Because this is in a geotechnical engineering context, and because of the use of the identifying soil symbol "SM" in the text, we know that this is a soil classification by the Unified Soil Classification System (USCS), used in the US and in much of the world for geotechnical soil classification other than for roads and airfields. In the USCS, the first letter is the primary classification - in this case "S" means sand. The second letter is a modifier, in this case "M;" this means silt - "S" was already taken for sand, so they used "M" for silt. Thus "silty sand." There is a brief explanation of the system in the Wikipedia article at the URL below. The complete soil description in the 2nd line above, would be: "a silty sand soil (SM), nonplastic, with some gravel and a fines content of less than 22%."