360R-06 Design of Slabs-on-Ground
DESIGN OF SLABS-ON-GROUND 360R-15
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| DESIGN OF SLABS-ON-GROUND 360R-15
Generally, the materials listed in Fig. 3.3 that yield a standard modulus of subgrade reaction above 100 lb/in. 3 (3000 kN/m 3 ) can be used. Highly compressible organic materials (OL) should be avoided, and high-plasticity clays (CH) may cause heave or swell problems. Much of the variation in support capacity is the result of compaction and moisture content; for example, the k value for a lean clay (CL) ranged from 70 to 250 lb/in. 3 (2000 to 7000 kN/m 3 ). The subbase material has better qualities than the subgrade, and may serve as a construction working surface and part of the floor support system. The subbase is generally omitted where the subgrades are of high quality. Thus, the use of a subbase in combination with a base course usually represents an economical alternative for construction on a poor subgrade with an expensive base course material. The subbase may be composed of stabilized subgrade soil, a fill of better quality soil, sand, crushed rock, reclaimed crushed concrete or asphalt pavement, or some local material that has properties that satisfy the requirements of the project. Normally, the materials selected for base materials are alluvial sands and gravels (S or G) or crushed rock. These materials are easily compacted and have high strengths and low compressibilities. If they have little or no fines (material passing a 200 mesh [75 μm] sieve), they are easily drained and act as a capillary break. Their effect on the support of the slab and the overall k value depends on the type and thickness of the base material, as is depicted in Fig. 3.6. Data for specific designs should be based on an analysis of laboratory and site- testing results. If an open-graded, crushed rock is used, the surface may have to be filled in, “choked off” with sand or fine gravels, and compacted to provide a smooth planar surface to reduce the restraint due to linear concrete shrinkage. tải về 2.35 Mb. Chia sẻ với bạn bè của bạn:
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