1、ANUAL ON SUBUWACE INVESTIGATIONS 1988 i -. -: -. . Li I. . . - -. I - . . Published of State Highway and T-tim Offii, 444 North cpitd streer, N.W., suite .- . (1) 1 - _ AASHTO TITLE MSI 88 m Ob39804 OOLLb31 266 m Manual on Subsurface Investigations for most projects, (2) related to other geotechnica
2、l project con- cerns and (3) for major compo- nents of transportation-related projects. Lists a general sequence for con- ducting subsurface explorations and sources of existing data one may draw upon in the process of these investigations. Discusses field subsurface map- ping and the field reconnai
3、ssance report. Covers geologic constraints and how subsurface investigations should identify potential geologic impacts early in the field recon- naissance and define their key as- pects so the proper engineering response can be provided. Outlines the geophysical tech- niques that apply to geotechni
4、cal investigations. Outlines various planning and contractural procedures and de- scribes drilling equipment, sam- pling, and logging methods. Discusses the relationship be- tween transportation structures and subsurface water and pre- sents some methods whereby hy- drologic information can be acqui
5、red, analyzed, and put to use to prevent, alleviate, or cor- rect undesirable conflicts between transportation structures and sub- surface water. Discusses the purpose and classi- fication of laboratory testing of soil and rock, requirements of the laboratory personnel, quality assurance, the primar
6、y tests and their approximate cost, sample handling, laboratory aspects of soild classification, shear strength determination, consolidation tests and permeability tests. Section 3.0 Section 4.0 Section 5.0 Section 6.0 Section 7.0 Section 8.0 Section 9.0 Section 10.0 Appendix A Appendix B Appendix C
7、 Appendix D Appendix E Appendix F Appendix G Appendix H Appendix I Outlines the formal presentation and use of geotechnical informa- tion consisting of both factual and interpreted data. Summarizes the various drilling sampling and instrumentation in- stailations procedures required to obtain the ne
8、cessary subsurface information. Describes in situ borehole tests which determine various proper- ties of soil or rock formations. The advantages, costs, limita- tions, and types of borehole test- ing are discussed. A selected summary of field test- ing procedures required to deter- mine various soil
9、 and rock properties and the forms used to record the data. A summary of the test pro- cedures discussed in Section 9.0. Outlines soil and rock classifica- tion. Discusses the various classi- fication systems, and in particular the Unified Soil Classification System (USCS). Suggests pro- cedures and
10、 guidelines for pre- paring a complete description of a soil sample. Discusses rock excavation methods. Describes instrumentation of en- gineering structures as a way of detecting present or potential structural damage before the magnitude of deformation be- comes uncorrectable. Describes the effect
11、s of earth- quakes on transportation systems and discusses subsurface investi- gation as an aid in earthquake re- sistant design. Discusses the contribution of sub- surface investigation to environ- mental impact analysis. 2 _ _s_II AASHTO TITLE MSI 88 0639804 0011632 IT2 W 2.0 SUBSURFACE DATA REQUI
12、REMENTS. 2.1 GENERAL Subsurface explorations for a transportation-related project typically have the objectives of providing: (1) general information on subsurface soil, rock and wa- ter conditions on the site or route, and (2) specific information on the subsurface conditions or soil or rock proper
13、ties that are important to the various stages of project planning. An understanding of basic site geology is necessary throughout the planning pro- cess for any project that has major components sup- ported on, or in the earth and underlying rock. In many cases, general geologic information, and in
14、some cases specific information on subsurface condi- tions in the project area, will be available from techni- cal references and reports, and previous subsurface explorations on and near the site or route. Whatever the extent of available information on a particular project or site, there may becom
15、e a need at some stage in the planning process for additional subsurface investigation. This investigation will usu- ally have to be accomplished within budgetary and time constraints that will limit the level of effort that can be applied. It is therefore important that subsur- face investigations
16、be carefully planned, and coordi- nated between those who will obtain and those who will use the information. The geotechnical data that are necessary for plan- ning a particular type of project will vary from project to project. In the early stages, it may be sufficient to obtain only preliminary g
17、eotechnical information for alternative sites or routes to enable planners to evalu- ate project feasibility and identm major constraints and premium costs. However, these early data must be extensive enough and have sufficient accuracy to be appropriate for these objectives, so that correct plannin
18、g decisions can be made before intensive de- sign effort is initiated. During project design, subsurface exploration and testing programs will be required to provide geo- technical data specific to the needs of the design team. The explorations and testing will serve the obvious 0 needs of civil and
19、 structural design, but must also provide information pertinent to other related consid- erations, such as corrosion and environmental protec- tion. The design-phase data must have sufficient accu- racy, coverage and applicability to support design analyses and decisions. It should also permit reaso
20、na- bly accurate estimates of material quantities and con- struction costs. In many cases relating to roadways, standard prac- tice for the agency will apply unless unforeseen condi- tions arise that require special attention. For many states, this means logged borings at 100-175 m-spac- ing, with v
21、ariations providing concentrated data at cut sections, borrow areas, or where geologically-related problems are expected. Structure foundations com- monly have individually-planned explorations. When a project is under construction there is not normally further subsurface investigation, except to re
22、solve questions or problems that have arisen during construction. Design-phase explorations would have provided adequate subsurface information for design and, in most cases, for contractor bidding for con- struction. However, in some instances there may be a need for limited or local explorations t
23、o confirm de- sign evaluations, particularly when there have been design changes subsequent to the main exploration program. There may also be a need for explorations and geotechnical data in connection with construc- tion-phase instrumentation and monitoring. As previously noted, the geotechnical d
24、ata that are required for a project can be broadly categorized as general or specific. The first category encompasses identification and delineation of various soil and rock strata and ground water levels. The second category will provide both qualitative and quantitative infor- mation on the charac
25、ter and engineering properties of all or part of one or more of the various strata. Data for the first category will normally be derived from one or more of the various methods of subsurface explorations, while data for the second category will quite often require field or laboratory testing. 3 AASH
26、TO TITLE MSI 88 Manilal on Silbsiirface Investigations It is not possible to establish strict criteria for the data that should be obtained for a particular type of project. However, the typical or usual geotechnical considerations are: (1) data requirements common to most projects, (2) data require
27、ments related to other geotechnical project concerns, and (3) usual data re- quirements for major components of transportation- related projects. It must be emphasized that the de- termination of data requirements is part of the plan- ning process, and requires individual and continued attention on
28、each project. 2.2 DATA REQUIREMENTS COMMON TO MOST PROJECTS 2.2.1 Definition of Stratum Boundaries This requires identification and determination of ver- tical and horizontal locations of the various subsur- face materials on a site or route. The data can range from visual observations or remote sen
29、sing output to detailed logs and physical samples of soil and rock from test borings or test pits. Relatively limited data are typically obtained for large areas during early project stages, while later stages will require increas- ingly detailed information, often for progressively smaller areas as
30、 project alternatives are narrowed down or final structure locations selected. Each addi- tion of data should improve stratum boundary defini- tion. The type of exploration that is selected for each stage should be appropriate for the data require- ments. In some cases field or laboratory testing ma
31、y be necessary to define boundaries that are not otherwise evident. As an example, Standard Penetration Test AASHTO (T-206) blow counts may acceptably differ- entiate between dense or stiff and loose or soft strata, but natural water content determinations, shear strength testing or laboratory conso
32、lidation tests may be necessary to define limits of sensitive or overcon- solidated clay. 2.2.2 Groundwater Level This is not a static condition, being a function of season and precipitation. In addition, the water level in a test boring can be affected by the introduction of water for the drilling
33、process. The ground-water level should be determined by readings over an extended period and by correlation with weather data. Water level data can range from observations in test borings or test pits to periodic observation well or piezometer Ob39804 0011633 039 readings, usually with corresponding
34、 improvement of data precision and reliability. It should be noted that a low permeability stratum can cause either an overlying “perched” water table or an underlying artesian condition. In this situation there may be a need to seal a piezometer or observa- tion well within each stratum of interest
35、 in order to yield a complete picture of groundwater behavior at the site. 2.2.3 Foundation Support The planning and design of structures requires a de- termination of the strength of proposed foundation material. For light to moderate design loads and rela- tively competent bearing materials, such
36、as rock, dense granular soil or stiff clay, data derived under the preceding two items may be sufficient to establish presumptive allowable bearing pressures for shallow foundations. Where there are clearly unsuitable near- surface soils, such as peat, the same data may also be sufficient for the de
37、sign of deep foundations, such as piles. For most projects stratum definition and groundwater data wiil at least be adequate for early project planning. The peformance or problems of existing foundations in the area should certainly be considered, and there must also be a determination that underlyi
38、ng geologic features, such as solution cavities, or weak, collapsing or compressible soils do not control the bearing capacity. In the case of shallow foundations, shear strength data for theoretical calculation of granular soil bear- ing capacity will usually be empirically derived from Standard Pe
39、netration Test blow-count determinations and laboratory gradation analyses. The shear strength of cohesive soils can be determined by field vane tests or laboratory shear tests on undisturbed samples. Where there are major foundation loads, or where further refinement of strength or bearing prop- er
40、ties is necessary there can be more sophisticated field tests or laboratory triaxial testing of undisturbed samples of granular or cohesive soil. In the case of deep foundations the need for addi- tional data depends on the types of foundations being considered. For bearing piles there is a need to
41、predict penetration into various strata. This is usually esti- mated on the basis of soil classification and density, or rock type and quality, as determined by test borings. Friction piles, unless designed on the basis of pre- sumptive code values, require data or assumptions as to soil friction an
42、d adhesion characteristics, and cais- sons similarly require shear strength information. Such strength data for deep foundations can be devel- oped by design-phase explorations and testing, but 4 _ - - y_- AASHTO TITLE MSI 88 W are normally substantiated by full-scale load tests of pile units and pe
43、netrometer tests of caisson bearing surfaces during construction. e 2.2.4 Settlement or Heave Potential This consideration can be pertinent whenever a new or increased structure or embankment loading is ap- plied to a compressible soil. Major excavations can also result in heave of the foundation bo
44、ttom and adjacent areas. Certain soils, such as soft clays, loose sands or organic deposits, are known to be compress- ible without demonstration by laboratory testing, and early planning can be based on this general knowl- edge. Knowledge of existing settlement problems in the project area can also
45、 be used for planning. How- ever, actual data are necessary to predict rates and amounts of settlement. Other soils require data and analysis to determine settlement or heave potential under particular loading conditions. In either case, stratum definition and groundwater information are necessary p
46、arts of the data. Settlement due to compression of granular soils can occur as the load is applied. Data for estimating settle- ment can be obtained from empirical Standard Pene- tration Test relationships, from field plate bearing tests and, in the case of elastic compression, from the results of l
47、aboratory triaxial testing of undisturbed samples. Estimates of the rate and amount of long-term settlement due to volume-change compression of co- hesive soils, such as clays or organic soil deposits, are commonly based on data derived from laboratory consolidation testing of undisturbed samples. E
48、lastic compression of cohesive soils can be calculated on the basis of modulus data from laboratory triaxial testing on undisturbed samples. In some areas the consolida- tion or compression properties of a major soil stratum are sufficiently well known for preliminary or general evaluations. The pre
49、sence and identification of the stratum may be confirmed by classification testing of disturbed samples from borings or test pits. At some locations there can also be potential for settlement due to subsidence caused by conditions in underlying strata, such as solution cavities, mines, groundwater lowering or soil erosion. 0 2.2.5 Slope or Bottom Stability This consideration is applicable to temporary or per- manent earth or rock slopes that exist or are con- structed as part of a project. It can also apply to the bottoms of major excavations. Instability can range from ravelling
