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Innovative Shallow and Deep Foundations and Foundation Treatment in Soft Ground

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Innovative Shallow and Deep Foundations and Foundation Treatment in Soft Ground Innovative Shallow and Deep Foundations and Foundation Treatment in Soft Ground Eun Chul Shin Prof. Incheon National University, Republic of Korea Vice president of ISSMGE for Asia Abstract It is a method to improve the soft ground and to separate the shallow foundation from the deep foundation, and introduces each case separately for honeycell, point foundation, and embankment support pile. Part 1 is about hexagonal concrete hollow block with a straw shape called honeycell. Replace the soft ground with crushed stone to fill the honeycell and install a shallow foundation. It can be said that it is the basic method which reduces the settlement amount and increases the bearing capacity of foundation. We analyze the support characteristics of honeycells by carrying out the plate loading test using the laboratory model soil, and introduce actual case construction examples. The point foundation of Part 2 is a method of shaping the top foundation, injecting the mortar mixed with cement and water in the soft clay soil, rotating the mixer, and mixing with stirring to form an upgrading body having a predetermined uniform strength in the soil layer. It is a method to secure the bearing capacity of low-rise structures. We analyzed the bearing capacity by field test, also introduce case studies. Part 3 analyzes the support performance of the soft ground by means of field pilot test with thegeosynthetic- reinforced supported pile of embankment 1. Honeycell (Shallow Foundation) 1.1 Introduction The hollow block is shaped like a hexagonal honeycomb shown is Fig.1.1. The honeycomb structure is the most economical structure for securing the maximum space with minimum material, and it is widely used in our daily life as a stable structure that distributes the force in a balanced manner. The hollow block foundation method is soft ground underneath the shallow foundation is replaced with a combination of mixed crushed stone. It can be said that it is a foundation improvement method which increases the bearing capacity by reducing the settling amount of foundation by forming artificial layered ground. The shallow foundation plate load test (KS F 2444) was carried out by using the sandstone as the soft ground and the crushed stone as the replacement material. The honeycomb shape is known to distribute the load, when this type is applied to the ground, the relationship between the stress distribution angle generated from the bottom of the hollow block and the internal friction angle of the ground increases the bearing capacity and decreases the settlement amount. It is necessary to analyze the stress distribution by installing the earth pressure system. Figure 1.1 Modeling of honeycell shallow foundation 1.2 Plate Load Test in Laboratory 1.2.1 Setting of plate load test in laboratory Fig.1.2 shows a schematic diagram of the model earthenware, and Fig.1.3 shows the planar and lateral photographs of the model earthenware. The size of the model earthenware is 100cm wide and 120cm high and is cylindrical steel earthenware. The rebound beam consists of two H beams and is secured with a full force gauge. The plate load test equipment is shown in Fig. 1.4, with a maximum load 50tonf and a torque of 40mm, Electronic data collectors are installed on plate load test equipment to record loads. Plate decks(D:250mm) are used and shown in Fig.1.5. Two LVDT is were also installed on the plate to check the amount of sediment. The earth-pressure system is installed on the construction site to measure the vertical and horizontal pressure of the load. Sand and Crushed Stone have been subjected to the materiality test as described in Table 1.1. H-beam Jack LVDT Measuring plate Hhoney cell H Honey cell Steel circular box H2 Data logger Computer Pump Figure 1.2 Schematic diagram of plate load test in laboratory Figure 1.3 View of circular steel box (a) hyraulic jack (b) data logger Figure 1.4 Equipment of plate load test (a) Honeycell (b) hexagon plate Figure 1.5 Shape of Honeycell and plate Table 1.1 Properties of soil (sand, crushed stone) Maximum Angle of Apparent Specific OMC dry unit internal cohesion USCS gravity (%) weight friction (KPa) (g/cm³) (°) Sand 2.65 1.91 0.99 9.4 1.69 4.92 33.44 SP Crushed 2.68 50 0.91 5.53 2.37 138.96 47.83 GW stone 1.2.1 Experimental conditions For the test conditions of a plate load test, the sand ground(1-a) was installed on the sand ground(1-b), the sand ground replaced by a crushed stone(1-c), and the hollow block were installed as shown in Table 1.2. Fig 1.6 shows the model diagram by experimental condition. The depth of the replacement (crushed stone) is 150mm, and the height of the hollow block is set at a 1:1 ratio. The width of the change was set at 400mm, wider than the lower plate. The relative density is 40%, which is the normal level of density. R`s level of relative strength is 95.9%. The hexagonal lower plate was used for the lower decks, While for the ground where the hollow block was installed, the hexagonal lower plate was identical to the hollow block shape. The relative density of the sand ground was 40 percent and a plate load test was conducted. The re-download method was performed in accordance with KS F 2444, Korea`s industry standard, by means of the plate load test on the shallow foundation. The end of the test stopped if the test load was more than three times the allowable load or if cumulative settlement exceeded 10% of the diameter of the lower plate (1-a) (1-b) (1-c) (1-d) Figure 1.6 Laboratory model test conditions for honeycell foundation Table 1.2 Cases of plate load test in laboratory model tests Depth of Relative Test Caes Method Load replacement density( ), % 1-a Sand - 5kN, 8kN Sand 1-b + - 5kN, 8kN Honeycell Snad + 1-c 150mm 5kN, 8kN Replacement (crushed stone) KS F 2444 40% Snad + Replacement 1-d 150mm 5kN, 8kN (crushed stone) + Honeycell 1.2.2 Results of plate load test When hollow blocks are installed, The P-S graph of the plate load test results on the sand ground or on the crushed rock face shows linear behavior up to a certain load strength, and then shows the P-S curves for sharp deposits. The initial load strength according to the shallow foundation plate load test method is shown in Fig 1.7, showing the P-S graph by the condition of the plate load test performed at 92.4 kN/m2. The conditions of installing hollow blocks on the replacement (crushed stone) ring and filling the interior with the interior of it showed the lowest subsidence relative to the ultimate load strength, and the alignment of the P-S curve was constant. While the sand ground hollow blocks showed linear motion up to the extreme load strength, it was clear that the heavy air blocks on the ground were replaced by the crushed rock, the difference in deposits and unfilled conditions was significant. As a result of filling the inside of the hollow block with a blanking test, the initial load was subjected to the linear support force generated by the hollow block concrete, but then the support was lost in the form of penetration breakage. As a result of a plate load test under 5 kN and 8 kN due to difference in load, the load strength of 5 kN was reduced by a point of 134 kN/m2. A similar P-S curve was seen in the sand ground, while in the case of a replacement (crushed stone) ring, it is believed that the load bearing on the replacement (crushed stone) ring is greater as the load increases. The difference between sand and clasts, the mouth, the modulus of elasticity, and the shear strength, is apparently working. In particular, the location of sand and clasts, the concrete thickness of hollow blocks and the internal hollow width of the hollow block, are expected to have a significant impact on the ground level. In the case of a replacement (crushed stone), the ratio of 1:2 relative to 50mm thick of hollow block concrete is less than 25mm. When the upper load is delivered to the lower part of hollow block concrete at a certain rate, the higher shear strength of the higher application can be assumed to increase the support force and reduce the amount of sediment. Load per unit area (kN/m2) 0 200 400 600 800 1000 1200 1400 1600 0 250 500 750 1000 1250 1500 (1/100 mm) (1/100 1750 2000 2250 Settlement 2500 2750 3000 Ultimate bearing capacity 3250 3500 Sand Replacement crushed stone Sand + Honeycell(unfilled hollow) Sand + Honeycell Sand + replacement + Honeycell(unfilled hollow) Sand + replacement + Honeycell (filled crushed stone) Figure 1.7 Total results of plate load test (Initial load = 5kN) Load per unit area (kN/m2) 0 500 1000 1500 2000 2500 0 500 Ultimate bearing capacity 1000 (1/100mm) 1500 Settlmement 2000 2500 Sand Replacement Sand + Honeycell Sand + replacement + Honeycell(filled) Sand + replacement + Honeycell(unfilled) Figure 1.8 Total results of plate load test (Initial load = 8kN) 1.2.3 Strengthening efficiency analysis An experiment was conducted indoors in accordance with the shallow foundation plate load test method (KS F 2444). To analyze the results of the sand ground, hollow block installation, and the replacement (crushed stone) zone, the reinforced ground was reinforced against the sand ground using Equation 1.1.
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