Field testing of stiffened deep cement mixing piles under lateral cyclic loading

Construction of seaside and underground wall bracing often uses stiffened deep cement mixed columns （SDCM）. This research investigates methods used to improve the level of bearing capacity of these SDCM when subjected to cyclic lateral loading via various types of stiffer cores. Eight piles, two deep cement mixed piles and six stiffened deep cement mixing piles with three different types of cores, H shape cross section prestressed concrete, steel pipe, and H-beam steel, were embedded though soft clay into medium-hard clay on site in Thailand. Cyclic horizontal loading was gradually applied until pile failure and the hysteresis loops of lateral load vs. lateral deformation were recorded. The lateral carrying capacities of the SDCM piles with an H-beam steel core increased by 3-4 times that of the DCM piles. This field research clearly shows that using H-beam steel as a stiffer core for SDCM piles is the best method to improve its lateral carrying capacity, ductility and energy dissipation capacity.

Reliability-based settlement analysis of embankments over soft soils reinforced with T-shaped deep cement mixing piles

This paper presents a reliability-based settlement analysis of T-shaped deep cement mixing(TDM)pile-supported embankments over soft soils.The uncertainties of the mechanical properties of the in-situ soil,pile,and embankment,and the effect of the pile shape are considered simultaneously.The analyses are performed using Monte Carlo Simulations in combination with an adaptive Kriging(using adaptive sampling algorithm).Individual and system failure probabilities,in terms of the differential and maximum settlements(serviceability limit state(SLS)requirements),are considered.The reliability results for the embankments supported by TDM piles,with various shapes,are compared and discussed together with the results for conventional deep cement mixing pile-supported embankments with equivalent pile volumes.The influences of the inherent variabilities in the material properties(mean and coefficient of variation values)on the reliability of the piled embankments,are also investigated.This study shows that large TDM piles,particularly those with a shape factor of greater than 3,can enhance the reliability of the embankment in terms of SLS requirements,and even avoid unacceptable reliability levels caused by variability in the material properties.

Protection of cement-soil reinforced regions for adjacent running tunnels during pit excavation

In pit excavation,cement is introduced into ground by deep mixing method to form an improved soil raft below final formation level to diminish deflection of retaining wall and effect on surrounding structure.Owning to complicated site conditions and improper workmanship,there are always some regions left untreated in the embedded improved soil raft.In this work,Several schemes of cement-soil mixed piles arrangement are modeled in order to discuss the effect of different cement-soil reinforced regions on protection for adjacent running tunnels.Finite element results show that:when lateral regions above tunnels are not enhanced by cement-soil mixed piles,effect of enlarging vertical enhanced regions around tunnels on diminishing lateral displacement of tunnel is really small;enhancing the lateral regions next to retaining wall is more effective in reducing the deflection of tunnel and retaining wall;uplifting of tunnel under the middle pit mainly depends on lateral reinforced regions and lateral displacements of retaining wall;as cement-soil mixed piles near retaining wall in east pit are removed during east pit excavation,effect of cement-soil mixed piles in east pit on reducing the final wall deflection can be neglected;upward shaft resistances are exerted along left side of diaphragm wall during excavation,which helps to reduce the wall deflection;positive effect of single-head cement-soil mixed piles in east pit is to decreasing the uplifting of soil inside east pit.Double-head cement-soil mixed piles arranged in"T"shape decrease the effect of east pit excavation on tunnels under middle pit apparently.