Specific Approach Method Statement Rotary Bored Piling Work in Karst Terrain
CONTENT
1.Basis of Compilation
2.Project Overview
3.Types of Karst
4.Approach for Works Involving Karst
5.Contingency Plan (To be prepared before commencing work)
1.Basis of Compilation 1).Contract signed with the owner. 2).Tender documents signed with the owner. 3).Design drawings provided by the owner. 4).Geological Report provided by owner. 5).Relevant Malaysian construction regulations, foundation construction specifications.
2.Project Overview Cadangan pembangunan 1 blok pangsapuri servis 51 tingkat (437 unit) termasuk 1 tingkat basemen dan kemudahan penduduk serta podium dan 1 unit pondok pengawal di atas Lot 11599, 1524, 1525 dan 1526, Jalan Ampang Kiri, Mukim Ampang, KL
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3.Types of Karst Karst can generally be divided into three types: completely void, half-filled, and fully-filled. Karst that are taller than 3 meters are classified as large karst.
4.Approach for Works Involving Karst Construction of bored piling works in karst terrain are becoming more and more common, performing concealed works in karst terrain comes with a high level of difficulties. Therefore it is of utmost importance for us to gain sufficient understanding of the development regularities, basic forms, sizes, thickness of top rock layer, integrity, shape of karst formations and features, so that the necessary measures can be taken to ensure the safety of works being performed. The geological data of the project shows that the project ground consists of complex underground karst structure. The owner ensures that pre-drilling work is done before the drilling of each pile, and an extra 5 meters is added to the designed depth, securing the safety and reliability of the works done. Specification of work: Based on the abovementioned Pre-drilling Geological Report provided by the owner. After precise setting-out of the pile foundation, carry out pre-drilling at the center of each bored pile -2-
location on the pile foundation platform, increase the number of drilling points when necessary. When karst is discovered in any specific piling location, drill 4 grouting holes around it. As illustrated by the diagram below:
After comparison is done based from the technical, economical aspects etc., when encounter large karst at any depth of 0—12 meters, shall be classified as half-filled or fully-filled type, by applying static pressure chemical grouting method. Internal pile casting covering method is applied for small karst. When encountering half-filled and fully-filled type at 12—30 meters deep, apply static pressure chemical grouting method. When encounter large karst or completely void type, use G20 backfilling concrete. When exceeding 30 meters deep, apply static -3-
pressure chemical grouting method. Application of the best suited methods will ensure expected results, as illustrated by the table below: Type of Karst Depth H<3m (H: height of karst) H≥3m (H: height of karst) (m) Void(without Half-filled/ Void(without Half-filled/ filling) fully-filled filling) fully-filled Static Static Static Pile pressure pressure pressure casting 0-12 chemical chemical chemical covering grouting grouting grouting
12-30
Static pressure chemical grouting
Static pressure chemical grouting
Backfill G20 concrete
Static pressure chemical grouting
Below 30
Static pressure chemical grouting
Static pressure chemical grouting
Static pressure chemical grouting
Static pressure chemical grouting
Description of work method Embed pile casing 8-12 according to geological condition. Backfilling concrete produces better results for large karst of such depth. Static pressure chemical grouting produces better results.
Item 1: Pile casting covering method: Based on the predrilling result, determine the depth to embed the pile casing. For piling location with detected karst, pile casing embed to the weathered rock layer, on surface of strong weathered rock layer, so that can penetrate soil caves. The bottom of the pile casing shall be the rock layer or top of the karst. For karst free piles, pile casing to be embedded underneath mucky clay, gravel layer, placed at least 2 meter deep in the gritty clay. Item 2: Backfill method (crushed rocks or concrete) for completely void or -4-
half-filled karst, height of karst is generally around 3 meters. When slurry leakage occurs, and the water level within the pile casing cannot be maintained, use flagstone plus clay (at 1:1 volume ration) to impact backfilling, to form stone clay retaining wall. Item 3: Specially reinforced slurry for static pressure chemical grouting can achieve speedy solidification within a matter of a few ten seconds. This will control the grouting within a certain range and avoid it from running-off, ensure that materials are used to their full capacity, hence much more economical. The setting percentage of slurry is at 100%, meaning that 1m³slurry can produce 1m³consolidated body. For sand, gravel and other earth forms in the karst, the slurry hardens them through permeation. For rare earth, clay soil and other earth forms in the karst, the slurry reinforces these earth form through split and compaction effects. While for completely void and half-filled karst, the slurry will be able to completely fill all the void spaces. The permeation of the slurry within the earth form is in the direction of the minor principal stress surface, once the slurry solidifies it will reinforce the minor principal stress surface. While permeating and compacting the void within the earth, filling the void, forming sealing curtain surrounding the pile, preventing sand and mud loss. On the other hand, increasing the bearing capacity and -5-
shearing resistance of the earth form in the karst creates retaining wall that will prevent the hole from collapsing. Static Pressure Chemical Grouting Method: Drill hole
Diameter:80mm,depth of hole to reach the base of the deepest karst.
Material
Portland 325# cement and chemical grout Apply grouting method with two types of grout and perform full hole grouting, perform more frequently with less amount, repetitive grouting. BW250 mud pump, BW150 mud pump, drilling rig model 100, concrete mixer and drainage tank, high pressure grouting pipe and its components.
Method Main equipment & facility
To prevent high pressure inside the hole from deterring the grouting works, apply other holes to relieve the pressure. Grouting Pressures The following pressures should be used for grouting cavities located at the corresponding depths below the existing ground surface. Depth(m)
Grouting pressure (pls)
20.1-30
87
30.1-40
116
40.1-50
145
50.1-60
174
60.1-70
203
70.1-80
232
80.1-90
261
90.1-100
290
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5.Contingency Plan (To be prepared before commencing work) Issues related to any existing karst below the construction ground has been solved during the construction preparation phase. The plans below has been made in view of the complex earth formation, to avoid any safety and quality accident that might lead to injury to workers and losses to company: 1).Regular checking on easily damaged parts of equipment, repair or replace in a timely manner. 2).Sufficient supply of steel plates on site, carefully plan the route of heavy machineries (such as drilling rig, crane etc.). To prevent slurry leakage, partial collapsing etc. when the drilling work is being performed. Emergency materials listed below is to be prepared at the site: ITEM Crushed rocks Clay Concrete Gunny sack & similar material Forklift model 50 220L excavator
QUANTITY 80m³ 120m³ 10 tonnes 200 sheets 1 unit 1 unit
Emergency Contact Persons No. 1 2 3 4 5
Type Project manager Safety officer Technical manager Site engineer Site supervisor
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Quantity 1 1 1 2 4
Remark Chinese Malay Malay Chinese Chinese Chinese
