Design and Construction of Foundation in Schedule Area No 2 (North-western New Territories) with vibration performance consideration

Transcription

1 Design and Construction of Foundation in Schedule Area No 2 (North-western New Territories) with vibration performance consideration Presented by Ir. Adam Choy (Director Meinhardt (C&S) Ltd) Ir. Alex Lai (Technical Director Meinhardt (C&S) Ltd) Ir. Jacqueline Tse (Senior Engineer Meinhardt (C&S) Ltd) 31 Aug 213

2 Content of Presentation Project Information Site Constraints Schedule Area No.2 Classification System Foundation Design in Marble Zone Vibration Assessment Monitoring and Public Relation Plan Construction Consideration

3 Project Information Proposed development in YLTL 518. Yuen Long Bounded by Yuen Long On Ning Road at the southern side, Tai Kiu Road at the western side and Yuen Long On Lok Road at the northern side Consists of 4 towers and each contains storeys with Podium and basement below West Rail Long Ping Station aligned along the northern side and 16m away from site WEST RAIL STATION YUEN LONG ON LOK ROAD WANG CHAU ROAD THE SITE TAI KIU ROAD YUEN LONG ON NING ROAD

4 Site Constraints Photo of the site Existing Aged Village THE SITE Housing Authority s Site

5 Major Concerns on Design and Construction Complex geology and possible presence of cavity Limitations of increased vertical stress on marble surface karst Vibration Effect on existing aged buildings Limitations of Induced Vibration to Surrounding Existing Structures

6 Schedule Area No. 2 Scheduled Area No. 2 is defined as an area where the presence of marble containing cavities is possible at depth. Scheduled Area No. 2 covers a large area where complex geology and marble-bearing rocks of the Yuen Long Formation and Tuen Mun Formation can be expected.

7 Geology of Yuen Long Distribution of marble-bearing sedimentary rock Typical geological section

8 Features in Marble Factors affecting Karst Dissolution Surface Karst Overhangs Dissolution Joints Deep Cavity Zone Underground Channel Underground Cavity Form by weakened and dissected marble Rock mass undercut Joints locally opened by dissolution Form by concentrated water flow, usually in form of series of medium size cavities. Form by collapse of small cavities Occurred at marble/non-marble boundary, usually large cavity.

9 Classification System Marble Quality Designation (MQD): Site Zoning and Classification: Stage 1 GI Calculate MQD (every 5m of all BH) Borehole Rating Plot BH Rating and Identify problem area Assign Site Classes

10 Classification System Marble Class

11 Classification System Site Zoning and Classification: BH Rating Site Classification Ref. GEO report 29 page 11&12

12 Site Zoning Of Classification Stage 1 BH / Existing BH rating = Stage 1 BH / Existing BH rating 5 Stage 2 BH rating = Zone 1 (Very Difficult Site) Stage 2 BH rating 5 2 Tower Tower Adjacent Site (Very Difficult Site) 5 Zone 2 (Fair Site) 2 2 Podium Tower 2 5 Tower 3 Adjacent Site (Fair Site)

13 Design Guidelines 1. Redundancy Factor Easy Site: Driven H-piles with 1% 2% redundancy Fair Site: Driven H-piles with 2% 3% redundancy Very Difficult / Extremely Difficult Site: No simple rules Ref. GEO report Limits on Increase of Vertical Stress on marble surface (Easy Site) (Fair Site) (Very Difficult Site) (Extremely Difficult Site) Ref. GEO publication No.1/26

14 Foundation Design in Marble Zone

15 Ground Investigation Problems need to verify in GI works: Present of cavities Cavity-fill material Highly irregular rockhead level Associated with collapse feature Special requirement in GI works: Carry out GI in stage 2m of continuous MARBLE / METHAMORPHIC rock class II or better cavity free rock with TCR> 85% Layout of the BH Drillholes shall be at the edges of the main pile foundation area

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17 Layers Appear Alternatively Stratum Description Approximate thickness(m) / level (mpd) Fill Sandy silty CLAY 2.m 9.1m Alluvium Stiff to very stiff sandy, silty CLAY and silty fine to medium SAND 5.5m 26.1m Metamorphosed Completely to highly decomposed 16.m 145m Siltstone metamorphosed SILTSTONE Fault Gouge Very stiff slightly sandy SILT 2.m 35m Karst Collapse Angular medium to coarse GRAVEL, COBBLES and BOULDERS of impure marble and pure marble 2m 35m Sound Marble Slightly decomposed MARBLE Approx. -82mPD ~ - 29mPD

18 T1 Average rockhead level (-1 ~ -11mPD) T5 Average rockhead level (below -15mPD) T2 Average rockhead level (-12 ~ -13mPD) T3 Average rockhead level (below -15mPD)

19 Geological Profile Fill Alluvium Founding E1 E1 Metamorphosed Siltstone, Fault Gouge, Karst Collapse Appear Alternatively Sound Marble Section E1-E1

20 Geological Profile Alluvium Fill F1 Founding Metamorphosed Siltstone, Fault Gouge, Karst Collapse Appear Alternatively F1 Marble Section F1-F1

21 Geological Profile Marble (light grey, depth 95-99m) Marble (white, depth 13-17m)

22 Geological Profile Cavity /cavity infill

23 Geological Profile Fault zone (fault gouge, depth ~68m)

24 Foundation Options Options Advantage Disadvantage Remark Driven H- pile with preboring Shaft- Grouted Friction Barrette / Friction Bored Pile End Bearing Bored Pile 1. Lower construction cost 2. Conventional foundation type for marble area 1. Higher capacity for piles terminated at shallower depth to avoid stress increase on the cavities 2. Minimal vibration and noise to the local residents 3. The existing Franki piles within the site can be removed by chiselling or pulling out 4. Hard layers can be overcome by trench cutter or chiseling 1. Higher capacity achieved at rockhead 2. Minimal vibration and noise to the local residents 1. H-pile driven to design level, otherwise review of additional stress on cavity is required 2. More nos. of pile required due to redundancy control 1. Trial pile with load-test is required 2. Excessive grout loss in Karst collapse layer 3. Friction cannot developed in Karst collapse layer 4. High construction cost 1. Sound marble bedrock over 11m below ground and exceeded the practical limit of conventional end bearing bored pile (except Tower 1) Adopted for Tower 2, 3 & 5 NOTadopted for this site Adoptedfor Tower 1 to minimize the additional stress due to Tower 2,3 & 5 foundation loading

25 Tower 1 Bored pile layout Average founding level around -1mPD~-11mPD Bored Piles dia. are 2.5m with 3.75m bellout Pile Capacity = kn

26 Tower 1 Bored pile section E2 T1 Average founding level (-1~-11mPD) T5 Average founding level (below -15mPD) E2 T2 Average founding level (-12~-13mPD) T3 Average founding level (below -15mPD)

27 Grade S45 35X35X18 kg/m to be used Pile length vary from 44-89m T2,3 and Zone B Podium T5 and Zone A Podium Pile Capacity (Without Wind) Pile Capacity (With Wind) Pile Capacity (Without Wind) Pile Capacity (With Wind) Without Group With Group Factor Factor 2958 kn 2514 kn 3697 kn 3143 kn 2 kn 17 kn 25 kn 2125 kn

28 The site is divided into three parts: T5 & Zone A Podium (Driven H-Pile) T2,3 & Zone B Podium (Driven H-Pile) T1 (Bored Pile) T5 ZONE A PODIUM T1 T2 T3 ZONE B PODIUM

29 Pile termination criteria will be based on : (i) ±5m range of proposed founding level (ii) Final set table If the pile terminated outside the termination criteria, the subjected pile will be investigated and foundation amendment will be submitted for approval

30 Overcome underground obstruction / Karst Cobbles obstruction Minimize vibration effect Backfill with compacted sand after preboring

31 Scope of vibration assessment: Piling activities, i.e. driven H-pile, induce vibration which may bring negative effect on surround structures. To control the effect of piling activities on surround structures and meet the requirement stated in PNAP APP-137 (Ground-borne Vibrations and Ground Settlements Arising from Pile Driving and Similar Operations)

32 Assessment on structure conditions of surround existing structures. Estimation of vibration effect on surround existing structures.

33 Housing Authority s Site Nullah Low-rise Building along Yuen Long On Ning Road Tai Kiu Village West-Rail Station

34 Surround Existing Structures Distance No. of Storeys Foundation Type Age(yr) Condition Tai Kiu Village, Tai Kiu Road ~ 2m 1 4 Footings 5-4 Fair Precast Low Rise Buildings, Yuen Long On Ning Road ~ 23m 6 13 Concrete Piles Nullah between On Lok Road, Long Yip Street Good ~ 2m N/A N/A N/A Good Site Occupied by Housing Authority Adjacent N/A N/A N/A N/A

35 Condition of surrounding buildings WANG CHAU ROAD YUEN LONG ON LOK ROAD YUEN LONG ON NING ROAD GOOD THE SITE TAI KIU ROAD FAIR GOOD WEST RAIL STATION

36 Photo 1 - Tai Kiu Village 1

37 Photo 2 - Tai Kiu Village (Arch) 2

38 Photo 3 - Tai Kiu Village (Entrance Tower) 3

39 Photo 4 - Tai Kiu Village (indoor condition) 4

40 Photo 5 - Tai Kiu Village (indoor condition) 5

41 Photo 6 - Tung Cheong Building, 59B Yuen Long On Ning Road 7 6 Photo 7 - Po Fung Building, 59A Yuen Long On Ning Road

42 9 8 Photo 8 - Nullah along Yuen Long On Lok Road Photo 9 - Adjacent site occupied by Housing Authority

43 Assessments process Based on BS5228-2:29 Given the Empirical formula, v res W 1. r = k p 3 Where v res resultant PPV (mm s -1 ) W nominal hammer energy (J) L pile toe depth (m) x distance measured along the ground surface (m) r slope distance from pile toe (m), r 2 = L 2 + x 2 kp for piles not at refusal 1 k p 3 depending on soil type (kp =1 adopted in vibration assessments) Range of parameters suggested in BS L 27m 1 x 111m 1.5 W 85kJ

44 According to PNAP APP-137, the following empirical values are used for assessment : Location Type of Building Maximum ppv (mm/s) Transient Vibration (e.g. Drop Continuous Vibration (e.g. hammer) Vibration hammer) Low rise side Tai Kiu Village side Robust and stable buildings in general Vibration sensitive / dilapidated buildings PNAP Proposed PNAP Proposed