3 rd ISSMGE McClelland Lecture Cyclic soil parameters for offshore - PowerPoint PPT Presentation

3 rd ISSMGE McClelland Lecture Cyclic soil parameters for offshore foundation design Knut H. Andersen Norwegian Geotechnical Institute

Cyclic soil parameters for offshore foundation design Main goals Cyclic contour diagram framework Data base with contour diagrams and correlations of required parameters

Presentation When do we need cyclic soil parameters? What parameters do we need? How does soil behave under cyclic loading? Cyclic contour diagram framework ─ Construction ─ Important parameters ─ Data base (diagrams and correlations with index parameters) Application of contour diagrams in design Calculation procedures Slope instability due to cyclic loading Verification by prototype observations and model tests

Presentation When do we need cyclic soil parameters? What parameters do we need? How does soil behave under cyclic loading? Cyclic contour diagram framework ─ Construction ─ Important parameters ─ Data base (diagrams and correlations with index parameters) Application of contour diagrams in design Calculation procedures Slope instability due to cyclic loading Verification by prototype observations and model tests

Presentation When do we need cyclic soil parameters? What parameters do we need? How does soil behave under cyclic loading? Cyclic contour diagram framework ─ Construction ─ Important parameters ─ Data base (diagrams and correlations with index parameters) Application of contour diagrams in design Calculation procedures Slope instability due to cyclic loading Verification by prototype observations and model tests

Wave loads: The Ekofisk Oil Storage Tank - 1973

Wave loads, Frigg TCP2, 1977 (Beryl A & Brent B Aug 1975) H 100 ~ 30?m Drammen clay JIP 1974/75

Snorre tension leg platform (1991)

Anchoring of floaters 2004: 485 suction anchors, 50 sites 2000m water depth

Offshore wind power structures 67 m 10 m 5 5 5 5 4 4 4 4 3 3 3 3 2 2 2 2 1 1 1 1 By Per Sparrevik

Sea protection; Oosterschelde 1986

Wave loads on harbour structures - Amalfi, Italy

Ice loading on bridge pillars; Great Belt bridge, Denmark Low frequency 10 sec High frequency 1 sec 1990

Arctic; ice loads Drawing: Per Sparrevik

Earthquakes Photo: Amir Kaynia

Earthquakes, slope instability Earthquake induced slide, El Salvador, 600 dead

Foundation design topics Cyclic bearing capacity Cyclic displacements Soil stiffness in global dynamic analyses Permanent displacements (settlements) due to cyclic loading ─ Dissipation of pore pressure due to cyclic loading ─ Increased average shear strains Soil reactions Static capacity reduction due to cyclic loading

Presentation When do we need cyclic soil parameters? What parameters do we need? How does soil behave under cyclic loading? Cyclic contour diagram framework ─ Construction ─ Important parameters ─ Data base (diagrams and correlations with index parameters) Application of contour diagrams in design Calculation procedures Slope instability due to cyclic loading Verification by prototype observations and model tests

Cyclic soil parameters needed in design Cyclic shear strength Cyclic shear modulus Permanent shear strain due to cyclic loading Pore pressure generation Recompression modulus Damping Static strength reduction due to cyclic loading

Cyclic soil parameters needed in design Cyclic shear strength Cyclic shear modulus Permanent shear strain due to cyclic loading Pore pressure generation Recompression modulus Damping Static strength reduction due to cyclic loading

Presentation When do we need cyclic soil parameters? What parameters do we need? How does soil behave under cyclic loading? Cyclic contour diagram framework ─ Construction ─ Important parameters ─ Data base (diagrams and correlations with index parameters) Application of contour diagrams in design Calculation procedures Slope instability due to cyclic loading Verification by prototype observations and model tests

Cyclic loading generates pore pressure τ τ τ τ cy τ a τ cy Monotonic Monotonic Monotonic τ a τ 0 0 time Cyclic Cyclic Cyclic τ cy τ cy τ cy τ a τ a τ a σ ’ σ ’ σ ’ u p u p u p Cycle N Cycle N Cycle N Cycle 1 Cycle 1 Cycle 1

Pore pressure & shear strain increase with no. of cycles τ τ cy τ a Cyclic and average τ cy τ a τ 0 shear stresses 0 time u cy u u cy Pore pressure u p generation 0 time γ γ cy Cyclic, average and γ p γ cy permanent shear strains γ a time

Shear strain definitions τ Cycle 1 Cycle N γ cy -> Cyclic displacements and soil τ cy stiffness for dynamic analyses γ a + γ cy -> Total displacements τ a γ p -> Displacements after storm τ 0 γ p γ Model to follow behavior during a cycle: Kaynia & Andersen (2015) γ cy γ cy γ a

Shear strains depend on test type and τ a DSS, τ a =0 Triaxial, τ a = τ cy Triaxial, τ a = 0 τ τ τ 0 0 0 Time Time Time τ cy τ cy τ cy τ a τ cy τ cy τ cy

Shear strains are not governed by τ max τ (kPa) Triaxial C +50 B 0 A Tid -50 τ max τ a τ cy Test Result Failure ( γ =15%) A 50 0 50 10 cycles γ p =0.8%, γ cy =0.3% B 50 25 25 2500 cycles γ p =0.03%, γ cy =0.02% C 50 42.5 7.5 2500 cycles

Soil elements follow different stress paths H W’ h τ τ Time τ 0 τ τ a 0 τ a Time τ a DSS 0 Triax ext. 0 DSS Triax comp.

Presentation When do we need cyclic soil parameters? What parameters do we need? How does soil behave under cyclic loading? Cyclic contour diagram framework ─ Construction ─ Important parameters ─ Data base (diagrams and correlations with index parameters) Application of contour diagrams in design Calculation procedures Slope instability due to cyclic loading Verification by prototype observations and model tests

No. of cycles to failure depends on τ a and τ cy Drammen Clay, OCR=1 τ γ γ cy τ cy γ cy γ a DSS τ a τ cy τ 0 0 0 time time τ τ τ τ τ cy /s u cy /s u DSS DSS cy /s u cy /s u cy /s u DSS DSS DSS 1.0 1.0 1.0 1.0 1.0 = γ p / γ cy = γ a / γ cy = γ p / γ cy = N f γ = N f γ a / γ p / γ cy cy 0.75 0.75 0.75 0.75 0.75 N f =10 N f =10 N f =10 100 100 100 0.5 0.5 0.5 0.5 0.5 1000 1000 1000 0.25 0.25 0.25 0.25 0.25 0 0 0 0 0 τ τ τ τ a /s u a /s u DSS DSS a /s u a /s u DSS DSS 1.0 1.0 1.0 1.0 1.0 0 0 0.25 0.25 0.5 0.5 0.75 0.75 0 0 0 0.25 0.25 0.25 0.5 0.5 0.5 0.75 0.75 0.75

No. of cycles to failure depends on τ a and τ cy Drammen Clay, OCR=1 τ γ γ cy τ cy γ cy γ a DSS τ a τ cy τ 0 0 0 time time τ τ τ cy /s u cy /s u cy /s u DSS DSS DSS 1.5 1.0 1.0 1.0 = γ cy (%) τ a = 0 = γ p / γ cy = γ p / γ cy = γ a / γ cy 15 0.75 0.75 0.75 3 Test 1 1.0 3 15 N f =10 N f =10 N f =10 1 τ cy /s u DSS 100 100 100 0.5 Test 2 15 0.5 1 3 0.5 0.5 0.5 1000 1000 1000 0.5 0.25 0.25 0.25 0.0 0 0 0 1 10 100 1000 10000 τ τ a /s u a /s u DSS DSS 1.0 1.0 1.0 0 0 0 0.25 0.25 0.25 0.5 0.5 0.5 0.75 0.75 0.75 log N

No. of cycles to failure depends on τ a and τ cy Drammen Clay, OCR=1 τ γ γ cy τ cy Triaxial γ cy γ a τ a τ cy τ 0 0 0 time time τ cy /s u C = γ a / γ cy 15%/15% 0/15 15/0.5 -0.5/15 0.5 N f =10 -15/15 100 15/0.1 -15/0.5 0.25 1000 τ 0 τ a /s u C -0.5 -0.25 1.0 0 0.25 0.5 0.75

Cyclic shear strength is τ f,cy = τ a + τ cy DSS τ f,cy = τ a + τ cy 15/15 15/15 = γ a / γ cy 3/15 3/15 15%/1% 15%/1% τ τ f,cy /s u τ f,cy /s u DSS DSS τ cy N f =1 N f =1 τ a 0.5/15 0.5/15 τ 0 1.5 1.5 0 15/0.25 15/0.25 0/15 0/15 10 10 time 1.25 1.25 τ cy /s u τ cy /s u τ cy /s u 100 100 DSS DSS DSS 15/0 15/0 1.0 1.0 1000 1000 1.0 1.0 1.0 = γ p / γ cy = γ p / γ cy = γ a / γ cy 0.75 0.75 0.75 0.75 0.75 N f =10 N f =10 N f =10 100 100 100 0.5 0.5 0.5 0.5 0.5 1000 1000 1000 0.25 0.25 0.25 0.25 0.25 0 0 0 0 0 τ a /s u τ a /s u τ a /s u τ a /s u DSS DSS DSS DSS 0 0 0 0.25 0.25 0.25 0.5 0.5 0.5 0.75 0.75 0.75 1.0 1.0 1.0 0.75 0.75 1.0 1.0 0 0 0.25 0.25 0.5 0.5

Cyclic shear strength is τ f,cy = τ a ± τ cy Triaxial τ f,cy /s u C τ f,cy τ f,cy C = τ a + τ cy C = τ a + τ cy 1.5 γ a / γ cy = 15%/0.5% N f =1 τ τ τ 15/0.1 15/15 τ cy τ cy τ cy 10 0.5/15 τ 0 τ 0 τ 0 τ a τ a τ a τ cy τ cy τ cy 0/15 100 0 0 0 15 / 0 1.0 tid tid tid Static Comp τ f,cy τ f,cy τ f,cy E = τ a - τ cy E = τ a - τ cy E = τ a - τ cy Extension 1000 -15/15 -0.5/15 Compression -15/0.5 0/15 -15/0.1 τ cy,f /s u τ cy,f /s u τ cy,f /s u C C C N f =1 = γ p / γ cy = γ a / γ cy 0.5 15%/15% 15%/15% -15 / 0 0/15 0/15 15/0.5 15/0.5 -0.5/15 -0.5/15 Static Ext 0.5 0.5 0.5 N f =10 N f =10 -15/15 -15/15 10 100 100 15/0.1 15/0.1 -15/0.5 -15/0.5 0.25 0.25 0.25 1000 1000 100 τ 0 τ 0 τ 0 1000 τ a,f /s u τ a,f /s u τ a,f /s u τ a,f /s u -0.5 -0.5 -0.5 -0.25 -0.25 -0.25 1.0 1.0 1.0 C C C 0 0 0 0.25 0.25 0.25 0.5 0.5 0.5 0.75 0.75 0.75 C -0.5 1.0 -0.25 0 0.25 0.5 0.75