Influence of Grout Permeation on Grouted Gravel Pile
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Grouted gravel pile is a new technique of soft soil improvement.The reinforcement of the pile is realized mainly by the grouting and the improvement of the surround soil induced by the grouting permeation,then settlements of composite foundation can be reduced.Considering the permeation of the grout into clay soil around the grouted gravel pile,the calculation formulas for impacted range of the grout and the modulus of the compression in grouted zone were obtained.The obtained formulas were verified based on model tests.In consideration of the grout permeation,the quantitative analysis of the impacted range by grouting was carried out and the calculation formulas of effectively reinforced soil radius were obtained by numerical analysis,which can give a reference to the engineering design.Keywords:
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Grouted gravel pile is a new technique of pile,bearing behaviors and load transfer of this pile are studied in model test.The results of the model test show that bearing capacity of grouted gravel pile is higher than that of bottom grouting piles and plain concrete piles,and that grouting could increase frictional resistance and tip resistance.The bearing behaviors of model piles is preliminarily studied and strengthen coefficients of frictional resistance and tip resistance are obtained by the way to analyse curve of load vs settlement and curves of tip resistance vs load and settlement.Furthermore,Flac~(3D) is employed to analysis grouted gravel pile model test.The bearing behaviors of grouted gravel pile is further studied and regularity of load transfer of model pile under vertical load is generalized in numerical analysis.
Settlement (finance)
Load testing
Dynamic load testing
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Grout rising along a pile is a general phenomenon in the process of post-grouting.The grout flew upward along the weak layer under pressure,squeezing the soil to a larger diameter and improving the shaft friction.By analyzing the mechanism of post grouting and applying the Bingham constitutive model and flowing equation,the formula to calculate the grout rising height was given.The formula to calculate radial displacement of soils around a pile was given by applying cavity-expanding theory.Compared with the measured results of a project,the calculated values were satisfactory relatively.
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Grouting gravel pile is a new technique of pile.It has the usual effectiveness of rigid pile composite foundation,furthermore,mechanical properties of soil around pile,which can increase bearing capacity of composite foundation and reduce its settlement.The property of soil around pile is tested in field before and after the pile is constructed,from which the grouting impact range and regularities of distribution are obtained.In allusion to clay soil around pile,the calculation formula of range impacted by grouting is obtained out by analysing balanced equation of cell cube in plastic zone.The calculation result is consistent with the grouting impact range obtained from in-situ test,so as to prove the rationality of calculation method.
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Shear displacement method is used to predict the settlement of the grouted pile in this paper. An empirical relationship is used to determine the improvement of shear modulus for the soil around the grouted pile. A parameter is also proposed to represent the improvement of the shear modulus for the grouted soil at the pile tip. Shear displacement method is modified to consider the influence of grouting. The detailed calculation process of the method is described and determine of the parameter is also given in the paper.
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Direct shear test
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Post-pressure grouting is an effective method to improve bearing capacity of ordinary bored cast-in-situ piles. The migration of the grout along the pile side is regarded as an important mechanism responsible for the improvement of the pile capacity. Research into the penetration height of the grout is of great important in evaluating the behavior of base grouted piles. In this paper, a prediction method of grouting penetration height along the shaft of the base grouted pile was proposed. Considering the balance and losses of the grout pressure during grouting, an iterative procedure was given to determine the penetration height of the grout in layered soils. Field test results were also provided to indicate the validity of the proposed method.
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Standard penetration test
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Grouted gravel pile is a new technique of piles for reinforcing soft soils.It has been successfully used in construction of projects of expressway and high-speed railway.In order to study the load transfer mechanism of the pile,under the assumption that the compression modulus is obeyed the exponential distribution in reinforced zone,and based on the solution of settlement in half-space under circular bearing plate,the settlements of different parts of grouted gravel pile composite foundation under loads are analyzed;and the formulas of axial force,lateral friction resistance along the grouted gravel pile,and settlement on the top of pile are derived.The practicability of this method is illustrated by a case study.It is shown that the theoretical calculation results are close to the actual measurement results.Therefore the deduced equations are reasonable.
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An analysis model of post-grouting bored pile and soil was built up by numerical method to simulate the bearing capacity of the pile.The results of numerical analysis on the pile load tests are agreement with the measured ones.The effects of post-grouting on bearing capacity were simulated by this method with considering the grouting volume,the strength of grouted soil body,the height of turn-up grout and the improvement of skin friction.The results show that the grouting volume and the strength of grouting soil body have a limited effect on the bearing capacity,and the increasing effect of the grouting volume is also influenced by the length of pile.The height of turn-up grout and the improvement of skin friction have a great effect on the bearing capacity,which is linearly increased with the increasing of the height of turn-up grout and the improvement of lateral friction.
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Under the laboratory conditions, by using unit pile model of composite foundation which is made up of gravels or lime soil cylindrical core reinforcement, a simulation test of working condition of site gravel pile and lime-soil pile was conducted, the relation between the deformation modulus of pile-soil composite and pile-soil stress ratio was discussed. Many test results showed that both lateral or vertical deformation modulus and strength of the composite sample can not be obtained by adding that of reinforcing pile and soil together simply in accordance with the geometric proportion. The deformation modulus ratio of the two materials can not reflect the stress distribution among the pile soil of composite samples.
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