4.12　Cement Flyash Gravel Piles

4.12.1　The laboratory mix design shall be performed in accordance with the design requirements before the construction.The mixture slump for continuous flight auger piles should be 160mm-200mm；the mixture slump for vibration tube sinking cast-in-situ piles should be 30mm-50mm.

4.12.2　The construction of cement-flyash-gravel piles shall meet the following requirements：

1　During construction of vibration tube sinking cast-in-situ piles and continuous flight auger bored piles，the flyash in the mixture may be selected as coarse ash collected in power plant；during forming of continuous flight auger piles with mixture pumping method，the flyash of GradeⅢor above，of which the fineness（percentage of residue on 0.045mm square hole sieve）is not greater than 45%should be selected；

2　During construction of continuous flight auger piles with mixture pumping method，the flyash amount in each cube of mixture should be 70kg-90kg；

3　The hole forming shall be carried out slowly first and then fast，drill pipe tolerance shall be inspected and corrected timely，and the pile installation process shall be continuous；

4　During construction of continuous flight auger piles with mixture pumping method，upon drilling to completion，the auger lifting time shall be properly controlled in order thatthe mixture pumping rate shall match the auger withdrawal rate；the pressure grouting shall be completed in one continuous operation.During pressure grouting，the discharge hole at the bottom of drilling tool shall not be higher than the grout surface within drilling hole；

5　For vibration tube sinking cast-in-situ piles，the pipe withdrawing rate shall be uniformly controlled within 1.2m/min-1.5m/min；where through mud or muddy soil layers，the pipe withdrawing rate shall be properly slowed down；the granular material or wet cohesive soil shall be used for capping after sunken pipe is lifted abovethe ground surface and the pile top elevation is confirmed；

6　The thickness of pile top laitance for vibration tube sinking cast-in-situ piles should not be greater than 200mm；

7　The pipe withdrawing shall start only after the core tube is fully filled with mixtures；pipe withdrawing prior to pumping is strictly forbidden；

8　The pile top elevation should be more than 0.5m above the designed pile top elevation.

4.12.3　The verticality tolerance of pile shall not be greater than 1/100.The pile position tolerance for mat foundation shall not be greater than 0.4 times the pile diameter；the pile position tolerance for strip foundation shall not be greater than 0.25 times the pile diameter；the pile position tolerance of single row pilelayout shall not be greater than 60mm.

4.12.4　The static compaction method should be used for placement of the cushion layer.Where the water content of the inter-pile subsoil is relatively small，dynamic compaction method may also be adopted.The degree of tamping and filling shall not be greater than 0.9.

4.12.5　During construction in winter，the mixture temperature shall not be less than 5℃prior to introduction into the hole.

4.12.6　The construction quality inspection shall meetthe following requirements：

1　During pile installation，the test cubesshall be sampled for the mixture；a group of（3）test cubes（150mm×150mm×150mm）shall be sampled each day for each piling equipment and subjected to standard curing，and the cube compressive strength shall be determined thereafter；

2　The construction records，slump of mixture，number of piles，pile position tolerance，cushion layer thickness，degree of tamping and filling，compressive strength of grout test cubes and other data shall be inspected for the construction quality；

3　The foundation bearing capacity shall be inspected through a single composite pile load test or a single pile load test；for a single project，the test quantity shall be 1%of the total number of piles but not less than 3；for inspection of pile body，no less than 10%of the total number of piles shall be subjected to low strain dynamic test to test the pile integrity.