Full scale tests on stiffended deep cement mixing (SDCM) pile including 3D finite element simulation | |
| Author | Pitthaya Jamsawang |
| Call Number | AIT Diss. no.GE-08-01 |
| Subject(s) | Concrete piling--Simulation methods Finite element method |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Geotechnical and Geoenvironmental Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. GE-08-01 |
| Abstract | The stiffened deep cement mixing (SDCM) pile employs a precast reinforced concrete pile inserted at the center of DCM pile. The Deep Cement Mixing (DCM) pile can be subjected to both vertical and horizontal forces i nduced by the embankment loads. Thus, the stiffened deep cement mixing (SDCM) pile is more suitable than DCM pile because SDCM pile has higher strength and stiffne ss and can sustain higher bending moment and resist higher lateral loads. This study presen ts results of laborat ory investigations on cement-admixed clay and SDCM pile, field full scale pile and embankment load tests on SDCM and DCM piles and 3D finite element simulations. From the unconfined compression strength ( q u ) of cement-admixed clay at liquid limit water contents, the optimum cement content by weight was found to be 15%. The relation of modulus of elasticity was found to be, E 50 = 129 q u . Similarly, the relations obtained for the flexural strength , σ f = 0.16 q u and the splitting tensile strength , σ t = 0.14 q u as well as the empirical relation of flexural strength a nd tensile strength of cement-admixed clay, σ f = 1.16 σ t . The values of unconfined compressive strength , q u , of DCM obtained from field specimens employing ranged from 500 kPa to 1,500 kPa with average of 900 kPa while the modulus of elasticity , E 50 , ranged from 50,000 kPa to 150,000 kPa with average value of 90,000 kPa indicating that E 50 = 100 q u with is similar to the laboratory empirical relation. The strength reduction factor, R inter , calculated from the ratio of the interface shear strength and cohesion of cement-admixed clay in the direct shear test varies from 0.38 to 0.50 for cement contents of 10% to 20%. The strength reduction factors, R inter , obtained from pullout interface test varies form 0.36 to 0.44 sim ilar to the values obtain from direct shear interface tests. The flexural stre ngth of DCM pile in the field was lower than in laboratory equal to 4 to 7% of the fi eld unconfined compressive st rength. In the laboratory, the modulus of rupture was 16 % of laboratory un confined compressive strength. The strength reduction factor for interfaces, R inter , obtained from full scale pull out interface test was 0.40 similar to the laboratory values. A series of the full pile scale tests involving SDCM and DCM piles under axial compression, lateral, and pullout loads were done. The ultima te bearing capa cities of 2 DCM piles have significant large difference as much as 60 kN or 30 % confirming the low quality that commonly occurs on DCM piles re sulting in its low bearing capacity. The ultimate bearing capacities of SDCM piles with higher length ratio of 0.85 and similar area ratios of 0.11 and 0.17 can be as much as 2.1 to 2.3 times compared to DCM piles. The length of concrete core pile affected both the ultimate bearing capacity and settlement whereas its sectional area has negligible effect. The DCM p iles failed by pile body failure. The SDCM pile with lengths ratio of 0.85 fail by soil failure. Thus, the effective length ratio of the SDCM pile shoul d be larger than 0.85. The av erage lateral ultimate bearing capacities of SDCM piles with area ratio of 0.11 and length ratios of 0.54 and 0.85 could be improved by 11 times compared to DCM piles. The average lateral ultimate bearing capacities of SDCM piles with area ratio of 0.17 and length ratios of 0.54 and 0.85 could be improved by 15 times compared to DCM piles. Thus, the sectional area of concrete core pile affected both the lateral ultimate bearing capacity and displacement. The 3D finite element simulation was performed to analyze results of full scale pile load tests. The parametric study on the effect of the length and the sectional area of concrete core pile on ultimate bearing capacity was performed by varying the concrete core pile length from 2 to 7 m and varying the size of concrete core pile from 0.18 to 0.30 m square. The length of core pile affected significantl y the ultimate bearing capacity whereas the effect of the sectional areas of concrete core pile was not significant. The parametric study on the effect of concrete core pile lengths on the ultimate lateral load was performed by varying the concrete core pile length from 0.5 to 5.5 m. The c oncrete core pile length of 0.5m yield the lowest ultimate lateral load a nd the concrete core p ile longer than 2.5 m yielded the same ultimate lateral loads. A full scale embankment on deep mixing improv ed soft clay foundation was constructed in AIT campus, Thailand. SDCM pile with ar ea ratio and length ratio of 0.17 and 0.85, respectively, has effectively reduced the sett lement and lateral movement induced by the embankment loading than DCM pile with se ttlement reduction of 40% less than the DCM pile. The lateral movement in SDCM piles was 60% less than the DCM pile. The lateral movement–settlement ratio can be reduced by SDCM pile, especially in the surrounding clay where the ratios can be reduced as much as 50%. The results of 3D finite elem ent simulation on the results full scale embankment show that the length of concrete core pile significantly affected the settlement of the SDCM pile. The effective length of concrete core pile s hould be greater than 6 m corresponding to length ratio of 0.85. The section area of concrete core pile affected lateral movement similar to the results full scale test. The magnitudes of lateral movement were reduced with increasing concrete core pile length. The effect ive length of concrete core pile to bear the embankment loading involving axial and lateral loads s hould be greater than 6 m corresponding length ratio of 0.85.B oth the length and sectional area of concrete core pile affected the lateral movement of SD CM pile under embankment loading. |
| Year | 2009 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. GE-08-01 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Geotechnical Engineering (GE) |
| Chairperson(s) | Bergado, Dennes T.; |
| Examination Committee(s) | Panich Voottipruex ;Kunnawee Kanitpong ;Giao, Pham Huy ;Noppadol Phien-wej; |
| Scholarship Donor(s) | The Royal Thai Government; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2008 |