Ground improvements Research Papers - Academia.edu (original) (raw)

In the scope of this study, selection process of ground improvement methods for soils, which has bearing capacity, settlement, liquefaction, permeability, stability, swelling or subsidence problems, are investigated. Soil improvement methods are investigated in detail. All improvement methods can be classified as surface and deep according to depth, mechanical, hydraulical, physical, chemical, biotechnical and reinforcement according to the method of application, for clayey soils, for sandy soils and for all soils according to the soil types, and reinforcement, improvement and treatment according to application for tunnels, underwater constructions, historical buildings, and other superstructure and infrastructure projects. In this study, soil improvement methods are classified according to depth and the soil improvement methods are explained under two main headings as surface and deep soil improvement methods that improve bearing capacity, settlement, liquefaction, permeability, stability, swelling and subsidence problems. Under surface ground improvement and deep ground improvement methods, improvement by reinforcement, improvements with admixtures, surface drainage, surface compaction methods are mentioned as surface improvement methods and biotechnical, deep dynamic compaction, deep drainage, deep mixing, deep dynamic modification, electrical signal compaction, grouting, hydro-blasting compaction, thermal treatment, improvement piles, jet grouting, sand compaciton pile (SCP), microbic methods, blasting, stone column were mentoined as deep improvement methods. Moreover, most used methods, which are jet grouting, cement grouting and stone column, were examined in detail.
Commonly used ground improvement methods jet grouting, cement grouting and stone column applications’ effects on soil behaviour were investigated. Improvement effects of these three methods on same soils were estimated. Jet grouting, cement grouting and stone column methods were modelled for a site where bored piles were applied. On this site, soil profiles which have bearing capacity and potential settlement problems were determined according to the available soil investigation report. Jet grouting, cement grouting and stone column materials were designed for these profiles. All these design parameters should be checked on site. Design parameters of jet grouting, cement grouting and stone column materials were used in empirical and Plaxis software analysis which use finite element methods. All the analysis were done on Profile 1, Profile 2 and Profile 3 which are determined as having porential bearing capacity and settlement. Profile 1 includes low plasticity clay and clayey gravel, Profile 2 includes high plasticity clay, low plasticity silt and clayey sand, and Profile 3 includes silty and clayey sand. First, lengths of columns and piles were optimized for these three soil profiles. Jet grouting, cement grouting and stone column applications were investigated in 3.4 m and 13 m excavation depths, different column lenghts, and 3 D (%8.7), 2 D (%19,6) and 1,5 D (%34,9) column spacings (improvement rates) whereby empirical and numerical analysis using Plaxis program column and composite soil, Terzaghi and Meyerhof bearing capacity theories and Bowles settlement theory. According to this, each soil improvement methods has an effective column length that change with soil samples and lengths. Even though, almost all the improvement methods’ bearing capacity and settlements were affected positively with increase of improvement ratio, however, there were also rare negative effects like settlement increase of stone column in sandy soil.
In terms of bearing capacity, stone column method gave better results than jet grouting and cement grouting applications. Although, in the application of stone column, in sand, bearing capacity has increased, increase of bearing capacity for jet grouting application gave far better results. Cement grouting, which is applicable only to sand on Profile 3, increased bearing capacity significantly. However, the effect of cement grouting on the bearing capacity was less than stone column and jet grouting applications.
Furthermore, jet grouting application affect settlements far possitively for clayey, silty and even sandy soils than the other methods, moreover, the settlement problem beneficially. Stone column method, which is applied through substitution is not rigid, and cause less settlements for clayey and silty soils, but settlements were increased in sandy soils. This situation could be better when alternative compacted stone column methods are applied. Moreover, cement grouting affected settlements well, but it could not be as much as jet grouting effects.
On the other hand, there were distinct results according to analysis types. It was observed that calculated empirical bearing capacity values were higher than the one’s found the other methods. Moreover, bearing capacity that calculated according to composite soil theory is higher than calculated value by Plaxis program. Also, empirical calculation of settlements is lower than calculated value by Plaxis program. Bearing capacity of stone columns calculated by using the composite soil theory gave high bearing capacity values on the internal friction angle is high. Bowles settlement theory results gave less settlement values than the one calculated by Plaxis program. Plaxis column calculations can be considered better due to the reason that column can be evaluated separate or group.
In addition, the stone column usage in the clay and silt soils gave better results than sand. As long as cement injection can be applied, it has been observed that it contributes to the bearing capacity of loose sands and improved to settlement behaviour. Also, jet grouting method contributed significantly to settlements including clayey, silty and sandy soils, however, it did not demonstrate a good performance in bearing capacity. Jet grouting method has been shown to contribute positively to the bearing capacity on clayey and silty soils, but it has not been able to make much contributions to settlement. As a result, jet grouting method can be effective in all soil types, and it can make significant contributions to settlements in all types of soil and has a positive effect on all soil types. Stone column method has positive effects on settlements on clayey and silty soils and contributes significantly to bearing capacity in all types of soils. Although, cement grouting method has narrow application area, it contributes to the bearing capacity and settlement of loose sand.
Finally, only jet grouting application has provided sufficient bearing capacity and limit settlement values in profile 3. While the jet grouting improvement was insufficient in profile 1 and profile 2, and stone column and cement grouting were not sufficient in all profiles. The bored pile method applied can be used as an alternative to soil improvement methods under high superstructure loads. Soil improvement can be preferred for soils that are under low loads.