Factors that Determine Wall Type Selection. Proximity to existing structures / roadways. Service Life: temporary / permanent

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1 EXCAVATION SUPPORT CONSTRUCTION IN URBAN ENVIRONENTS: CHALLENGES and SOLUTIONS Presented to: DELAWARE VALLE ASSOCIATION OF STRUCTURAL ENGINEERS Domenic D Argenzio, PE, Senior Associate ueser Rutledge Consulting Engineers New ork, New ork Lecture Overview: Factors that Determine Selection of Excavation Support Excavation Support Wall Types Wall Lateral Support Systems Waterproofing Inspection & onitoring Relative Costs Example Projects How is Excavation Support Defined? Temporary or permanent structure that will retain the lateral forces from soils and/or water in order to permit excavation for, and construction of underground permanent structures Excavation Support Wall Brace Load Soil Pressure Water Pressure When is Excavation Support Needed? Factors that Determine Wall Type Selection Excavation Support Wall Types Wedge geometry is defined by soil properties 45 Ø/2 45 Excavation Depth and Width Proximity to existing structures / roadways Service Life: temporary / permanent Excavation support is required when it is not practical to provide sloped sides that fit safely within the available work space Soil and Rock Conditions Groundwater Level Relative Costs 1

2 Flexible Wall Types Flexible Wall Types: Timber Sheeting Applications Flexible Wall Types: Soldier Pile & Lagging Applications Timber Sheeting Soldier Pile and Lagging Steel Sheet Piles Narrow Excavations Depth < 20 feet Above Water Table Installed with hand tools Excavations < 50 ft. Above Water Table Granular or cohesive soils with stand up time for lagging installation Flexible Wall Types: Soldier Pile & Lagging Applications Pile spacing 5 8 ft. max Timber lagging 2 4 thick Installed with vibratory or impact hammers Voids behind lagging packed with soil Flexible Wall Types: Soldier Pile & Lagging Limitations Pre drilling required through: an made obstructions Dense, gravelly soils Till; bouldery soil Problematic in running sands and soft clays Prone to loss of ground and settlements outside wall High risk use adjacent to sensitive structures not supported on piles or underpinned Flexible Wall Types: Steel Sheet Piles Applications Excavations < 55 ft. Excavations above or below water table Granular or cohesive soils Can be used for groundwater cutoff (interlock sealant) Installed with vibratory or impact hammers 2

3 Flexible Wall Types: Steel Sheet Piles Applications Flexible Wall Types: Steel Sheet Piles Limitations Rigid Wall Types Not appropriate if buried obstructions or cobbles / boulders are present Common sheet pile length = 65 ft. without splicing; limits their use Prone to settlement in loose granular soils, especially when vibratory hammers are used Secant Pile Walls Soil ix/jet Grout Walls Slurry Walls Combination Shapes Various Single Shapes High risk use adjacent to existing sensitive structures that are not pile supported or underpinned Rigid Wall Types: Secant Pile Walls Applications Rigid Walls Secant Pile Wall Rigid Walls Secant Pile Wall Excava on Depths 80 ft Above or below groundwater table; good groundwater cutoff Drilled overlapped holes reinforced with beams Individual 3 ±ftdiameter cased holes in primary/secondary pattern; soil completely replaced with concrete Less vibrations than driven systems Can eliminate the need for underpinning adjacent structures Can be incorporated into permanent structure Pre fabricated forms Guide wall 3

4 Rigid Walls Secant Pile Wall Rigid Walls Secant Pile Walls: Limitations Rigid Walls Slurry Walls: Practical Applications Obstructions, cobbles / boulders hinder installation Excavation depths: 50 ft. >100 ft. Temporary support and permanent foundation walls Difficult ground conditions and obstructions Wall continuity in deep applications can be a problem (verticality control is critical) Recommended adjacent to sensitive structures Eliminates need for underpinning Top down construction Typical construction sequence Excavation Support Systems Rigid Walls Slurry Walls: Practical Applications Rigid Walls Slurry Walls Rigid Walls Slurry Walls Sequenced trench excavation under slurry Provides temporary excavation support Slurry walls are most economical when the following uses are combined: Becomes the permanent foundation wall Carries permanent vertical load of the structure Provides permanent groundwater cutoff Trench panels: 8 ft 24 ft. Wall thickness: 2 4 ft. Can be post tensioned for high capacity Can be constructed in various shapes and used as load bearing elements Typical guide wall construction 4

5 Rigid Walls Slurry Wall Panel Construction Sequence Primary (typ) Rigid Walls Slurry Wall Rigid Walls Slurry Wall Panel Construction Sequence Secondary Secondary Secondary 1. Install guide walls concreted excavating concreted panels concreting 2. Excavate panel Clamshell bucket Tremie concrete Slurry displaced 3. De sand excavated panel 4. Install rebar cage Hydraulic Clamshell Buckets 5. Place concrete Slurry Walls: Limitations Requires large laydown area Requires slurry plant and bentonite storage facility essy operation High costs for slurry containment and disposal Slurry Walls: Challenges Vertical alignment control Problems with tremie concrete cold joints soil inclusions Overpours Leaky joints Poor finish Lateral Wall Supports Cantilever Walls Internal Cross Lot Braces External Tiebacks Rakers Deadman 5

6 Cantilevered Walls Lateral Wall Supports: Cross Lot Bracing Lateral Wall Supports: Rakers No external means of lateral support Embedment depth below subgrade is critical Performance is sensitive to soil properties H 1.5H ± No external easements required Obstructs excavation & construction Vertical supports generally required for widths >100 ft. Load capacity generally unlimited Excavation widths >100 ft. Temporary stable soil slopes Partial construction of foundation or temporary heel blocks Capacity limited by: Bearing capacity of heel blocks Uplift capacity of support wall Limited In Height 15 ft Lateral Supports: Tiebacks Unobstructed excavation Exterior easements required Special seals at wall penetration below water Special care below existing structures to prevent settlement Capacities: Clays < 85 tons Sands < 250 tons Rock < 500 tons Waterproofing Blind Side (embranes) Negative Side (Capillary) Admixture (Crystalline) Waterproofing: Blindside embrane on Sheet Piling Flexibility Conformability 6

7 Waterproofing: Blindside embrane on Soldier Pile & Lagging Waterproofing: Slurry Wall; Drainage Collectors & Finish Wall Waterproofing: Slurry Wall; Drainage Chase & Finish Wall Detailed around penetrations with accessory products ethane barrier Spray on/brush waterproofing Horizontal drain board Collector pipes Block wall partition Continuous trench drain Drain board at panel joints Collector pipes Waterproofing: Slurry Wall; Liner Wall Construction Inspection Construction onitoring During Installation & Excavation Shotcrete finish embrane Horizontal drain board Concrete liner Collector pipe inimum tip elevation is achieved Vertical alignment within specified tolerances Steel sheet piles interlocked throughout installation Bracing properly installed Quality Control Vibrations Existing Structure Settlement/ovement Excavation Support Wall ovement Ground Surface Cracks Ground Heave/Settlement Noise Levels 7

8 Types and General Uses KE = ES = ABE N = NO Site Condition Timber SP & Sheet Piles Secant Slurry Sheeting Lagging Piles Walls Depth 0-15 N N Relative Excavation Support Costs Example Projects Slurry Wall N Law School anhattan, N Depth N Depth >60 N N N SOIL TPE TABLE Granular Weak Clay Stiff Clay N N Boulder Till N N N Rock Groundwater N N Present Sensitive Utilities Sensitive N Structures Vertical Load N Capacity Suitable for Permanent N N Structure Soldier Pile & Lagging $30 to $40 per sf Steel Sheet Piling $40 to $50 per sf Secant Pile Walls $100 to $125 per sf Slurry Walls $150 to $200 per sf Permanent Applications Secant Piles Williams Street anhattan, N Steel Sheet Piling Newtown Creek WWTP Upgrade Brooklyn, N Slurry Wall: Top Down Construction New ork Law School, New ork, N Slurry Wall: New ork Law School Slurry Wall: New ork Law School Record for excavation support in anhattan 3 thick x 106 deep slurry wall 65,000 sq ft of slurry wall 44 LBE s Site = 200 x Basement Levels Adjacent Buildings on Spread Footings Adjacent Subway 60 ft Excavation 36 Inch Slurry Wall Glacial Sand Load Bearing Elements 8

9 Slurry Wall: New ork Law School: Top Down Construction Slurry Wall: New ork Law School Slurry Wall: New ork Law School Foundation walls & column foundations installed prior to excavation Slurry walls are permanent foundation walls Permanent slabs provide lateral support for walls during excavation Excavation performed through openings in floor slabs Guide walls adjacent to buildings Slurry Wall: New ork Law School Slurry Wall: New ork Law School Slurry Wall: New ork Law School Congested Site Cage delivered by truck Lowering cage Soil removal through slab opening 9

10 Slurry Wall: New ork Law School Soil removal through slab opening Superstructure construction above underground space New ork Law School: Advantages of Slurry Wall Shortened construction schedule: Top down construction eliminated temporary excavation support walls and bracing Williams Street, N, N Secant Pile Wall Buildings on 2 sides Supported on timber piles Adjacent to subway 2 Basement Levels Reduced risk of damage to existing adjacent tunnels and buildings Groundwater cutoff: underslab drainage system; no pressure slab required Fill (10 ft) Groundwater (12 to 25 ft) Silt (20 ft) Till (5 to 10 ft) Rock (40 ft below grade) William Street, N, N Secant Pile Wall Williams Street, N, N Secant Pile Wall Williams Street, N, N Secant Pile Wall Buried obstructions Trimming of existing brick foundation wall Cast in place concrete footing for guide wall installation Guide wall installation 10

11 Williams Street, N, N Secant Pile Wall Williams Street, N, N Secant Pile Wall Williams Street N, N Secant Pile Wall Core beam installation Secant pile wall drilling against adjacent building wall Down the hole hammer Key cut in secant pile wall for floor slab installation Williams Street, N, N Secant Pile Wall Williams Street, N, N Secant Pile Wall Steel Sheet Piling in Urban Environment Newtown Creek WWTP Upgrade, Brooklyn N Capillary Waterproofing Applied to Interior Surface of Secant Pile Wall Tieback Bracing Raker Bracing against building 11

12 Steel Sheet Piling Newtown Creek WWTP, Brooklyn N Steel Sheet Piling Newtown Creek WWTP, Brooklyn N Steel Sheet Piling Newtown Creek WWTP, Brooklyn N N Steel Sheet Piling Newtown Creek WWTP, Brooklyn N Steel Sheet Piling Newtown Creek WWTP, Brooklyn N Steel Sheet Piling Newtown Creek WWTP, Brooklyn N Rakers to at Foundation Excavation adjacent to existing tanks supported on timber piles 12

13 Steel Sheet Piling Newtown Creek WWTP, Brooklyn N Situations To Avoid When Selecting Excavation Support Wall Types Situations To Avoid When Selecting Excavation Support Wall Types Excavating below bearing level of adjacent structures without underpinning or installing rigid excavation support walls Excavating below bearing level of adjacent structures without underpinning or installing rigid excavation support walls Driving piles with impact or vibratory hammer in granular soils adjacent to existing structures Cross Lot Bracing Situations To Avoid When Selecting Excavation Support Wall Types Situations to Avoid in Excavation Support Wall Selection Excavating below bearing level of adjacent structures without underpinning or installing rigid excavation support walls Driving piles with impact or vibratory hammer in granular soils adjacent to existing structures Excavating below bearing level of adjacent structures without underpinning or installing rigid excavation support walls Driving piles with impact or vibratory hammer in granular soils adjacent to existing structures Installing soil anchors below existing structures Installing soil anchors below existing structures Widespread dewatering where fill placed over organic soils ueser Rutledge Consulting Engineers 14 Penn Plaza 225 West 34 th Street New ork, N USA Direct: E mail: ddargenzio@mrce.com 13