Geotechnical Interpretation of CPT and CPTu

Conceptual Framework

CPT records cone resistance and sleeve friction continuously with depth; CPTu also measures pore pressure. Corrected resistance, friction ratio and normalized variables support soil-behaviour-type charts.

Engineering Assessment

CPT offers high vertical resolution, but drainage, stress and grain size influence readings. Behaviour type is not identical to geological lithology, and empirical design correlations require geological calibration.

Field and Laboratory Practice

Calibration, area ratio, zero readings, rate and verticality require control. CPTu filters must remain saturated, and boreholes should provide targeted ground truth.

Limitations and Quality Control

Gravel, cobbles and cemented layers may stop penetration. CPT yields no sample, so composition and exact lithology require direct evidence; correlation validity must be documented.

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.