings should not be placed on landslides; 2. High-rise buildings located on the top or the shore should consider the overall stability of the slope, and if necessary, the possibility of overall sliding should be verified. 3. When the slope is stable as a whole, it should also comply with the provisions of the current "Code for Design of Building Foundations" and verify the safe distance from the outer edge of the foundation to the top of the slope.
4. Consider the possibility of high and steep slopes around high-rise buildings sliding and determine the safe distance between the building and the foot of the slope.
Article 6.1.3 The site of a high-rise building should not be selected in a dangerous area for building earthquake resistance, and should avoid areas that are unfavorable for building earthquake resistance. When it is impossible to avoid unfavorable areas, protective and control measures should be taken. Article 6.1.4 In underground mining areas with the possibility of collapse, or areas with strong development of karst soil caves, foundation reinforcement measures should be considered. If it is considered undesirable after technical and economic analysis, another site should be selected.
Section 2 Evaluation and Calculation of Natural Foundation
Article 6.2.1 The evaluation and calculation of the natural foundation of high-rise buildings shall be determined according to the design requirements and actual needs, and generally include the following contents: 1. Analyze and evaluate the uniformity of the foundation.
2. Provide the basic value (in.) and standard value (k) of the foundation bearing capacity; according to the design requirements, calculate whether the bearing capacity of the foundation bearing layer and the underlying layer can meet the foundation bottom surface pressure requirements. When the requirements cannot be met, put forward suggestions for changing the foundation burial depth or bearing layer.
3. Calculate whether the average settlement of the building foundation exceeds the allowable value and whether its differential settlement or inclination meets the requirements, especially the impact of differential settlement between high-rise and low-rise, new and existing buildings. If necessary, a settlement analysis of the combined action of the foundation and the foundation or superstructure should be carried out. High-rise buildings and commercial structures are controlled by the allowable inclination value.||tt ||4. Evaluate the stability of the reverse slope of deep foundation excavation and its impact on adjacent buildings, provide the protective measures and relevant calculation parameters to be taken, and propose support plans such as anchor rods and sheet piles when necessary.
5. When the groundwater level is high, the possibility of dewatering construction should be evaluated, the parameters required for dewatering design should be provided, and a dewatering plan should be proposed when necessary. 6. Demonstrate and evaluate the technical and economic rationality of the foundation plan. When the natural foundation plan cannot be adopted, the suitability of other artificial foundation plans should be demonstrated and evaluated.
The uniformity of the foundation should be evaluated and evaluated from the following aspects: Article
Take corresponding measures:
When the slope of the foundation bearing layer is greater than 10%, it can be regarded as an uneven foundation. At this time, the foundation can be buried deeper to exceed the lowest depth of the bearing layer. When deepening the foundation is impossible, measures such as cushioning can be taken to adjust it. 2. When the difference in the thickness of the foundation bearing layer and the first underlying layer in the foundation width direction is less than 0.056 (b is the foundation width), it can be regarded as a uniform foundation. When it is greater than 0.05b, the lateral inclination should be calculated. Whether it meets the requirements, if not, structural or foundation treatment measures should be taken. 3. The uniformity of the foundation soil is evaluated based on the compression molds of each soil layer in the compression layer.
1. When the average value of E.. and E. is less than 10MPa, the one that meets the following requirements is a uniform foundation.
(6.2.2-1)
2. When the average value of E.1 and E.: is greater than 10MPa, the one that meets the following requirements is a uniform foundation.
.1-B<2(B++ E,t)
(6.2.2-2)
Wherein, E.1 and E——are the weighted average values of the compression modulus in the compression layer range according to the thickness in the two drilled holes in the width direction of the foundation (MPa), the larger one is E. and the smaller one is E. When the requirements of formula (6.2.2-1) or (6.2.2-2) cannot be met, it is an uneven foundation, and a lateral inclination verification should be carried out, and structural or foundation treatment measures should be taken.
Section 6.2.3 The assessment of the bearing capacity of the foundation should be based on the principle of simultaneously satisfying the ultimate stability and not exceeding the allowable deformation. It should be determined comprehensively by load tests, theoretical formula calculations and other in-situ test methods in combination with local construction experience. When calculating with theoretical formulas, the lower value of the following two formulas can be taken. The ultimate bearing capacity can be calculated according to the following formula:
fu=N,stby+N.5ayod+N.seck
N..N., N.-
Ultimate bearing capacity (kPa)
(6.2.3-1)
-Bearing capacity coefficient, determined according to the standard value of the internal friction angle of the soil below the bottom of the foundation, check Appendix 1;
Foundation shape coefficient, determined according to Table 6.2.3-1.
, ... For basements, if box foundation or small foundation is adopted, the foundation burial depth is calculated from the outdoor ground. In other cases, it should be calculated from the indoor ground.
— Standard value of the adhesive force in the bearing layer under the base (kPa); Ck
4-10—-8
Foundation form
■ shape and square
Foundation shadow coefficient
I+tang
Table 6.2.3-1
The design value of foundation bearing capacity f is obtained by dividing the ultimate bearing capacity by the safety factor K. The K value is selected within the range of K = 2 to 3 according to factors such as the importance of the building, the severity of the consequences of damage, and the credibility of the test data. Second, the foundation bearing capacity can also be calculated according to the following formula: f, - k.(Mrykrb+ Mayod + M.Ch)(6.2.3-2)
Design formula for foundation bearing capacity calculated by the formula for controlling plastic zone
value (kPa),
-bearing capacity coefficient, determined according to Table 6.2.3-2 based on the standard value of the internal friction angle of the soil below the bottom of the foundation; bearing capacity coefficient M., MM.
Standard value of the internal friction angle of the soil.
Table 6.2.3-2
-structural measurement coefficient, determined according to the length-to-height ratio of the building L/H. According to Table 6.2.3-3;
k—coefficient, when b<10m, take =1, when b≥10m, take kb=
The other symbols are the same as before.
Structural measurement coefficient table 1
Frozen, H
Clay and
" Fine sand, silt sand
Case 6.2.3-3
Silt soil and clay
11≤0.25
is the building height (m) calculated from the outdoor ground (excluding the elevator sound of the actual benefit surface. Water-filled rooms and other local bodies attached to it).
Building length (m)
When L/, in to, 5~4, r result using the insertion method. Article 6.2.4 For general clay, silt, saturated loess and soft soil, the following layered summation method can be used to calculate the final settlement. 3s* point (2 points, 2)
(6.2.4-1)
Most potential settlement of foundation (mm)
st—-The settlement of foundation calculated by summing up the layers (mm)
Es(MPa)
-Empirical coefficient for settlement calculation. When there is regional experience, it shall be determined according to regional experience. When there is no regional experience, it can be determined by referring to Table 6.2.4-1.
Empirical coefficient for large foundation settlement calculation
1. 81.20 0.80
Table 6.2.4-1
The comprehensive compression modulus of the foundation within the compression layer below the bottom of the foundation (MPa) is calculated according to the following formula:
The stress distribution area of the i-th soil layer below the base, (6.2.4-2)
n ——-The number of soil layers divided within the depth range of foundation deformation calculation Po
The additional pressure at the bottom of the foundation corresponding to the standard load value (kPa),
The compression modulus of the i-th soil layer below the bottom of the foundation, taken from the self-weight pressure of the soil to the sum of the self-weight pressure of the soil and the additional pressure (MPa)
The distance from the bottom of the foundation to the bottom of the i-th and i-1-th layers (m) t
The average additional pressure coefficient in the range from the calculation point of the bottom of the foundation to the bottom of the i-th and i-1-th layers, may be adopted according to Appendix 2. The calculated depth of foundation settlement zn shall meet the following requirements: 4s#<0.025 24s?
(6.2.4-3)
s! Within the range of calculated depth, the calculated settlement of the first layer of soil is the calculated settlement value of the soil layer with a thickness of 42 from the calculated depth upward, and 42 is determined according to Table 6.2.4-2. A8
5人630
Table 6.2.4-2
However, for box foundations and raft foundations with large excavation areas and depths, the final settlement calculated by the above formula shall also take into account the rebound and recompression caused by the excavation of the foundation pit.
Article 6.2.5 For general clay, silt, soft soil and saturated yellow soil, when the stress consolidation history needs to be considered, the foundation consolidation settlement method can be used to calculate the final settlement.
, use the indoor high pressure consolidation test to draw the e-logp curve, second, according to the ratio of the initial consolidation pressure p. to the soil self-weight pressure β, the over-consolidation ratio (OCR) determines the consolidation state of the soil. When OCR>1 is over-consolidated soil, when OCR~1 is normal consolidation soil, when OCR<.1 is under-consolidated soil, third, the settlement calculation of over-consolidated soil is divided into two cases; 1. When p: +Po:pe, when, consider in two sections, pe value before using C. p value after using Ce, if there are n layers of soil in the depth of the foundation compression layer, it can be calculated as follows:
f c.log Pet.
+ C.log(pupt pa-)
Wu Zhongguo
n County settlement (mm),
(6.2.5-2)
3. If there are soil layers in the above two situations within the foundation compression layer, the total settlement is the sum of the above two parts, that is:
where s
Total settlement within the compression layer (mm). (6.2.5-3)
4. The settlement s (mm) of normal consolidated soil can be calculated as follows. [c.log (-Prt pa-)l
(6.2.5-4)
5. The settlement of underconsolidated soil s (mm) can be calculated as follows: [celog (put po-)]
2i+eoil
(6.2.5-5)
6. When calculating the settlement according to the above formula, the depth of the foundation compression layer, for silt, general clay and saturated loess, is calculated from the bottom of the foundation to the point where the additional pressure is equal to 20% of the soil's self-weight pressure, and for soft soil to the point where the additional pressure is equal to 10% of the self-weight pressure. If there are adjacent buildings, the additional pressure should be considered. Section 6.2.6 For general clay, soft soil, saturated loess under large rigid foundations and foundation soils for which the compression modulus value cannot be accurately obtained, such as crushed stone, sand, silt and granite residual soil, the settlement can be calculated using the deformation modulus according to the following formula.
s= pbn 2-
settlement (mm),
(6.2.6-1)
Average pressure at the bottom of the foundation corresponding to the standard value of the load (kPa);
Width of the bottom of the foundation (m);
Dimensionless coefficient related to 1/b, which can be determined by referring to Appendix III, Table 6;
Deformation modulus of the i-th layer of soil under the bottom of the foundation obtained by load test (MPa),
Correction coefficient, which can be determined by referring to Table 6.2.6-1; Depth of foundation compression layer (m).
4-10-9
Coefficient table
Table 6.2.6-1
When calculating the settlement according to the above formula, the depth of the foundation compression layer is 2. Calculate as follows 2h = (zm + Eb) β
Where 2m2
(6.2.6-2)
The empirical value related to the length-to-width ratio of the foundation (m) is determined according to Table 6.2.62:
Coefficient, determined according to Table 6.2.6-2,
- Adjustment coefficient, determined according to Table 6.2.6-3. Must m value and E prime number table
Xue stone soil
B coefficient table
Table 6.2.6-3
Cohesive soil
For general cohesive soil, soft soil and saturated loess, when no load test is carried out, the comprehensive deformation modulus can be calculated by back calculation. Calculate the settlement as follows. pbn.
Where E.
E,(MPa)
(0, -8,-1)
(6.2.6-3)
According to the comprehensive deformation modulus (MPa) calculated by the measured settlement, the following formula is used to obtain:
(6.2.6-4)
The ratio of the calculated comprehensive deformation modulus E to the comprehensive compression modulus E, (calculated according to formula 6.2.4-2) can be selected according to the following table. Ratio table
Table 6.2.6-4
.20.0-
The inclination caused by uneven foundation can be calculated according to the 6.,2.7 turbulent
borehole column chart and physical and mechanical indicators of each corner point, and the settlement is calculated according to the center point of the foundation, and then multiplied by the empirical coefficient obtained by comparing with the measured settlement to obtain the settlement value at each corner point, and the foundation inclination value is approximately calculated based on this. Article 6.2.8 The allowable deformation of the foundation of high-rise buildings and high-α structures shall be determined in accordance with the provisions of Table 6.2.8.
Allowable deformation of foundation increase
Allowable deflection of foundation research
24
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