On the issue of using foreign soil classification charts according to CPTU data

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Abstract

The main data on piezostatic soil sensing (“Piezocone Penetration Testing — CPTU”), which allows, in addition to the soil resistance to probing, to determine the pore pressure in the soil adjacent to the probe, are considered. Focus is done on the pore pressure measured between the cone and the friction coupling u2. The normalized probing parameters (qt, Qt, Bq, Fr) implicitly account the pore pressure u2 are given, Foreign experts often use these parameters when drawing up map-diagrams to identify soil varieties (“qt–Bq”, “qt–Fr”, “Qt–Fr”, “Qt–Bq”, “Qt(1–Bq)–Fr”, etc.). Recently, many of the foreign map-diagrams, starts to be used in Russian geotechnical practice, including compiling computer programs for processing sensing data without conducting comparative studies. The article presents the experimental results to verify possibility of using foreign “qt–Rf” and “qt–Bq” card schemes proposed by P.K. Robertson et. al. The comparative experimental studies shown impossibility to use these foreign maps-schemes for soil varieties identification and determination on the territory of Russia during engineering and geological surveys due to their unreliability.

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About the authors

O. N. Isaev

JSC “Research Center of Construction” – Gersevanov Research Institute of Bases and Underground Structures

Author for correspondence.
Email: geotechnika2017@mail.ru

Candidate of Science (Engineering)

Russian Federation, 59, Ryazansky Avenue, Moscow, 109428

References

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  2. Ryzhkov I.B., Isaev O.N. Staticheskoe zondirovanie gruntov [Static sounding of soils]. Moscow: ASV. 2016. 220 p. EDN: YJOXAJ
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2. Fig. 1. Locations of pore pressure filters (ISO 22476-1): u1 – pore pressure filter on the face of the cone; u2 – pore pressure filter on the cylindrical section of the cone (preferably in the gap between the cone and the friction sleeve); u3 – pore pressure filter just behind the friction sleeve

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3. Fig. 2. Correction of the cone and the friction sleeve resistance due to unequal end area effect (ISO 22476-1): 1 – the friction sleeve cross sectional area (top); 2 – the friction sleeve side surface area; 3 – the friction sleeve cross sectional area (bottom); 4 – the cone base cross sectional area

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4. Fig. 3. CPTU soil behavior type “qt–Rf” (a) “qt–Bq” (b) classification charts by Robertson et. al. [3]: е – void ratio; St=su/s´u – sensitivity; OCR – overconsolidation ratio; ID – density index; qt – the ground resistance under the probe cone adjusted value, concidering the piezometer readings and some piezo probe design features; the arrows indicate direction of parameter values increasing. Types of soils: 1 – sensitive fine grained; 2 – organic material; 3 – clay; 4 – silty clay to clay; 5 – clayey silt to silty clay; 6 – sandy silt to clayey silt; 7 – silty sand to sandy silt; 8 – sand to silty sand; 9 – sands; 10 – gravely sand to sand; 11 – very stiff fine grained (overconsolidated or cemented); 12 – send to clayey sand (overconsolidated or cemented)

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5. Fig. 4. CPTU soil behavior type “qt–Rf” classification chart by SP 504.1325800.2021: 1 – silt; 2 – loamy silt; 3 – clayey silt; 4 – clay; 5 – clay loam; 6 – silt sandy loam; 7 – sandy loam; 8 – fine sand to silty sand; 9 – silty sand – medium sand; 10 – sand, overconsolidated or cemented; 11 – very stiff clay, overconsolidated; dз – average grain diameter; Id – density index; e – void ratio; IL – consistency index

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6. Fig. 5. Results of piezocone penetration test of clayey soils plotted on the “qt–Rf” chart [3]

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7. Fig. 6. Results of piezocone penetration test of sand, water saturated peat and decayed sandstone plotted on the “qt–Rf” chart [3]

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8. Fig. 7. Results of piezocone penetration test of clay loam plotted on the “qt–Rf” chart [3]

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9. Fig. 8. Results of piezocone penetration test of sands plotted on the “qt–Rf” chart [3]

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10. Fig. 9. Results of piezocone penetration test of clayey soils plotted on the “qt–Bq” chart (after Robertson P.K. et al.) [3]

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11. Fig. 10. Results of piezocone penetration test of sand, water saturated peat and decayed sandstone plotted on the “qt–Bq” chart [3]

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12. Fig. 11. Results of piezocone penetration test of clay loam plotted on the “qt–Bq” chart [3]

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13. Fig. 12. Results of piezocone penetration test of sands plotted on the “qt–Bq” chart [3]

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