Numerical modelling of shallow foundation on multi-layer soil with varying stiffness

The load-deformation observation under the footing is essential for foundation design. Either experimental methods or numerical modelling generally determines this phenomenon in engineering practices. This study determined the settlement of shallow foundations on Multi-layer soil profile numerically. The settlement behavior was investigated through numerical modelling with Plaxis 2D. This study site was Jamshoro region, located in province Sindh, Pakistan. From the geotechnical investigation, the soil of Jamshoro region consists of a combination of different soils, mainly shale and limestone. This type of soil shows common challenges for the serviceable and sustainable design and construction of structural foundations. The standard penetration test conducted accompanied by other geotechnical tests on shale and limestone to determine the input parameters for the model and observe the soil profile. The Mohr-Coloumb model used for shale and linear elastic for limestone. The settlement of the foundation is attended by varying the limestone layer’s depth. In this research, the settlement reduced under the footing by increasing the thickness of the limestone layer. The study observed that stiffness of lower layer significantly reduces the settlement of shallow foundation. Therefore, the effect of lower layer should be considered for the designing of foundation on multi-layered soil

1-g physical modelling of shallow foundation treated with polypropylene-reinforced soil-cement columns in liquefiable soil

The fibre-reinforced soil-cement columns are used as remediation measure against earthquake induced soil-liquefaction associated large settlements in liquefiable loose surface layer of sand. This loose surface layer of sand was overlying on the non-liquefiable dense bottom layer of sand. 1-g physical modelling of shallow foundation was carried out using shaking table. There were four 1-g physical models constructed for testing and the two types of improvements were used such as adjacent and beneath the structure. First model was 1-g physical model constructed without improvement, and three models were constructed with the provision of polypropylene-reinforced soil-cement columns. In the first treated model the columns were installed in the wooden fixity plate and adjacent to the structure, the second treated model was improved with improvement installed upon the soil-cemented fixity plate and provided adjacent to the structure, and in the third treated model with improvement installed upon the wooden fixity plate and provided beneath the structure. The results obtained in case of untreated 1-g physical model concludes that the penetration of structure inside the soil and settlement of structure, both are up to unacceptable limits. The results of first treated 1-g physical model concludes that the penetration and settlement of structure both are unacceptable. The results of penetration and settlement of structure in the case of second treated 1-g physical model are achieved up-to acceptable limits. The most successful type of improvement against the liquefaction-induced penetration and settlement of structure was achieved in case of third treated 1-g physical model in which the values of settlement and penetration are negligible. It is concluded that the improvement installed upon wooden fixity plate and provided beneath the structure is relatively the most efficient remediation measure against the earthquake induced soil-liquefaction induced settlement of structure

Estimation of Parameters and Flow Characteristics for the Design of Sanitary Sewers in Malaysia

Determination of the flow characteristics is very important for the design of sanitary sewers in any area. In the present study these are determined in the running sewers for the two parameters; per capita flow contribution and the peak flow factor. ISCO area - velocity flow meter model 4250 is used for this purpose. The flow meter, before being used in the running sewers, is calibrated first in the Hydraulics and Hydrology Laboratory of the UTM (Universiti Teknologi Malaysia). During the study the flow meter is installed inside the manhole in 10 different phases in the months of June, August, September, and October 2005 to monitor the sewage flow running in it. Continuous data is recorded in the flow meter during the process and the recorded time varies between 47 hours 25 minutes and 128 hours 35 minutes. The rainfall data is also collected during the same time using an automatic rain gauge which recorded rainfall at every five minutes of interval. Both the parameters thus calculated are then compared with the Malaysian Standard for sewer design i.e. MS 1228:1991. The results show that higher values of these parameters are being used in the design of sanitary sewers and extensive study needs to be carried out to review these values for future us

Effect of Variation in Blending Variables on the Properties of CRMB

The enhancement in the properties of the modified blends largely depends on the proper understanding of the interaction between CR (Crumb Rubber) and bitumen, where the CR particles swell after absorbing lighter fraction from the bitumen phase. However, the properties of CRMB (Crumb Rubber Modified Bitumen) blends at a wide range of temperatures are considered to be somewhat unclear due to the various interaction effects of CR and base bitumen. This largely depends on the interaction conditions such as blending time, temperature, speed and device, which may alter the properties of the blend to great extent. In this study, influence of the interaction condition was investigated by looking at the viscosity with a Brookfield viscometer. For this, CR and bitumen proportions along with other material characteristics were kept constant to understand the effect of interaction parameters of the properties of the CRMB blend. A total of 12 CRMB blends were produced with unvarying combinations of material constituents. However, selected variation in the blending parameters were; blending device, duration, speed and temperature. Observations from this laboratory study indicated: (1) blending performed with the high shear mixer resulted in higher viscosity values compared to the blends produced with the low shear mixer; (2) reduced blending time was required to achieve peak and ultimate stable viscosities, when blends were produced with the high shear mixer; (3) blending temperature of 180°C has resulted in the blends with consistent properties for longer blending durations compared to the blends produced at higher temperature. As a result, results with high shear mixer were always promising, which required comparatively lower interaction temperature, time and speed

Influence of the Scrap Tyre Processing Techniques on the Physical Properties of the Crumb Rubber

The processing mechanism of scrap tyres to produce CR (Crumb Rubber) has a great influence on the properties of the CRMB (Crumb Rubber Modified Bitumen). A fair amount of research was observed in the literature on the bitumen modified by CR processed cryogenically and ambiently. However, little or no work has been done on the CR processed by the other methods such as the Aquablast processing technique, which is a relatively a new waste tyre rubber processing technique within the CR industry. In this study, CR obtained from the two sources; ambient and Aquablast grinding techniques were primarily assessed with a helium pycnometer and SEM (Scanning Electron Microscopy) for their physical properties and appearance respectively. Observations from this laboratory study indicated: (1) the density of the ambient CR was slightly higher than the CR obtained from Aquablast technique; (2) difference in physical appearance was found insignificant

Liquefaction Potential of Silty Sand in Simple Shear

In this paper, the liquefaction potential of medium dense and dense sand layers was studied by performing constant volume (undrained) cyclic simple shear tests using cyclic simple shear apparatus. Strain-controlled approach was adopted. The liquefaction potential of two layers of a silty sand soil profile consisting of surface medium dense layer and underlying dense sand layers were studied. A medium dense sand surface layer exhibited flow type total liquefaction in cyclic loading in few cycles after initial liquefaction. An underlying dense sand base layer showed initial liquefaction in relatively more number of cycles and then cyclic mobility due to which pore pressure increases and decreases with cycles that is the characteristics of dense sand. The pore pressure increase and decrease is directly related to decrease and increase of effective stress

Stiff Columns as Liquefaction Mitigation Measure for Retrofit of Existing Buildings

In this paper, ground reinforcement with jet grouted columns under shallow foundations of existing buildings was analysed using numerical modelling. This study is related with ground reinforcement by installing stiff jet grouted columns around the shallow foundations of existing building when the foundation soil is liquefied during an earthquake. The isolated shallow square footing pad supporting a typical simple frame structure was constructed on the reinforced ground with stiff jet grouted column rows at the shallow depth from the ground surface. This soil-structure system was modelled and analyzed as plane-strain using the FLAC (Fast Lagrangian Analysis of Continua) 2D dynamic modelling and analysis software. The results showed that liquefaction-induced large settlement of shallow foundation of existing building can be reduced to tolerable limits by applying ground reinforcement with continuous rows vertical jet grouted columns adjacent to footing pad

Effects of the Length of Jet Grouted Columns and Soil Profile on the Settlement of Shallow Foundations

In this paper, the effect of length of jet grouted columns and varying soil profile under shallow foundations of buildings constructed on the liquefiable ground was studied. The isolated shallow footing pad which supports a typical simple frame structure was constructed on the liquefiable ground. This ground was reinforced with jet grouted column rows under the shallow foundations of structure. The system was modeled as plane-strain using the FLAC 2D (Fast Lagrangian Analysis of Continua) dynamic modelling and analysis code. This case focuses on the length of jet grouted columns in a soil profile and the effect of soil profiles of varying thickness on the settlements of building structure when the soil is liquefied during an earthquake. The results show that liquefaction-induced large settlements of shallow foundation of building decrease to tolerable limits with the increase in the length of columns. For soil profiles, with a relatively thinner liquefiable layer, a certain minimum length of columns (extended in base non liquefiable layer) is required to meet the settlement tolerable limits. For soil profiles, with a relatively thicker liquefiable layer, this length should be equal to the thickness of the liquefiable layer from the footing base plus some extension in the base non liquefiable dense layer. In the soil profile with the base liquefiable layer underlying the non liquefiable layer, settlements could not be reduced to the tolerable limits even with columns of relatively larger length which may be critical

Heavy Metal Diffusion through Soft Clay under High Hydraulic Gradients

This study was focused on the determination of contaminant transport parameters of heavy metal Zinc moving through saturated soft Bangkok undisturbed clay under high hydraulic gradients. These parameters were compared with contaminant transport determined under concentration gradient alone (pure diffusion). In total fifteen column tests were conducted and a mathematical model was applied to determine the coefficients. Two different source concentrations conditions, constant and decreasing, were applied. Testing periods were ranged from 15-60 days while hydraulic gradients were ranged from 0-500. The curves between relative concentration and time and pore volume were developed for the constant source condition whereas curves between source reservoirs concentrations and time were developed for decreasing source condition. The effective diffusion and distribution coefficients, De and Kd, were determined by curve fitting using the computer code POLLUTE v 6.3. The results showed that diffusion coefficient increases and distribution coefficient decreases as hydraulic gradient increases from 0 to high value of 500 due to contribution of dispersion and additional molecular diffusion at high advective velocity. Thus, testing at high gradients ensures the safe performance of earthen barriers under worse conditions

A Conditioned Model for Choice of Mode Under Information

This paper examines the influence of time and cost information obtained from different sources on choice of mode of Leeds' long distance travellers. The choice of mode was investigated through modal attributes provided by at least two different information sources which might provide contrary or corroborating information rather than on actual attributes. The experiment included telephone administered questionnaire including RP (Revealed Preference) questions and an SP (Stated Preference) exercise dealing with the choice of modes conditioned by the information received from various sources. Information on travel time and cost was provided from two different information sources for each mode to facilitate the conditioning of mode choice on corroborating/contradictory information. The research employs a wide range of modelling methodologies and examines a range of traditional and newly developed calibration and estimation procedures including Mixed Logit models with individual specific parameters and the newly developed RRM (Random Regret Minimisation) framework. The study confirms that the market share of the modes increases when information sources show decreased travel time and cost values and shows that the maximum shares are achieved when different information sources give the same information to the travellers. The study found that pre-trip time information has more influence on mode choice when derived from websites than when derived from other sources. Pre-trip information on costs was, however, less influential when derived from websites than when derived from other sources