Measuring deformation, pile body stress - the necessity to pile load tests.
09/08/2016
Usually when static load test for pile, the result obtained is only Load-Displacement relationship graph. This information is too few. We hardly know how the load transmits in the pile body, the reaction of each soil layer when the load is. Distribution bearing capacity with friction of the soil layer around the pile and soil resistance under the pile tip are not clear. Based on this testing results is difficult for the designer decides to adjust the design of working piles that can really exploit all the load capacity of the pile and optimizes foundation cost for the investor.
By far, the scientists in the world have tested the deformation sensor (strain gage) in the pile body and then proceed with the measuring supply load testing. Whereby can clearly identify the load transmission of pile and the reaction of the ground. Brief sequence for this is:
• Install strain gages at certain levels and signal cable in pile body.
• Measure the deformation signal during loading, receive deformation εi
• From deformation can be calculated stress σi=E.εi, E is elastic modulus of pile material.
• From stress σi can be calculated internal force at mearsurement elevation Qi = A. σi
• From internal force at two elevations can be calculated frictional resistance of the soil layer around pile between two elevations Fmsi=Qi-Qi+1.
• From frictional resistance can be calculated unit frictional resistance fmsi=Fmsi/Sxqi, Sxqi is the surface area of pile between two elevations.
• If calculate friction resistance of all soil layers around pile body then calculate resistance of soil layer under pile tip Fmui=P-ΣFmsi
• Measure the deformation signal during loading, receive deformation εi
• From deformation can be calculated stress σi=E.εi, E is elastic modulus of pile material.
• From stress σi can be calculated internal force at mearsurement elevation Qi = A. σi
• From internal force at two elevations can be calculated frictional resistance of the soil layer around pile between two elevations Fmsi=Qi-Qi+1.
• From frictional resistance can be calculated unit frictional resistance fmsi=Fmsi/Sxqi, Sxqi is the surface area of pile between two elevations.
• If calculate friction resistance of all soil layers around pile body then calculate resistance of soil layer under pile tip Fmui=P-ΣFmsi
The cost for this is expensive due to costs for fix strain gages and signal cable in pile body but bringing value are usually much larger. Based on the testing results, designer can be adjusted to reduce the pile quantity or reduce the depth or diameter, as well as reduce the amount of reinforcement.
Worldwide, most of the designers are using strain gages when design trial piles. Many countries have regulations on the standards of the test. In Vietnam, there was a lot of projects using strain gages, more and more designers and investors are aware of the importance of measuring deformation - stress of pile body.
Accompanying the designers and investors, ADCOM is proud to provide load testing services including pile body stress test credibility and quality. Some of the feature projects as follows: Vinh Tan 2 Thermal Power Plant, Duyen Hai 1 Thermal Power Plant, Danang airports, Hesco office building, D'.San Raffles 22-24 Hang Bai, Xuan Mai Riverside, Vinhomes Sky Lake ...
