《既有建筑地基基础加固技术规范

《既有建筑地基基础加固技术 规范 编程规范下载gsp规范下载钢格栅规范下载警徽规范下载建设厅规范下载 本英文版为内部资料，仅供参考，以中文 版为准。 The Chinese version of standards has precedence to their English translations which are only for internal reference. Industrial Standard of the People’s Republic of China JGJ 123-2000 Technical Code for Improvement of Soil and Foundation of Existing Buildings Beijing, 2000 Industrial Standard of the People’s Republic of China 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 — 1 — 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 — 2 — 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. — 3 — Table of Content 1 General Rules ......................................................................................................................... 5 2 Symbols .................................................................................................................................. 5 3 Basic stipulation ..................................................................................................................... 6 4 Verification of Soil and Foundation ...................................................................................... 7 5 Foundation Calculation .......................................................................................................... 9 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 — 4 — 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. 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 — 5 — 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 3.0.1 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. — 6 — 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. 4.1 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. — 7 — 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. — 8 — 1 Visual check of foundation 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. 5.1 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) — 9 — Where, 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 — 10 — improvement or increased load shall be determined through the following formula. 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). 6.1 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. — 11 — 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. — 12 — 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 existing foundation. The pour should be stopped when it is 80mm from the bottom of original foundation. After one day of curing, thick cement mortar with expansion agent and quick cure agent should be inserted into the gap under the existing foundation. Hammer the wood pieces to make the mortar tight. 6.4 Anchor Rod Static Load Pile Method 6.4.1 The subject method is applicable for mud, muddy soil, clay, silt and manual backfill. 6.4.2 The design of the Anchor rod static load pile should meet the following requirements. 1. The vertical bearing capacity of the subject pile should be determined through single pile load test. When there is not test information, the current national standard “Code for Building Foundation Design” (GBJ 7) can be referred to estimate the bearing capacity. 2. The pile should located next to the wall body or columns. Number of piles should be determined through the load of upper structure and single pile vertical bearing capacity. Static load on the pile should be controlled as not to exceed the sold weight of the structure to be improved. The hole for driving piles should be a square pyramid with small top and large bottom. The side of hole should be 50 to 100 mm greater than the dimension of the pile. 3. When the bearing capacity of the foundation for existing building can not meet static load requirement, foundation should be improved, or newly-poured reinforced concrete beam can be used as a platform for driving piles. 4. Manufacture of pile should meet the following requirements — 13 — 1) Reinforced concrete or steel should be used as pile material; 2) For reinforced concrete pile, square section is recommended with 200 to 300 mm section dimension. 3) Length of each section of pile should be determined based on the net construction space (height) and conditions of the construction machinery, which is recommended for 1.0 to 2.5 meters; 4) Main re-bar in the pile should be determined through calculation. When the section is 200mm, re-bar should be no less than 4ф10; when the section is 250 mm, re-bar no less than 4ф12ф; section 300mm, re-bar no less than 4ф16. 5) Concrete grade for pile should be no less than C30. 6) When the pile is under tensile force, welded connection should be adopted. In other cases, sulfur glue may be used as connection material. When sulfur glue is used for connection, re-bar mesh for welding should be put on both ends of the pile, one end with embedded re-bar, and the other end with reserved holes for re-bar and holes for lifting. When welding connection is used, embedded connection iron pieces should be put on both ends of the pile. 5. Besides meeting the requirement for bearing capacity, the following requirements should be observed for original foundation. 1) The net distance between side of the base and side pile is not suitable to be less than 200 mm, 2) The thickness of the base should be no less than 350mm. 3) The length of pile tip into the base should be between 50 to 100mm. When the pile bears tensile forces or there is any special requirement, anchor re-bar should be places at four corners of pile top. The length of anchor into the base should meeting anchor requirement of re-bar. 4) The hole for driving pile should be filled and compacted with C30 slight expansive concrete; 5) When the thickness of original foundation is less than 350 mm, hole for seal pile should have 2ф16 re-bar cross welded onto the anchor bar. When pouring concrete to the hole for driving piles, pile cap should be poured on top of the hole, with the thickness no less than 150mm. 6. Straight bolts or welded bolts maybe used as anchor rod. At the same time, the following requirements should be met. 1) When the static load for driving pile is less than 400kN, M24 anchor bar may be used; and when the load is between 400 to 500 kN, M27 anchor bar may be used. 2) The embedded depth of anchor bolt may be 10 to 12 times of bolt diameter, and — 14 — should be no less than 300 mm. Anchor rod above the base should meet the requirement of piling rig, which normally should be no less than 120mm. 3) Epoxy mortar or sulfur glue may be used in the anchor rod hole as the adhesive agent for anchor bolts. 4) The distances between anchor rod and hole for driving piles, or adjacent structure or side of base should be no less than 200mm. 6.4.3 During construction of anchor rod static load pile, the following stipulations should be observed. 1. The following preparation should be carried out prior to construction 1) Clean the construction faces for hole for driving piles and anchor hole. 2) Preparation for manufacture of anchor bolts and pile sections. 3) Excavate hole for driving piles, make the hole rough, and then make it clean. Cut the re-bar of the original foundation and bend it, ready to be welded after pile driven. 4) Excavate anchor hole, make sure the hole is clean and dry before put the anchor rod, and then seal the hole with adhesive. 2. The following stipulations should be observed during construction. 1) Piling rig should be kept vertical during driving. The nut and anchor should be balanced and tightened. Tighten loosed nuts during pile driving. 2) Pile sections placed should be kept vertical. Make sure the jack, pile section, and driving hole are aligned at the same axial. No eccentric pressure is allowed for driving piles. Steel plate or plastic bag should be used as cushion material, and steel cap should be in place before driving piles. Plan difference of the pile location should not exceed ?20mm. The verticality of pile should not exceed 1% of the total pile length. 3) A pile should be driven to the design elevation at one attempt. If driving needs to be suspended, pile tip should be left in a soft soil layer, and driving should be resumed in no more than 24 hours. 4) Driving should be carried out symmetrically. It is not suitable using several rigs working on one single foundation. 5) Vertical axial of top and bottom section should be lined before welding of two sections. Full penetration is required after removal of rust on the surface of the welding face. 6) When sulfur glue is used to connect two pile sections, the relevant clauses in the current national standard “Code for Construction and Acceptance of Soil and Foundation Engineering” GBJ 202 should be observed. — 15 — 7) Pile tip should be embedded into the designed bearing layer. The driving force should reach 1.5 time the standard value for single pile vertical bearing capacity stipulated in the current national standard “Code for Building Foundation Design” GBJ 7, and the time should be no less than 5 minutes. 8) Pile top and sides should be made rough and clean before concrete interface agent is applied. Non-pre-stressed method or pre-stressed method can be chosen for sealing piles. When non-pre-stressed method is adopted, jack should be discharged, and pile rig removed when the pile reaches the designed driving force and the designed depth. Weld crossing re-bar for the anchor rod, removed debris, water or any slurry in the driving hole, and then pour C30 slight expansion accelerated concrete together with pile cap beam. When pre-stressed method is adopted, jack should not be discharged, and steel beam support should be used. Clean the driving hole and then immediately anchor the pile and driving hole together. When the sealing concrete reaches design strength, jack should be discharged. 6.4.4 The quality inspection of the pile should meet the following stipulation, 1 The final driving force and depth should meet the design requirement. 2 Strength of the cube for pile and cube for the sealing concrete should meet the design requirement. The strength of the sulfur glue should meet the stipulations in the current national standard “Code for Construction and Acceptance of Soil and Foundation Engineering” GBJ 202. 6.5 Tree Root Pile 6.5.1 The so-called tree root pile is suitable for repair or increase of stories of existing buildings, repairs of ancient buildings, or reinforcement of tunnel work on top of mud, muddy soil, clay, silt, sand, gravel or manual backfill. 6.5.2 The design of tree root pile should meet the following stipulations. 1 The diameter of pile is recommended as 150 to 300mm. The pile length is not suitable to be more than 30m. The layout of piles can be vertical type or network inclined type. 2 Vertical bearing capacity of tree root pile may be determined through single pile loading test. If there is not testing information, the capacity may be estimated according to the — 16 — relevant stipulations in the current national standard “Code for Building Foundation Design” GBJ 7. 3 The strength of concrete for the pile should be no less than C20. The outside diameter of the reinforcement cage should be 40-60mm less than the design pile diameter. Main re-bars should be no less than 3. For soft foundations, the length of re-bars taking main vertical load should be no less than 1/2 of the pile length. Re-bar under horizontal load should be arranged full length. 4 When designing tree root piles, bearing capacity of the foundation of existing building should be verified through calculation. If the above requirements are not met, the original foundation should be improved or new pile platform should be added. 6.5.3 The construction of the subject pile should meet the following stipulations. 1 The plan difference of pile location allowed is ?20mm. The verticality or degree of incline for inclined pile should not exceed 1% as per the design requirement. 2 Rig may be used to drill holes through existing foundations. Clean water, natural slurry or sleeve should be used to maintain the wall of holes. 3 It is recommended that reinforcement cage should be placed into the hole at one attempt. When the cage is placed by different sections, the overlapping of double-faced welding should be no less than 5 times of the re-bar diameter; if single-faced, 10 times. Mortar fill tube should be inserted to the bottom of the hole. Two filling tubes are required if a second filling is needed. Lifting and welding time should be kept as short as possible during construction. 4 When crushed stone or gravel is used as filling materials, it should be washed and the amount of filling should be no less than 0.9 time of the calculated volume of the hole. Water should be filled through the filling tube to clean the hole when filling mortar. 5 Cement slurry, cement mortar or gravel concrete may be used as filling material. When gravel is used, cement slurry should be used as filling mortar. 6 When one-time filling is adopted, the maximum working pressure of the pump should be no less than 1.5 Mpa. When starting to fill, an initial pressure of 1 Mpa is required to pump filling material through the tube to the bottom of the hole. Then filling pressure — 17 — should be adjusted to 0.1 to 0.3 Mpa so that the filling will start to flow up. Stop filling when the filling overflow in the hole. When two-time filling is adopted, the maximum working pressure of the pump should be no less than 4 Mpa. The second filling should not be started until the first filling is initially cured. The initial curing time may be determined through the type of cement and amount of agent added to the cement. Cement mortar or gravel concrete is not suitable for second filling. 7 Filling operations should be carried out at different times or adding more accelerator to avoid filling coming out from the next hole. Shrinking or collapse of pile should be also avoided. 8 Fill gravel at the top of the pile right after the filling tube is pulled out. Fill more mortar at the depth of 1-2 meters. 6.5.4 The quality inspection of tree root pile should meet the following stipulations. 1 One group of test cube should be kept for every 3 to 6 piles. Measure compression strength and make sure the pile strength meets design requirements. 2 Loading test should be carried out to determine the vertical bearing capacity of the pile. When experienced, dynamic test can be used to test pile quality. Either method should be in accordance with design requirements. 6.6 Pit Static Load Pile 6.6.1 Pit static load pile is applicable for mud, muddy soil, clay, silt, or manual backfill, with low water table. 6.6.2 The design of pit static load pile should meet the following stipulations. 1 Single pile bearing capacity of pit static load pile should be estimated in accordance with the current national standard “Code for Building Foundation Design” GBJ 7. 2 Open steel tube with 150 to 300mm diameter or pre-cast square concrete, 150 to 250mm in dimension may be used. Length of each pile section may be determined based on the net height of the pit under the foundation or the travel distance of the jack. — 18 — 3 Location plan of piles should be decided according to the wall body, type of foundation and load of existing building. Avoid weak points like windows or doors, and locate piles at the point of load. 4 If the strength of structure for existing building can not meet the counter force required to drive piles, reinforced concrete beam or channel beam should be placed at the reinforced part of the foundation to strengthen the strength and stiffness of the foundation structure, and to ensure safe work. 6.6.3 The construction of the pile should meet the following stipulations. 1 Excavate a 1.2-meter long, 0.9-meter wide vertical pit along the building to be improved, for sandy soil or soft soil, supports may be required to keep the pit vertical. Then excavate a 0.8-meter long, 0.5-meter wide foundation pit under the foundation, or foundation beam or platform beam. 2. Place the first pile section in the foundation pit, and then put the jack and force measurement sensor on top of the pile. Start the jack to drive pile. When the first section is driven, place the next section. For steel tube pile, sleeve connection may be used between different sections. When the section is very long or there is obstacle in the soil, and welding connection is required. Full penetration is required for the whole welding length including the connection of the sleeve. For pre-cast square concrete pile, combine main re-bars and then weld to the secondary re-bars on the tip. In the condensed sand or gravel type soil, steel pile cap may be use to wrap the pile tip. Welding connection or sulfur glue may be used between pile sections. 3 Plan displacement of the pile should not exceed ?20mm. Verticality of the pile should be less than 1% of the pile length. 4 Pile tip should be embedded to the designed bearing layer and the driving force should reach 1.5 times the standard value of single pile vertical bearing capacity stipulated in the current national standard “Code for Foundation Building Design” GBJ 7, and should last for no less than 5 minutes. 5 For square reinforced concrete pile, jack may be removed right after the pile reach the design depth, and then C30 slight expansive accelerated concrete may be used to make the pile and the original foundation one body. When pre-stress is applied to seal the pile, beam steel support may be used before pouring concrete. — 19 — For steel tube pile, pour C20 slight expansive accelerated concrete into the tube according to the requirement of the project, and then used C30 concrete to make the pile and original foundation one body. Pre-stressed method or non-pre-stressed method may be used for sealing the pile. 6.6.4 The quality inspection of the pile should meet the following stipulations. 1 The final driving force and depth should meet the design requirements. 2 Strength of cube for the pile should meet the design requirement. 6.7 Lime Pile Method 6.7.1 Lime pile method is applicable for improvement of clay, silt, loose silt sand, mud, muddy soil, mixed back fill, or saturated yellow soil under groundwater level. For important project, complex geotechnical condition or areas lack of experience, site test should be carried out to determine applicability of the method prior to construction. 6.7.2 The design of lime pile should meet the following stipulations. 1 Lime pile is made of raw lime and fly ash. CaO content of raw lime should not be less than 70%, silt content should not exceed 10%, water content should not exceed 5%, and maximum diameter should not be greater than 50mm. Fly ash used should be grade I or II. 2 According to geotechnical condition, different mixing ration may be used for lime pile. Common ration used (volume ratio) is 1:1, 1:1.5 or 1: 2 raw lime to fly ash. To increase the strength of pile, a certain amount of cement, sand or crushed stone may be added. 3 Pile diameter depends on the rigging machine. Pile distance should be 2.5 to 3.5 times pile diameter, located in triangle or square. The area improved should be foundation width plus one to two rows of piles, and the depth should not be less than half of improvement depth. Pile length should be determined according to objective of improvement and geotechnical conditions. 4 Lime for each meter of pouring may be estimated according to the following formula, q=ηc (πd 2/4) (6.7.2 – 1) Where q – lime required for each meter — 20 — d – design diameter ηc – Factor for expansion which may be 1.4 to 1.8. For vibration tube driven pile, high number should be used, and for spiral auger pile, low number. 3 Dry density of material during pouring should be controlled ρd = 1.1 t/m 5 A layer of 200 to 300 mm thick crushed stone or gravel is recommended to be placed at the top of lime pile. 6 Standard value of bearing capacity should be determined through load test at site or be calculated through the following formula. ƒ = m ƒ + (1-m) ƒ sp,kp,ks,k Where, ƒ - Standard value of bearing capacity sp,k ƒ – Standard value of bearing capacity for section area p,k ƒ – Standard value of bearing capacity for soil between piles after s,k improvement. m – Area replacement factor 2 m = πd’ / 4ll (6.7.2 – 3) 12 Where, d’ – pile diameter after expansion, usually 1.1 to 1.2 time pile diameter l, l – row or line distance respectively. 12 Load test of compound foundation may be carried out according to stipulations in the current national standard “Technical Code for Building Foundation Improvement” JGJ79. When the basic bearing capacity of compound foundation is determined through relevant deformation value, corresponding value to s/b or s/d = 0.010 – 0.015 may be used. (s – corresponding compression plate settlement under basic bearing capacity of compound foundation. b and d are the width and diameter of compression plate respectively.) 7 Deformation calculation for soil with lime pile improvement should be carried out according to the current national standard “Code for Building Foundation Design” GBJ 7. The compression modulus of compounded subsoil may be estimated according to the following formula. E = mE + (1-m)E spps Where E– compression modulus of compound foundation sp E– compression modulus of pile body p E – compression modulus of soil between piles after improvement s 6.7.3 The construction of lime pile should meet the following stipulations. 1 According to improvement design requirement, geotechnical condition, site condition, — 21 — and machinery availability, vibration piling method ( inside tube or outside tube), hammer compaction piling method, spiral drilling pile or Luoyang shovel piling method may be used. The center point of pile location should not exceed 8% of the designed pile distance. The verticality of pile should not exceed 1.5%. 2 Vibration piling method and hammer compaction piling method 1) If inside tube filling is used for vibration pile, to avoid block of tube due to lime expansion, compression air or in-air filling device should be added, and if outside tube filling, amount of filling and depth of tube should be controlled. If hammer compaction piling method is used amount of filling and depth of tube should be controlled according to the energy of hammer. 2) Empty part on top of pile should be seal with 3:7 gray soil or plain soil 3 Spiral drilling piling method 1) When drilling, some soil is taken out to ground, and other is push into pile hole wall, thus a hole is produced. Check site condition against original geotechnical report to see if it meets the design requirements based on current of drilling machine and soil conditions. 2) When drilling rod arrives design depth, lift it up to check hole quality, clear off the soil on the drilling rod 3) Put filling material for whole pile around drilling rod in proportion, then put the drilling rod into ground again, this time the drilling rod will push filling material into bottom of hole and drilling rod will be pushed up by compacted filling material. When drilling rod is 1 to 1.5 meters below grade or preset elevation, stop filling and use 3:7 gray soil or plain fill to seal the hole. 4 Luoyang shovel piling method The method is applicable for improvement of congested construction site. Pile diameter cn be 200 to 300 mm with each layer of filling material no more than 300 mm thick. Rod hammer is to be used for compaction by layers. 5 During construction, dedicated personnel is required to monitor quality of hole and filling material, and make records. If soil is found to be different from geotechnical report, investigation should be made and effective measures should be taken before construction continues. 6 When water content of subsoil is high, piling should be from outside to inside or along water flow direction, jump piling is also recommended. — 22 — 6.7.4 Quality inspection of lime pile should meeting the following stipulations. 1 Construction records should be checked in a timely manner during construction. When filling material is found to be not enough, and pile diameter is less than design, effective remedial measures should be taken immediately. 2 Check if ground is pushed out, or any pile is missed. Check pile location and distance and take records as per the design requirements. When non-conformance is found, remedy should be taken out. 3 For general construction, standard penetration test, cone penetration test or laboratory test of drilled samples can be used 28 days after completion of construction to test strength of pile and soil between piles for verification. 4 For important or large project, load test of compound foundation should be carried out. 5 Pile inspected should be no less than 2% of total piles, and should not be less than 3 piles. 6.8 Grouting Method 6.8.1 Grouting improvement method is applicable for sand, silt, clay or manual backfill. Usually the method is used to seal leakage, improve the strength and deformation modulus of the soil and to control settlement of ground. Before design, indoor mix ratio test and site grouting test should be conducted to determine design parameters and inspect construction method and equipment. Local experience of similar project can be referred to determine design parameters. 6.8.2 The design of grouting should meet the following stipulations. 1 For improvement of soft soil, grout with cement as main agent may be selected or a mixture of cement and water glass may be used. When there is flowing groundwater, single fluid cement grout should not be used. 2 Distance between grouting holes should be 1.0 to 2.0 meters, and make sure that the soil to be improved can be interconnected horizontally and vertically. — 23 — 3 Initial curing time of grout should be determined according to soil condition and objective of grouting. In sand soil, the initial curing time should be 5 to 20 minutes; while in clay soil, 1 to 2 hours. 4 Amount of grouting and effective range of grouting should be determined through site grouting test. In clay soil, the filling percentage should be 15% to 20%. The soil layer above the filling point should be greater than 2 meters. 5 For cracking grouting, 0.2 to 0.5 Mpa should be used for sand while 0.2 to 0.3 Mpa for clay. For compaction grouting, if cement mortar is used as grouting material, the slump should be 25 to 75mm with grouting pressure 1 to 7Mpa. If the slump is fairly small, the maximum value may be used for grouting pressure. When quick-cure double-fluid grouting, mixture of cement and water glass is used, the filling pressure should be less than 1Mpa. 6.8.3 The construction of grouting method should meet the following stipulations. 1 The site should be leveled prior to construction. Trenches and water sump should be excavated along location of bore-holes. 2 When filling, auto flow meter and pressure recording gauge should be used, and records should be collected and analyzed in a timely manner. 3 Hole diameter for filling should be 70 to 100mm. Verticality should be within 1%. 4 Construction of flower tube grouting should be carried out in the following steps. 1) Rig and grouting equipment mobilized to location; 2) Drill hole or use vibration method to put tube into soil; 3) When drilling method is used, seal slurry should be filled through drilling rod, and then insert a 50mm diameter metal tube; 4) When the seal slurry is cured, move tube from bottom to top or vice versa to fill. 5 Construction of compaction grouting should be carried out in the following steps. 1) Rig and grouting equipment mobilized to location; 2) Drill hole or use vibration method to put metal filling tube into soil; 3) When drilling method is used, seal slurry should be filled through drilling rod, and then insert a 50mm diameter metal tube; 4) When the seal slurry is cured, removed the plug on the tube and then lift the tube to fill double-fluid quick cure grout from bottom to top or top to bottom, which is — 24 — mixed by cement and mortar or mixed by cement and water glass. 6 The compression strength of 7-day test cube for seal slurry (side length 7.07cm) should be 0.3 to 0.5 Mpa, with a velocity of 80 to 90s. 7 No. 425 or 525 Portland cement should be used as grouting material. 8 Fly ash may be used to replace some cement for grouting. Quantity of fly ash may be 20% to 50% of cement weight. 9 If required, accelerator, water reducing agent or other agent may be added to the grout. 10 Water used for grouting should not be acid water with PH value less than 4 or industrial waste water. 11 Water and ash ratio can be between 0.6 to 2.0 for cement mortar. Common ration used is 1.0. 12 Flow velocity of grouting may be 7 to 10 L/min. For filling type grouting, the flow velocity should not exceed 20 L/min. 13 When using flower tube or metal tube with plug, the height of lifting or drilling should be 0.5 meter. 14 Grout should be mixed thoroughly in a mixed before filling. Grout should constantly stirred during filling and the mixed time should be less than the initial curing time of grout. Grout should be filtered through a mesh before filling. 15 Measures should be taken to avoid frost of grout when the day average temperature is less than 5 degrees or the lowest temperature is less than –3 degrees. 16 Water temperature should not exceed 30 to 35 degrees. Grout bucket or tube should not be exposed to sunlight when filling is not going to avoid cure of grout. 17 Filling should be carried out in the sequence of jump fill and should be started from outside to inside. When the ground water flow is fairly large, fill should be started from the high end of the flow. — 25 — 18 For soil layers with same permeability, the top should be seal with grout first, and then fill from bottom to top to avoid overflow of grout. If the permeability increases as depth increases, then filling should be carried out from bottom to top. For inter-bedding layers, fill should be first carried out in layers with large permeability or pore ratio. 19 When grouting is carried out to improve soil or foundation of existing building, monitor the existing building and adjacent building, settlement, incline, displacement or cracks of underground pipelines and ground. Try to avoid any additional settlement to the existing building by using multi-hole filling at different times, and reduce curing time of grout. 6.8.4 The quality inspection of grout should meet the following regulations. 1 Test of grout should be carried out 28 days after filling. Standard penetration, light dynamic penetration or cone penetration may be used to test the improved soil or foundation. For important project, loading test may be used to measure. 2 2% to 5% of the total fill holes should be tested. When the pass percentage is less or equal to 80%, or if the percentage is greater than 80%, but the average value can not meet the requirements on strength or leakage, then the unqualified area should be filled again. 6.9 Other Foundation Improvement Methods 6.9.1 High-pressure jet grouting method is applicable for mud, muddy soil, clay, silt, yellow soil, sand, manual backfill and gravel. 6.9.2 Soil-lime compaction pile method is applicable for collapsible loess, plain back fill or mixed backfill about the ground water. 6.9.3 Deep mixing method is applicable for mud, muddy soil, silt or clay with fairly high water content. 6.9.4 Silicide method, either double-fluid method or single-fluid method may be used. If the permeability factor is greater than 2.0m/d grain soil, double-fluid method may be used (water glass and potassium chloride); if the permeability factor is between 1.0 to 2.0 m/d for collapsible loess, single-fluid method may be used (water glass). For sole weight collapsible loess, single-fluid method without pressure should be used. — 26 — 6.9.5 Lye method is applicable for non-sole weight collapsible loess. 6.9.6 The design and construction of high-pressure jet grouting method, soil-lime compression method, deep mixing method, silicide method and lye method should meeting the relevant stipulations in the current national standard "Code for Building Foundation Improvement" JGJ79. 7.1 Remedy for Incident caused by Design, Construction or Improper Operations 7.1.1 For buildings on soil soft which experience damages, the following remedy may be carried out. 1 If damages are caused by differential settlement because of complex structure of building or heavy load, partial unloading, increase stiffness of upper structure or foundation, deepen foundation, anchor rod static load pile, tree root pile, or grouting method may be selected. 2 If damages are caused by differential settlement because of soft soil or hidden gullies or trenches in some part, anchor rod static load pile, tree root pile or spray grouting pile may be used to improve that part. 3 If damages are caused by large differential settlement or settlement due to heavy load or fast loading velocity, partial unloading, foundation bottom enlargement or foundation deepen method may be selected. 4. If there is uneven settlement of column foundation or wall foundation, large sediment of ground, or crack in columns or walls due to large area load or large area back fill, anchor rod static load pile or tree root pile may be used to improve the foundation. 5 If building inclines due to complex geotechnical conditions or uneven distribution of load, correction measures set forth in Chapter 9 in this code can be applied. 7.1.2 When damage occurs to buildings on the collapsible loess, the following remedies may be adopted. — 27 — 1 For non-sole weight collapsible loess, when the layer is not thick and deformation is getting stabilized, or if collapsible amount is not to be great when re-immersed with water, measures to improve upper structure may be used. If the layer is thick and deformation is great, or if collapsible amount will be great when re-immersed with water, lime pile, lime-soil compression pile, pit static load pile, anchor rod static load pile, tree root pile, silicide method or lye method may be selected. The depth improved should be to the lower limit of the compressive layer under the foundation. 2 For sole weight collapsible loess, lime-soil well, pit static load pile, anchor rod static load pile, tree root pile or poured pile may be used to improve. The improvement depth should go through the whole collapsible loess layer. 7.1.3 If damage occurs to building on manual backfill soil, the following remedies may be considered. 1 If damage is caused by uneven settlement because plain fill is immersed with water, anchor rod static load pile, tree root pile, pit static load pile, lime pile, or grouting method may be used to improve. The improvement depth should go through the plain fill layer. 2 For damage to buildings on mixed back fill, upper structure or foundation stiffness improvement, anchor rod static load pile, tree root pile, spray jet pile, lime pile or grouting may be used according to the degree of damage. 3 For damage to buildings on dredged back fill, use improvement method listed in Article 7.1.1 of this code. 7.1.4 For damage to building on the expansive soil, the following remedies may be used. 1 If damage is slight, and degree of expansion for soil is grade I, then widen water discharge or plant grass aground the building; 2 If damage is moderate, and degree of expansion for soil is grade I or II, then widen water discharge or strength structure stiffness. 3 If damage is serious, and degree of expansion for soil is grade III, then anchor rod static load pile, tree root pile, pit static load pile or foundation deepening may be adopted. Pile tip or foundation bottom should be embedded to the non-expansive layer or to the depth outside — 28 — the affect of atmosphere. 4 If damaged building is located in a sloped field, beside selecting corresponding improvement methods, measures should be taken to maintain water and to avoid water going different directions. 7.1.5 For damaged building on compound foundation of soil and rock, the following remedies may be taken. 1 If damage is caused by large differential settlement at the interface of soil and rock, partial foundation deepening, anchor rod static load pile, tree root pile, pit static load pile or spray jet pile may be used for improvement. 2 If damage is caused by large differential settlement due to soft soil in some part, foundation may be deepened or pile foundation may be used for improvement. 3 If damage is caused by exposure of bed rock in some part or big lonely stone, chip off exposed bed rock or lonely stone, place cushion mat, and then deepen the foundation or use pile foundation for improvement in the soil. 7.2 Prevention and Remedy to Incidents During Underground Construction 7.2.1 Underground construction may bring impact to existing building, underground pipeline or road. When the affected area is fairly large, partition wall may be used to separate existing building, underground pipeline or road. Steel plate pile, tree root pile, deep mixing pile grouting or underground continuous wall may be used as partition wall. 7.2.2 When underground construction brings impacts to existing building, the foundation of building may be improved. Anchor rod pile, tree root pile or grouting may be used as improvement method. The depth improved should exceed the depth of underground construction works. 7.2.3 When the impact from underground construction to existing building is small, methods may be used to improve the stiffness and strength of the existing building. 7.2.4 For communication cables, high-pressure, flammable, or explosive lines located in the affected area which are sensitive to ground deformation, beside general prevention — 29 — measures, they should be exposed and run overhead. 7.2.5 During underground construction, the settlement and displacement of existing building and underground line in the affected area should be monitored closely. Once a problem is found, effective measures should be taken in a timely manner. 7.3 Prevention and Remedy for Incident Due to Adjacent Construction 7.3.1 When construction of adjacent project may have an impact on existing building, type of foundation, structure status, year of completion, and operation condition should be investigated. Analyze possible impact according to the structure type, load requirement, type of foundation, distance from existing building and soil conditions, and then provide relevant prevention measures. 7.3.2 When pile foundation with compaction effect is used for soil soil which may have an effect to existing building. Sand pit, plastic water-discharge band, stress release hole or partition trench may be adopted along the side of existing building to reduce pore water pressure or compaction effect caused by driving of piles. Underground protection wall may be used for important buildings. 7.3.3 When piling construction has vibration effect, a vibration release trench may be excavated to reduce transfer of vibration wave. 7.3.4 When construction is carried out on adjacent building to excavate foundation pit, manually lower groundwater level, or correct incline, which may cause lateral deformation or applied stress, foundation of existing building may require improvement in some part to reduce the applied stress at that side and to control the settlement of existing foundation. 7.3.6 When adjacent construction causes crack or incline to existing building, according to the structure character , degree of impact, and subsoil condition, methods listed in Chapter 6 and 9 in this code may be used for improvement. 7.4 Prevention and Remedies to Incidents Caused by Construction of Deep Foundation Pit 7.4.1 Verification calculation and analysis should be carried for soil stability of adjacent — 30 — existing building and foundation pit before a foundation pit is excavated. If necessary, the soil or foundation of adjacent existing building may require improvement in advance to avoid any possible incidents. 7.4.2 When a foundation pit is excavated with water discharged which causes adjacent building or underground pipeline to settle, incline or crack, water discharge in the pit should be stopped at once to find out cause of incident and carry out effective improvement. When placing foundation pit supporting structure, water stop wall should be set at the outer side of foundation pit. Water table observation hole or recharge hole should be arranged next to adjacent building. 7.4.3 If pile foundation is used for building adjacent to foundation pit or pile foundation is used for new building, to ensure safety of adjacent existing building, the outer side of foundation pit support should be away from adjacent building 1.2 to 1.5 times depth of the foundation pit. When the minimum safe distance can not be met, vibration release trench or reinforced concrete underground continuous wall or other effective foundation pit support structure should be used. 7.4.4 When anchor rod support structure is used for foundation pit, foundation type and depth of adjacent building should be investigated in advance. Anchor rod driving operations are not allowed which will damage stability of soil or safety of foundation for adjacent existing foundation. 7.4.5 When existing building is close to foundation pit, no temporary construction building or warehouse is allowed around foundation pit. No construction material or spoil should be placed there. Large construction equipment or vehicles should not be placed next to the pit. These measures are to prevent any negative effect from above mentioned loads to the side wall of foundation pit or stability of adjacent existing building. 7.4.6 When existing building is close to foundation it, protective ground or water trench should be arrange around the pit so that ground water would flow to the outside of the pit, and rain water or construction water can be prevented from leaking into underground or pit. 7.4.7 When existing building or underground pipeline experiences incline, crack or damage because of foundation pit works around, remedy measures listed in Chapter 6 and 9 of this code should be used based on degree of affect. — 31 — 8.1 General Stipulation 8.1.2 When more stories need to be added to existing building, the structure of the building should be verified, then work out an execution plan and determine bearing capacity of soil according to stipulations in this chapter. When outer structure is used to increase stories, the bearing capacity of soil should be determined same as a new project. 8.1.2 Soil deformation and stability after modification to add stories should be verified through calculation as per the requirements in Chapter 5 of this code. 8.1.3 When old structure and new structure are to be connected through structural measures to add more stories, beside meeting the requirement for soil bearing capacity, soil deformation should be calculated separately for new structure and old structure and designed per the principle of deformation coordination. 8.1.4 When soil bearing capacity or deformation of existing building can not meet the loading requirement for adding stories, methods in Chapter 6 of this code may be used for improvement. 8.1.5 Quality of improvement to soil or foundation of existing building to enable adding stories should be inspected and evaluated same requirement as a new project. When the concealed work is checked and passed, construction of upper structure then can be started. 8.2 Direct Adding Stories 8.2.1 When directly adding stories to a building with stabilized settlement, the standard value of soil bearing capacity may be determined selecting from following methods according to the requirement for adding stories. 1 Testing 1) Loading Test Before adding stories, load test may be carried out according to the requirements in Attachment A of this code to directly determine the bearing capacity of soil. 2) Indoor Laboratory Test — 32 — Before adding stories, undisturbed soil may be taken at the depth of 1.0 to 1.5 time foundation bottom width under the foundation of original building. Test the soil sample in the laboratory and determine the standard bearing capacity of soil according to current codes. 2 Experiential Method When adding stories, the standard value of bearing capacity may be increased in consideration of the compaction effect. Degree of increase should be determined based on the average pressure at the bottom of foundation, years of services, type of soil and maturity of experience. 8.2.2 When stories are added directly, the design value for soil bearing capacity may be determined according to the stipulation in Article 5.1.1 of this code. 8.2.3 When new bearing wall is required for adding stories, bottom area of old and new foundation may be adjusted, pile foundation or soil improvement may be adopted to ensure even settlement of old and new bearing system. 8.2.4 Improvement to soil or foundation when adding stories may be chosen from the following methods based on type of foundation and soil condition. 1 When the soil under existing building is fairly good with high bearing capacity, bottom area of foundation may be enlarged and the enlarged area should be 10% higher than the calculated value. 2 When verifying strength of original foundation, strength should be deducted according to the actual situation. 3 When the soil under existing building is soft with low bearing capacity, pile foundation may be used to support the load of added stories. When the pile strength achieved the design requirement, construct the enlarged new foundation platform, connect the foundation to pile as per the requirement and calculated foundation settlement based on actual situation. 4 When the foundation of existing building is strip foundation of reinforced concrete, according to the loading requirement of added stories, anchor rod static load pile may be used for improvement. When the width or thickness of original reinforced concrete strip foundation can not meet the requirement for pile driving, foundation should be made wider or thicker to enable pile driving. Tree root pile or spray jet pile can be used as well for — 33 — improvement. 5 When the stiffness or integrity of original foundation is fairly good or there is reinforced concrete ground beam, supporting beam or suspended beam may be used to support the structural load of added stories, in which case, original foundation does not require any improvement. Beam may be placed under the original foundation or ground beam, when using pre-cast supporting beam, beam, column and foundation should be connected tightly, and loading requirement between beam and foundation or between ground beams. 6 When stiffness of upper structure and foundation is fairly good and bearing layer is embedded shallow with low groundwater level, and excavation will not bring any additional settlement or crack to the original structure, then block foundation or pit static load pile under original foundation may be used for improvement. 7 When using grouting method to improve soil of existing building, expansive agent and acceleration agent should be added for collapsible loess or back fill or if grouting will cause additional deformation of soil. 8 When pile foundation is used for existing building, quality and condition of piles should be checked. Measure physical mechanical properties of soil to determine compactness of soil between piles. Increase bearing capacity of original pile foundation if pile and soil are working together. If platform and soil are not connected, pile and soil should not be considered as working together. When number of piles is not enough, additional piles should be driven. For wooden piles or reinforced concrete piles which are rotten or damaged, repairs should be carried out before adding stories. 9 If original geotechnical investigation information for existing building is too simple or there is not geotechnical investigation information, and there are underground buildings or complex site conditions, additional geotechnical survey is required to find out site condition. 10 When column type structure on the wall is used for adding stories, column should be located on new foundations. Old and new foundations should be connected together. If soil is used as new foundation, gravel should be compacted into ground or other improvement method should be adopted to strength the soil before foundation construction. 8.3 Encased Structure for Adding Stories — 34 — 8.3.1 When encased structure is used for adding stories, appropriate foundation type should be selected according to soil condition, groundwater, structure type of added stories, and loading requirement. If there is not enough geotechnical investigation information, a geotechnical survey should be conducted. 8.3.2 When encased structure is above rock layer, foundation type and embedded depth may be different from original foundation. Old and new foundation may be connected together or separate. 8.3.3 When encased structure is used on natural foundation, impact from new foundation to old foundation should be considered, and should be kept certain distance away from adjacent existing building. It is forbidden to have a new building too close to an old building, which will cause add-up of stress on the bottom of foundations, which may cause adjacent building to incline or crack. 8.3.4 Piling construction of encased structure should not disturb original foundation. 8.3.5 If natural foundation or composite foundation with spray jet pile, mixing pile or lime pile are adopted, deformation of foundation when load is applied should be considered so as to avoid elevation difference of old and new structure after adding stories. 8.3.6 When there is basement of existing building and pile foundation is used for encased structure. Pile locations should avoid the side of bottom slab for original basement. If slab can not be avoided, chip off the side of slab and verify through calculation. However, old and new foundations should not be connected. — 35 — Notes on some words used in this standard I. This standard has used the following words to indicate the different strictness for abiding different clauses: 1. To show the extreme strictness that the clauses must be followed strictly: Positive word: “must” is used; Negative words: “strictly forbidden” is used. 2. To show the strictness that the clauses must be followed in normal circumstance: Positive word: “shall” is used; Negative words: “shall not” or “never” are used. 3. To show there can be some margin, if condition allows to do so: Positive words: “should” or “usually” are used; Negative word: “should not” is used. II When the clauses indicate that other related standards and specifications must be followed, such expressions as “in accordance with such and such specifications” or “follow such and such standards”. — 36 —