WHAT DO YOU MEAN MOISTURE IS 110%!
provided the ne fraction does not ex- ceed 5%. Conversely, because the same sand shows reduced permeability com- pared to sand of the same median size with a narrow range of sizes, a geologist
Table 1. Pitfalls in Word Usage Concept 1.
Cementation 2. Clay Geology
Binding together of particles of a soil or sediment by precipitated minerals
Rock or mineral fragment 4 m; in soil science, the limit is 2 m, the size below which all particles are clay minerals
3. Compaction
Volume reduction from overburden pressure
4. Consolidation Lithication of a sediment by com- paction or cementation
5. 6. 7. Dike Grade Graded
A tabular igneous rock cutting across the planar structures of the surrounding rocks
In mining, metal content of an orebody
Vertical trend in grain size in a bed or bedding sequence. Normally graded is ning-up Reverse graded is coarsening-up
8. Grain-size units = -log2(mm)
9. Grain-size distribution
10. Grain-size distribution parameters
11.
Grain-size distribution quality desig- nators
12. Grain size distribution qualiers
Sorting: the degree of similarity of grain sizes of a sediment
Inclusive graphic standard devia- tion: SD=(84
- 16 )/4(95 - 5 )/6.6
Poorly-sorted = wide range of grain sizes
0.35 very well sorted 0.35-0.50 well sorted 0.51-0.70 moderately well sorted 0.71-1.00 moderately sorted 1.01-2.00 poorly sorted 2.01-4.00 very poorly sorted 4.00 extremely poorly sorted
13.
Moisture content
14. Permeability units
15. Pore space 16. Rock
Weight water/total weight x 100 (also used by environmental engineers)
Geologists and engineers in the pe- troleum industry will use darcys as the unit of intrinsic permeability
Porosity: Volume of pores/total volume x 100. In hydrogeology, expressed as a decimal
Naturally formed consolidated mate- rial formed of one or more minerals and having a degree of chemical consistency
17. Sand 18. Silt
A detrital particle between 1/16 mm (0.062 mm) and 2 mm. US soil scientists use 0.05 to 2 mm
A detrital particle between 1/256 mm (0.004 mm) and 1/16 mm (0.062 mm). US soil scientists use 0.002 to 0.05 mm.
19. Soil
Unconsolidated earthy materials over bedrock supporting or capable of supporting plant life (includes only in situ material)
20. Soft
Commonly refers to rocks of sedimentary origin. Soft-rock vs. hard-rock geology
refers to it as “poorly sorted.” Even more confusing, geologists speak of a bed or bed sequence as being graded if it shows consistent vertical trends in grain size whereas in engineering gradation refers
Civil Engineering
Inection of cementing agents into permeable or ssured soil or rock to reduce uid ow or improve strength
Plastic material consisting mainly of particles ner than 2 m
Densication by mechanical means
Gradual reduction of soil void ratio from dissipation of excess pore pressure (owing to an increase in effective stress) and in a squeezing of uids from the soil pores
Articial wall or embankment of earth or rock ll Degree of inclination of an engineering structure Possessing a range of grain sizes
to the grain size distribution of a single sample.
Confusion can also arise in describ-
ing the ner sizes. Geologists tend to concentrate on mineralogy and to divide ne-grained materials into silt and clay on the basis of size, and to further sub- divide clay-sized material into clay and non-clay minerals. Engineers rely more on physical behavior, namely plastic- ity, and divide silts and clays using the Atterberg limits into low-plasticity (ML and CL) and highly plastic (MH and CH) nes based on the material’s position on the plasticity chart. Kehew (2006) provides a helpful reference for geologists hoping to improve their grasp of geotechnical basics such as the Atter- berg limits.
One might argue that the engineer- ing approach to soils is their business and of no concern to geologists; how- ever, consider the data shown in Fig. 1. The data represent a glaciated area in Greater Cincinnati that has experienced repeated landslide movement on some
US standard sieve mesh sizes; mm
Gradation: the frequency distribution of sizes of a granular material
Coefcient of uniformity: CU
= D60 /D10
Coefcient of gradation or concavity: CC
= D30 2 /D60 *D10 Well-graded = wide range of coarser grain sizes
Well-graded: 5 % nes; CU
1 < CC
> 6 (sand) or 4 (gravel) < 3
Poorly graded: not meeting the CU requirements
May be uniformly graded or gap graded
Weight water/dry weight x 100 (used by geotechnical engineers)
Hydrogeologists and civil engineers will use cm2 for intrinsic permeability or cm/sec for hydraulic conductivity
Void ratio: Volume of voids/volume of solids (ex- pressed as a decimal, not a percent)
Any natural material that requires drilling and blasting or similar methods of brute force for excavation
A soil particle retained on U. S. standard sieve no. 200 (0.074 mm) and passing sieve no. 4 (4.76 mm)
Nonplastic or slightly plastic material exhibiting little or no strength when air-dried consisting mainly of particles passing U. S. standard sieve no. 200 (0.075 mm) yet > 0.002 mm
Uncemented aggregate of mineral grains and de- cayed organic matter down to solid rock, along with the liquid and gas that occupy the interparticle spaces (includes in situ and transported material); the corresponding term in geologic usage is regolith
Refers to a cohesive soil that can be molded by slight pressure. The opposite term is stiff (not com- monly used in geology). Non-cohesive soils would be termed loose or dense
and/or CC
Figure 1. Example of use of plasticity chart to characterize landslide-prone soil mate- rial (referred to as soils in Civil Engineering usage, but sediments in Geology).
tracts, but has stable soils on other ad- acent properties. Much of this behavior seems random to developers and their engineering consultants. Geological re- ports tend to speak in terms of Wiscon- sinin vs. Illinoian deposits and to focus on genetic features such as kame ter- races because of the potential for gravel resources. But the information and the effectiveness of communicating could be increased if the geologist includes a few Atterberg limits so the soils also can be classied in the engineering approach as well. If this engineering informa- tion were included, the engineer could see at a glance that there is a group of soils (the lake bed clays) at this site that needs to be avoided or at least be given extra attention. Figure 2 illustrates the
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