Centrifuge model study on settlement of strip footing subject to rising water table in loess

Owing to man-made activities and natural conditions, the groundwater table experiences considerable changes in Lanzhou. Centrifugal model tests were performed to investigate the settlement of strip footings on loess subject to rising water table under different foundation pressures. The air-fall method was employed to reconstitute the artificial loess samples. The applicability of the air-fall prepared samples was evaluated against the parameters of the undisturbed loess samples obtained from the same location. The results of centrifuge tests reveal that the footing settlement increases significantly with increasing foundation loading pressure or increasing rising water table. However, the rate of increase in ultimate footing settlement under combined rising water level and footing pressure is established to be more intriguing. A simplified method for predicting the ultimate footing settlement on collapsible loess due to rising water table height is proposed. The proposed formulation is verified, as there is a good agreement between the test results under various loading pressures and rising water heights and the predicted ultimate footing settlements. A discussion on the ultimate settlement of strip footings subjected to rising water table against conventional bearing capacity safety factors is presented to provide some basis for the foundation design consideration under rising water scenario.

Qatar will grow more assertive, but not hubristic

Significance The withdrawal came with neither notice nor any obvious precipitating event, and is ultimately more a piece of political showmanship than a decision rooted in fiscal calculation. This underscores the frenetic, changeable nature of Gulf politics. It also speaks to possible fragility at the core of OPEC. Impacts Doha will aggressively court inward investment and will do so increasingly on its own terms. Ratings agencies and investors may interpret this move as a sign of a bullish and reinvigorated government. The decision will not affect the ultimate settlement of the Gulf crisis, which will be resolved when Saudi Arabia and its allies choose. Doha will remain a predictable energy supplier, prizing its reputation as a reliable exporter that does not use trade as a political weapon.

Model Test Ultimate Bearing Capacity of Bakau Piles Foundation on Soft Soil Deposit

The pile foundation is one of the deep foundation types commonly used to support building loads when hard soil layers are deeply located. To determine the ultimate bearing capacity of a pile foundation of the load test results, there are several methods commonly used to interpretation test results such as Davisson method, Mazurkiewich method, Chin method, Buttler Hoy method and De Beer method. The aim of this study was to determine the characteristics of soft soil and bakau piles used in the study and to analyze the size of the bearing capacity ultimate of pile foundation that is modeled on a small scale in the laboratory. From the test results of material characteristics of the soil used is organic clay type with medium plasticity with specific gravity 2.75, liquid limit, LL = 50.36% and plasticity index, PI = 13.2%. While the results of testing the characteristics of bakau piles obtained average water content of 21.58%, tensile strength of 18.51 MPa, compressive strength of parallel fiber 23.75 MPa and perpendicular fiber 14.10 MPa, bending strength 106, 22 MPa, and strong split 29.91 MPa. From the result of loading test of the foundation model in the laboratory, it is found that the ultimate bearing capacity of the model without foundation is 41.00 kN with the ultimate settlement of 14.00 mm, the model of the 20 cm long bakau piles foundation is 52.00 kN with the ultimate settlement of 13.00 mm, the foundation model a 30 cm long bakau piles foundation of 54.00 kN with a 10.00 mm ultimate settlement, a 40 cm long bakau piles foundation model of 56.00 kN with an ultimate settlement of 8.50 mm.

PERFORMANCE PREDICTION OF PREFABRICATED VERTICAL DRAIN IN SOFT SOIL USING FINITE ELEMENT METHOD

Prefabricated vertical drain (PVD) had successfully been applied in many soft ground construction projects. Finite element method (FEM) could assist designers to model very complex subsoil and structural elements. In this study, finite element analysis (FEA) is performed to verify the effectiveness of modelling of PVD in subsoil using computer software, Plaxis V8. The field settlement data were collected at two particular locations and were analysed using Asaoka’s method to estimate the ultimate settlement and back-calculated the coefficient of horizontal consolidation for these two particular location. Thereafter, by using back-calculated coefficient of horizontal consolidation, FEA were performed to predict the time rate settlement and compared against field settlement results. From the time rate settlement curves generated by FEM, the ultimate settlements were predicted using Asaoka’s method. The ultimate settlement predicted from FEM is slightly lower compared to actual field settlement monitoring result, but the degree of consolidation settlement achieved were higher.

Research of Calculation Method for Final Soft Clay Ground Settlement by Preloading Method

Preloading method is a common way to dispose large-scale soft soil foundation, and its methods of calculating the settlement amount mainly include exponential curve method, hyperbolic method, and Asaoka method. This paper chose exponential curve method and hyperbolic method to conduct ultimate settlement calculation on some reclamation project of Yingkou Port against measured data of settlement in the project, and compared the result to that calculated by splitting summation method. The accuracy was also verified by measured data of settlement amount in later phase to reach the conclusion that hyperbolic method is more suitable for calculating the ultimate settlement amount considering the soft soil foundation of marine facies in Liaoning.

Deformation Monitoring and Evaluating Technology for Subgrade of Unballasted Track on Lan-Xin Passenger Dedicated Line

Lanzhou-Xinjiang passenger dedicated line is the first high speed railway on chinas northwestern Gobi where the temperature range is large and the wind is huge. Most road section of Lan-Xin passenger dedicated line is subgrade. This paper researches the ballastless track subgrade settlement observation scheme and assessment method on area where climatic conditions is harsh and geologic conditions is complex. The result shows that: the observation accuracy of subgrade settlement tests satisfies the requirement by using Layered settlement instrument, intelligent static force level and high-accuracy Hydraulic settlement instrument; Subgrade lies upon bedrock or Gobi soil with great bearing capacity in gale area, and distance between observation sections could be increased seemly. The space between observation sections generally should be less than 100m in areas where bedrock exposed, thick gravel soil distribute commonly; the distance between observation sections should be less than 50m in pre-mountain Alluvial-pluvial plain areas; hyperbolic method adapt the estimate of subgrade settlement on Gobi area, and the correlation coefficient is 0.97; Subgrade settlement deformation curve converges quickly and the settlement value after 40 days reaches 85% of ultimate settlement.

Study on Prediction Models for Time-Dependent Settlement of Soft Road Foundation

The characteristics of soft clay roadbed settlement prediction model are studied in this paper. Firstly, based on one-dimension soil consolidation theory, the shape of time-dependent settlement process curve was analysed. Then, Mathematical analysis of traditional settlement models, including Gompertz model and Logistic model, was conducted, and the mathematical deficiency of above two traditional models were pointed out, which the settlement corresponding to inflection point has a constant ratio to the ultimate settlement. Further, Weibull model was proposed to describe the time-dependent settlement process of roadbed. This proposed model overcomes the deficiency of above two traditional models, and exponent model is one of its degraded expressions. Moreover, it can predict the total settlement processes of both the instantaneous load and the ramp load conditions. Finally, according to a group settlement observation data, the prediction results of different models are compared, and Weibull model has a good agreements.

Long-term settlement of soft subsoil clay under rectangular or semi-sinusoidal repeated loading of low amplitude

By applying Yin and Graham’s one-dimensional (1-D) equivalent-time rheological model, which can predict both primary and secondary settlement, the expressions for calculating the long-term subsoil settlement under rectangular or semi-sinusoidal repeated loading of low amplitude are obtained without considering the fluid–solid coupling. A property has been proven that ultimate settlement of clay is independent of stress increasing history under 1-D conditions. According to this property, the expressions are derived considering the solid–fluid coupling to approximately calculate the long-term total settlement and the long-term settlement of soft subsoil clay after construction of the road embankment. Because the expressions of the long-term settlement are analytical solutions in the present paper, they can not only avoid cumulative calculation errors in the numerical analysis, but also have more solid theoretical foundations than empirical equations.

Preliminary Results of Demonstration Capping Project in Hamilton Harbour

Placement of a pilot-scale sand cap occurred in Hamilton Harbour between July 31 and September 20, 1995. The harbour site is at a location where contamination of the bottom sediments is of concern. One ha of contaminated finegrained sediments was covered with 6,600 tonnes of clean sand to an average thickness of 30 cm. A very accurate positioning system was required and placement with adequate accuracy was possible up to wind speeds of about 30 km/h. Initial readings of settlement gauges taken in September 1995 show the ultimate settlement due to primary consolidation to range between 6 and 8 cm. Preliminary results indicate that the suspended material found in the water column during cap placement was almost entirely composed of fines associated with the cap sand. Vibracores showed a sharp interface between the sand cap and sediments with no signs of extensive mixing. Based on multibeam echo sounding results and other supporting data collected at the site, the sand cap was successfully placed in the designated area without any significant sediment disturbance. Some horizontal spreading of sand fines occurred beyond the site boundary.