SOIL ENGINEERING: TESTING, DESIGN, AND REMEDIATION phần 3

Unified soil legend — By using the soil legend suggested by the Bureau of Reclamation, a soil engineer or an architect is able to identify the soil without reading the description. The types of soil presented in this legend are limited to only eight, with three additional symbols for fill and six for bedrock. Complicated and detailed classifications are not considered nec-essary in general exploration and sometimes may confuse the issue. Typical logs are shown in Figure 4.3. Plotting — All test holes should be plotted according to elevation. When elevations are not taken, notes and explanations should be given. A hori-zontal line should be drawn across the log, indicating the proposed floor level. In this manner, a concise idea on the subsoil conditions immediately beneath the footings can be obtained. Without the proposed floor level, it will be necessary to assume one or several possible floor levels and build the recommendations around the assumptions. Typical soil legends and symbols are shown in Figure 4.4. Water level — The water table is an integral part of a soil log. The depth of the water table should be carefully recorded. Stabilized water table con-ditions can generally be obtained in the test hole after 24 hours. Such records should be plotted. In cohesive soils due to their low permeability, no water or low water table conditions are generally recorded. The field engineer should record the water level with clear explanations. Others — The log should also include such data as the date of drilling, the location of bench mark, type of drilling equipment, climate condition, and the engineer’s name. ©2000 CRC Press LLC FIGURE 4.4 Typical soil legend and symbols used by consultants. ©2000 CRC Press LLC REFERENCES Arthur Casagrande. Classification and Identification of Soils, Trans. ASCE 113, New York, 1948. Corps of Engineers, Department of the Army, VII. I. B.M. Das, Principles of Geotechnical Engineering, PWS Publishing, Boston, 1994. R. Peck, W. Hanson, and T.H. Thornburn, Foundation Engineering, John Wiley & Sons, New York, 1974. U.S. Department of the Interior, Bureau of Reclamation, Soil Manual,Washington, D.C., 1974. ©2000 CRC Press LLC 5 Laboratory Soil Tests CONTENTS 5.1 Scope of Testing 5.1.1 Standard Tests 5.1.2 Minimum Testing Capability 5.2 Interpretation of Test Results 5.2.1 Swell Test 5.2.2 Consolidation Test 5.2.3 Direct Shear Test 5.2.4 Triaxial Shear Test 5.2.5 Compaction Test References Soil testing is essential in establishing the design criteria. Distinction should be made between the needs of the consulting engineer and those of the research engineer. For a practicing engineer, the purpose of laboratory testing is mainly to confirm his or her preconceived concept. Exotic laboratory equipment and refined analyses are in the realm of the research engineer or the academician. Neither time nor budget will allow the practicing engineer or the consultant to follow the researcher’s procedures. An experienced consulting geotechnical engineer usually has an idea as to the type of foundation and the design value for the assigned project before the com-mencement of laboratory testing. Such a concept is usually derived from the field drilling log, field penetration data, visual examination of the sample, and the expe- rience of the area. To most geotechnical engineers, the difference between sand and clay is appar-ent. However, in the case of sand, the symbols SW should be used with care, since clean sands as the symbol implies are rarely encountered. In the case of fine-grained soils, the difference between “clay” and “silt” is not apparent visually; a plasticity test will be required. The crude and the most elementary method used by the engineer to identify soil is to take a small lump of soil and roll it on the palm after spitting on it. If color appears on the palm, it is likely to be CL or CH. Otherwise, it is probably silt. For granular soils, one can chew the soil between the teeth. A gritty feeling indicates sandy soil, probably SC. 0-8493-????-?/97/$0.00+$.50 © 1997 by CRC Press LLC ©2000 CRC Press LLC 5.1 SCOPE OF TESTING The extent of soil testing required for a project varies. It depends on the type of client; the importance of the project; the funding available; the time required; and to some extent, the capability of the consultant’s laboratory. 5.1.1 STANDARD TESTS The commonly conducted soil tests by the consulting engineering firms consist of the following: Moisture content and index tests Moisture content Liquid limit Plasticity limit Shrinkage limit Density and specific gravity Particle size analysis Compaction test Shear strength Triaxial shear test Direct shear test Unconfined compression test Compressibility and settlement Consolidation test Swell test Permeability test (Figure 5.1) All the above tests are well described in almost all soil mechanics literature. In addition, most of the test procedures are now listed in ASTM as standard. Improve-ments are necessary in many areas, especially in the subject of swelling soils. 5.1.2 MINIMUM TESTING CAPABILITY A consulting soil engineer usually starts with minimum financial backing and cannot afford to buy all the elaborate testing apparatus found in the specialized catalogs. Some of the successful consulting firms want to expand their operations to another location but hesitate because they are unable to purchase the necessary costly testing apparatus. In fact, in the U.S., only government organizations such as the Bureau of Reclamation or the Corps of Engineers can afford to purchase all the up-to-date new items. Visitation to several soil laboratories in Asia and in the Middle East found them modern, well equipped, and unusually clean. Clean apparatus indicated that the facilities were seldom used. Other governmental institutes located short distances from each other had duplicate equipment. Sharing the use of high-cost equipment was never considered. ©2000 CRC Press LLC ... - tailieumienphi.vn