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中華人民共和國行業(yè)標(biāo)準(zhǔn) Industrial Standard of the People’s Republic of China JGJ 123-2000 既 有 建 筑 地 基 基 礎(chǔ) 加 固 技 術(shù) 規(guī) 范 Technical Code for Improvement of Soil and Foundation of Existing Buildings Beijing, 2000 本英文版為內(nèi)部資料，僅供參考，以中文 版為準(zhǔn)。 The Chinese version of standards has precedence to their English translations which are only for internal reference. — 1 — 中華人民共和國行業(yè)標(biāo)準(zhǔn) Industrial Standard of the People’s Republic of China 既 有 建 筑 地 基 基 礎(chǔ) 加 固 技 術(shù) 規(guī) 范 Technical Code for Improvement of Soil and Foundation of Existing Buildings JGJ 123-2000 Mainly prepared by: Research Institute of Construction Science of the People’s Republic of China Approved by: Ministry of Construction of the People’s Republic of China Implementation date: June 1, 2000 — 2 — Notice on issuing the industrial standard “Technical Code for Improvement of Soil and foundation of Existing Buildings” Jian Biao [2000] No.35 As per the requirement in “Notice on Issuing Compilation and Revision Project Plan for Construction Project Industrial Standards of 1993” (Jian Biao 1993 No. 285), “Technical Code for Improvement of Soil and Foundation of Existing Buildings” compiled by Research Institute of Construction Science of People’s Republic of China is hereby reviewed and approved as compulsory industrial standard, number as JGJ 123-2000, and should come into force from June 1, 2000. The subject standard will be managed and interpreted by the Research Institute of Construction Science of P. R. China which is the technical responsible unit for the Ministry of Construction. The Research Institute of Standard Quotas organized China Construction Publishing House to publish the standard. Ministry of Construction of People’s Republic of China February 12, 2000 — 3 — Forward As per the requirement of Jian Biao 1993 No. 285 issued by the Ministry of Construction, the code compilation team hereby compiled this code through extensive investigation and research, with many research results home and abroad and a large amount of construction practice experiences summarized, and through opinions broadly solicited. The technical contents of this code many consist of general rules, symbols, basic stipulation, verification of soil and foundation, foundation calculation, improvement methods of soil and foundation, remedy and prevention of soil and foundation incident or accident, improvement through added layers, reinforcement to rectify incline or replacement, and etc. The code is managed and interpreted by the Research Institute of Construction Science of P. R. China which is the technical responsible unit for the Ministry of Construction. The code is mainly compiled by the Research Institute of Construction Science of P. R. China (Address: 30 East Third North Ring Road, Beijing; Postcode 100013) The code is jointly compiled by Tongji University, Nothern Communication University, Research Institute of Construction Science of Fujian province. The code is mainly compiled by following personnel: Zhang Yongjun, Ye Shuqi, Tang Yeqing, and Hou Weisheng. — 4 — Table of Content 1 General Rules.5 2 Symbols .5 3 Basic stipulation.6 4 Verification of Soil and Foundation 7 5 Foundation Calculation9 6 Methods for Improvement of Soil and Foundation .11 7 Remedy and Prevention of Soil and Foundation Incident .27 8 Modification to Add Stories 32 — 5 — 1 General Rules 1.0.1 In order to execute the technical and economical policy of the country during the design and construction of the improvement of soil and foundation, the code is compiled so that “advanced technology, reasonable economy, safety and adequacy, ensured quality and protected environment” can be achieved. 1.0.2 This code is applicable to design and construction of any improvement to soil and foundation caused by inadequate soil investigation, design, construction, or operations, by increased load, incline, displacement, reconstruction or protection of ancient buildings, or by nearby new buildings, excavation of deep foundation pits, new underground services, or natural disaster. 1.0.3 The design and construction of improvement of soil and foundation of existing buildings, besides meeting the requirements of this code, should meet the requirement of relevant national compulsory standards which is in force. 2 Symbols A – Bottom area of foundation d – Pile diameter d’ – Diameter of lime pile after expansion Ep – Compression modulus of pile body Es – Compression modulus of soil between piles Esp – Compression modulus of compound soil layer F – Design value of the vertical force on the top surface of foundation from upper structure after reinforcement of foundation or load increased. f – Design value of foundation bearing capacity fs,k – Standard value of bearing capacity of soil between piles after improvement fp,k – Standard value of bearing capacity of pile unit section fsp,k – Standard value of bearing capacity of compound foundation G – Design value of foundation weight and weight of soil on top of foundation l1 – Line distance of piles l2 – Row distance of piles M – Design value of moment applied to the bottom of foundation after improvement or increased load m – Replacement ratio of area Na – Design value of bearing load for uplifting point — 6 — N – Number of uplifting points p – Design value of average pressure on the bottom of foundation after improvement or increased load pmax – Design value of maximum pressure along the side of the bottom of foundation after improvement or increased load pmin – Design value of minimum pressure along the side of the bottom of foundation after improvement or increased load Q – Design value of total load for building q – Lime volume for each meter of lime pile s – Final settlement of foundation s0 – Settlement achieved before improvement or increased load s1 – Settlement achieved after improvement or increased load s2 – Settlement to be achieved under original building load W – Sectional modulus at the bottom of foundation after improvement or increased load ηc – Expansion factor 3 Basic stipulation 3.0.1 Before improvement of soil and foundation of existing buildings, soil and foundation should be examined to enable design and construction. The examination of soil and foundation, and design and construction of improvement should be carried out by companies with relevant certifications and by professional personnel with experiences. 3.0.2 Design of improvement of soil and foundation of existing buildings should be carried out according to the following steps: 1 When selecting method for improvement, objective of improvement, joint function of upper structure, foundation and soil should be considered to decide initially whether soil, foundation, stiffness of upper structure or combination of soil and foundation should be improved. 2 After the initial schemes are selected, they should be compared through expected achievement, difficulty of construction, material availability and delivery conditions, safe constructability, impact to adjacent building or environment, conditions of construction equipment, construction period and cost, so that a optimum scheme can be selected. 3.0.3 The construction people should understand the objective of improvement, theory, technical requirement and quality standard for the improvement project undertaken. — 7 — Dedicated personnel are required for quality control through strict monitoring. Whenever an abnormal condition is observed, meeting should be held with designers and relevant department to analyze the problem and find solutions. 3.0.4 A dedicated organization is required to supervise quality during construction. When the construction is complete, quality inspection and acceptance should be conducted. 3.0.5 Settlement observation is required during construction of improved to soil and foundation. For buildings of importance or of strict restriction of settlement, settlement observation should be continued after the improvement until it becomes stable. Adjacent buildings and underground services should be monitored at the same time. 4 Verification of Soil and Foundation 4.1 Verification of Soil 4.1.1 The following steps should be observed when examining soil of existing buildings, 1 Collect geotechnical investigation information, design documents and drawings of foundations for existing buildings and upper structure, construction recorded of concealed parts, and as-built drawings. 2 The following things should be analyzed when studying the original geotechnical investigation information. 1) Distribution and evenness of subsoil, weak underlying layer, special soil, gullies, ditches, rivers, tombs, caves, and holes. 2) Physical and mechanical properties of subsoil. 3) Water level and corrosivity of groundwater 4) Liquefaction characteristic of silt or sand, and earthquake characteristic of soft soil 5) Stability of site 3 Investigate the current condition of the building, actual working load, settlement, and settlement stability, differential settlement, distortion, incline and crack etc, and find causes. 4 Investigate adjacent buildings, underground services, and pipeline. 5 Work out inspection method to verify the soil based on the objective of improved, together with information collected and analyses of information. 4.1.2 The following methods can be adopted for inspection of soil according to improvement requirement and site condition. — 8 — 1 Drilling, pit exploration, channel exploration, or earth physical method can be adopted. 2 Indoor physical mechanical property test can be carried out on undisturbed soil. 3 In-situ tests like load test, cone penetration test, standard penetration test, dynamic penetration test, cross-board shear test or side pressure test can be adopted. 4.1.3 Inspection of soil of existing buildings should comply the following requirements. 1 According to the importance fo the building and original geotechnical investigation information, supplementary borehole or in-situ test hole should be provided to find out subsoil distribution and soil physical and mechanical properties. Holes should be close to foundation. 2 For important buildings that require adding stories or increase load, it is suitable to take undisturbed soil and carry out indoor physical mechanical property test or load test under the foundation. 4.1.4 When evaluating soil of existing building, the following requirements should be met. 1 According to the inspection result, together with local experience, a compressive evaluation of the soil should be prepared. 2 Decide whether it is necessary to improve soil and provide recommendations of improvement method based on the soil condition and upper structure. 4.2 Verification of foundation 4.2.1 Inspection of foundation of existing building should be carried out according to the following steps. 1 Collect design and construction documents for foundation, upper structure, and pipeline, and as-built drawings. Understand the actual load on different parts of the building. 2 Site proof is required. Exploration channel may be required to verify foundation type, material, dimension, and embedded depth. Examine crack in the foundation, corrosiveness, degree of damage, strength and grade of foundation materials. If the building inclines, then degree of incline and distortion should be investigated as well. For piled foundations, pile depth, bearing layer and pile quality should also be investigated. 4.2.2 The following methods can be adopted for the inspection of foundation of existing building. 1 Visual check of foundation — 9 — 2 Initial check with hand hammer to find out foundation quality. Find out strength or grade of foundation material using non-destructive method or core-taking method. 3 Check rebar diameter, number of piles, location, and corrosiveness. 4 Observe settlement of pile foundation. 4.2.3 When evaluating foundation of existing building, the following requirements should be met. 1 Evaluate completeness of the foundation based on cracks, corrosiveness, degree of damage and grade of materials. 2 Calculate bearing capacity and deformation based on the actual load and deformation characteristics. Decide whether it is necessary to improve, and recommend method of improvement. 5 Foundation Calculation 5.1 Calculation of bearing capacity 5.1.1 When the foundation of existing building need to be improved or the load is to be increased, the bearing capacity of soil should be calculated in accordance with following requirements. When the axial load works p=f (5.1.1-1) Where, p – design value of average pressure at the bottom of foundation after improved or increased load. f – Design value of soil bearing capacity, which should be determined based on the standard value determined through this code in accordance with current national standard “Code for building foundation design” (GBJ 7). For foundation that requires improvement, the standard value of soil bearing capacity should be determined through examination after the improvement. For soil with increased load, standard value of soil bearing capacity should be determined through examination before load is increased. For buildings with stabilized settlement, when adding stories, article 8.2 of this code may be referred to determine standard value of soil bearing capacity. When the eccentric load works, besides meeting the requirement of formula 5.1.1-1, the following formula should be met as well. pmax=1.2f (5.1.1-2) Where, — 10 — pmax – design value of maximum pressure along the bottom of foundation after improvement or increased load. 5.1.2 Pressure at the bottom of foundation after improvement or increased load may be determined through the following formula When the axial load works, p=(F+G)/A (5.1.2-1) Where, F – design value of vertical force on the top of foundation from upper structure after improvement or increased load G – design value of foundation weight and soil weight on top of foundation. If below water level, floating force should be deducted. A – foundation bottom area When the eccentric load works, pmax = (F+G)/A + M/W (5.1.2-2) pmin = (F+G)/A - M/W (5.1.2-3) Where, M – design value of moment applied to the bottom of foundation after improvement or increased load W – sectional modulus of foundation bottom after improvement or increased load. pmin – design value of minimum pressure along foundation bottom after improvement or increased load. 5.1.3 When there is weak underlying layer within the bearing layers of foundation, the bearing capacity of weak underlying layer should be calculated. 5.1.4 For existing buildings on a slope or adjacent to deep foundation pit, soil stability should be calculated as well. 5.2 Calculation of Soil Deformation 5.2.1 The calculated value of soil deformation after improvement or inreased load should not exceed the allowable value in the current national standard “Code for Building Foundation Design” (GBJ 7). 5.2.2 The final settlement of foundation for existing building after soil and foundation improvement or increased load shall be determined through the following formula. — 11 — s=s0+s1+s2 (5.2.2) Where, s – final settlement of foundation s0 – settlement achieved before improvement or increased load, which can be determined through settlement observation information or estimated according to local experience. s1 – settlement achieved after improvement or increased load. If soil and foundation are improved, the value can be calculated with the compression modulus after improvement. If the load is increased, the value can be calculated with the compression modulus before increased load. s2 - settlement to be achieved under original building load. The value can be estimated based on the settlement observation information or local experience. If the foundation settlement under original building load is stabilized, then the value should be zero. 5.2.3 Calculation of foundation settlement may be referred to the current national standard “Code for Building Foundation Design” (GBJ 7). 6 Methods for Improvement of Soil and Foundation 6.1 Mortar Filling Method 6.1.1 The method is applicable when cracks are found in foundations due to uneven settlement, frost heaving or other reasons. 6.1.2 When the method is applies, first drill a hole at the crack. The filling tube can be 25mm in diameter. Angle between the hole and the horizon should be no less than 30 degrees. The diameter of the hole should be 2-3mm greater than the diameter of the filling tube. The distance between holes may be 0.5 to 1.0 meter. 6.1.3 Cement Mortar can be used as filling material. Filling pressure can be 0.1 to 0.3 Mpa. If the mortar is not going inside, the pressure maybe increased to 0.6 Mpa slowly. If the filling material is not going inside for 10 to 15 minutes, filling can be stopped. The effective diameter of filling is 0.6 to 1.2 meters. 6.1.4 For single foundations, holes on each side of the foundation should be no less than two. For strip foundations, construction should be carried out by sections, with each section between 1.5 to 2.0 meters. — 12 — 6.2 Foundation Bottom Enlargement Method 6.2.1 When the bearing capacity of the foundation or the size of the foundation for the existing building can not meeting design requirement, foundation bottom enlargement method can be adopted. Concrete or reinforced concrete may be used to make the bottom of foundation bigger. The design and construction should meet the following requirements when making the bottom of foundation bigger. 1. If the foundation is under eccentric load, asymmetrical enlargement can be adopted while if the foundation is under central load, symmetrical enlargement. 2. The surface of original foundation should be made rough and washed clean, and a layer of high-strength cement mortar or concrete agent to increase the adhesive force of old concrete foundation and new concrete foundations. 3. For the enlarged area, a compacted blinding layer of the same thickness and materiel as the original blinding should be used. 4. When using concrete to improve the foundation, the dimension of added concrete should meeting the allowable height and width ration for stiff foundation stipulated in the current national standard “Code for Building Foundation Design” (GBJ 7). Anchor re-bar should be placed at certain distance along the height of the foundation. 5. When using reinforced concrete to improve the foundation, the main re-bars in the added part should be welded to the main re-bars in the original foundation. 6. For the improvement to strip foundation, sections of 1.5 to 2.0 meters should be planned, and construction should be carried by batches and sections at different times. 6.2.2 When concrete or reinforced concrete is not suitable for making the bottom of foundation bigger, single foundation may be changed into strip foundation, original strip foundation to cross strip foundation or raft foundation, or original raft foundation to box foundation. 6.3 Foundation Deepen Method 6.3.1 The method is applicable when good subsoil layer exists near grade, which can be used as bearing layer, and with low water table. Make the original foundation deeper, so that it sits on a better bearing layer to meet the bearing and deformation requirements of the design. When the water table is high, dewater or draining measures should be carried out. 6.3.2 The following steps should be observed when making foundation deeper. — 13 — 1. Excavate a 1.2 meter long, 0.9 meter wide vertical pit along the foundation of existing buildings by sections or batches. If the pit wall can not be upright due to sand soil or soft soil, then supports are required for the walls. The bottom of the pit may be 1.5 meters lower than the existing foundation. 2. Excavate a foundation pit under the original foundation, the width of which should be the same as the original foundation, and the excavation depth should reach the bearing layer required by the design. 3. Concrete should be poured at the site under the existin