Design, calculation and device shallow-buried foundations of low-rise residential buildings in Moscow region

TSN MF-97 DoD regulation and standardization REGIONAL CONSTRUCTION STANDARDS design, calculation and device shallow-buried foundations of low-rise residential buildings in Moscow region Effective date 06/01/1998 Developed by: the Ministry of Construction of Moscow Region (IB Zakharov, K. called; BK Baikov, Ph.D.); Mosgiproniselstroem (BCSazhin, Prof.; AG Beira, Ph.D.; VV . Borshchev, Ph.D.; TA Prikazchikova, Ph.D., I. K. Melnikov, Eng.; D. Sazhin, Ing.) Institute of Foundations and Underground Structures State Construction Code ( Vladimir Orlov, Prof..; Yu.B. Badu, PhD; NS Nikiforova, Ph.D., VY Shishkin , Ph.D.); TsNIIEPselstroem (VA Zarenin, Ph.D., LP Karabanov, Ph.D., LM Zarbuev, Ph.D.; T. A. Maltsev, PhD, N. Maltsev, Ph.D., V. Novgorod, Ph.D.; AF Svetenko, PhD ., K. S. Pogosyan, Ing.) Institute Mosstroem (VA Trushkov, Ph.D., B. H. Kim, Ph.D.). AGREED: License and expert department of the Moscow region (LD Mandel, VI Mischerin, LV Golovacheva) Mosoblkomprirodoy (MP Goncharov, NA Belopol'skaya). Approved by the Government of Moscow region from 30.03.98 № 28 / 9. Introduction In connection with the implementation of a program of low-rise and cottage construction administration of the Moscow region holds a set of measures aimed at reducing the cost of construction, including the use of lightweight construction, new building materials and advanced technologies. A large proportion of the total cost of construction of low-rise buildings is the cost of installation of foundations. Load on a running meter strip foundations in one-, two-story buildings generally are 40 ... 120 kN, and only in some cases - 150 ... 180 kN. Small load on the foundations cause increased sensitivity to the forces of frost heaving. The territory of the Moscow region for more than 80% composed of heaving soils. These include clay loam, sandy loam, silty sand and shallow. At a certain moisture content, these soils, was frozen in winter, increasing in volume, which leads to a rise in soil layers within the depth of its freezing. Found in such soils foundations are buckling, if the load acting on them does not balance the forces of frost heave. Since deformations of swelling ground is uneven, there is uneven growth of foundations, which over time accumulates, resulting in construction of buildings undergo unacceptable deformation and collapse. Applied in the practice of building activity against buckling by laying the foundations to a depth of freezing does not ensure the stability of lung buildings, because such foundations have developed a lateral surface on which are great value for the tangential heaving forces. Thus, universally applicable, material-and costly foundations do not provide reliable operation of low-rise buildings constructed na heaving soils. One way to solve the problems of construction on heaving soils of low-rise buildings is the use of shallow-buried foundations laid in SEASONALLY layer of soil. In accordance with Chapter SNIP 2.02.01-83 * "Foundations of buildings and structures," the depth of the foundation is allowed to appoint, regardless of the calculated depth of freezing, if the "special studies and calculations revealed that the deformation of soil at the base of the freezing and thawing does not violate the integrity of the building . The basic principle of constructing shallow-buried foundations of buildings with bearing walls on heaving soils lies in the fact that the strip foundations of walls of buildings are combined into a single system and form a rather rigid horizontal frame, redistribution of deformation bases. When shallow-buried pier foundation frame is formed from the foundation beams which are rigidly interconnected to the piers. Application of shallow-buried foundations based on a fundamentally new approach to their design, which is based on the grounds laid reckoning in the deformations of swelling. In this case, the deformation of the base (growth, including uneven), but they must be less than the limits, which depend on the design features of the building. When calculating the grounds of heaving deformations are taken into account distending soil properties passed to it the pressure, the stiffness of the base and nadfundamentnyh structures in bending. Nadfundamentnye designs are considered not only as a source of stress on the bases, but also as an active element is involved in joint work with the foundation base. The greater rigidity in bending, the lower the relative deformation bases. One of the measures to reduce or eliminate heaving properties of soil is to increase its density and creating clay waterproof screen, which significantly reduces the suction of water into the zone of freezing from the underlying layers of soil and infiltration of surface water in the basement area of ??contact with the ground. This is achieved, if the installation of foundations and apply methods vytrambovyvaniya vyshtampovyvaniya combining device cavity under the foundation and future of compacted soil core. Thereby improves the mechanical characteristics of the soil, which is a prerequisite for increasing the bearing capacity of foundations. However, soil compaction reduces its distending properties: the intensity and strength of swelling. This effect is achieved and immersed in driven into the soil blocks. For low-rise buildings such foundations can settle into sezonnopromerzayushem layer of soil, ie they are also shallow-buried. Of the bases on a locally compacted foundations for buildings with bearing walls are the most acceptable tape vytrambovannyh or stamped in the trenches. Pier foundation on such grounds it is expedient to use primarily at bezrostverkovom bearing walls. This applies to short-knock (pyramidal and prismatic) and the bored piles. However, in the soft ground and pier foundation and the pile can be applied in the construction of low-rise buildings. Since 1987, many Russian regions, including in the Moscow region, at shallow-buried foundations built thousands of low-rise buildings with walls made of different materials - bricks, blocks, panels, wood panels. Their application has reduced the consumption of concrete by 50-80%, labor costs - by 40-70%. Long service life of buildings on shallow-buried evidence of foundations of their reliability. In these rules contain requirements for design and calculation of shallow-buried foundations in the ground conditions of the Moscow region. The provisions of rules made by performing long-term complex of experimental investigations carried institutions, developers of these standards, experience in the design, construction and operation of buildings. 1. General 1.1. These rules apply to the design and installation of shallow-buried foundations of residential buildings up to 3 floors including the Moscow region. Note. Standards can be used for buildings of cultural and community purposes, garden houses, garages. 1.2. Standards are complementary and the development of SNIP 2.02.01-83 * "Foundations of buildings and structures" (p. Stroiizdat, 1995). 1.3. Standards provide for the use of layer sezonnoppomepzayuschego soil as a base foundation, with finely buried foundations can be constructed as a natural basis, and on locally compact. 1.4. Type and design of shallow-buried foundations, methods of preparing its base depends on the soil properties of the construction site and, above all, its degree of heaving. 1.5. In the design of shallow-buried foundations on heaving soils required is the calculation basis of the deformations of swelling soil. 1.6. When selecting the construction site should be preferred sites with nepuchinistymi or less heaving soils, uniform in composition, both in terms of, and depth of the part sezonnopromerzayushego soil, which is projected as a base shallow-buried basement. 1.7. In the design of foundations on heaving soils should include activities aimed at reducing both swelling strains of soil and their influence on the design of foundations and above-ground parts of buildings, including: - waterproofing to ensure reduction of soil moisture, lowering of groundwater, surface water drainage from the building by a device grading, drainage, drainage ditches, gutters, ditches, drainage layers and etc. 2. Evaluation of frost heaving base 2.1. By distending include clay soils, sands, silt and fine and coarse soils with clay filler content over 15% of the total weight, with the beginning of freezing moisture that exceeds the levels defined in accordance with Clause 2.8. Coarse sandy soils with filler, sand gravelistye, large and medium-sized, not containing clay fractions are considered nepuchinistymi soils at any level of free-flow of groundwater. 2.2. Quantitative index of soil heaving is the relative strain of frost heaving, which is the ratio lifting the unloaded surface of the ground freezing and the thickness of the layer. 2.3. According to the strain of frost heaving soils are classified according to the table. 2.1. Table 2.1: The strain of frost heaving of soil, the share of units. Variety of soil and 0.07 Silnopuchinisty overly distending 2.4. The strain of frost heaving, as a rule, should be based on empirical data. In the absence of experimental data allowed to determine the physical characteristics of soils. 2.5. In carrying out engineering and geological surveys at the site of planned construction of sampling of soil for laboratory testing should be performed every 25 cm in depth workings in the layer of seasonal freezing. Generation are placed in the most characteristic points of the site (at high and low areas) within the contour of the projected building. Note. For all varieties of soil heaving normative depth of seasonal frost in the Moscow region can be taken as 1.5 m. 2.6. To determine the strain of frost heaving on soil physical characteristics necessary to establish: - size distribution of soil classifying its kind - the density of soil in the dry state - the density of solid particles of soil - the plasticity of the soil: moisture on the plastic limit () and stress ( ), the number of plasticity - the estimated pre-winter moisture W in the layer of seasonal freezing of soil - the depth of seasonal soil freezing. 2.7. The strain of frost heaving of soil is determined from the graphs (Figure 2.1) using the parameters calculated by the formula (2.1) Here - the critical moisture content, decimal fraction., Which is lower than in freezing heaving soils stops the redistribution of moisture, causing frost heaving, is determined by the schedules (Figure 2.2) - the density of water, ton / m - the absolute value of long-term average air temperature in winter, for the Moscow region = 7 ° C - total moisture content of soil, the share of units. as defined by (2.2) Fig. 2.1. Relative deformation of swelling on the parameter: a) almost nepuchinisty b) slabopuchinisty c) srednepuchinisty d) silnopuchinisty e) excessive distending 1,2 -, respectively, sandy loam and sandy loam silt (0,020,07) 3 - loam (0,070,17 ) 4 - silty clay loam (0.07 0.13), 5 - silty clay loam (0.13 0.17), 6 - clay (> 0.17). Fig. 2.2. Dependence of the critical humidity of the number of ductility and yield strength of the soil. Other designations are the same as in 2.6. 2.8. Clay soils are heaving, if they estimated pre-winter moisture W within the layer of seasonal freezing exceed the following levels: (2.3) (2.4) where - humidity that characterizes the degree of pore filling of ground ice is determined by (2.5) 2.9. Estimated pre-winter soil moisture is taken equal to the weighted average soil moisture in a layer of normative depth of freezing obtained during investigations at construction site in the summer-autumn period. It is assumed that the runoff of precipitation that fell in front of researches, the same with a drain in the pre-winter period. Note. In calculations by formulas (2.1, 2.3, 2.4) introduced the weighted average value of soil moisture in most wetlands area. 2.10. With a deep groundwater estimated pre-winter soil moisture should be determined in accordance with Annex 1. Deep groundwater is characterized by the condition (2.6) where - the distance from the planning to mark the groundwater level, m; - normative depth of freezing ground, m; z - the minimum distance between the edge of seasonal freezing of soil and groundwater level at which these waters are not effect on the freezing of soil moisture, determined according to Table. 2.2. Table 2.2 Description of soil value Z, m clay with montmorillonite and illitovoy framework 3.5 with kaolinite clay foundation, loam, including silt loam 2.5, including 1.5 silty fine sand and silt 1.0 2.11. Silty sands and fine when the moisture 0,6 0,8, coarse soils with aggregate (sand, silty clay and fine) of 10 to 30% by weight are slabopuchinistym soils for which is taken = 0,035. Silty sands and shallow (at 0,80,95), coarse soils with the same aggregate of more than 30% by weight are srednepuchinistym soil (= 0.07). Silty sands and fine at 0.95 are silnopuchinistym soil (= 0.10). 2.12. The degree of heaving soils should be considered when choosing the type of foundation and method of preparation of the base in accordance with Appendix 2. 3. Design of shallow-buried FOUNDATION 3.1. Requirements for construction shallow-buried foundations 3.1.1. During construction on virtually nepuchinistyh soils shallow-buried foundations are re-leveling of the sand bank filling on heaving soils - on a bed of nepuchinistogo material (sand gravelisty, large or medium size, fine gravel, clinker, etc.), which can be either mortise or and arranged on the ground surface. 3.1.2. Shallow-buried strip foundations should arrange: - on virtually nepuchinistyh and slabopuchinistyh ground - from the concrete (expanded clay concrete) blocks arranged freely, without any connection to each other, of cast concrete, rubble concrete, tsementogrunta, rubble or mud brick - on srednepuchinistyh soils (at 0, 05) - made of concrete (expanded clay concrete) blocks arranged freely, without any connection between themselves or of monolithic concrete - on srednepuchinistyh (at> 0.05) and silnopuchinistyh soils (with < 0,12) - из сборных железобетонных блоков, жестко соединенных между собой, или из монолитного железобетона; - на чрезмерно пучинистых грунтах (при 0,12) - из монолитного железобетона. Примеры конструктивных решений мелкозаглубленных ленточных фундаментов приведены в Приложении 3. 3.1.3. При >0,05 strip foundations of walls of buildings should be rigidly connected to each other and merged into a single structure - a system of cross-belts. 3.1.4. The lack of rigidity of the walls of buildings built on silnopuchinistyh and excessive heaving soils should be carried out to gain through the device or a reinforced concrete belts at the level of overlap. 3.1.5 . shallow-buried columnar foundations on srednepuchinistyh (> 0,05), silnopuchinistyh and excessive heaving soils should be rigidly connected to each foundation beam, combined into a single system. 3.1.6. When the device pier foundation is necessary to provide clearance between the lower edges of the foundation beams and planning ground surface not less than the calculated strain (lifting) unloaded base. 3.1.7. Sections of buildings with different heights, you should arrange for separate foundations. 3.1.8. adjacent to the verandah on silnopuchinistyh and excessive heaving soils should build on the foundations, non- with foundations of buildings. 3.1.9. The length of the building, constructed on soils with 0.05, you must cut the entire height of the individual sections, the length of which shall be made: for srednepuchinistyh soils - up to 30m, silnopuchinistyh (at 0.12) - up to 24 m excessively heaving (at> 0.12) - up to 18 m. 3.1.10. silnopuchinistyh shallow-buried foundations on heaving soils and excessively should be made of heavy concrete B15. Working longitudinal reinforcement in all cases be taken from the class AIII steel according to GOST 5781 - 82 *, cross - made of steel grade 4 Bp-1 according to GOST 6727-80. 3.1.11. In the manufacture of shallow-buried foundations of reinforced concrete stamps concrete on frost resistance and water resistance should not be lower than the F50 and W2. 3.2. Calculation of shallow-buried foundations 3.2.1 . Calculation of shallow-buried foundations in the following order: a) on the basis of surveys to determine the degree of soil heaving ground, and depending on her chosen type of foundation and construction of foundations in accordance with Annex 2 and section 3.1, and b) given the size of pre-foundation base, depth its inception, the thickness of sand (sand and gravel), pillows, and c) in accordance with the requirements of SNIP 2.02.01-83 * "Foundations of buildings and structures" are calculated base on the deformation, in the case where a sole cushion overlies the soil less strength than strength of the material cushions, need to check that the soil in accordance with SNIP 2.02.01-83 *, d) calculates the base shallow-buried basement in the deformations of frost heaving of the soil. 3.2.2. The calculation of the base of the deformations of swelling soil freezing below the foundation base is made on the basis of the following conditions: (3.1) (3.2) - a calculated value of lifting the base of the swelling soil under the foundation, taking into account the pressure under the soles of his - the estimated relative deformation of swelling foundation soil under the foundation - respectively the limiting values ??of recovery and the strain base, taken from Table. 3.1. 3.2.3. Calculation of recovery and the strain of swelling for foundation shall be in accordance with Appendix 4. Table 3.1 Values ??of ultimate strains reason to limit deformation of the ground foundation design features of buildings relative deformation recovery,, sm kind of value frameless buildings with bearing walls: 2.5 panel deflection or camber 0.00035 blocks and masonry without reinforcement 2,5 - " - 0.0005 * block and masonry or reinforced concrete with reinforcing belts in the presence of precast-monolithic (monolithic) tape or columnar foundations with precast-monolithic foundation beam 3.5 - - 0.0006 * Buildings with wooden structures on the strip foundations 5 , 0 - - 0,002 on the pier foundation 5.0 relative difference ups _________________ 0.006 * allowed to take larger values, if based on the calculation of the wall in strength will be found that the stresses in masonry shall not exceed the calculated resistance of masonry tensile strength in bending. 4. DESIGN FEATURES shallow-buried FOUNDATION FOR LOCALLY BASED SEAL 4.1. Requirements for soils and construction of foundations on the basis of locally densified 4.1.1. to the foundation of locally compacted under the foundations are in vytrambovannyh (stamped), pits or trenches, foundations of driven piles of blocks. 4.1.2. The characteristic feature of these types of foundations is the presence of the surrounding compacted soil zone, which is formed during vytrambovyvanii vyshtampovyvanii or cavities in the ground, submerged blocks by driving. 4.1.3. the depth of the foundation should be equal to 0,5-1 m. 4.1.4. The foundation should have a truncated pyramid with an angle of inclination to the vertical faces of 5-10 ° and the size of the upper section, the large size of the lower section. 4.1.5. The use of shallow-buried foundations in vytrambovannyh (stamped), pits or trenches is limited to the following ground conditions: clay soils with the index yield 0, 2 - 0,7 and sandy soils (silt and fine, loose and medium density) in groundwater from the bottom of the bases at a distance of not less than 1 m. 4.1.6. The use of driven piles of blocks is limited to the following ground conditions: clay soils with the index yield 0 ,2-0, 8, and sandy soils (silt and fine, loose and medium density) at the level of groundwater, which are separated from the planning mark at least 0,5 m. 4.1.7. To increase the bearing capacity of foundations in the pit or vytrambovannom trench along the ground should be the formation of pits (trenches) vtrambovyvat in its base gravel. 4.1.8. pier foundation on locally based on highly compressed and extremely heaving soils with> 0.1 should be rigidly interconnect foundation beam. 4.1.9. Foundations in vytrambovannyh (stamped) trenches arranged in heaving soils with