Optimization of the Ultimate Bearing Capacity of Reinforced Soft Soils through the Concept of the Critical Length of Stone Columns

The objective of this paper is to develop an analytical equation based on the concept of the critical-length of columns in order to optimize the ultimate bearing-capacity of soft soils, supporting a strip footing and reinforced by a group of floating stone columns. Optimization procedure was performed on three-dimensional numerical models simulated on the Flac3D computer code, for various soft-soils with different undrained-cohesions (Cu=15–35kPa), reinforced by columns of varying lengths (L) and area replacement ratio (As=10-40%), considering different footing widths B. Obtained results indicate that the optimal bearing-capacity ratio (Ultimate bearing-capacity of reinforced soil/unreinforced soil) is reached for the column critical-length ratio (Lc/B) and increase with increase of the later ratio, depending on As and Cu. Analysis of results also showed that the optimal values of the bearing-capacity ratio in the reinforced soils remain bounded between the lower and higher values (1.28-2.32), respectively for minimal and maximal values of the critical-length ratio (1.1) and (4.4). Based on these results, a useful analytical equation is proposed by the authors, for the expression of the critical-length; thus ensuring an optimal pre-dimensioning of the stone columns. The proposed equation was compared with the data available in the literature and showed good agreement. Doi: 10.28991/cej-2021-03091737 Full Text: PDF

Behaviour of eccentrically inclined loaded rectangular foundation on reinforced sand

This study presents the behaviour of model footing resting over unreinforced and reinforced sand bed under different loading conditions carried out experimentally. The parameters investigated in this study includes the number of reinforced layers (N = 0, 1, 2, 3, 4), embedment ratio (Df /B = 0, 0.5, 1.0), eccentric and inclined ratio (e/L, e/B = 0, 0.05, 0.10, 0.15) and (a = 0°, 7°, 14°). The test sand was reinforced with bi-axial geogrid (Bx20/20). The test results show that the ultimate bearing capacities decrease with axial eccentricity and inclination of applied loads. The test results also show that the depth of model footing increase zero to B (B = width of model footing), an increase of ultimate bearing capacity (UBC) approximated at 93%. Similarly, the multi-layered geogrid reinforced sand (N = 0 to 4) increases the UBC by about 75%. The bearing capacity ratio (BCR) of the model footing increases with an increasing load eccentricity to the core boundary of footing; if the load eccentricities increase continuity, the BCR decreases. The tilt of the model footing is increased by increasing the eccentricity and decreases with increasing the number of reinforcing layers.

PERBAIKAN TANAH LEMPUNG BERLANAU MENGGUNAKAN KOMBINASI PERKUATAN ANYAMAN BAMBU DAN GRID BAMBU

Berbagai metode perbaikan tanah telah banyak dikembangkan, salah satunya dengan perkuatan tanah sebagai alternatif pemecahan masalah terhadap daya dukung tanah yang rendah dan besarnya penurunan. Dalam penelitian ini, anyaman bambu dan grid bambu digunakan sebagai material perkuatan yang diharapkan dapat menjadi alternatif material perkuatan untuk meningkatkan daya dukung tanah lempung dengan variasi kedalaman perkuatan, jarak grid dan spasi lapis perkuatan. Tujuan dari penelitian ini adalah untuk mengetahui peningkatan daya dukung dari setiap variasi dengan nilai daya dukung tanpa perkuatan. Metodologi peneltian yang digunakan adalah pengujian dengan skala laboratorium. Data yang didapatkan dari pengujian tersebut kemudian dianalisa dengan membandingkan nilai daya dukung antara tanah tanpa perkuatan dengan menggunakan perkuatan yang dinyatakan dalam Bearing Capacity Ratio (BCR). Dari studi model di laboratorium diperoleh hasil bahwa dengan adanya pengurangan kedalaman perkuatan, jarak grid dan pengurangan spasi lapis perkuatan akan memberikan angka rasio daya dukung (BCR) yang semakin besar. Hasil diperoleh kombinasi yang memberikan nilai daya dukung tertinggi adalah penggunaan jarak grid 5 cm perkuatan dengan jarak kedalaman 0,15B (B adalah lebar pondasi) dengan spasi perkuatan (z) 0.4B. Nilai daya dukung tersebut sebesar 68 kPa dengan rasio daya dukung (BCR) sebesar 4 atau persen peningkatannya sebesar 300%.

Influence of Infill Wall Configuration on Failure Modes of RC Frames

An improper configuration of masonry infill walls in RC frame may lead to short column effect on the columns, which is harmful to the seismic behavior of the structure. In this study, a bare frame and two single-story, single-bay RC frames, partially infilled with masonry, were tested under cyclic loading. The failure mechanism and seismic performance of these partially infilled RC frames (with an infill height of 600 mm) with different types of connections were analysed. Based on the experiment, nonlinear finite element simulation and analysis were conducted to study the effects of the infill walls and connections. The results show that both mechanical performance and failure mode are affected by the infill height, the type of connection between the frame and the infill, and the ratio of shear bearing capacity of the frame column to that of the infill. For the masonry-infilled frame with rigid connection, the higher the infill wall is, the lower the shear bearing capacity ratio will be. Thus, the effect of the lateral constraint of the infill wall on the column increases, and the shear span ratio of the free segment of the column decreases, resulting in the short column effect. Based on the analysis results, a value of 2.0 is suggested for the critical shear bearing capacity ratio of the frame column to the infill wall. If the shear bearing capacity ratio is less than 2.0 and the shear span ratio of the column free segment is not more than 2.0, the short column effect will occur. For the infilled frame with flexible connection, both the lateral constraint from the wall to the column and the wall-frame interaction decrease; this reduces or prevents the short column effect. The conclusion can present guidance for the design and construction of masonry-infilled RC frame structure.

BEHAVIOR OF STRIP FOOTING ON REINFORCED SAND SLOPE

This study evaluated the effects of single, double, and triple reinforcing layers on the bearing capacity ratio (BCR) of strip footing on a sand slope system. Seventy-two laboratory-loading tests were conducted on a stripfooting model on a reinforced sand slope. Moreover, this study illustrated the effects of the different parameters of two reinforcing layers on the bearing capacity of a double-reinforced sand slope. The BCR increased from 1.06 to 3.00 for single-reinforced slope soils, 1.09 to 7.73 for double-reinforced slope soils, and up to 8.00 for three-layered reinforced systems. For double-reinforced soil slopes, the most effective spacing between the two reinforcing layers is 0.3 B.