This study examined strength and permeability characteristics of J.S.P improvement body closely, and also found quantitatively horizontal displacement reduction of earth retaining walls and effect of earth pressure reduction. This study purposed to find jet grouting parameter value by examining a pr...
This study examined strength and permeability characteristics of J.S.P improvement body closely, and also found quantitatively horizontal displacement reduction of earth retaining walls and effect of earth pressure reduction. This study purposed to find jet grouting parameter value by examining a proper jet mechanism to be used in J.S.P construction. Via J.S.P method, five areas adjacent to similar stratum structure were selected in subway construction fields where excavation work is in progress, and core was collected from J.S.P improvement ground formed by ground behind propped retaining walls, and then N values of original ground and coefficient of permeability were compared by performing unconfined compressive strength test and In-situ permeability test. In order to decide jet grouting parameter value appropriate for each earth stratum, this study performed a test-construction by using jet mechanism made with two different kinds of jet pressure, pull-out velocity, amount of jet, and also cornpared · analyzed the result through the excavation of ground and the measurement of the shape and diameter of ground improvement body as well as an experiment on unconfined compressive strength. With a view of examining the effect of horizontal displacement restraint on ground behind propped retaining walls caused by J.S.P improvement body and the effect of earth pressure reduction, this study applied the strength characteristic value represented in strength test on J.S.P improvement body and compared horizontal displacement of earth retaining walls changeable according to the step by excavation, axial force having an influence on the strut, and earth pressure affecting to walls, with those of the monitoring measured in inclinometer and load cell by means of the finite element method based on the proper model in pre-and pro- J.S.P construction and the numerical analysis using general elasto-plastic analysis such as SUNEX, EXCAV. The results were as follows: 1) In case of construction using the same jet mechanism, the strength characteristic of J.S.P improvement body showed that sandy gravel had more unconfined compressive strength than sandy soil by 1.6 times. Therefore, it means that strength difference according to the soil properties of original ground and the grain size of soil. 2) It showed that the effect of cut-off water of J.S.P method constructed in ground behind propped retaining walls reduced permeability coefficient of the original ground by l0^(-2)∼10^(-3)cm/sec. And also the effect of permeability using J.S.P method in sandy gravel had more than about 10^(-1)cm/sec compared with silty sand. And judging from the strength and permeability characteristic, J.S.P improvement body in sandy gravel estimated to be characteristic of soft rock. 3) In the downtown area where there are neighboring buildings, id there is necessity of a critical grouting that grout's coverage ranges from 0.5m to l.0m in grouting holes, jet mechanism eliminated air pressure and raised Jet pressure to 400kg/㎠ will be the best method to reduce the displacement in the surrounding ground as well as to be a safe and economical because of the construction of speed. 4) Horizontal displacement reduction was analysised by FEM through excavation steps in pre- and pro-J.S.P construction It concludes that the reduction amount was showed from 0.lmm to 0.3mm by single lap while the reduction amount by double lap was represented from 10.9mm to 13.8mm. It showed that the effect of horizontal displacement restraint caused by the growth of rigidity in walls. It showed that the place of maximum displacement generation was 0.22 - 0.25H distant from excavation ground. 5) When excavation was proceeded step by step, axial force on the strut were analysised by FEM in pre- and pro-J.S.P construction. As the result, axial force reduction by single lap were showed 0.6∼0.9ton in the lower strut while axial force reduction by double lap were represented 1.3∼1.6ton in the upper strut. It was evaluated that the effect of axial force reduction caused by the growth of rigidity in walls. 6) The distribution type of earth pressure was analysised by FEM in pre- and pro-JSP construction according to the step by excavation. The results were that the earth pressure at the place of strut was grown while it. was reduced in the upper, lower of strut. The redistribution of earth pressure by arching caused this and total pressure was a bit more reduced than in pre-J.S.P construction in terms of its distribution area. And also the earth pressure analysised by SUNEX was all but same with experience earth pressure of Terzaghi-Peck while the earth pressure analysised by FEM was more under estimated than SUNEX.
This study examined strength and permeability characteristics of J.S.P improvement body closely, and also found quantitatively horizontal displacement reduction of earth retaining walls and effect of earth pressure reduction. This study purposed to find jet grouting parameter value by examining a proper jet mechanism to be used in J.S.P construction. Via J.S.P method, five areas adjacent to similar stratum structure were selected in subway construction fields where excavation work is in progress, and core was collected from J.S.P improvement ground formed by ground behind propped retaining walls, and then N values of original ground and coefficient of permeability were compared by performing unconfined compressive strength test and In-situ permeability test. In order to decide jet grouting parameter value appropriate for each earth stratum, this study performed a test-construction by using jet mechanism made with two different kinds of jet pressure, pull-out velocity, amount of jet, and also cornpared · analyzed the result through the excavation of ground and the measurement of the shape and diameter of ground improvement body as well as an experiment on unconfined compressive strength. With a view of examining the effect of horizontal displacement restraint on ground behind propped retaining walls caused by J.S.P improvement body and the effect of earth pressure reduction, this study applied the strength characteristic value represented in strength test on J.S.P improvement body and compared horizontal displacement of earth retaining walls changeable according to the step by excavation, axial force having an influence on the strut, and earth pressure affecting to walls, with those of the monitoring measured in inclinometer and load cell by means of the finite element method based on the proper model in pre-and pro- J.S.P construction and the numerical analysis using general elasto-plastic analysis such as SUNEX, EXCAV. The results were as follows: 1) In case of construction using the same jet mechanism, the strength characteristic of J.S.P improvement body showed that sandy gravel had more unconfined compressive strength than sandy soil by 1.6 times. Therefore, it means that strength difference according to the soil properties of original ground and the grain size of soil. 2) It showed that the effect of cut-off water of J.S.P method constructed in ground behind propped retaining walls reduced permeability coefficient of the original ground by l0^(-2)∼10^(-3)cm/sec. And also the effect of permeability using J.S.P method in sandy gravel had more than about 10^(-1)cm/sec compared with silty sand. And judging from the strength and permeability characteristic, J.S.P improvement body in sandy gravel estimated to be characteristic of soft rock. 3) In the downtown area where there are neighboring buildings, id there is necessity of a critical grouting that grout's coverage ranges from 0.5m to l.0m in grouting holes, jet mechanism eliminated air pressure and raised Jet pressure to 400kg/㎠ will be the best method to reduce the displacement in the surrounding ground as well as to be a safe and economical because of the construction of speed. 4) Horizontal displacement reduction was analysised by FEM through excavation steps in pre- and pro-J.S.P construction It concludes that the reduction amount was showed from 0.lmm to 0.3mm by single lap while the reduction amount by double lap was represented from 10.9mm to 13.8mm. It showed that the effect of horizontal displacement restraint caused by the growth of rigidity in walls. It showed that the place of maximum displacement generation was 0.22 - 0.25H distant from excavation ground. 5) When excavation was proceeded step by step, axial force on the strut were analysised by FEM in pre- and pro-J.S.P construction. As the result, axial force reduction by single lap were showed 0.6∼0.9ton in the lower strut while axial force reduction by double lap were represented 1.3∼1.6ton in the upper strut. It was evaluated that the effect of axial force reduction caused by the growth of rigidity in walls. 6) The distribution type of earth pressure was analysised by FEM in pre- and pro-JSP construction according to the step by excavation. The results were that the earth pressure at the place of strut was grown while it. was reduced in the upper, lower of strut. The redistribution of earth pressure by arching caused this and total pressure was a bit more reduced than in pre-J.S.P construction in terms of its distribution area. And also the earth pressure analysised by SUNEX was all but same with experience earth pressure of Terzaghi-Peck while the earth pressure analysised by FEM was more under estimated than SUNEX.
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