Problems of spun concrete piles constructed in soft soil in HCMC and Mekong delta – Vietnam

The use of spun concrete piles under geological layer that has the thick soft soil layer reveals many flaws, many incidents of tilting pile or broken pile have occurred during construction process in many projects, cause great damage to the cost of the project as well as the slow construction progress. In this paper, the author analyzes the causes inclined piles during construction of spun concrete piles, as well as provide the method to determine the inclination of the pile along the pile body.
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Problems of spun concrete piles constructed in soft soil in HCMC and Mekong delta – Vietnam PROBLEMS OF SPUN CONCRETE PILES CONSTRUCTED IN SOFT SOIL IN HCMC AND MEKONG DELTA – VIETNAM Nguyen Thanh Trung Civil Engineering Faculty, Ho Chi Minh City University of Technology (HUTECH)ABSTRACTIn recent years, the use of spun concrete piles for foundation of high buildings in HCMC and provincesin Mekong Delta is popular. Because of the advantage that the length of each segments of pile is longer,the number of joints is reduced, as well as load bearing capacity under material strength is greater andtotal cost is reduced for the Client. However, the use of spun concrete piles under geological layer thathas the thick soft soil layer reveals many flaws, many incidents of tilting pile or broken pile haveoccurred during construction process in many projects, cause great damage to the cost of the project aswell as the slow construction progress. In this paper, the author analyzes the causes inclined piles duringconstruction of spun concrete piles, as well as provide the method to determine the inclination of thepile along the pile body.Keywords: Incident, inclinometer, soft soil, spun concrete pile, tripot.1. INCIDENT OF PILE INCLINATION Figure 1. Photos of pile tilt at project in District 2, HCMCDuring the construction process, in order to shorten the construction period, contractor often uses Robotcompressor, which is 600 tons and 900 tons of Robot weight and compressing load. During the pileconstruction process, the robot will apply the load and move above between the pile positions. With suchheavy loads, Robot even moves on the thick sand layer around 1.5m to 2m, there is still able to create thesliding surface, causing the tilt of the previous pre-constructed piles.472 Figure 2. The appearance of sliding surface during pressingApart from the case of the piles are inclined due to the appearance of sliding surface during the pilepressing construction, there are also some reasons cause the pile inclination as follows: – Piles are inclined during deflected pile pressing construction. – Piles are inclined due to the sliding surface appearance during the pile driving machine (robot) is moving. – Previous pressed pile is inclined due to the nearby pile construction that leads to the appearance of horizontal force effects to the previous pressed pile. – Piles are inclined due to the excavation of basement2. METHOD OF SURVEYING OF PILE INCLINATIONUpon detecting potential inclined piles, aim to assess the inclination of the piles as well as the load bearingcapacity of piles, here the author applies the method to measure inclination along the pile body by usinginclinometer equipment.The operation of the inclinometer equipment is to measure the horizontal displacement of pile for eachsurveying position throughout the depth of pile under the gravitational direction. The inclinometerequipment will be sliding into the grooves of the inclinometer tube that is inserted in the body of the pilein advance. The tube is fixed by tripod system to ensure the tube position is always in the centre of thespun concrete piles.Horizontal displacement measuring equipment (Inclinometer tube) is installed inside spun RC piles afterfinishing construction of piles. Horizontal displacement measuring tube is composed of dedicated plastictubes interconnect with each other, the measuring tube has a length depends on the depth of spunreinforced concrete piles. Measuring tubes are made of composite plastic reinforced fiber glass, have highelasticity and strength (ABS tubes). Measuring tubes outer diameter is 70mm. Inside the tube, there are 4different perpendicular grooves. Each 3m tubes is connected by joints system.The tubes are placed inside the pile cage, relying on tripod 3 feet, with wheels touching the pile„s wallaim to keep the tube in the middle of the pile. Only install measuring tubes at the measured piles.473 Figure 3. Installing of tripod system Measurement principles of inclinometer method and preparing for testing3. COMMON TYPES OF INCLINED PILESAfter analyzing the results of inclination measuring, there are generally two types of inclination form ofthe pile as following: Figure 5. Inclination - Axis A Inclination - Axis B Figure 6. Inclination - Axis A Inclination - Axis B Inclination - Axis AD Inclination - Axis ADType 1: Even inclined piles: Pile head are inclined Type 2: Pile is broken at joint position or in acompared to the initial pile position due to Robot‟s position adjoining the weak geology and the goodweight. This is the most popular type of inclined geology, or due to the previous pressed pilepiles. segments are obliqued, the following pile segments is corrected to straighten during pressing.4744. ANALYSIS OF CAUSESApart from the case of the piles are inclined due to the appearance of sliding surface during the pilepressing construction. In this part, anaysis cause of problem is: – Piles are inclined due to the sliding surface appearance during the pile driving machine (robot) is moving.Using Plaxis software version 8.5 to modelling the interaction between the soil and the prestress concetepiles when pressing machine (Robot) and moving of the robot with a great pressing load (42 kN/m2). Table 1. Characteractic of soil Modulus Modulus Modulus ...