Investigation of the Mechanism of Grout Penetration in Intersected Fractures
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To study the penetration mechanism of cement-based slurry in intersected fractures during grouting and the related pressure distribution, we have used two different variants of cement, namely, basic cement slurry and fast-setting cement slurry. The influence of a retarder, time-varying viscosity, fracture width and location of injection hole is also considered. A finite element software is used to implement two and three-dimensional numerical models for grouting of intersected fractures in hydrostatic conditions. Results show that there are significant differences in the diffusion morphology and pressure distribution depending on the considered cement slurry. Retarder can effectively slow down the rising rate of injection pressure and extend the diffusion distance of grout. The influence of the branch fracture is more important when basic cement slurry is considered, indicating that the change of grout pressure is correlated with the slurry viscosity. The faster the viscosity increases, the less evident is the effect.Keywords:
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Penetration (warfare)
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.
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Generally, grout extent and ground deformation are of great concern in soil grouting practice. In this paper, the ground behaviour, injection mechanism and grout distribution relating to field grouting in soils are discussed. It is found that the mechanisms of injection comply with generally accepted groutability requirements based on particle size ratio, where suspension grouts fracture clayey soils and solution grout permeates sandy soils. Ground heaving is affected by the sealing effect of grouts in upper soil layers. This study shows ground heave increases with the depth of grouting. The final heave volume reaches about 22% of the total grout injected. Lateral ground expansion is influenced by the hydraulic fracturing of grouts. Hydraulic fractures, which are nearly vertically formed in soils, produce lateral movements of the ground. The final lateral expansion of the ground, within 1 m radial zone of the grout hole, is approximately 12% of the total grout injected. A three-dimensional grout distribution is postulated based on the mapped grout traces in soils. The observed vertical grout fractures, with apertures of less than 15 mm and lateral extents of 1~4 m, confirm that the site soil strata are normally consolidated.
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The effectiveness of grouting to reduce surface settlements during underground construction in clayey ground was investigated by a field trial and laboratory tests. The field trial was carried out during shield tunnelling work conducted in alluvial clay deposits in Koto-Ku, Tokyo. Grout was injected at some distance away from the tunnel, and both surface and subsurface settlements above the tunnel were monitored. Although the initial heave was achieved immediately after the grout injection, the ground continued to settle with time, owing to soil consolidation and grout shrinkage. A laboratory investigation was conducted to investigate the parameters that control the long-term behaviour of grouting in clay. It was found that better long-term grout efficiency can be achieved in overconsolidated clay than in normally consolidated clay, and the efficiency increased with increasing injection volume. Finite element analysis of the laboratory experiments confirmed that the amount and extent of excess pore pressures generated during injection govern the long-term grout efficiency. Finite element analysis of the field trial was also performed to simulate the long-term ground deformation after grout injection.
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Consolidation
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Tunnel Construction
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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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Based on construction projects,the powder-jetting and grout-jetting cement piles are studied.The results indicate that:the powder-jetting pile has higher strength than the grout-jetting one under the same period; both piles follow a rule that upper strength decreases while going deeper;it's quite possible that penetration destruction happens to the piles once the static load of single-pile reaches the limit;the deformation characteristics and distribution of cracks vary with the strength of piles;in terms of improvement of bearing capacity of soft soil foundation,powder-jetting pile is better than grout-jetting pile.
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This paper describes pullout tests that were conducted in stiff clay near Austin, Tex., to determine the tension capacity of grouted piles and to assess the effect of lateral loading on pullout resistance. In some tests, failures occurred at the pile-grout interface with maximum shearing stresses of 30 psi. In most tests, failures occurred at the grout-soil interfaces with shearing stresses of 50 percent of the soil-shear strength. Introduction Pullout tests on grouted piles in stiff clay were run at a site Pullout tests on grouted piles in stiff clay were run at a site 5 miles northeast of Austin, Tex., adjacent to U.S. Highway 290. The pullout tests followed a series of lateral-load tests on 6- and 24-in.-diameter pipe piles. Four W-piles were routed in drilled holes to serve as anchors for a reaction frame used during the lateral-load tests. After these tests, three W-piles were pulled in the investigation of the strength of grouted piles. In addition, pull tests were made on two 16-in.-diameter pipe piles pull tests were made on two 16-in.-diameter pipe piles that were grouted in drilled holes. The tests on pipe piles were made before and after lateral loadings. Soil Investigations Nine soil borings were made at the test site to provide information for the lateral and pullout test. Details of these borings and of the preparation of the test pit were reported previously and are not repeated here. The bottom of the test pit was approximately 6 ft below the original ground surface. The pit had been inundated 9 months before the first pullout tests. A composite profile of soil types, Atterberg limits, and shear strengths of the stiff clay is given in Fig. 1. To represent the in-situ properties of the clay, the following distribution of shear strength with depth was selected. Undrained Depth Shear Strength (ft) (tons/sq ft) --------- ----------------------- 0 0.1 1 0.8 13 3.5 21 3.5 31 12.4 Installation of W-Piles A plan of the test pit is given in Fig. 2, indicating locations of the three W-piles (W-1, W-2, and W-3) and of the two pipe piles (P-1 and P-2). In addition, locations are indicated for five of the nine soil borings. Boring 9 located 2 ft from Pile P-2 was taken 3 months after the pullout tests. The 24-in.-diameter pipe piles used for pullout tests. The 24-in.-diameter pipe piles used for the lateral-load tests are designated as Pile 1 and Pile 2 in fig. 2. The W-piles were 14 in. deep with a 12-in. flange, and weighed 78 lb/ft. Two piles (W-1 and W-3) were installed in holes that had been drilled wet with a fishtail bit and Pile W-2 was installed in a hole that had been dry augered. The holes were approximately 25 in. in diameter and 30 ft deep, After the holes had been drilled, the W-piles were lowered into the holes through a template to assure proper positioning. Concrete with a mix ratio of 1:2:2 by weight positioning. Concrete with a mix ratio of 1:2:2 by weight of cement, sand, and gravel, respectively, then was placed into the holes using a 20 ft-long tremie pipe. For placed into the holes using a 20 ft-long tremie pipe. For ease in placing concrete, the maximum gravel size was 3/4 in. The placement of concrete continued until returns were received at the ground line. The concrete had a 7-day compressive strength of 3,020 psi with an estimated 28-day compressive strength of 4,530 psi. Concrete was not placed along the total 30-ft penetration of the W-piles. The grouted lengths for Piles W-1, penetration of the W-piles. The grouted lengths for Piles W-1, W-2, and W-3 were 20, 27, and 24 ft, respectively. These grouted lengths were determined at the end of pullout tests when the piles were salvaged. JPT P. 349
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This case study presents the results of column supported foundation by both the conventional jet grout and the jet grout expanded bases in a soil improvement project for a food storage garages and yards.The ground surface settlements,soil mass deformations,lateral deflections of soil around the columns,excessive pore pressures and the stress ratioes were monitored by the geotechnical instrumentations.The site was also tested by the field vane shear,cone penetration and static plate loading tests before and after the soil improvement.The results indicate that the belled column has a better performance compared with the conventional jot grout columns.
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Preliminary results of small-scale model compaction grouting tests performed in a geotechnical centrifuge are presented. The soil response to a one-stage grout bulb injection in dry uniform sand was examined at various prototype depths, and the effects of grout composition on grout bulb development and shape and on soil response are evaluated. Preliminary results indicate that the shape of the injected grout bulb is a function of overburden pressure. For specific grouting conditions, there is a maximum size that the grout bulb will achieve. Observed soil deformations were similar to those observed in models of deep uplift anchors. The addition of either clay or fly ash to the grout mix reduced the ability to sustain high injection pressures.
Grout
Centrifuge
Overburden
Soil gradation
Soil Compaction
Bulb
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The effectiveness of grouting to reduce surface settlements during underground construction in clayey ground was investigated by a field trial and laboratory tests. The field trial was carried out during shield tunnelling work conducted in alluvial clay deposits in Koto-Ku, Tokyo. Grout was injected at some distance away from the tunnel, and both surface and subsurface settlements above the tunnel were monitored. Although the initial heave was achieved immediately after the grout injection, the ground continued to settle with time, owing to soil consolidation and grout shrinkage. A laboratory investigation was conducted to investigate the parameters that control the long-term behaviour of grouting in clay. It was found that better long-term grout efficiency can be achieved in overconsolidated clay than in normally consolidated clay, and the efficiency increased with increasing injection volume. Finite element analysis of the laboratory experiments confirmed that the amount and extent of excess pore pressures generated during injection govern the long-term grout efficiency. Finite element analysis of the field trial was also performed to simulate the long-term ground deformation after grout injection.
Grout
Consolidation
Settlement (finance)
Tunnel Construction
Shrinkage
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