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SOIL ENGINEERING: TESTING, DESIGN, AND REMEDIATION phần 5

Khi đất tự nhiên có khả năng chịu lực rất thấp và nó là cần thiết để đặt một cơ cấu tương đối nặng vào nó, nó có thể đặt một điền vào cấu trúc để phân phối tải áp đặt. Một cuộc điều tra kỹ lưỡng là cần thiết để biện minh cho một cam kết như vậy. Một số trong những yếu tố để xem xét là trình bày dưới đây: | 9.1.1 Fill on Soft Ground When the natural soils have a very low bearing capacity and it is necessary to place a relatively heavy structure on it it is possible to place a structural fill to distribute the imposed load. A thorough investigation is required to justify such an undertaking. Some of the factors to consider are outlined below 1. To know the extent and thickness of the soft soil strata 2. The compressibility of the soft soil strata must be determined 3. Under certain loads it is necessary to estimate the time required to complete the consolidation 4. The location of the water table is sometimes necessary to control the feasibility of such a project 5. The feasibility of the installation of a dewatering system 6. The availability of suitable fill material 7. The tolerable amount of settlement 8. The type of compacting equipment available The most difficult problem confronting a geotechnical engineer is the erection of structures on very soft organic clay or silt. Such problems often rise during the construction of highways or railroads. Natural deposits of this type are common in regions formerly occupied by shallow lakes or lagoons. The deposits usually consist of peat moss or other types of marsh vegetation. Such soils may not be able to sustain the weight of a fill more than few feet in height. Fill on such foundations may continue to settle excessively for many years or decades. During the construction of the Tibet Highway a vast area of marshy ground was encountered Figure 9.1 . The deposit extended many square miles and was located at elevations above 18 000 ft. It was believed that the area constitutes part of the sources of the Yellow River. The deposit was so soft that it did not sustain even horseback riders. The subsoil contains about 50 silt and clay with a liquid limit of more than 100. Since no granular soils were available ditches were dug along both sides of the proposed roadway to a depth of about 10 ft to lower the water table. The .