Detail of DBJ/T 15-38-2019

Introduction of DBJ/T 15-38-2019

Technical code for ground treatment of buildings 1 General provisions 1.0.1 This Code is formulated with a view to implementing the technical and economic policies of the nation during the design and construction of building foundation in Guangdong Province, and thus achieving safety and applicability, advanced technology, economic rationality, guaranteed quality and environment protection. 1.0.2 This Code is applicable to the design, construction, surveillance and quality inspection of ground treatment of buildings in Guangdong Province. 1.0.3 The design of building ground treatment shall be based on the foundation design grade and geotechnical engineering investigation data, comprehensively taking into account factors such as structure type, construction conditions, construction cost and use requirements, so as to adjust measures to local conditions, use local materials and save resources. 1.0.4 In addition to those specified in this Code, the building ground treatment shall also meet those specified in the current relevant standards of the nation and Guangdong province. 2 Terms and symbols 2.1 Terms 2.1.1 ground treatment, ground improvement technical measures taken to increase the bearing capacity of foundation or improve its deformation or permeability performance 2.1.2 composite ground, composite foundation foundation formed by reinforcing or replacing some soil so that the load is borne by both foundation soil and vertical reinforcement   2.1.3 characteristic value of composite ground bearing capacity pressure value corresponding to the deformation specified by the composite foundation soil pressure deformation curve measured by load test, of which the maximum value does not exceed half the limit value 2.1.4 replacement layer of compacted fill cushion layer formed by excavating the soft soil layer or uneven soil layer within a certain range under the base bottom surface and backfilling other non-erosive materials with stable performance and high strength which are tamped and compacted 2.1.5 compacted ground, compacted fill foundation in which the fill is compacted in layers by rolling equipment for flat rolling, vibration rolling, impact rolling or other types of rolling 2.1.6 rammed ground, rammed earth foundation with the soil forming compacted pier body by compaction with a rammer freely falling from a high place repeatedly or by replacement 2.1.7 composite foundation with dynamic-replaced stone column composite foundation formed by soil between piers and pier body formed inside by continuously backfilling hard granular materials such as crushed stone into the tamping pit which is formed with a rammer freely falling from a high place repeatedly 2.1.8 preloaded ground, preloaded foundation consolidated and compacted foundation formed by carrying out preloading with surcharge of fill or vacuum preloading or both on the foundation 2.1.9 preloading with surcharge of fill ground treatment method in which loads are piled on the foundation to consolidate and compact the foundation soil 2.1.10 vacuum preloading ground treatment method of consolidating and compacting the foundation soil by vacuumizing the closed film covering the surface of the shaft foundation to drain 2.1.11 preloading dynamic consolidation foundation foundation formed after the foundation soil is drained and consolidated by subjecting the foundation with drainage body to preloading with surcharge of fill and dynamic compaction 2.1.12 composite foundation with vibroflotation gravel pile composite foundation with dense vertical reinforcement consisting of crushed stones or sand stones which are pressed into the holes made in the foundation soil through vibration, impact or water flushing 2.1.13 composite foundation with cement deep mixed columns composite foundation with vertical reinforcement formed by forced mixing the curing agent, with cement as the main material, and foundation soil with deep mixing machine 2.1.14 filling degree ratio of the thickness of the compacted cushion to the loose paving thickness   2.1.15 composite foundation with jet grouting composite foundation with cement soil vertical reinforcement formed by soil and cement slurry which, or water, is pressed by lifting through rotating the drill stem and ejected from horizontal nozzles to form jet flow to cut the soil body and mix the cement slurry and soil 2.1.16 composite piles with different materials or lengths pile formed by combination of piles of two or more different types or piles of the same type while different lengths 2.1.17 composite foundation with different piles or lengths composite foundation reinforced by composite piles with different materials or lengths 2.1.18 rigid pile composite foundation composite foundation with rigid piles as vertical reinforcement 2.1.19 pile-reinforced earth composite foundation artificial foundation formed by adding supporting plate on top of rigid pile and spreading reinforced cushion on the supporting plate 2.1.20 ground improvement by permeation and high hydrofracture grouting ground treatment method of injecting cement slurry or other chemical grout into the foundation soil layer, so as to strengthen the connection between soil particles, and improve the strength and reduce the deformation and the permeability of the soil body   2.1.21 polluted earth soil layer with the original physical and mechanical property character and chemical property changed due to the invasion of foreign pollutants 2.1.22 micropile root pile, precast concrete pile or steel pipe pile with diameter less than 300mm 2.1.23 building rectified a deviation righting measures taken when the building deviates from the vertical position and inclines which affects the normal use 2.2 Symbols 2.2.1 Actions and action effects Nk——the pile top load; pp0——the pile top pressure stress; p0——the net foundation pressure of soil between piles; △pi——the average additional stress increment; Δpk——the foundation bottom pressure increment; pcz——the deadweight pressure value of soil at the bottom of cushion; pk——the average pressure at the foundation bottom; pc——the deadweight pressure of the soil on the foundation bottom; p0i——the additional stress acting on soft soil surface; pz——the net foundation pressure of soil between piles; the additional pressure stress on the top of composite soil layer; Pzl——the additional pressure of the bottom of composite soil layer; ΣΔp——the accumulated value of loads at all levels before the period of t; pp0——the pressure stress at pile top; ps——the standard stress value acting on the supporting plate; M——the design bending moment acting on the section at the edge of pile; the mass of hammer; Qng——the standard value of downward load caused by negative skin friction at pile side; q——the service load of roads, stackyards, airport runways, building yards, etc., such as vehicle load; ——the loading rate of Class i load; Vs——the standard value of the maximum punching shear acting on the supporting plate; ΣΔp——the accumulated value of loads at all levels before the period of t; z——the vertical additional stress caused by preloading load at this point. 2.2.2 Resistance and material property E0——the deformation modulus of pile tip bearing stratum; Esp——the compression modulus of composite soil layer; Es——the compression modulus of soil between piles; Ep——the compression modulus of flexible pile shaft; Ep0——the deformation modulus of cushion; EC0——the deformation modulus of cushion; Esi——the average additional stress increment of the i-th layer of rock and soil; e——the void ratio; e0i——the void ratio corresponding to deadweight stress of soil at the midpoint in the i-th layer; e1i——the void ratio corresponding to the sum of deadweight stress and additional stress of soil at the midpoint in the i-th layer ft——the axial tensile strength of concrete; fcu——the average compressive strength of cube at 90 days under standard curing conditions; fpk——the characteristic value of bearing capacity per unit sectional area of pile shaft; fsk——the characteristic value of bearing capacity of soil between piles; fspk——the characteristic value of bearing capacity of composite foundation; fak——the corrected bearing capacity characteristic value of soft soil foundation, kPa; faz——the characteristic value of foundation bearing capacity of soil layer after depth correction is carried out at the cushion bottom; fk——the bearing capacity shared by soil, which is determined by coordination of settlement; fck——the standard concrete strength of pile shaft; MR——the bending bearing capacity of the supporting plate section; qpa——the tip resistance of the pile-bottom bearing stratum; qpk——the characteristic value of bearing capacity of foundation soil at pile tip, and the pile tip resistance characteristic value; qsk——the characteristic value of side resistance of the soil around the pile; qsi——the characteristic value of side resistance of the i-th layer of soil around the pile; qp——the characteristic value of bearing capacity of foundation soil at pile tip without correction; qpa——the characteristic value of tip resistance of pile tip bearing stratum; Ra——the characteristic value of the vertical bearing capacity of a single pile; Ra1——the characteristic value of vertical bearing capacity of long piles; Ra2——the characteristic value of vertical bearing capacity of short piles; Rk——the bearing capacity shared by pile determined by coordination of settlement; Rp——the plastic influence radius; the characteristic value of bearing capacity of foundation soil at pile tip without correction; T——the design tensile strength of reinforced materials; Ta——the tensile strength of geosynthetics under allowable elongation; Tp——the maximum tensile force of geosynthetics per unit width; Tlower——the design tensile strength of the first layer of reinforced materials on the supporting plate; Tupper——the design tensile strength of the second layer of reinforced materials on the supporting plate; d——the dry density of soil; dmax——the maximum dry density of soil; w——the density of water; ωop——the optimum moisture content; f0——the natural shear strength of foundation soil before reinforcement; ft——the shear strength of a certain point in the foundation after loading for a period of t; cu——the internal friction angle of soil determined by triaxial consolidated undrained compression test; φ——the internal friction angle of fill; γ——the average weight of filler and surface structure above the elevation of the top surface of the supporting plate; γm——the average weight of filler above reinforced materials. 2.2.3 Geometric parameters A——the area of bottom of foundation; Ae——the treated foundation area shared by single pile; Ap——the sectional area of pile; Ap1——the sectional area of single long pile; Ap2——the sectional area of single short pile; A and a1——the side length of the supporting plate; b——the width of the foundation bottom surface; the width of the plastic drainage plate; b′——the width of the cushion bottom surface; d——the diameter of pile shaft; de——the equivalent circle diameter of treated foundation area shared by single pile and effective drainage diameter of drainage body; dw——the diameter of ordinary sand well, diameter of sand bag well and equivalent conversion diameter of plastic drainage plate; ds——the relative density of soil particles; D——the pile diameter or pile side length; the hole spacing; H1——the depth of a replacement pier; H2——the thickness of compressed soil layer below vertical drainage body; H——the thickness of filler and surface structure above the elevation of the top surface of the supporting plate; the vertical drainage distance of consolidated soil layer; the grouting hole (section) depth (m); Hc——the height of soil arch; Hg——the height of the building from the natural ground; Hmax——the maximum uplift amount required for rectification; Hmax——the maximum uplift amount that the structure can bear at one time; h——the falling distance; the minimum design thickness of fill above cushion; the width of stirring vane; h0——the vertical distance from the bottom of the supporting plate to the upper fabric reinforcement; hi——the thickness of the i-th soil layer; hc0 and h1——the cushion thickness; the thickness of supporting plates; h1i——the adjusted value of the existing uneven settlement of the building; h2i——the overall uplift amount; h3i——the measured and adjusted value of residual uneven deformation of foundation soil; L——the depth of vertical drainage body; LNi and LEi——the distance calculated from point i to the base point of the building in the north-south and east-west directions; l——the length of foundation bottom surface, the pile length and the pile spacing; li——the thickness of rock and soil in i-th layer; R′——the effective diffusion distance or diffusion radius of slurry; Ri——the hole radius; S——the pile spacing; the settlement of flexible structures; s1——the compression deformation amount of soil layers within the pile reinforcement depth; s2——the compression deformation amount of soil layers below the pile reinforcement depth; s3——the compression deformation amount of the cushion and filler above the supporting plate; Sd——the instantaneous settlement; Sf——the final vertical deformation amount; S——the final settlement; Ss1——the compression amount of the composite soil layer composed of short piles and soil between piles; Ss2——the compression deformation amount of the soil layer under the pile tip of short piles; Sp1——the compression deformation of the cushion between the pile top and base; Sp2——the deformation amount of pile shaft and pile tip soil layer; Sp——the corresponding settlement of the base at the pile top under the characteristic value (Ra) of the pile bearing capacity; Ss——the settlement of natural foundation at the corrected bearing capacity characteristic value under base action fak; Ssp——the settlement of reinforcement area; S2——the settlement of soil layer below the bottom of reinforcement area; Sf——the final vertical deformation amount; SH——the actual horizontal displacement value of the building; sH——the building declination reduced amount; the design control value of horizontal displacement when building is rectified; up——the perimeter of pile; Qtotal and Qsingle——the total grouting amount and the grouting amount of single hole respectively; V——the sinking (or lifting) speed of stirring head; v——the volume of soil grouted; wop——the optimum moisture content; z——the thickness of replacement layer of compacted fill under base bottom surface; ∑z——the total number of stirring vanes; θ——the pressure diffusion angle; δ——the thickness of plastic drainage plates; △——the allowable sag height of reinforced material. 2.2.4 Calculation coefficients Ch and Cv——the radial and vertical drainage consolidation coefficient of soil; Fn——the drain spacing ratio factor; ——the conversion coefficient, ranging from 0.75 to 1.0, generally 1.0; Ip——the plasticity index; m——the area replacement rate; n′——the pile-soil stress ratio; n——the number of layers of foundation soil; the drain spacing ratio; the rotating speed of stirring head; the porosity of soil; Q——the driving depth ratio of vertical drainage body; Ti and Ti-1——the start and end time for loading the Class i load; ——the average consolidation degree of radial drainage to vertical drainage body foundation when load for a period of t; ——the average consolidation degree of foundation at the time of t; Urz——the average consolidation degree of soil layer within the driving depth of vertical drainage body; Uz——the average consolidation degree of compressed soil layer below the driving depth of vertical drainage body; um——the average consolidation degree of foundation soil; α——the reduction coefficient of bearing capacity of natural foundation soil at pile tip; the drainage consolidation parameters of foundation soil; the loss coefficient of slurry; β——the reduction coefficient of bearing capacity of soil between piles; the vertical included angle between stirring vane and stirring shaft; the drainage consolidation parameters of foundation soil; the slurry filling coefficient; βhp——the influence coefficient of punching shear height; βN and βE——the base inclination of the building in north-south direction and east-west direction; λc——the compaction coefficient; ——the efficiency factor of bearing capacity of single pile; the growth rate of base pressure; ——the empirical coefficient considering the influence of lateral deformation; ——the strength reduction coefficient of cement-soil of pile shaft; the partial coefficient of combination of permanent load and variable load; 3——the efficiency factor of bearing capacity of soil between piles; ψp——the empirical coefficient of pile shaft compression; ψs2——the empirical coefficient for calculating the compression deformation amount of rock-soil layers below the pile reinforcement depth. 3 Basic requirements 3.0.1 Before foundation soil treatment and design, the following work shall be completed: 1 Collect the geotechnical investigation data, superstructure and base design data of the site; When there is no experience in the physical and mechanical indexes of soft soil, reference may be made to Annex D. 2 Learn the local ground treatment experience and construction conditions according to the engineering situation. For engineering with special requirements, learn the ground treatment experience and usage of similar engineering on similar sites in other regions.   3 Determine the purpose and scope of the ground treatment as well as the technical and economic indexes required to be met after treatment based on the engineering requirements and major problems by using of natural foundations; 4 Investigate the present situation of adjacent buildings (structures), underground works, surrounding roads and buried pipelines. 3.0.2 During the selection of the ground treatment scheme, the combined action of superstructure, base and foundation should be considered, and multiple schemes shall be compared technically and economically. 3.0.3 The determination of ground treatment method shall meet the following requirements: 1 Determine the feasible ground treatment scheme according to the superstructure type, load size, use requirements and foundation and base design grade and through comprehensive analysis made based on topography, stratum structure, soil conditions, groundwater characteristics, environmental conditions and influence on adjacent buildings (structures), construction conditions and other factors. 2 For the selected ground treatment methods, experimental construction should be carried out in representative sites based on the design grade of building foundations and bases and the complexity of the site, and field tests shall be carried out to inspect the design parameters and treatment effect. 3.0.4 For the treated foundation, the characteristic value of the bearing capacity of the foundation shall be corrected if the bottom area and buried depth of the foundation are determined according to the bearing capacity of the foundation, and the following requirements shall be met: 1 For large-area compacted filling foundation, the correction coefficient of foundation bearing capacity of base width shall be zero; the correction coefficient of foundation bearing capacity of base buried depth shall be 1.5 for silty soil with compaction coefficient greater than 0.95 and clay particles content ρc ≥ 10%, and shall be 2.0 for graded sand and stone with maximum dry density greater than 2.0t/m3. 2 For other treated foundations, the correction coefficient of foundation bearing capacity of the base width may be zero; and the correction coefficient of foundation bearing capacity of the embedded depth of base may be 1.0. 3.0.5 For the cement-soil pile composite foundation and rigid pile composite foundation, the pile shaft strength shall be checked according to the corrected characteristic value of composite foundation bearing capacity. 3.0.6 The treated foundation shall meet the requirements for bearing capacity, deformation and stability of building foundations. The ground treatment design shall be checked in the following cases: 1 For the treated foundations, the checking of bearing capacity of soft substratum foundation shall be carried out if there still is a soft substratum within the scope of stress layer. 2 According to the current standard of Guangdong DBJ 15-31 Design code for building foundation, the foundation deformation calculation shall be carried out, and for the buildings or structures ought to be subjected to ground treatment, the treated foundation shall be subjected to deformation checking. 3 The foundation stability shall be checked if buildings and structures are subjected to large horizontal loads on the treated foundation or are located on slopes. 4 The bearing capacity checking of treated foundation shall meet the requirements for axial load action and eccentric load action. 5 For integral large-area bases with large stiffness difference, the combined action of superstructure, base and foundation should be carried out for the ground treatment, and the foundation bearing capacity and deformation shall be checked. 3.0.7 The circular sliding method may be used for the overall stability analysis of the treated foundation, and its stability safety factor shall not be less than 1.30. The shear strength index of granular reinforcement materials may be determined by test according to the compactness of solid materials; the shear strength index of cementing materials may be determined according to the friction performance of sliding surface material after pile shaft fracture. 3.0.8 The materials used for ground treatment shall meet the requirements for durability design and use in current relevant standards. 3.0.9 For the bearing capacity inspection of foundation treated with multiple methods, large-size bearing plates involving each of the aforesaid methods should be used for load test, and the maximum load shall not be less than 2.0 times of the characteristic value of bearing capacity. 3.0.10 After treatment, the foundation load test, composite foundation load test and composite foundation reinforcement single pile load test shall be carried out according to Annexes A, B and C of this Code respectively.   3.0.11 For buildings or structures that need to be subjected to foundation deformation calculation according to the current national standard GB 50007 Code for design of building foundation, after ground treatment, settlement observation shall be carried out until the settlement meets the stability criteria. 4 Replacement layer of compacted fill and compacted ground 4.1 General requirements 4.1.1 The replacement layer of compacted fill is suitable for ground treatment of shallow soft soil layers or uneven soil layers. Compacted ground is suitable for treating large-area filling foundations. 4.1.2 The replacement layer of compacted fill shall be designed and the construction method shall be selected after comprehensive analysis is carried out based on building shape, structural characteristics, load nature, site soil conditions, construction machinery and equipment, and filler properties and sources. 4.1.3 For replacement layer of compacted fill with large quantities, field test shall be carried out based on the selected construction machinery, replacement materials and soil conditions of the site to determine the compaction effect of replacement layer of compacted fill and the construction quality control criteria. 4.1.4 The thickness of the replacement layer of compacted fill shall be determined based on the depth of replacement soft soil and the bearing capacity of the underlying soil layer, and should be 0.5m~3.0m. 4.2 Design (I) Foundation of replacement layer of compacted fill 4.2.1 The thickness of replacement layer of compacted fill, z, shall be determined based on the depth requiring soft soil replacement or the bearing capacity of the underlying soil layer, and shall meet the following equation: pz＋pcz≤faz (4.2.1-1) where, pz——the additional pressure at the cushion bottom if the action equivalents to the standard combination of actions, kPa; pcz——the deadweight pressure value of soil at the bottom of cushion, kpa; faz——the characteristic value of foundation bearing capacity after the soil layer at the cushion bottom after depth correction, kPa; The additional pressure at the bottom of the cushion, pz, may be calculated using Equations (4.2.1-2) and (4.2.1-3) respectively: For strip foundations: (4.2.1-2) For rectangular foundations: (4.2.1-3) where, b——the width of bottom of rectangular foundation or strip foundation, m; l——the length of bottom of rectangular foundation, m; pk——the average pressure value of base bottom (weight transmitted from superstructure, deadweight of base and backfill weight on base surface) if the action equivalents to the standard combination of actions, kPa; pc——the deadweight pressure of soil at the base bottom surface, kpa; z——the thickness of the cushion under the base bottom surface, m; θ——the pressure diffusion angle of cushion (material), °, which should be determined by test. If no test data is available, it may be selected according to Table 4.2.1.

Contents of DBJ/T 15-38-2019

Foreword i 1 General provisions 2 Terms and symbols 2.1 Terms 2.2 Symbols 3 Basic requirements 4 Replacement layer of compacted fill and compacted ground 4.1 General requirements 4.2 Design 4.3 Construction 4.4 Quality inspection 5 Dynamic compaction and composite foundation with dynamic-replaced stone column 5.1 General requirements 5.2 Design 5.3 Construction 5.4 Monitoring and quality inspection 6 Preloaded foundation 6.1 General requirements 6.2 Design 6.3 Construction 6.4 Monitoring and quality inspection 7 Composite foundation with vibroflotation gravel pile 7.1 General requirements 7.2 Design 7.3 Construction 7.4 Quality inspection 8 Composite foundation with cement deep mixed columns 8.1 General requirements 8.2 Design 8.3 Construction 8.4 Quality inspection 9 Composite foundation with jet grouting 9.1 General requirements 9.2 Design 9.3 Construction 9.4 Quality inspection 10 Rigid pile composite foundation 10.1 General requirements 10.2 Design 10.3 Construction 10.4 Quality inspection 11 Composite foundation with different piles or lengths 11.1 General requirements 11.2 Design 11.3 Construction 11.4 Quality inspection 12 Pile-reinforced earth composite foundations 12.1 General requirements 12.2 Design 12.3 Construction 12.4 Quality inspection 13 Ground improvement by permeation and high hydrofracture grouting 13.1 General requirements 13.2 Design 13.3 Construction 13.4 Monitoring and quality inspection 14 Reinforcement of micropiles 14.1 General requirements 14.2 Design 14.3 Construction 14.4 Quality inspection 15 Foundation reinforcement of existing building 15.1 General requirements 15.2 Design 15.3 Reinforcement construction 15.4 Rectification construction 15.5 Monitoring and quality inspection 16 Treatment of polluted earth foundation 16.1 General requirements 16.2 Design 16.3 Construction 16.4 Quality inspection Annex A Key points of static load test for treated foundation Annex B Key points of static load test for composite foundation Annex C Key points of single pile load test of composite foundation reinforcement Annex D Statistical table of physical and mechanical property indexes of main soft soils in Pearl River Delta Explanation of wording in this code List of quoted standards