What are the key points in the design and review of foundation construction drawings?

The following are the key points of basic construction drawing design audit brought by Zhong Da Consulting for your reference.

Key points of basic construction drawing design and review

I. Buried depth of foundation

1. natural foundation: make full use of the brown clay layer as the bearing layer (see above: 5.2. 1-2), which is generally buried on two layers of soil:

2. Box foundation: generally1/8 ~112 of the building height (above: Article 5.2.2);

3. The buried depth at the bottom of the platform plate of tube structure in high-rise building should not be less than 1/20 of the building height (upper tube: 7. 1.4);

4. Raft foundation and box foundation of high-rise buildings. The buried depth of natural foundation should not be less than115 of the building height, and the buried depth of pile raft and pile box foundation should not be less than118 ~1/20 of the building height (China: Article 5.65438+0.3); 5. Foundations with different burial depths: The elevation difference of burial depths of two foundations is generally 1/2 of the clear distance between the two foundations (above: Article 5.2.3-2);

6. After foundation trench excavation, trench inspection shall be conducted (China: Article 10. 1. 1).

Second, the basic type selection

1. Independent Foundation:

(1) The length-width ratio of rectangular foundation shall be less than or equal to 3 (I: Article 5.4. 1);

(2) The step height of stepped foundation should be 300 ~ 500, the side height of conical foundation should not be less than 200, and the slope should not be greater than 1:2(I:5. 4. 2);

(3) The insertion depth of the cup mouth should be selected according to (Table 5.4.6 above). At the same time, the anchorage length of the stressed main reinforcement should be met, and the stability of the column during hoisting should be considered. The insertion depth should be 0.05 times or more of the column length (see Article 5.4.6).

2. Strip foundation (reinforced concrete)

(1) The slab thickness of the strip foundation under the wall shall not be less than 250mm, and the edge height shall not be less than 150mm (above: Article 5.5.2);

(2)(2) Strip foundation under the wall: when the soil quality is uneven in the longitudinal direction, a ribbed beam shall be set under the wall, and the diameter of the steel bar in the rib shall not be less than 10mm (above: Article 5.5.3);

(3) Strip foundation beam under column:

(a) The height of foundation beam shall not be less than 1/4 ~ 1/8 of column spacing (above: Article 5.5.5);

(b) The longitudinal tensile main bars at the bottom of the beam should have 2-4 full-length configurations, and their area should not be less than 1/3 of the total area of longitudinal reinforcement (above: 5.5.6- 1 bar);

(c) The minimum reinforcement ratio of longitudinal reinforced bars at the top and bottom of the beam is 0. 15% (above: Article 5.5.6-2);

(d) When the height of the foundation beam (excluding the plate thickness) is greater than 600mm, φ 10 structural steel bars (above: article 5.5.6-3) shall be set at intervals of 300 ~ 400 on both sides of the beam.

3. Raft foundation

(1) The raft thickness of foundation beam should be 200 ~ 400, and when waterproof is required, the minimum thickness should be 250, and the span ratio of plate thickness to calculated section should not be less than 1/20 (above: 5.6.2);

(2) The protruding length of the cantilever plate of the raft foundation shall not be more than 2m (I: Article 5.6.4);

(3) The total amount of longitudinal and transverse reinforced bars of the raft shall be 1/4, and all the reinforced bars in the midspan shall pass according to the actual reinforcement ratio (I:5. 6. 7).

4. Box foundation

(1) The average wall length per square meter of box foundation area is not less than 40cm, or the horizontal cross-sectional area of the wall is not less than110 of the box foundation area, in which the longitudinal wall configuration is not less than 3/5 of the total configuration (above: 5.7. 1 piece);

(2) The shape of the superstructure should be as regular as possible, symmetrically arranged in plane, with uniform load distribution, and the center of gravity of the structure coincides with the centroid (I:5. 7. 2);

(3) The height of the box foundation should be greater than the length of the box foundation of118, and should not be less than 3m (above: Article 5.7.3-2);

(4) The thickness of bottom plate and external wall shall not be less than 250, the thickness of internal wall shall not be less than 200, and the thickness of top plate shall not be less than 150 (above: Article 5.7.3-3);

(5) Considering the influence of overall bending, in addition to meeting the calculation requirements, the total amount of reinforced bars in the longitudinal and transverse directions should be 1/4, and all the reinforced bars in the midspan should pass through (I:5. 7. 4);

(6) When analyzing the internal force of box foundation, overall bending plus local bending should be considered as far as possible (I:5. 7. 5);

(7) During construction and use, the box foundation shall be checked by anti-floating stability, and the partial coefficient of buoyancy is 1.2 (above: Article 5.7.9);

(8) The protective layer of steel bars near the water surface shall not be less than 50, and the crack width of concrete shall be ≤ 0.2 (ground: 4. 1.6).

5. Pile foundation

(1) pile type

(a) 300× 300 ~ 500× 500 precast piles (country: atlas 97Q36 1)

(b)φ550 ~φ800 bored piles

(c)φ300 ~φ800 prestressed pipe piles (I: Atlas DBJT08-92-2000)

(2) Selection of bearing stratum of pile foundation

(a) The bearing stratum of pile foundation should be low compressibility cohesive soil, silty soil and medium density sandy soil (above: 6. 1.3);

(b) The depth of the whole section of the pile end entering the cohesive soil layer or the medium-dense sand layer shall not be less than 0.5m, and shall not be less than twice the length or diameter of the pile side. When there is a soft substratum under the bearing stratum, the bearing stratum under the pile tip should have sufficient thickness (above figure: 6. 1.4);

(3) Determination of bearing capacity of pile foundation

(a) Static load test RD = Rk/T. (I: Article 6.2.3) shall be adopted;

(b) When the static load test of the pile is not carried out, it shall be determined according to the bearing capacity of the foundation soil to the pile: rd = RSK/υ srpk/υ p = = up Σ fsili/υ sfpap/υ p (above: 6.2.4);

(c) If there is no static load test, but there is static penetration test data, it should be determined according to the bearing capacity of foundation soil to the pile: rd = RSK/υ srpk/υ s = up ∑ fsili/υ s α bps BAP)/υ p (above: 6.2.5);

(d) According to the structural strength of pile body (I:6. 2. 6)

Precast pile RD ≤ (0.6 ~ 0.75) fcap

Prestressed pile RD ≤ (0.6 ~ 0.75) fcap-0.34apσ pc

Filling pile Rd≤0.60fcAp

Steel pipe pile Rd≤0.55fA

(e) Determination of uplift pile bearing capacity: rd' = up Σ FSI λ ili/υ SGP (above: article 6.2.7).

(4) Cast-in-place pile structure (Part I: Article 6. 1.9)

(a) The design pile diameter is equal to the drill bit diameter;

(b) The concrete strength grade should not be lower than C20, and the underwater construction should not be higher than C30；;

(c) The reinforcing cage shall pass through the silt layer and liquefied soil layer, and shall not be less than 2/3 of the pile length (China: Article 8.5.2);

(d) The stirrup spacing is 200 ~ 300, and the protective layer of the main reinforcement should not be less than 50;

(e) Reinforcement ratio: 0.42% for piles bearing axial force and 0.65% for piles bearing horizontal force.

(5) Pile arrangement principle (I: Article 6. 1. 1l)

(a) The centroid of the pile group coincides with the load center;

(b) The distance between the centers of piles shall not be less than 3 times the diameter or side length of piles;

(c) There should be no less than three piles under the independent platform;

(d) When one or two piles are used for independent caps and axial piles are used for strip foundation, coupling beams shall be set between caps;

(e) When there are axial piles under the wall, piles should be set at the corners and intersections of the wall; It is not advisable to set piles under the bottom doorway.

(6) Pile foundation detection

(1) Static load test: the number of test piles shall not be less than 1% of the total number of piles, and shall not be less than 3 (above: 14. 2. 3-5);

(b) No less than 5% of the total number of high strain tests and no less than 5 pieces (above: Article 14.5.2-3);

(c) For low strain testing, the number of driven piles shall not be less than 20-30% of the total number of piles, and shall not be less than 10, and the number of cast-in-place piles shall be more than 50% (above: Article 14. 5. 2-3).

6. Double-wall foundation: when setting settlement joints or expansion joints, the foundation design under double-wall load should be considered;

7. In general, the matching point of vertical load (long-term) above the basement coincides with the centroid of the basement area (Article 5. 1.3);

8. Protective layer of foundation slab reinforcement: 40 when there is cushion and 70 when there is no cushion (China: Article 8.2.2).

Three. Calculation of foundation bearing capacity

1. When the axial load is used to determine the foundation bottom area, according to the formula PD = (FDGD)/A ≤ FD (above: 4.2.1-1article);

2. Under eccentric load, the ratio of the maximum and minimum design values of the base edge, pdmax/pdmin ≤ 3, and should satisfy Pdmax≤ 1.2fd (above: 4.2. 1-2);

3. When the static load test is adopted to determine the bearing capacity of foundation, the formula FD = FK/υ R (Article 4.2.2 above) should be adopted;

4. When the shear strength index of soil is used to calculate the bearing capacity of foundation, the formula FD = υ dfdg (above formula: Article 4.2.3) should be adopted;

5. For the independent foundation, the punching bearing capacity of the joint between the column and the foundation and the change of the foundation step should be checked (China: Article 8.2.7-2);

6. The thickness of the slab of beam-slab raft foundation shall meet the requirements of punching bearing capacity and shear bearing capacity (China: Article 8.4.5);

7. For a flat raft, the punching and shearing bearing capacity of the plate at the edge of the inner tube or the hanging edge should be checked. When the thickness of the raft is variable, the shear bearing capacity of the raft at the variable thickness should be checked (China: Article 8.4.9).

Fourth, the foundation treatment method

1. Settlement control composite pile foundation

(1) piles are precast piles of 200×200 and 250×250, with the slenderness ratio of about 80 (above:11.6.1-1), and the pile length is generally/kloc-0.

(2) The pile spacing should not be less than 5 ~ 6 times of the side length of the pile segment (above:11.6.1-1strip);

(3) The pile tip should pass through the highly compressible muddy soil layer and enter the soil layer with relatively low compressibility, but not very hard, as the bearing layer (above:11.6.1-1);

(4) The standard value of ultimate bearing capacity of single pile of composite pile foundation should be determined by static load test of single pile, and the gap time after pile sinking during the test should not be less than 30 days. When the static load test of the pile is not carried out, it can be determined according to the following formula: rk = upσfsilifpap, and rk ≤ (0.6 ~ 0.75) fcac (top:11.

(5) The overall bearing capacity of composite pile foundation shall meet the following requirements: FdGd≤ζkRkACfsd. If the above formula cannot be satisfied, it is suggested to adjust the top area (above: 1 1.6.6);

(6) Composite pile foundation is mainly suitable for multi-storey buildings with less than eight floors (above: article 1 1.6. 1);

(7) The total vertical load borne by the cap area of composite pile foundation shall not exceed 1.5 ~ 1.7 times the foundation bearing capacity (above: article 1 1.6.3- 1);

(8) Miscellaneous fill, buried soil and liquefied soil cannot be used as composite pile foundation, and should be treated when encountering the above soil layers.

2. Soil replacement construction method

(1) Classification by materials (Part I: Article 1 1.2.2)

(1) Sand (gravel) cushion

(b) Dry slag cushion (blast furnace)

Fly ash cushion

(2) The size of the bottom surface of the cushion is determined by the linear expansion of the foundation edge down to 45 degrees (above: article 1 1.2.3);

(3) The thickness of the cushion should be determined according to the bearing capacity of the soil layer under the cushion. Generally not more than 3m and not less than 1m (above: Article 1 1.2.4);

(4) The design value fspd of cushion bearing capacity shall be determined through field test (above: Article 1 1.2.5);

(5) Quality inspection standard: The quality standard of layered construction is compactness. The engineering quality can pass the load test, standard penetration test or static penetration test (I: Article 1 1.2.6).

3. Cement-soil mixing method (I: Article 1 1.5.4)

(1) is suitable for the treatment of silt, cohesive soil and silt with the design value of foundation bearing capacity not greater than 120Kpa;

(2) Before design, the indoor compressive strength test of cement-soil should be carried out, and the standard strength of cement-soil pile under vertical load for 90 days should be provided;

(3) The cement content is generally 65,438+02% ~ 65,438+05% of the weight of reinforced soil or 220 ~ 270 kg cement per cubic meter of reinforced soft soil;

(4) The water-cement ratio of cement slurry can be 0.45 ~ 0.55;

(5) The design value of bearing capacity of cement-soil composite foundation should be determined by composite foundation load test. When there is no load test, it can be estimated by the formula 1 1.5.4- 1.

Five, weak substratum should check its strength and control deformation.

1. When there is a weak substratum under the bearing stratum, and the ratio of bearing stratum thickness h to foundation width b is 0.25 ≤ H 1/b ≤ 0.7, the influence of weak substratum on foundation bearing capacity should be considered; H 1/b >; 0.7, calculate the foundation bearing capacity according to the bearing stratum index; When h 1/b

2. The deformation value of building foundation is controlled according to the building structure and foundation type (I: Table 4.3.6) (I: Article 4.3.6);

3. According to the document of Shanghai Municipal Construction Committee [Jian (99) No.0037], the length of multi-storey buildings should be controlled within 55m. When the shape is complex and the longitudinal stiffness is poor, the final settlement of the foundation must be controlled within 150, and the eccentricity should be controlled within 15‰;

4. There is no need to check the foundation deformation for general civil buildings with three floors or below (4. 1.2- 1 part);

5. Settlement observation points shall be set at the four corners and midpoint of the building and on the internal load-bearing wall (column) with the building width greater than 15m at intervals of 6 ~ 12m along the perimeter of the building (above: Article 14. 10.3);

Key points of seismic design of intransitive verbs

1. When there is saturated sandy soil or saturated sandy silt in the building foundation (generally considering the depth below the ground 15m), the liquefaction possibility of this soil layer should be determined and the liquefaction risk level should be determined (above: 7.2. 1 article);

2. Discrimination of foundation liquefaction (I: Article 7.2. 1):

(1) standard penetration test results, when the standard penetration hits reach NCR.

(2) Determination of static cone penetration test: When the measured specific penetration resistance Ps or the measured cone tip resistance Qc3 of the double-bridge probe is close to the bottom of the pile cap and the thickness is

4. Selection of anti-liquefaction treatment of foundation according to the seismic fortification category of building and liquefaction grade of foundation (I:7. 4. 3):

(1) Measures to completely eliminate liquefaction settlement of foundation, such as pile foundation;

(2) Measures to partially eliminate liquefaction settlement of foundation, such as reinforcing or excavating part of liquefied soil layer;

(3) Treatment of foundation and superstructure, measures to reduce uneven settlement or better adapt to uneven settlement.

5. When using pile foundation to eliminate the settlement of foundation liquefied soil, the pile tip should enter the stable soil layer below the liquefied soil layer not less than 1.5m or twice the pile diameter (above: 7.4.4- 1 strip);

6. When the foundation is buried to eliminate the settlement of liquefied soil, the bottom surface of the foundation should enter the stable soil layer not less than 0.5m below the liquefied soil layer (above: 7.4.4-2).

Seven. Measures to reduce and adapt to foundation deformation

1. Design principle of multi-storey building foundation (Part I: Article 12.2.3);

(1) The same structural unit shall adopt the same type of foundation;

(2) The foundation of the same structural unit should be set on the soil layer with the same elevation and consistent nature;

(3) Strengthen the rigidity of strip foundation, or adopt the foundation form with large rigidity, or set basement and semi-basement, so as to reduce the additional pressure on the basement;

(4) It is advisable to make the centroid of the foundation bottom surface coincide with the resultant point of the load.

2. The load of each unit of the building should not be too different, and the plane should be concise and tidy (on: 12.3. 1);

3. Consider the mutual influence caused by foundation deformation of adjacent buildings, otherwise adjacent buildings should keep a certain distance, and the minimum distance can be determined according to the expected settlement and the length-width ratio of the affected buildings (I: 12. 3. 2);

4. Setting settlement joints at the parts of the building where large uneven settlement may occur (I: Article 12.3.3);

(1) A significant turning point in the architectural plane;

(2) where the building height or load difference and settlement difference are large;

(3) Appropriate parts of masonry load-bearing structure and reinforced concrete frame structure with large aspect ratio;

(4) The compressibility of foundation soil is significantly different;

(5) the joint of two structural units or houses built by stages;

(6) Different types of building structures (or foundations);

(7) The settlement joint should have sufficient width (Table 12.3.3).

5. For a high-rise building consisting of a main building and a podium, when the following measures are taken, the main building and the podium can be integrated without settlement joints (I: Article 12.3.4):

(1) The podium foundation is selected from the main building foundation;

(2) Reduce the settlement of the main building and control the settlement difference;

(3) Adopt reasonable construction procedures and measures such as post-pouring belt to reduce the late settlement difference.

6. For masonry bearing multi-storey buildings, the longitudinal walls should rotate as little as possible, and the spacing between internal transverse walls should not be too large. Closed ring beams should be set up layer by layer to strengthen the overall stiffness and strength (I: 12. 3. 7);

7. Ground stacking (Part I: Articles 12.3.8 and 12.3.9)

(1) Estimated settlement;

(2) considering the influence on the superstructure;

(3) It should not be directly pressed on the foundation;

(4) The statically determinate structure should be adopted.

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