The influence of changing shaft friction of the pile to wave propagation

Abstract

In most cases, the bearing capacity of the pile under natural conditions can be determined by applying static and dynamic pile tests as well as the numerical modelling of a dynamic test. The integrated business problem is employed for calculating vertical displacements. This integral is calculated using the summing method. In the majority of cases, real pile strength capacity can be investigated referring to the adapted means of testing applying the mathematical model that can calculate static or dynamic investigations. The idealized scheme of a pile test is presented including a hammering system and soil properties. Moreover, information on the analysis and work of the scheme is disclosed. The article also describes pile hammering models and the equation for Smith method improved by Edwards, Holloway, Briaud and Trucker, Rieke and Crowser, _”GRL“, including the advantages and disadvantages of the introduced method. Smith realized the mathematical analysis of wave propagation supported by a real hammer-pile-soil scheme by discretic elements interaction. Basing on this for classical one dimensional method of wave propagation (that is programmed in computer program MW87) the code of the computer program was changed by authors of this article. When using a computer program, an algorithm for an integral equation was created. The introduced algorithm was made for counting experimental displacement the growth of which along the pile was analyzed. All obtained results were compared with the engineering method indicating that diff erence in results made less than 2%. Using computer program MW87, a diff erent distribution of shaft friction along the pile was studied when the total shaft friction in all cases was constant, because, the results of numerical modelling disclosed that the shaft friction of the pile in one diameter above the pile’s toe was larger than that in the middle or at the top. The hammer-pile-soil system was analyzed with reference to the impact of the returning wave at the top of the pile. Wave propagation in the pile is vertical: the first wave moves from the top to the bottom of the pile. When the bottom is reached, impact wave returns to the top of the pile. All information about the pile of the returning wave is useful as then we can analyze the integrity and bearing capacity of the pile. All this information received from the returning wave is integrated and later shown in the scheme where we can see all steps of performed operations. This article investigates soil deformations and these deformations in soil influence for a hammering pile. A pile of 0,8 m in diameter and 3 m in height, which is in sand, is an object of investigation in this article. For calculation purposes, the pile is divided into 20 segments. Changes in velocities and displacements of pile segments during analysis are graphically shown. Aft er calculating tests on pile dynamics considering diff erent masses of hammers, falling heights of hammers, contribution of shaft friction and static resistances of the piles, a nomograme for determining static resistance of the pile was made. The article explains how the use of the nomograme determines static resistance of the pile and what data on conducting a pile test are needed.

Article in Lithuanian.

Grunto stiprio, kintančio išilgai polio, įtaka smūgio bangos sklidimui polyje

Santrauka. Daugeliu atvejų tikroji polio laikomoji galia gali būti nustatyta natūraliomis sąlygomis atlikus polio laikomosios galios statinius arba dinaminius bandymus bei atlikus skaitinį dinaminių bandymų modeliavimą. Pateikiama idealizuota polio bandymo arba kalimo sistema, kuri apima plaktą, kalimo sistemą ir grunto savybes. Nurodoma, kokia informacija reikalinga norint atlikti minėtos sistemos analizę, aprašoma, kaip ši sistema veikia. Pateikta idealizuotos polio bandymo arba kalimo sistemos sprendimo veiksmų seka – vienmatės bangos sklidimo polyje skaičiavimo metodas, užprogramuotas kompiuterinėje programoje MW87, kuri straipsnio autorių buvo pakoreguota. Šiame straipsnyje nagrinėjama skirtingai pasiskirsčiusio grunto stiprio, kintančio išilgai polio, įtaka polio kalimo atsakui, kai visas grunto stipris, kintantis išilgai polio, nekinta, nes, remiantis esant tampriajai stadijai gautais skaitinio modeliavimo rezultatais, nustatyta, kad grunto stipris, kintantis išilgai polio, virš pado vieno polio skersmens intervale yra kur kas didesnis negu per polio vidurį arba jo viršuje. Straipsnyje nagrinėjamas 0,8 m skersmens 3 m ilgio polis, esantis smėlio grunte. Skaičiuojant polis yra išdalintas į 20 baigtinių elementų (segmentų). Grafiškai pavaizduota, kaip, priklausomai nuo laiko intervalų, idealizuotoje polio skaičiuojamojoje schemoje kinta segmentų greičiai ir poslinkiai. Atlikus polio dinaminio bandymo skaičiavimus, kai plakto masės ir suminiai grunto stipriai, kintantys išilgai polio, yra skirtingi,buvo sudaryta nomograma, kuria naudojantis galima nustatyti polio statinį stiprį. Straipsnyje pateikiama, kaip, naudojantis nomograma, nustatyti polio laikomąją galią, kokie polio dinaminio bandymo duomenys tam reikalingi.

Reikšminiai žodžiai: Smith modelis, grunto stipris, smūgio bangos sklidimas, nomograma.

First Published Online: 16 May 2013

Keyword : Smith model, soil resistance, impact wave propagation, nomograme