Particle-Size Distribution: Sieve and Hydrometer Analysis

Conceptual Framework

Particle-size distribution describes the mass proportion of size fractions in soil. Sieving addresses coarse particles while sedimentation-based hydrometer testing addresses fines. Characteristic diameters and gradation coefficients are read from a semi-logarithmic curve.

Engineering Assessment

Gradation affects compaction, filtration, drainage and erosion behaviour. It cannot, however, describe soil response without particle shape, mineralogy, density and the plasticity of fines.

Field and Laboratory Practice

Representative splitting, gentle disaggregation, wash-loss control and mass balance are central to quality. Temperature, meniscus, dispersant and specific-gravity corrections must be applied in hydrometer testing, and the two test curves should join consistently.

Limitations and Quality Control

Hydrometer analysis assumes equivalent spheres and Stokes-law sedimentation. Platy clay particles and aggregation may violate these assumptions, so preparation and test standards must be reported.

Professional Application and Quality Approach

A defensible cross-section begins with data validation rather than drafting. Borehole coordinates, collar elevations, final depths, boundaries, sample intervals and observation dates should be checked against approved sources. All elevations must share a vertical datum and all distances must refer to a defined section origin. Where information comes from different campaigns, methods, units and naming conventions should also be reconciled.

Information recorded within a borehole is direct point evidence; boundaries drawn between boreholes are geological interpretation. These levels of knowledge should not be presented as equally certain. Confidence generally decreases with wider spacing, sparse data and more complex geology. Dashed lines, explanatory notes and data-limit symbols communicate this uncertainty. The model should be reconsidered when new boreholes, excavations or monitoring results become available.

A scaled section is not merely an illustration. Horizontal distances, elevations, borehole depths, foundation level and topography must use one consistent coordinate logic. Any vertical exaggeration should be stated because apparent dips and slopes can differ from true geometry. PDF output should be reviewed at its intended paper size, while PNG output should be checked at its intended screen resolution.

Automation can reduce calculation, repetitive drafting and presentation errors, but it cannot guarantee the correctness of source data or the validity of the geological model. A qualified engineer or geologist should review the final section together with field observations, laboratory testing, project objectives and applicable requirements. Assumptions, data gaps and significant revisions should remain traceable in the project archive.