We Don t Need No Stinkin Anchors! Using the Box Reinforcing Effect for Self Supporting SOE

Transcription

1 We Don t Need No Stinkin Anchors! Using the Box Reinforcing Effect for Self Supporting SOE ADSC West Coast Chapter Annual Meeting Spring 2018 Pismo Beach, CA Presented by Ben Turner, Ph.D., P.E. Dan Brown and Associates, California Treasure of the Sierra Madre (1948), Warner Bros. Project Overview High GWT SAND/ Mixed Alluvium + Boulders GLACIAL TILL Boulders CLAY Mixed soil profile with variable, uncertain depth to hydraulic barrier layers SHALE, LIMESTONE Annual Meeting Spring

2 Project Overview How can we design and build a supportof excavation (SOE) system for a 35+ ft deep cut? Annual Meeting Spring Project Overview Limited ROW How can we design and build a supportof excavation (SOE) system for a 35 ft deep cut without anchors? Annual Meeting Spring

3 Project Overview How can we design and build a supportof excavation (SOE) system for a 35 ft deep cut without anchors or internal bracing? Annual Meeting Spring East Side Pump Station SOE Project Team: SOE D B Team: Goettle Construction and DBA GC: Dugan & Meyers Owner: City of Miamisburg, Ohio Owner s Engineer: Hazen and Sawyer Annual Meeting Spring

4 East Side Pump Station SOE DBA Team: Mark Madgett Tim Seigel Ben Turner Tayler Day Goettle Team: Brent Burman PM Chad Linz PM Wes Campbell Super. Annual Meeting Spring Location Annual Meeting Spring

5 Initial Project Development Specs originally called for dewatering Difficult with high groundwater, variable ground conditions Concerns re/ mobilizing nearby contaminant plume Annual Meeting Spring Alternative Concept Cutoff wall around footprint of pump station to separate from surrounding aquifer, eliminating need for dewatering outside wall Annual Meeting Spring

6 Alternative Concept Cutoff wall around footprint of pump station to separate from surrounding aquifer, eliminating need for dewatering outside wall Requires stiff wall? Uncertainty w.r.t. water cutoff Annual Meeting Spring Alternative Concept Requires stiff wall Uncertainty w.r.t. water cutoff Boulders sheetpile Alternatives: Secant pile wall (DBA/Goettle)? Diaphragm wall Annual Meeting Spring

7 Preliminary Design ~ Stage 1: Excavate to elev If excavation remains dry, pour slab/walls done. Stage 2: If can t maintain dry excavation, flood, then excavate another 8 15 for seal slab Stage 3: Tremie pour seal slab; dewater when cured. Similar to Stage 1 (dry), but with slab in place is less critical. Annual Meeting Spring Preliminary Design 1500 mm diam. secant piles 18 No. 11 bars, or Wide flange section ft piles desirable Longer would require significant drilling through till w/ large boulders; uncertain depth to rock Annual Meeting Spring

8 Preliminary Design Stage 2 unstable even with W44x335 Annual Meeting Spring Preliminary Design Based on 2 D (plane strain) methods, cantilever wall does not work even with large diam., heavily reinforced secant piles. Annual Meeting Spring

9 Preliminary Design Based on 2 D (plane strain) methods, cantilever wall does not work even with large diam., heavily reinforced secant piles. But, this is not a 2 D problem! Annual Meeting Spring D Effects in Excavations lateral earth/water pressure deflected shape PLAN Long excavation sides are not influenced by adjoining wall segments Plane strain, 2 D analysis is appropriate ELEVATION Annual Meeting Spring

10 3 D Effects in Excavations PLAN In circular excavations, lateral loads (radial stress) are converted to in plane loads (hoop stress) through arch effect E. Lindquist and R. Jameson. (2011). Secant Pile Shoring Developments in Design and Construction. Proc. DFI Annual Conf. 8 p. 3 D Effects in Excavations lateral earth/water pressure? deflected shape PLAN Short sides are restrained by adjoining segments Analogous to simply supported beam ELEVATION Annual Meeting Spring

11 3 D Effects in Excavations Despite simple conceptual basis, support of adjoining wall segments not typically accounted for in design of rectangular excavations lateral earth/water pressure deflected shape PLAN Annual Meeting Spring D Effects in Excavations Despite simple conceptual basis, support of adjoining wall segments not typically accounted for in design of rectangular excavations Why? Lack of awareness, or perceived as poorly understood mechanism Commonly used analysis tools (e.g., PYWALL, LPILE) are poorly suited to capturing this effect lateral earth/water pressure deflected shape PLAN Annual Meeting Spring

12 Finno et al. (2007) 3D 2D Finno, RJ, Blackburn, JT, and Roboski, JF (2007). 3 D Effects for Supported Excavation in Clay. JGGE, 133(1). Annual Meeting Spring Proposal Developed on the basis of box reinforcing effect Match contractor s tooling and strengths 1500 mm diam. secant piles Construction considerations Corner radius for guide wall construction Reinf. beams versus cages limited stockpile space, more overlap Annual Meeting Spring

13 Design Phase More robust analysis method required to support 3 D box effect Provides means for estimating behavior and order of magnitude of deformation and stresses Provides point of reference for monitoring during construct. A tool, not a design method! Annual Meeting Spring Modeling Annual Meeting Spring

14 Modeling Annual Meeting Spring Modeling Allow interface slip Annual Meeting Spring

15 Modeling Reduced order model allows parametric analysis Vary stratigraphy and soil props Evaluate different pile lengths and reinf. Annual Meeting Spring Results 55 ft, 1500 mm diam. piles w/ W36x135 Max. conc. Stress 600 psi; min. 200 psi Max. inward deflect. 0.2 in. Informed monitoring plan ¼ in.) Insights into box effect behavior Deformation patterns Stress concentrations corners and inside of piles Annual Meeting Spring

16 Results Design sufficient to excavate extra 12 ft for seal slab if needed Allows computation of basal heave FoS index (also a 3D mechanism) Model allows evaluating effects of significant water infiltration or flooding to control basal heave Annual Meeting Spring Results Model allows evaluating effects of significant water infiltration But not a means for determining if it will happen in the first place! Depends on ground + hydraulic conditions (uncertain) Annual Meeting Spring

17 Construction Guide wall template: Alignment Primary/secondary overlap Corners Annual Meeting Spring Construction: Corners Original Design Annual Meeting Spring

18 Construction: Corners Potential kickout during drilling Original Design Annual Meeting Spring Construction: Corners Potential kickout during drilling Original Design Constructed Annual Meeting Spring

19 Construction A572 GR50 W36x135 Annual Meeting Spring Construction Pour + drill same time Primary piles f c =2 ksi Secondary piles f c = 4 ksi 7 10 in. slump specified 9 in target Annual Meeting Spring

20 Excavation Annual Meeting Spring Excavation Annual Meeting Spring

21 Excavation Dry! Annual Meeting Spring Pump Station Floor Annual Meeting Spring

22 Monitoring Prediction Measured Annual Meeting Spring Monitoring Prediction range Measured range System is very stiff good! Gives confidence that predictions of max. stress used in design are within range Annual Meeting Spring

23 Success! 45 Not so fast Annual Meeting Spring

24 Just when you think it s over Annual Meeting Spring Just when you think it s over Annual Meeting Spring

25 Just when you think it s over Annual Meeting Spring Just when you think it s over Analysis results gave confidence could dewater safely Annual Meeting Spring

26 Final Disp. after Pumping Dry Annual Meeting Spring Summary Well built finished product Guide template High slump concrete Segmental casing With box effect, W36x135 worked compared to 2 D analysis (PYWALL) which predicted that W44x335 was insufficient Many applications where ROW or internal bracing undesirable Annual Meeting Spring

27 Summary Numerical modeling should not drive a project; nature of project should dictate the appropriate analysis tool The best analysis tool is as simple as possible, but no simpler. ( Albert Einstein) Sometimes the software you have the license for is not the best tool for the job! Nonetheless, every program has weaknesses. Especially 3 D finite element/difference software. Annual Meeting Spring Summary When used appropriately, modeling can provide a good link between simpler analysis methods, expected behavior, and monitoring during construction Handled unforeseen flooding with confidence thanks to analysis Good agreement between model and observed behavior sleep better Annual Meeting Spring

28 Thanks Annual Meeting Spring