Bearing Capacity Of Soft Ground Research Articles

A modified equal-strain solution for consolidation behavior of composite foundation reinforced by precast concrete piles improved with cement-treated soil

To effectively mobilize concrete strength, a newly developed composite pile, the so-called “Precast Concrete Piles Reinforced with Cement-treated soil (PCCS)”, has been used to improve the bearing capacity of soft ground. However, there are limited studies on the consolidation behavior of the PCCS in soft ground. This paper proposes an analytical solution for the consolidation of the composite ground reinforced by PCCSs based on a modified equal strain assumption. This composite ground is simplified as a double-layered consolidation ground according to the geometrical configuration of the PCCS. Subsequently, the analytical expression of the average consolidation degree is derived by considering the pile pierced into the gravel cushion and the additional stress that varies with time and depth. The accuracy of the proposed solution for consolidation is compared and validated by numerical analysis and current calculation methods. Furthermore, a parametric analysis is conducted to systematically investigate the influence factors of replacement ratio, core length ratio, modulus ratio of inner core-soil, modulus ratio of inner-outer core, modulus ratio of cushion-soil, permeability coefficient ratio and loading period on the consolidation behaviors of PCCSs reinforced ground. The proposed solution provides a theoretical guideline available for calculating the long-term settlements of such composite piled foundation.

Failure modes and bearing capacity of strip footings on soft ground reinforced by floating stone columns

This study evaluates the failure modes and the bearing capacity of soft ground reinforced by a group of floating stone columns. A finite difference method was adopted to analyze the performance of reinforced ground under strip footings subjected to a vertical load. The investigation was carried out by varying the aspect ratio of the reinforced zone, the area replacement ratio, and the surface surcharge. General shear failure of the reinforced ground was investigated numerically without the surcharge. The results show the existence of an effective length of the columns for the bearing capacity factors N c and N γ. When certain surcharge was applied, the failure mode of the reinforced ground changed from the general shear failure to the block failure. The aspect ratio of the reinforced zone and the area replacement ratio also contributed to this failure mode transition. A counterintuitive trend of the bearing capacity factor N q can be justified with a shift in the critical failure mode. An upper-bound limit method based on the general shear failure mode was presented, and the results agree well with those of the previous studies of reinforced ground. Equivalent properties based on the area-weighted average of the stone columns and clay parameters were used to convert the individual column model to an equivalent area model. The numerical model produced reasonable equivalent properties. Finally, a theoretical method based on the comparison of the analytical equations for different failure modes was developed for engineering design. Good agreement was found between the theoretical and numerical results for the critical failure mode and its corresponding bearing capacity factors.

Bearing capacity charts of soft soil reinforced by deep mixing

A series of preliminary design charts were developed to predict the bearing capacity of fully and partially penetrated deep mixing (DM) of soft soil. The charts were produced by a new numerical analysis tool based on discontinuity layout optimisation (DLO) in which a previously proposed homogenisation method was used to define the improvement area. To measure the applicability of implementation of the homogenisation method in the DLO, a series of validation processes was performed against several previous studies under uniform soil strength. A new empirical solution was developed from the DLO method using the homogenisation method for the bearing capacity of soft ground under uniform soil strength, improved by the fully penetrated DM method. Results produced by the DLO approach were compared with existing analytical solutions and better agreement was found from the present model. The charts consider variation in improvement area ratio, column length and strength, and foundation width for the fully and partially penetrated DM cases. The simulations were related to real field cases in which the strength characteristics of soft soil increase with depth. An example is given to demonstrate use of the charts.

폐어망 보강 깊이에 따른 모래지반의 지지력 특성

Geosynthetics such as geogrids or geotextiles have been widely used to improve the bearing capacity of soft ground. This study investigated the California bearing ratio (CBR) of waste fishing net (WFN)-reinforced sand. CBR tests were carried out to evaluate the improvement in the bearing capacity of WFN-reinforced sand with different embedded depths. The experimental results indicated that the CBR increased as the embedded depth of the WFN decreased. The bearing capacity ratio (BCR) is the ratio of the bearing capacity of reinforced ground to that of unreinforced ground. The BCR at the penetration depths of 2.5 mm, 5 mm, and the peak point decreased with an increase in the embedded depth.

Geosynthetic Reinforcement of Sand-Mat Layer above Soft Ground.

In order to improve the bearing capacity of soft ground for the purpose of getting trafficability of construction vehicles, the reinforcement of geosynthetics for sand-mat layers on soft ground has often been used. As the strength of the geosynthetics increases, and the sand-mat system becomes stronger, the bearing capacity of sand-mat systems will be increased. The depths of geosynthetics, reinforced in sand-mat layers, were varied with respect to the width of footing. The tensile strengths of geosynthetics were also varied to evaluate the effect of reinforcement on the bearing capacity of soft ground. The dispersion angles, with varying sand-mat thicknesses, were also determined in consideration of the tensile strength of geosynthetics and the depths of reinforcement installations. The bearing capacity ratios, with the variation of footing width and reinforced embedment depth, were determined for the geosynthetics-only, reinforced soft ground, 1-layer sand-mat system and 2-layer sand-mat system against the non-reinforced soft ground. From the test results of various models, a principle that better explains the concept of geosynthetic reinforcement has been found. On the basis of this principle, a new bearing capacity equation for practical use in the design of geosynthetically reinforced soft ground has been proposed by modifying Yamanouchi’s equation.

Study on Strength Characteristics of Reinforced Soil by Cement and Bamboo Chips

Soft ground with low bearing capacities is found to large areas in the world. In order to increase the bearing capacity of soft ground and to decreases settlement, some methods were developed for improving the mechanical properties of ground. As a stiffener of soil improvement, bamboo chips were used in this study. Bamboo is one of the fastest-growing plants on Earth and with a large distribution around the world. As a natural material, it is even better for environment and has excellently mechanical characteristic. The bamboo chips were mixed into the test specimen as a stiffener of soil improvement. Unconfined compression test were performed with test specimen, then mechanical characteristics of reinforced soil by cement and bamboo chips were investigated. From the test results, the strength and ductility characteristic of soil improvement are rather better when the bamboo chips are mixed.

Earth reinforcement using soilbags

This paper describes the method of earth reinforcement using soilbags and illustrates its application for case studies involving a pond and the expansive soil slope protection for a highway. The strength properties of soilbags were investigated using unconfined compression tests and bearing capacity tests on real soilbags containing either medium grained sands or gravels. The test results show that soilbags have high strength when subjected to an external load. This is primarily attributed to the mobilization of tensile forces in the bags. It is concluded that earth reinforcement using soilbags could substantially improve the bearing capacity of soft ground as well as minimizing deformation under working loads.

Reinforcement Effects of Geocell Mattress on Bearing Capacity of Soft Ground

A geocell mattress, which takes the interlinked form of three dimensionally build up multiple cells with thin geosynthetics vertical partition walls and the inner parts of which are filled with soils, has wide application such as an improvement of poor bearing power of ground.A series of two dimensional plate loading laboratory model tests was carried out to investigating major influence factors related to the reinforcement of soft clay ground. It was found from the test results that the lower the bearing capacity of supporting ground was, the higher the reinforcement effects were obtained. Moreover the results indicated that the coefficient of bearing capacity and the bearing power were increased with the width of geocell mattress.