Information Paper for the Legislative Council Panel on Housing
Special meeting on 27 September 1999
Excessive uneven foundation settlement
observed in Tin Shui Wai Area 31 Phase 1
This paper briefs Members on the excessive uneven settlement in foundation works revealed in Block 1 of Tin Shui Wai Area 31 Phase 1(i.e. Block L of Tin Chung Court) and the subsequent investigation undertaken by the Housing Department (HD). A layout plan showing the block location within Tin Shui Wai Area 31 Phase 1 is at Annex A.
2. Details of the Tin Shui Wai Area 31 Phase 1 project are as follows-
|Number of blocks||: ||6
||Phase 20A/Blocks F, G, H, J, K & L of Tin Chung Court/1,920 flats
||Hsin Yieh Architects & Associates Ltd.
|Piling Contractor||:||B + B Construction Company Limited
|Piling Contract Period||:||September 1996 to July 1997
||:||Yiu Wing Construction Company Limited
|Building Contract Period
||:||July 1997 to October 1999|
(anticipated completion date)
|Agreement of Sales and |
Purchase under HOS Phase 20A
(anticipated completion date)
3. On 27 August 1999 the contract manager Messrs. Hsin Yieh Architects & Associates Ltd. (HYA) of Tin Shui Wai Area 31 Phase 1 reported that there was excessive uneven foundation settlements at wings 2 and 4 of Block L through an assessment of the settlement monitoring records. In the report, HYA proposed to increase the frequency of settlement monitoring of Block L and to carry out additional site investigation near the block site.
4. The piling contractor Messrs. B+B Construction Co. Ltd. (B+B) was instructed on 27 August 1999 to demonstrate compliance with the foundation contract. HYA was directed to carry out a comprehensive assessment and propose any required remedial measures to ensure that the buildings are structurally safe and fit for domestic use.
5. At the same time, an independent structural consultant Messrs. C.M. Wong & Associates Ltd. (CMW) was appointed by HD to carry out a third party check on overall structural safety of the blocks. Though the problems as mentioned in para. 3 were found to be localised in one block, investigation was extended to all the 15 blocks of the same court.
6. The block in question, together with ten other blocks (Blocks A to K) have been sold under HOS Phase 20A. Another two blocks (Blocks M & N) have been sold under BRO Phase 1 and two other blocks (Blocks O & P) are being put up for sale in the upcoming HOS Phase 21A.
INVESTIGATION BY CONTRACT MANAGER
7. HYA has instigated a number of investigation measures to define cause of the problems, to confirm structural safety of the buildings and to propose any remedial works required.
8. HYA has employed Ove Arup & Partners as its independent advisor to review the piling records, piling design and settlement calculations.
9. In response to HYA's enquiry, B+B has confirmed that the piles are installed as shown in the piling record drawings. HYA has requested B+B to witness the investigation process as it so wishes.
10. Ten additional boreholes were being sunk to obtain more geotechnical information around Blocks L and K. From end August 99 onwards, the frequency of settlement monitoring had been stepped up to bi-weekly for Blocks L and K. Verticality check of external walls and lift shafts for all six blocks has been carried out since early September. Two piles in Block L have been selected for integrity tests to verify the actual pile length. The testing work is still in process.
11. Based on the investigation findings available, HYA submitted a situation report on the structural safety of Block L on 18.09.99. Salient points of HYA's report are as follows -
(a) Settlement Analysis
The predicted global uneven foundation settlement under full occupation will be within the specified limit of 1/300 under the foundation contract. The predicted maximum uneven foundation settlement under full occupation at wings 2 and 4 of Block L at localized position will be 1/211 which exceeds the specified limit of 1/300 under the foundation contract.
(b) Effect at Lift Shaft
Lifts no. 3 & 4 of Block L could not be installed due to insufficient clearance between the structure and the counter weight. The use of thinner counter weight and its associated smaller accessories would be an alternative for installation.
(c) Probable Cause of Uneven Foundation Settlement
(d) Preliminary Stabilisation Proposal
- Unforeseen ground conditions - These could be either the extent or depths of weaker materials, which are significantly different from those originally adopted by the piling contractor.
- Adequacy of pile length
(e) Structural Safety
- To enlarge the pile caps at the perimeters of existing piles and install additional piles down to the required founding materials below.
- To increase the thickness of pile caps for those existing pile caps which are found over-stressed due to uneven foundation settlement.
- To apply surcharge load 1.25 times the total load to the area of pile caps where maximum uneven foundation settlement is above the acceptable limit.
It is pre-mature to express opinion in structural safety until further investigations on foundation and structure are completed.
INVESTIGATIONS BY INDEPENDENT STRUCTURAL CONSULTANT
12. CMW was appointed to carry out an independent review of the piling records and checking on overall structural safety of the buildings.
13. CMW would check the assessment of the structural/geotechnical engineer on the cause, trend of uneven settlement and structural safety of the buildings, and carry out further investigation works including building settlement monitoring, verticality check, ground investigation, laboratory and field testing.
14. CMW would assess the results of field tests, advise the structural safety of the buildings and recommend the strengthening works that will be complying with the Buildings (Construction) Regulations.
15. An Executive Summary of the Report produced by CMW is at Annex B.
SPECIAL ARRANGEMENTS FOR PURCHASERS
16. It is estimated that the time for strengthening and reinstatement works including the tendering period would take nearly 15 months to complete. The Housing Authority Home Ownership Committee approved at its meeting on 23 September 1999 to offer the following three options to purchasers of the six blocks of Tin Chung Court Phase I (Block F, G, H, J, K and L) to suit their individual circumstances.
Option A : Rescission and Purchase of another HOS Flat
Refund of Deposit with Interest
17. Purchasers are allowed to rescind the Agreement for Sale and Purchase (ASP) with full refund of deposit plus interest at a rate of 2% above the prime rate calculated from the date of their signing of ASP up to the date of repayment of deposit to purchasers. We will be sending the rescission option form to purchasers by end September 1999 requesting them to return the form by end October 1999. Refund of deposit will be made to the purchasers in November 1999. As we anticipate that selection of flats in HOS Phase 21B will be around January 2000, the purchasers can make use of the refund to pay for the deposit of another flat.
Purchase of another HOS Flat in HOS Phase 21B
18. Purchasers who choose to rescind will be given top priority to buy another flat at Phase 21B comprising 9,400 in three projects viz. Tin Fu Court Stage II (3,200 flats) in Tin Shui Wai, Bauhinia Garden (3,200 flats) in Tseung Kwan O and Rhythm Garden (3,000 flats) in San Po Kong. Their flat selection sequence will be in the same order under which they bought their flats in Phase 20A. Tin Fu Court Stage 2 in Tin Shui Wai comprising 10 blocks of the same design scheduled for completion in September 2000 will be available to them at the lower of -
Option B : Awaiting Building Completion
- the then prevailing sale price of Tin Fu Court Stage 2; or
- the original Tin Chung Court price level, i.e. $15,100/m2 Saleable Area (SA), which most purchasers opted under the flexible discount arrangement.
Payment of Interest
19. If the purchasers choose to proceed with the purchase and wait for building completion, HA will have to account for the interest on the delay in completion of the project in accordance with the terms and conditions as stipulated in the ASP. The amount of interest will be calculated from the day following the original scheduled completion date up to the date of issue of Completion Certificate which is estimated to be around December 2000.
20. In anticipation of completion of the strengthening and reinstatement works by December 2000, the six blocks will be put up for resale in mid 2000. In the event the resale price falls below the original price of $15,100/m* SA, HA will refund the price difference to the existing purchasers.
Guarantee on Building Conditions
21. To ease the purchasers' worry, HA will provide a guarantee on the structural safety of the blocks after strengthening works. HA will take up the maintenance responsibility resulting from ground settlement for 10 years for the five blocks in question. Notwithstanding no strengthening work is required for Block G, such guarantee is extended to the purchasers of Block G as well in order to alleviate their worry.
Option C : Rescission and Other Housing Arrangements
22. If the purchasers do not want to make another purchase after the rescission, they will have their application for public rental housing (PRH) reinstated if they are Waiting List applicants. Allocation of flats will then be made as appropriate.
23. For those who are tenants of PRH or licensees of Temporary Housing Area (THA), Interim Housing (IH), or Cottage Area (CA), they can retain their units which have not been surrendered. They are, of course, free to participate in future HOS sale exercises or to apply for the Home Purchase Loan Scheme. Those who are required to vacate their flats due to clearance or redevelopment will be offered another PRH flat or IH unit according to their eligibility.
24. To clearly explain the situation to the public and the special arrangements for purchasers of flats in Tin Chung Court, Phase I, we have issued two press releases at Annex C.
24 September 1999