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GL1721-
2001, Almer E.C. Van der Stoel, PhD thesis, Delft University, 233 Pages, 26.2 MB pdf

Abstract:

The aim of this research was to examine the use of grouting methods for pile foundation improvement, a generic term that is used here to define both foundation renovation (increasing the bearing capacity of a pile foundation that has insufficient bearing capacity) and foundation protection (safeguarding the piles of the foundation against possible damage resulting from underground construction activities in the vicinity). First some definitions and standards relating to pile foundations are outlined after which a short account of pile foundation history is given. Subsequently the causes and detection of foundation damage and possible methods for foundation renovation are explained. One of these methods, foundation improvement by means of grouting techniques, can usually be executed from outside the structure and therefore the need to shore up the structure is avoided. However this application did raise questions regarding the response of the foundation piles to the installation process and to the grouting process, thus it was considered necessary to conduct further research. A full-scale test, of which the general set-up and consistency check are outlined in the thesis, was conducted in Amsterdam. By using the pile displacements, soil stresses, pore pressures and pile bearing capacity measured in this test it was possible to examine the influence of grouting methods on pile foundations. The main part of the thesis focuses on permeation grouting, jet grouting and compaction grouting. For each method, first some more general aspects like history, grouting equipment, grouting parameters and fields of application are outlined. Subsequently existing theories used in modelling the grouting process are examined and compared. It could be generally concluded that all the techniques, and especially jet grouting, are so complex that modelling serves only to increase understanding of the process. The existing models are not designed for use in engineering practice. There are many similarities between the processes of installing the permeation grouting TAMs or compaction grouting tubes and of drilling the jet grouting monitor to depth. From the tests it was concluded that in most cases significant pile displacements caused by installation effects occur only when the minimum distance between the TAM/tube/monitor and a wooden pile is less than 0.5 m. Permeation groutability tests were conducted. These showed that the known applicability limits for permeation grouting using a silica gel, are fairly correct for the Amsterdam situation. The influence of grouting on pile displacements, total stresses and pore water pressures during the actual grouting process is insignificant, which confirms the nondisturbing character of the grouting process when properly conducted. The bearing capacity and stiffness of the piles can be considerably increased by the use of this method. When jet grouting for foundation protection, the pile settlement during the jetting stage remained limited to 2 mm for each column, regardless of the distance between the pile and the jet grouted column and the diameter of the column. Neither the bearing capacity nor the stiffness of the wooden piles was negatively influenced. When jet grouting for foundation renovation, the pile displacements increased exponentially, especially when grouting just below pile toe level. After grouting the extended concrete piles showed almost exclusively elastic deformations and showed no sign of reaching their ultimate bearing capacity. From the samples obtained from the jet grouting columns, it was deduced that although satisfactory strength and stiffness parameters had been achieved, the variation coefficients of the grout parameters were high. Some empirical relations have been derived from the test results. During the test, compaction grouting subsequently caused the soil and piles to heave (caused by the large volumes of grout that are injected) and to settle (as a result of consolidation). Generally the measurement points closest to the injection point showed the largest displacement and excess pore pressures. When the excess pore pressures had dissipated the settling of the piles ceased. The bearing capacity could be considerably increased, which agreed with the calculations of the compaction ratio. The use of and suitability of geophysical verification methods for grouting, which were necessary to determine the shape and position of grouted elements, were also considered. On the whole, the results of electrical resistance measurement seem to be in accordance with the actual geometry of the grouted elements. The use of Bore Hole Radar measurements in permeation grouting applications is not considered feasible. Verification by using BHR measurements in jet grouting columns showed that they usually underestimate the actual column diameter. To determine how grouting methods can best be applied for foundation renovation purposes, the cost of grouting methods and the hindrance that they cause have been compared with those of conventional foundation renovation methods. The construction cost of grouting can be up to about 50% lower than that of conventional methods of underpinning a structure. Taking cost, hindrance and the test results into consideration, it can be concluded that permeation grouting and compaction grouting are economic and effective alternatives to conventional underpinning methods for renovating pile foundations. The methods may also be used for pile foundation protection. Jet grouting is only suitable for use in the renovation of end bearing piles when the structure is strong and stiff enough to redistribute the loads from the grouted pile. Jet grouting is very suitable for use in protecting pile foundations because it can be applied in any type of soil. The future perspective regarding jet grouting is that until a database containing the relation between the input and output parameters is available, trial columns should be constructed before the actual project is started. Because of the wide scatter that is generally found when analysing strength and stiffness parameters, adequate risk assessments should be made or material factors of 2 to 3 should be used. In addition, because of the risk of blowouts, the significance of careful monitoring of the jet grouting process is emphasised. To counteract this risk, the spoil return flow and the pressure at the monitor should be constantly monitored. The most important recommendations on compaction grouting are that the volume of the grouted element should be carefully controlled and that it is necessary to ensure that the installation procedure is accurate.

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