Browsing by Author "Tennakoon, BL"

Now showing 1 - 3 of 3

item: Thesis-Abstract
PDA Test as a method of pile testing for bored and cast in-situ R.C. piles end bearing on rock
Abeysinghe, RM; Thilakasiri, HS; Tennakoon, BL
The Pile Driving Analyzer (PDA) is a powerful tool to assess pile driving and High Strain Dynamic Pile (HSDP) load testing which may supplement or replace static testing. The PDA is seeing increasing usage in the testing of the various types of cast-in-place piles. In some parts of the world, this type of testing is the most common use for the PDA. This solution is particularly attractive for very large, high capacity piles where the large capacity makes a static test extremely costly. The rapidly increased use of pile foundations and the appearance of the new driving techniques, as well as stress wave measurement equipment have led researchers to look for better understanding of the dynamic and static behavior of the hammer-pile -soil system and to develop more reliable methods of pile analysis. The reliability of the pile driving analysis is primarily a function of the accuracy of the soil parameters and the theological model of the soil. The application of stress wave theory on piles is critically revived in literature. The scope of this study is an attempt to find a reliable range for dynamic soil parameters for end bearing bored piles in residual formation and to improve the accuracy of the wave equation analysis methods. The investigation has been focused on the comparison of the soil parameters used in practice from those used in conventional soil mechanics and soil dynamics. The solution of the stress wave equation is based on Smith's approach. Dynamic analysis of the field-recorded data was performed using CAPW AP (Case Pile Wave Analysis Program) and based on the Case Method. Ground investigation is done for evaluation of static soil properties before installation of piles. Static pile load tests were also performed on the same pile which were subjected to dynamic load test to study the load settlement behavior of the bored cast insitu piles. Further more, the static' piles capacity variation of driven piles with time termed set-up effect was studied in details for piles driven in residual formations.
item: Conference-Full-text
Prediction settlements of foundations on soft soils - a case study
(1999) Thilakasiri, HS; Peiris, TA; Tennakoon, BL
Excessive settlement of engineering structures and subsequent correction procedure have become a major concern for both the public and the engineering community. The severity of the above problem has increased due to the use of more filled marshy lands for construction. If one studies the problem of excessive settlement of most domestic structures constructed on fills, it could be clearly attributed to the violation of fundamental engineering principles. Lack of engineering knowledge and judgement or sheer negligence of basic engineering principles could be main reasons. If a structure is to be constructed on soft grounds it is clear that the ground should be improved before the construction or the construction procedure should be phased out in such a way that the final settlement, more importantly differential settlement, is within allowable limits for that particular structure. Pre-loading (with or without sand drains), replacement of the soft soil with good material, dynamic replacement and electro-osmosis are some of the methods used for improvement of clayey or peaty deposits. Of the above methods, pre-loading is widely used due to its economy and simplicity. Important considerations in pre-loading are: duration of pre-loading; height of pre-load heap (surcharge load) and the monitoring of settlement experienced. In this paper a case study of construction of a building in marshy lands violating some basic engineering principles is presented. Use of some basic soil properties together with in-situ testing (e.g. Standard Cone Penetration Test) to predict the ultimate settlement under the pre-loading is illustrated. Furthermore, the rate of settlement, an essential component of the pre-loading design, is obtained by curve fitting the settlement data while the pre-loading is in progress. This method of using basic soil properties together with in-situ tests to predict ultimate settlement and curve fitting data to predict the rate of settlement does not require the almost impossible process of obtaining undisturbed soft soil samples for laboratory testing.
item: Conference-Extended-Abstract
A study of strength gain of driven piles
(2003) Thilakasiri, HS; Abeysinghe, RM; Tennakoon, BL
Piles can be classified into three categories depending on the amount of soil displaced during installation: (i) Large volume displacement piles: (ii) Small volume displacement piles and: (iii) Replacement piles. Installation of piles can disturb the soil surrounding the pile and have an effect on the surrounding area by two different ways: (i) Due to variation of the material properties of the soil surrounding the pile and: (ii) Due to changes in the pore water pressure in the soil surrounding the pile. Magnitude of these variations is highest in large volume displacement piles compared with small volume displacement piles and replacement piles due to the high disturbance in the surrounding area caused by large volume of soil displaced. Moreover. the pore pressure generated during installation process might be dissipated with time depending on the permeability of the surrounding soils and the structure of the soil disturbed due to driving may also be recovered with time. The recovering of the soil structure with time and the equalization of pore pressure with time is termed, "Tixotropic Recover". Time taken for the recovery to complete depends on the amount of disturbance caused by the pile installation process and the properties of the surrounding soil. Due to the strength regaining of the soil surrounding the pile as a result or rixotropic recovery, the ultimate carrying capacity of the pile will vary with time. If the ultimate carrying capacity of the pile is increased due to tixotropic recovery it is termed 'setup' whereas if it's decreased it is termed 'relaxation'.