Copyright National University of Singapore. All Rights Reserved.
Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations Pile Driveability Analysis – Tutorial Prof Chow Yean Khow Email : chowyk@nus.edu.sg Phone : 6516 2161 Office : E1A-07-07 Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 GRLWEAP Installation 2 Installation Download the GRLWEAP 2010 installation file and the background manual at http://downloads.pile.com/GRLWEAPUniversity Enter user name and password below: User name: PDI-user2 Password : drEp7esw Copy the GRLWEAP_2010_Univ.exe file to your computer. Double click on the file to install it onto your computer. When the window appears that asks for the company name and serial number, enter the following: Company : NU Singapore-NOT FOR COMMERCIAL USE Serial number: 8GCTCN2-6008-7NYT5ZK The first time you run the GRLWEAP program right click on the GRLWEAP icon and select “Run as Administrator”. You will get a dialog box saying that it is a Demo version and how many days you have left. Click “OK” to start using the program. Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 GRLWEAP Overview 3 A Quick Overview One-dimensional wave equation analysis of pile driving Extensive library of pile driving hammer and cushion information It can be used for developing: Bearing graph Ultimate capacity vs blow count for a specific pile depth Inspector chart Stroke vs blow count for a specific pile ultimate capacity Pile driveability Pile depth vs blow count and pile stresses during driving Despite its complete features and user-friendliness, geotechnical expertise is required to ensure correctness of the geotechnical input parameters and sensibility of the analysis outcomes Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Various Usage GRLWEAP Overview 4 Bearing graph For a specific pile depth Inspector chart For a specific pile ultimate capacity Pile driveability For a specific or varying hammer stroke Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Main Input Window GRLWEAP Input 5 Hammer library and user input parameters Cushion input parameters General pile geometry [Length can be modified] Gain/ loss factor for unit soil resistance [see next slide for details] Schematic of key input parameters Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Hammer Parameters Hammer Model To select a suitable model from the list Double click the list at the main input for hammer details Stroke Defined as equivalent stroke instead of physical stroke; automatically calculated from rated hammer energy over ram weight Default value can be used unless a lower stroke is required; varying strokes can be defined [see advanced features] Efficiency For design, the recommended value can be used which was based on measurements. Alternatively, a specific value may be assigned to suit a pile driving plan. Varying efficiency as a function of pile penetration depth can be input using depth modified function [see advanced features] GRLWEAP Input 6 Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Pile Parameters Geometry Cross sectional properties must be entered Total pile length is to be defined and consists of design penetration depth plus length above the seabed; temporary pile length can also be set in “Depth Modifier” [see advanced feature] Penetration refers to design penetration depth of the pile Non-uniform piles can be entered in “Pile Type” drop down menu and select “Non Uniform Pile” Batter/inclination of pile can be set in “Pile Parameter” Material properties Default elastic modulus of steel piles is 210 000 MPa Default unit weight of steel piles is 77.5 kN/m3 Resulting pile stresses has to be checked against allowable stress manually GRLWEAP Input 7 Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Soil Parameters Unit shaft resistance Total resistance from external and internal shaft Unit toe resistance “Unplugged” is the default option For “plugged” pile during driving at specific layers, [Toe Area] is to be modified to full bearing area Skin and toe quakes Typically 2.5mm (0.1 inch) for unplugged driving Skin and toe damping Each soil has its values (refer to the table for the standard values for impact driven piles) GRLWEAP Input 8 Soil type Shaft Damping* Toe Damping Non cohesive (“Sand”) 0.16 s/m 0.50 s/m Cohesive (“Clay”) 0.65 s/m 0.50 s/m Note: * for mixed soils, intermediate values may be appropriate; for example, a sandy silt or clayey sand may be modeled with 0.33 s/m Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Soil Parameters Setup factor Conversion from long-term static resistance (LTSR) to static resistance to driving (SRD) Only applicable for shaft resistance and the value may vary for each layer Generally equivalent to sensitivity (undisturbed and remolded strength ratio) for clay soils Input shaft resistance must be compatible with the setup factor Input shaft resistance is LTSR set fs ≠ 1.0 (SRD will be computed accordingly) Input shaft resistance is SRD set fs = 1.0 (simplest approach) GRLWEAP Input 9 = Soil type Setup factor Remarks Clay 3.0 Range of 2 – 5 is possible Sand 1.2 For loose to medium dense sand; dense to very dense sand may result in relaxation and thus fs < 1.0 Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Soil Parameters - Advanced Features Variable setup factor [setup time, limit distance] If pile driving is interrupted, soil may gain strength which magnitude is a function of elapse time since the driving is halted. If a setup factor, fs, (indicating the maximum loss) is defined, the change in the loss factor with time is modeled in GRLWEAP with the following exponential relationship, where t = wait time since driving halted (in hrs) tS = setup time to achieve full gain (in hrs) Wait time is to be input in “Depth Modifier” input form [see advanced features] Limit distance defines the minimum driving distance to effect maximum strength loss The limit distance must be input and can be estimated as 2m. GRLWEAP Input 10 = 1 + log 0.01 = 1 1 log 0.01 Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Soil Parameters - Advanced Features Gain/Loss Factor (Shaft) The setup factor, fS, controls the maximum loss of soil resistance with respect to the long term static resistance (LTSR) for individual soil layers. The Gain/Loss factor, fGL, allows variations in the static resistance to driving (SRD) for the entire soil layers between minimum SRD and LTSR At maximum loss fGL = 1/fs (SRD = SRDmin) At partial setup 1/fs < fGL < 1.0 (SRDmin< SRD < LTSR) At complete setup fGL = 1.0 (SRD = LTSR) For multi-layered soils, the Gain/Loss factor will adjust the reduction factor fRD proportional to the ratio of setup factor for individual layers fS [fsx = max fS of all layers] GRLWEAP Input 11 = 1 11 1 = 1 + × 0.8 1.00.9 0.4 1.00.7fRD fRD Example for multi layers G/L fGL = 0.4; 0.7; 1.0 Clay fS = 2.50 (fSX) Sand fS = 1.25 0.4 1.00.7fGL Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 GRLWEAP Input 12 Driving Process - Advanced Features This tutorial only covers the advanced features for hydraulic hammer (typically used offshore) Depth Modifier Input Any changes/variation during pile driving can be entered using “Depth Modifier Input” form. The modification is set according to specific pile penetration depths. For hydraulic hammers, the parameters that can be modified include: Temporary pile length Wait time (in hrs) Stroke length Hammer efficiency Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Pile Installation Pile driving at 60m water depth Design pile depth of 100m based on static capacity Assess hammer suitability GRLWEAP Example Problem 13 C la y Sa nd Te m p pi le l en gt h 3 Te m p pi le l en gt h 1 Te m p pi le le ng th 2 Water level Seabed level Pile segment 1 Pile segment 2 Pi le se gm en t 3 Varying hammer energy Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Pile driving at 60m water depth Hammer parameters Hammer model : Menck MHU-750T Stroke length : 1.84m (equivalent) Efficiency : 50% (0-50m depth) and 95% (50-100m depth) Cushion : Not used GRLWEAP Example Problem 14 Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Pile driving at 60m water depth Pile parameters Vertical pile Pile outer diameter : 1.524m (60in.) Pile thickness : 38.1mm (1.5in.) and 50.8mm (2.0in) Total pile length : 190m Design pile penetration depth : 100m below seabed level Temporary pile length : 0-30m depth (120m long); 30-60m depth (150m long); 60-100m depth (190m long); Yield strength : 450 MPa GRLWEAP Example Problem 15 Section Length (m) OD (m) Thickness (mm) Annulus (cm2) Perimeter (m) 1 0 – 60 1.524 38.1 1779 4.788 2 60 – 120 1.524 50.8 2351 4.788 3 120 –190 1.524 38.1 1779 4.788 Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Pile driving at 60m water depth Soil Parameters Two layer soils consisting of clay overlying dense sand Clay sensitivity St = 2.5 Sand interface friction angle δ = 30o, K = 0.8, Nq = 40 (refer to next slide) Unplugged driving, 50% internal shaft friction is assumed Calculated external unit shaft friction is to be multiplied by 1.5 for GRLWEAP input Fully remolded strength for clay shaft friction during driving, no soil setup is assumed Shaft friction and end bearing for sand during driving is capped by limiting values (refer to next slide), no soil setup/relaxation GRLWEAP Example Problem 16 Depth (m) Soil Strength parameters γ’ (kN/m3) Unit shaft friction Unit toe resistance 0.0 – 80.0 Clay Su (kPa) = 25T – 125B 8.0 Su / St 9 Su 80.0 – 150.0 Dense sand φ’ = 35o 10.0 Κ σ’v tan δ σ’v × Nq Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Pile driving at 60m water depth Soil Parameters API RP2A GRLWEAP Example Problem 17 Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Pile driving at 60m water depth Soil Parameters Effective vertical stress at 80m depth : σ’v = 80 x 8 = 640 kPa Effective vertical stress at 150m depth : σ’v = 640 + (70 x 10) = 1340 kPa Calculated shaft and toe resistance of the dense sand layer is capped by limiting values (refer to API RP2A) * No limiting shaft friction for clay; the toe resistance is based on undisturbed strength Unit shaft friction for all layers is to be multiplied by 1.5 to account for 50% internal friction Input soil resistance directly corresponds to SRD; the setup factor is to be set to 1.0 GRLWEAP Example Problem 18 Depth (m) Soil Unit shaft friction (kPa) Unit toe resistance (kPa) Skin and toe quake (mm) Skin and toe damping (s/m) 0.0 – 80.0 Clay 15T – 75B 225T – 1,125B 2.5; 2.5 0.65 ; 0.50 80.0 – 150.0 Dense sand* 144 9,600 2.5; 2.5 0.16 ; 0.50 (Original) 443T – 928B 25,600T – 53,600B Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Main input window Refer to main input parameters Hammer Total pile length Pile penetration Gain/Loss factor Model diagram etc GRLWEAP Example Problem 19 Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Pile parameters Pile segment 0 – 60m : 38.1mm 60 – 120m: 50.8mm 120 – 190m: 38.1mm GRLWEAP Example Problem 20 Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Soil parameters Soil profiles and input parameters Limiting shaft and toe resistance for sands GRLWEAP Example Problem 21 Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Depth modifier input Temporary length at various penetration depths: 0 – 30m : 120m 30 – 60m: 150m 60 – 100m: 190m Efficiency at various penetration depths: 0 – 50m : 0.50 50 – 100m: 0.95 GRLWEAP Example Problem 22 Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022 Analysis output Predicted blow counts SRD profiles Pile stresses Energy profile Acceptance Criteria Blow counts Refusal criteria is often taken to be 150 blows/0.3m Pile stresses Allowable compression and tension stress for steel piles < 0.9 fy GRLWEAP Example Problem 23 Copyright National University of Singapore. All Rights Reserved. QUESTIONS 24
