AASHTO HB-17 DIVISION I SEC 4-2002 Division I Design - Foundations ((Part A Part B and Part C) Errata 01 2003)《抗振设计-抗震性能范围C的桥梁设计要求》.pdf
《AASHTO HB-17 DIVISION I SEC 4-2002 Division I Design - Foundations ((Part A Part B and Part C) Errata 01 2003)《抗振设计-抗震性能范围C的桥梁设计要求》.pdf》由会员分享,可在线阅读,更多相关《AASHTO HB-17 DIVISION I SEC 4-2002 Division I Design - Foundations ((Part A Part B and Part C) Errata 01 2003)《抗振设计-抗震性能范围C的桥梁设计要求》.pdf(69页珍藏版)》请在麦多课文档分享上搜索。
1、Section 4 FOUNDATIONS 4.1 GENERAL Part A GENERAL REQUIREMENTS AND MATERIALS Foundations shall be designed to support all live and dead loads, and earth and water pressure loadings in ac- cordance with the general principles specified in this sec- tion. The design shall be made either with reference
2、to ser- vice loads and allowable stresses as provided in SERVICE LOAD DESIGN or, alternatively, with reference to load factors, and factored strength as provided in STRENGTH DESIGN. 4.2 FOUNDATION TYPE AND CAPACITY 4.2.1 Selection of Foundation Type Selection of foundation type shall be based on an
3、assessment of the magnitude and direction of loading, depth to suitable bearing materials, evidence of previous flooding, potential for liquefaction, undermining or scour, swelling potential, frost depth and ease and cost of construction. 4.2.2 Foundation Capacity Foundations shall be designed to pr
4、ovide adequate structural capacity, adequate foundation bearing capacity with acceptable settlements, and acceptable overall sta- bility of slopes adjacent to the foundations. The tolerable level of structural deformation is controlled by the type and span of the superstructure. 4.2.2.1 Bearing Capa
5、city The bearing capacity of foundations may be estimated using procedures described in Articles 4.4,4.5, or 4.6 for service load design and Articles 4.11, 4.12, or 4.13 for strength design, or other generally accepted theories. Such theories are based on soil and rock parameters measured by in situ
6、 and/or laboratory tests. The bearing capacity may also be determined using load tests. 4.2.2.2 Settlement The settlement of foundations may be determined using procedures described in Articles 4.4,4.5, or 4.6 for service load design and Articles 4.11, 4.12, or 4.13 for strength design, or other gen
7、erally accepted methodolo- gies. Such methods are based on soil and rock parameters measured directly or inferred from the results of in situ andor laboratory tests. 4.2.2.3 Overall Stability The overall stability of slopes in the vicinity of foundations shall be considered as part of the design of
8、foundations. 4.2.3 Soil, Rock, and Other Problem Conditions Geologic and environmental conditions can influence the performance of foundations and may require special consideration during design. To the extent possible, the presence and influence of such conditions shall be evalu- ated as part of th
9、e subsurface exploration program. A rep- resentative, but not exclusive, listing of problem condi- tions requiring special consideration is presented in Table 4.2.3A for general guidance. 4.3 SUBSURFACE EXPLORATION AND TESTING PROGRAMS The elements of the subsurface exploration and testing programs
10、shall be the responsibility of the designer based on the specific requirements of the project and his or her experience with local geologic conditions. 4.3.1 General Requirements As a minimum, the subsurface exploration and testing 0 Soil strata programs shall define the following, where applicable:
11、 -Depth, thickness, and variability 43 44 HIGHWAY BRIDGES 4.3.1 TABLE 4.2.3A Problem Conditions Requiring Special Consideration Problem Type Description Comments Organic soil; highly plastic clay Sensitive clay Micaceous soil Soil Expansive clay/silt; expansive slag Liquefiable soil Collapsible soil
12、 Pyritic soil Laminated rock Expansive shale Pyritic shale Rock Soluble rock Cretaceous shale Weak claystone (Red Beds) Gneissic and Schistose Rock Subsidence Sinkholes/solutioning Condition Negative skin friction/ expansion loading Corrosive environments Permafrost/frost Capillary water Low strengt
13、h and high compressibility Potentially large strength loss upon large straining Potentially high compressibility (often saprolitic) Potentially large expansion upon wetting Complete strength loss and high deformations due to earthquake Potentially large deformations upon wetting (Caliche; Loess) Pot
14、entially large expansion upon oxidation Low strength when loaded parallel to bedding Potentially large expansion upon wetting; degrades readily upon Expands upon exposure to aidwater Soluble in flowing and standing water (Limestone, Limerock, Indicator of potentially corrosive ground water Low stren
15、gth and readily degradable upon exposure to aidwater Highly distorted with irregular weathering profiles and steep Typical in areas of underground mining or high ground water Karst topography; typical of areas underlain by carbonate rock Additional compressive/uplift load on deep foundations due to
16、settlemenihplift of soil Acid mine drainage; degradation of certain soilhock types Typical in northern climates Rise of water level in silts and fine sands leading to strength loss loading exposure to aidwater Gypsum) discontinuities extraction strata -Identification and classification -Relevant eng
17、ineering properties (Le., shear strength, compressibility, stiffness, permeability, expansion or collapse potential, and frost suscep- tibility) 0 Rock strata -Depth to rock -Identification and classification -Quality (Le., soundness, hardness, jointing and presence of joint filling, resistance to w
18、eathering, if exposed, and solutioning) -Compressive strength (e.g., uniaxial compres- sion, point load index) -Expansion potential Ground water elevation Ground surface elevation Local conditions requiring special consideration Exploration logs shall include soil and rock strata de- scriptions, pen
19、etration resistance for soils (e.g., SPT or qc), and sample recovery and RQD for rock strata. The drilling equipment and method, use of drilling mud, type of SPT hammer (i.e. safety, donut, hydraulic) or cone pen- etrometer (i.e., mechanical or electrical), and any unusual subsurface conditions such
20、 as artesian pressures, boulders or other obstructions, or voids shall also be noted on the exploration logs. 4.3.2 Minimum Depth Where substructure units will be supported on spread footings, the minimum depth of the subsurface explo- ration shall extend below the anticipated bearing level a minimu
21、m of two footing widths for isolated, individual footings where L 5 2B, and four footing widths for foot- ings where L 5B. For intermediate footing lengths, the minimum depth of exploration may be estimated by lin- ear interpolation as a function of L between depths of 2B and 5B below the bearing le
22、vel. Greater depths may be re- quired where warranted by local conditions. 4.3.2 DIVISION I-DESIGN 45 Where substructure units will be supported on deep foundations, the depth of the subsurface exploration shall xtend a minimum of 20 feet below the anticipated pile or shaft tip elevation. Where pile
23、 or shaft groups will be used, the subsurface exploration shall extend at least two times the maximum pile group dimension below the an- ticipated tip elevation, unless the foundations will be end bearing on or in rock. For piles bearing on rock, a mini- mum of 10 feet of rock core shall be obtained
24、 at each ex- ploration location to insure the exploration has not been terminated on a boulder. For shafts supported on or ex- tending into rock, a minimum of 10 feet of rock core, or a length of rock core equal to at least three times the shaft diameter for isolated shafts or two times the maximum
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