CPTu in Consolidating Soils PAULUS P. RAHARDJO. PROFESSOR OF GEOTECNICAL ENGINEERING, UNIVERSITAS KATOLIK PARAHYANGAN - INDONESIA

Outline of Presentation 1. Background of Study 2. CPTu and its interpretation 3. Consolidating Soils 4. Method of Analysis 5. Examples and Case Histories 6. Conclusion Summary

Back Ground of Study Soft Soils in South East Asia are Consolidating Soils (Cox 1970)

Background of Study Due to the thickness and recent formation, the site is known as underconsolidated Mahakam Delta, East Borneo

Consolidating Soils In Consolidating Soils, there is existing excess pore pressure due to - Its own weight during sedimentation - Load or fill placement - Pile driving FOCUS OF INTEREST : What is the value of the existing excess pore pressure? What is the degree of consolidation? What is the current shear strength? What is the Rate of Pore Pressure Dissipation?

Background of Study : WHY CPTu Tests? - Continuity of data along the depth of penetration - Repeatability - Measure Pore Pressure - Mesure tip resistance representing trend of effective stress (Larsson, 1992) SATURATION OF THE PORE ELEMENT CONE PENETRATION TEST IN THE FIELD

BACKGROUND OF STUDY The interpretation of CPTu for normally consolidated clay soils and slightly, or strongly overconsolidated soils there is hydrostatic pore water pressure BUT NO INITIAL EXCESS PORE PRESSURE The interpretation of CPTu for Consolidating soils there is hydrostatic pore water pressure BUT THERE IS INITIAL EXCESS PORE PRESSURE THERE should be A DIFFERENCE IN THE METHOD OF INTERPRETATION

BACKGROUND OF STUDY PREVIOUS Study : Schmertmann (1978) based on the shape of tip resistance qc Robertson (1986) classify consolidating soils as sensitive fine grains (high Bq, small qc) Tanaka and Sakagami (1989) high value of Bq > 0.75 Rahardjo et al (Atlanta, 2009) Use of Dissipation Test Rahardjo et al (Fukuoka, 2015) Use of Bq value Rahardjo et al (Bandung, 2016) Effective Stress Concept

Classification Chart by Robertson et al (1986) Consolidating Soils are refered as Small value of qc Small value of Rf High value of Bq But no information On the Degree of Consolidation

DETERMINATION OF THE DEGREE OF Consolidation UNDERSTANDING THE MEASUREMENT OF CPTu ON RECLAIMED SITE u i Unreclaimed Site u i Reclaimed Site u 3 u f u f = u 0 Log time u 0 Log time u 1 u 2 u 2 Du p = excess pore pressure due to cone penetration Du = residual excess pore pressure u 0 = hydrostatic pore water pressure In Consolidating Soils qc = lower tip resistance fs = lower friction u2 = higher pore pressure

Excess Pore Water Pressure (MPa) Degree of Consolidation interpreted by Method of extrapolation of dissipation test (Rahardjo et al, Atlanta 2009) Dissipation Curve at 8.38 m t 50 = 59.95 Minute 0.2 U [%] = 1-(ut/ui) 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 Excess Pore Pressure Due To Insertion Of CPTu Cone Excess Pore Pressure Due To Fill Material Weight Hydrostatic Pore Water Pressure 1 10 100 1000 10000 Log Time (Min.) Measured Extrapolated t50 u0 U [%] = 1-(ut/p) Find u50 ui uf u50 t50 p = pressures due to fill placement Garis t50 1 2 3 Depth = 9.82 m Garis u0 1 u0 = 68 kpa 2 uf = 117 kpa ut = 117-68 = 49 kpa Ds = 64.6 kpa U = 24.54 %

Method of Determination of the Degree of Consolidation Based on Bq value DEGREE OF CONSOLIDA TION OVERCONSOLIDATION RATIO (OCR) Setionegoro 2012 Rahardjo et al 2013

Investigation of Mud eruption and Dyke Failure Hazard

Investigation of Mud Deposit East Java damages of the thousands of houses and infrastructures including highways The second mud eruption center was also shown

Investigation of Mud Eruption Disaster Area CPTu-2 CPTu-5 CPTU-1 CPTu-9 CPTu-10 CPTu-8

Results of CPTu at MUD ERUPTION AREA CPTu-9 : through the mud Ground water -2.0 m 0-2 m : mud crust 6-14 m : mud 14-15m: silty sand (lenses) > 15m : soft clays

Interpretation of CPTu-09 (inside the dyke)

Mud Characterization by CPTu-10 CPTu-10

Results of CPTu at MUD ERUPTION AREA CPTu-10 : through the mud Ground water -0.0 m 0-2 m : mud crust 2-21 m : mud (consolidating mud) Bq = 0.8-1.2) > 21m : soft clays

Interpretation of CPTu-10 (center of eruption)

Method Based on Effective Stress (Rahardjo, 2016) ISOCHRONE - excess pore pressure - effective stress profile

Method based on Effective Stress Approach Effective Stress in Consolidating Layer Pore water pressure

METHOD BASED ON EFFECTIVE STRESS (Rahardjo et al, 2016)

Depth (m) Depth (m) 0 2 4 6 8 10 12 14 16 18 20 qt (MPa) 0 0.5 1 O qt (MPa) Perkiraan grafik q t saat U=100% berdasarkan Metode Schmertman untuk NC Clay Nilai q t pada akhir lengkung Determination of the degree of Consolidation based on Effective Stress Concept 0 2 4 6 8 10 12 14 16 18 20 qt (MPa) qt (MPa) 0 0.5 1 Determine Thickness of Consolidating Layer based on qt Draw qt for the Normally Consolidating Layer Degree of Consolidation at Specific Depth U t,z = q t(at current CPTu) q t(at U=100%)

z/h Determination of the degree of Consolidation based on Effective Stress Concept Isochrone U vs z/h U 0 0.5 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Plot data U t,z VS z/h The degree of Consolidation can be Calculated by : ഥU = න U t d z H 0 1

Example of Calculation

CONCLUSIONS The use of CPTu for investigation of CONSOLIDATING SOILS and the degree of consolidation (specially residual pore pressure) is very effective and prospective for future use and application. The use of empirical correlation for degree of consolidation (OCR < 1.0) as well as the over-consolidation ratio using Bq value is very usefull. To obtain information on the proportion of soil resistance and pore pressure, Bq** = u2 / qt is prospective.