Objectives of ELS System - Geotechnical Division

1 T3 Top Up course ELS part I of II 2011/4/29. Objectives of ELS System Provide structural support with adequate margin of factor of safety to facilitate the HKIE Geotechnical Division &. excavation under lateral earth pressures & possible surcharges Department of Civil Engineering, The University of Hong Kong Without impair the integrity of the surrounding roads & properties Top up course for TCP T3 on GIFW and Building Works with significant Geotechnical content Excavation and Lateral Support Excavation and Lateral Support Part I. Ir. James Sze Associate Director Ove Arup & Partners HK Ltd Nicholl Highway before collapse After collapse on 20 Apr 2004.

2 1 2. Content Part I. Common retaining walls for excavation works Common lateral support systems Basement construction sequence Design and submission procedures Geotechnical design & considerations Common Retaining Walls for Structural designs g Points to note in ELS Design Excavation Works Part II. Site supervision requirement Technical supervision & reminders Instrumentation and monitoring Pumping test issues and a lesson learnt Case histories to illustrate key issues during site supervision Police HQ III, TSTE Extension over CHT, TKR development, HKPolyU School of Hotel & Tourist Management 3 4. Commonly Embedded Wall Types in Hong Kong Temporary Channel Planking Steel usually temporary Aligned channel sections Channel planking Suitable of shallow Sheet pile wall excavation above Adjacent building Pipe pile wall groundwater table, eg.

3 Soldier pile wall pile cap construction Usually pushed or Cast in situ Reinforced Concrete may be permanent Cast in situ Reinforced Concrete may be permanent vibrated into ground g Able to be extracted Secant pile/contiguous bored pile (RCD) wall afterwards Diaphragm (slurry) wall Other less common ones not covered Soil cement mix wall Pre cast diaphragm wall 5 6. Ir. James Sze, Ove Arup & Partners HK Ltd. 1. T3 Top Up course ELS part I of II 2011/4/29. Temporary Sheet Pile Walls Temporary Sheet Pile Wall Hammer In basement construction usually used for temporary support Coupled sheet pile sections are effective in terms of strength/mass ratio Vibrator and drop/hydraulic hammer are common installation method Noise and vibration controls could inhibit use of sheet piles in urban areas Jacking method is available but less common In weathered rocks and colluvium, hard corestones and boulders are the obstacles whereas in fill the problems are boulders old foundation and obstacles, whereas in fill, the problems are boulders.

4 Old foundation and seawalls. Pre boring through obstructions may be required Seepage cut off performance generally satisfactory but provision of grout curtains beneath toe may be necessary in deep excavations Usually left in with top few metres trimmed upon completion of permanent structures Typical Larrsen 6 to 15W, FSP I to VI. 7 8. Temporary Sheet Piling Vibrator / Giken Sheet Pile Wall Installation (Silent) Piling Method Application Limitation Readily available in HK Noise & vibration Vibratory/ Drop Efficient Restricted working hour Hammer Cheap High head room required Cause ground settlement Quiet Heavy counter weight is Soft/weak ground only required Jack In System High head room Large working space Limited head room Expensive Limited work space Limited trained local Giken System Soft/weak ground operators Tight alignment tolerance East Rail Mody Road Subway, CLP Cable Tunnel TWS access shaft 9 10.

5 Pipe Pile Walls Pipe Pile Wall ODEX with Air Flushing ODEX or similar construction technique has been used to overcome the problem of inadequate penetration when driving sheet piles through weathered rock with corestones and through old foundations. By carrying a circular hollow section with the drillbit, it forms pipe piles. Expandable wings Circular hollow section Typical 219mm dia. 610mm dia. CHS. 11 12. Ir. James Sze, Ove Arup & Partners HK Ltd. 2. T3 Top Up course ELS part I of II 2011/4/29. Concentric drilling & Close loop drilling Pipe Pile Wall Installation Concentric drilling less disturbance to surrounding ground due to better air.

6 Flow Close loop drilling air only used for powering the hammering action. Low pressure water/bentonite used lifting debris 1: advance ODEX drill bit 2: terminate the drill bit at 6: completed pile into ground with steel design founding level ODEX drill bit Concentric/ringbit drill bit CHS followed 13 14. Pipe Pile Wall Installation Soldier Pile Wall Soldier pile walls have two basic components : Soldier pile (vertical component) & Lagging (horizontal component). Soldier piles are either driven or placed in pre drilled holes, which are backfilled to the ground surface with lean concrete Excavate in lifts, weld on channel or steel plate lagging between the soldier piles Lagging serves as a secondary support to soil face and prevents progressive Mixing of cement grout Mixing of cement grout deterioration of soil arching between the piles Requires moderately dry ground conditions and soil with sufficient strength to maintain vertical face prior to support from horizontal lagging Installation of pipe pile Tremie grouting 15 16.

7 Soldier Pile Wall Soldier Pile Wall Installation 1: ODEX drilling onto 2: extract ODEX bit & change 3: clean the hole & sound bedrock with to down the hole hammer to lower H pile section temporary casing form rock socket 17 18. Ir. James Sze, Ove Arup & Partners HK Ltd. 3. T3 Top Up course ELS part I of II 2011/4/29. Soldier Pile Wall Installation Soldier Pile Wall Installation Installation of H pile section 4: tremie grout to cut 5: extract temporary casing, 6: completed pile Mixing of cement grout off level top up grout level 19 20. Soldier Pile Wall Installation Contiguous/Secant Bored Pile Wall Contiguous piles: bored or CFA piles built to be almost touching.

8 Typically nominal 50mm gap between adjacent piles Secant piles: interlocking concrete piles formed using bored or CFA equipment. Spacing to suit verticality tolerances but typically 50mm to 100mm overlap between piles Hard soft wall: concrete male' piles H d ft ll t l ' il interlocking with low strength unreinforced female piles. Built using bored or CFA equipment. Spacing of male piles typically to It provides a near water proof wall for Tremie grouting Extraction of temporary casing both the temporary and permanent soil support. Typical 21 22. Contiguous/Secant Bored Pile Wall Contiguous/Secant Bored Pile Wall Installation Secant pile wall Guide wall Cantilever contiguous bored pile wall 23 24.

9 Ir. James Sze, Ove Arup & Partners HK Ltd. 4. T3 Top Up course ELS part I of II 2011/4/29. Conventional Bored Pile Construction (1 of 2) Conventional Bored pile Construction (2 of 2). Concrete water delivery 1: Grabbing out soil with 2: RCD to excavate rock if 3: Install steel cage, 4: Concreting and tremie 5: Removal of casing advanced necessary airlifting record temporary casing 25 26. Alternative Bored Pile Construction (1 of 2) Alternative Bored Pile Construction (2 of 2). Recycling of bentonite Soil Soil Rock Rock 1: Guide casing & excavate in soil & rock 2: Cage installation 3: Tremie Concreting 4: Casing extraction 27 28.

10 Diaphragm (Slurry) Wall Diaphragm Wall Continuous wall built in aligned discrete panels typically of 4m to 6m in length (on plan). Wall thickness 800mm to 1500mm Panel Diaphragm wall techniques was used extensively in the construction of the length MTR underground stations and of deep basements for high rise buildings (temporary as well as permanent walls). Trench excavated under bentonite slurry support. Cable grabs still used but hydraulically operated trench cutter machines becoming more common Usually cast in situ. Pre cast panels can be used but limited to relatively Usually cast in situ Pre cast panels can be used but limited to relatively shallow depth by lifting weight of individual units Bentonite slurry properties and net slurry pressure are key factors in maintaining stability of the trench so proper site quality control is vital Guide wall to maintain slurry head, guide position & orientation, provide temporary support for cage installation Typical thk.