Engineering reference

Built from the same data the ISKRIT calculators run on

Each page covers one method: the formula, the thresholds, a worked example with numbers, and a link to the calculator that does it.

• ASTM D4253 and D4254: maximum and minimum index density
  What the vibratory table and the loose-fill test give you, how relative density follows from the two limits, and what changed when ASTM withdrew both standards in 2025.
• Relative density Dr and density index Id are not the same number
  Two definitions in circulation, one symbol used for both, and a systematic gap of several percentage points. Where each comes from and which one your specification means.
• USCS classification step by step: ASTM D2487
  How a grain size curve turns into a USCS group symbol: the 50 % fines split, the gravel-sand comparison, the well-graded criteria and where Atterberg limits become mandatory.
• Cu and Cc: what the two gradation coefficients actually tell you
  Coefficient of uniformity and coefficient of curvature: formulas, the well-graded thresholds for sand and gravel, and why a high Cu alone does not mean well graded.
• Dual symbols in USCS: the 5 to 12 percent fines band
  Why soils with 5 to 12 percent fines get two symbols like SW-SM, how the pair is assembled, and what a dual symbol tells a designer that a single symbol would hide.
• EN ISO 14688-1 against USCS: two different size ladders
  Sand ends at 2 mm in Europe and at 4.75 mm in the American system, fines start at 0.063 versus 0.075 mm. What that does to a percentage table and to the resulting class.
• AGS4 file validation: what the rules actually check
  The AGS Data Format v4 rules a validator can enforce from the file alone: line structure, group order, mandatory PROJ and TRAN, data types, units and abbreviations, key links.
• AGS4 syntax: the five rules that break a delivery
  Unquoted fields, stray characters between commas, unescaped quotes inside a value and heading count mismatches. The line-level AGS4 rules, what triggers them and how to fix the file.
• ASTM D2435 oedometer test: from the curve to Cc, mv and Eoed
  One-dimensional consolidation: what the pressure-void ratio curve gives, the difference between the logarithmic compression index and the linear coefficients, worked with numbers.
• Converting oedometer modulus to Young’s modulus
  The elastic relation between Eoed and E, why the correction always reduces the number, what Poisson ratio to assume by soil type, and how large the error is if you skip it.
• EN ISO 17892-5 and ASTM D2435: where the two diverge
  Two oedometer standards that share a formula set but differ in loading increments, time criteria for a step, specimen requirements and what the report must contain.
• ASTM D1196 plate load test: modulus and subgrade reaction
  The rigid circular plate formula, why the American method drops the embedment coefficient, how the modulus of subgrade reaction is obtained and what plate size does to it.
• DIN 18134: Ev1, Ev2 and the compaction ratio
  The two-cycle plate test used across Europe for earthwork acceptance: parabolic fit, tangent modulus at maximum stress, and the Ev2 to Ev1 criterion with a worked example.
• Ménard pressuremeter modulus: ASTM D4719 and EN ISO 22476-4
  How the pressuremeter modulus is calculated from the expansion curve, why the mean cavity radius is used instead of the initial one, and the fixed Poisson ratio convention.
• Shewhart control chart constants: A2, A3, B3, B4, D3, D4, d2, c4
  The ISO 8258 table of control chart factors for subgroup sizes 2 to 10, what each constant multiplies, and the individuals chart constants 2.66 and 1.128.
• The eight out of control tests on a Shewhart chart
  Zones A, B and C, the eight pattern tests from ISO 8258, what each one detects, and why running all eight raises the false alarm rate.
• Repeatability and reproducibility limits: where 2.77 comes from
  The r and R limits of ISO 5725, the factor 2.77 at 95 percent confidence, what counts as repeatability conditions, and how the limits are used to accept or reject a pair of results.
• How rebar cutting plans are optimised: the cutting stock problem
  Why greedy cutting leaves material on the floor, what column generation adds, how kerf and reusable offcuts enter the arithmetic, and what a good plan actually minimises.
• Cutting waste in rebar fabrication: what percentage is normal
  Offcut waste against unavoidable loss, why the two are budgeted separately, what drives the number up, and how to read a waste figure quoted by a supplier.
• Earthwork volume from survey points: grid, TIN and cross sections
  Three ways to turn surveyed levels into cut and fill volumes, what each one assumes about the surface, and where they disagree on the same site.