Centrifuge modeling of PGD response of buried pipe

A new centrifuge based method for determining the response of continuous buried pipe to PGD is presented. The physical characteristics of the RPI's 100 g-ton geotechnical centrifuge and the current lifeline experiment split-box are described: The split-box contains the model pipeline and surrounding soil and is manufactured such that half can be offset, in flight, simulating PGD. In addition, governing similitude relations which allow one to determine the physical characteristics, (diameter, wall thickness and material modulus of elasticity) of the model pipeline are presented. Finally, recorded strains induced in two buried pipes with prototype diameters of 0.63 m and 0.95 m (24 and 36 inch) subject to 0.6 and 2.0 meters (2 and 6 feet) of full scale fault offsets and presented and compared to corresponding FE results.

Numerical simulation of heat release performance of filling body under condition of heat extracted by fluid flowing in buried tube

It is the basic requirement of the synergetic exploitation of deep mineral resources and geothermal resources to arrange the heat transfer tube in filling body. The heat release performance of filling body directly impacts on the exploiting efficiency of geothermal energy. Based on heat transfer theory, a three-dimensional unsteady heat transfer model of filling body is established by using FLUENT simulation software. Taking the horizontal U-shaped buried pipe as research object, the variation of temperature field in filling body around buried pipe is analyzed during the heat release process of filling body;the initial temperature of filling body, the diameter of buried pipe, the inlet temperature and inlet velocity of heat transfer fluid influencing of coupling heat transfer, which exists between heat transfer fluid and surrounding filling body within a certain axial distance of buried tube, and influencing of temperature difference between inlet and outlet of heat transfer fluid and on heat transfer performance of filling body are also discussed. It not only lays a theoretical foundation for the synergetic exploitation of mineral resources and geothermal energy in deep mines, but also provides a reference basis for the arrangement of buried pipes in filling body as well as the selection of working conditions for heat transfer fluid.

Comparison between the Seismic Performance of Buried Pipes and Pipes in a Utility Tunnel

A utility tunnel system consists of pipes and ancillary facilities.In this paper,a finite element model of a concrete utility tunnel with pipes inside is established.Several tunnel segments were built to simulate a real utility tunnel,while the pipe was fixed by springs on the brackets in the utility tunnel.Using the discrete soil spring element to simulate the soil-structure interaction,actual earthquake records were adopted as excitation to analyze the seismic responses of pipes in a utility tunnel.Moreover,the influences of different parameters,including soil type,earthquake records,and field apparent wave velocity on the seismic responses of the utility tunnel and the pipes inside were studied.Finally,the seismic responses of buried pipes were analyzed and compared with those of pipes in a utility tunnel to evaluate the seismic performance of pipes for two working conditions.

Influence of Shear Effects on the Characteristics of Axisymmetric Wave Propagation in a Buried Fluid‑Filled Pipe

The acoustic propagation characteristics of axisymmetric waves have been widely used in leak detection of fluid-filled pipes.The related acoustic methods and equipment are gradually coming to the market,but their theoretical research obviously lags behind the field practice,which seriously restricts the breakthrough and innovation of this technology.Based on the fully three-dimensional effect of the surrounding medium,a coupled motion equation of axisymmetric wave of buried liquid-filled pipes is derived in detail,a contact coefficient is used to express the coupling strength between surrounding medium and pipe,then,a general equation of motion was derived which contain the pipe soil lubrication contact,pipe soil compact contact and pipe in water and air.Finally,the corresponding numerical calculation model is established and solved used numerical method.The shear effects of the surrounding medium and the shear effects at the interface between surrounding medium and pipe are discussed in detail.The output indicates that the surrounding medium is to add mass to the pipe wall,but the shear effect is to add stiffness.With the consideration of the contact strength between the pipe and the medium,the additional mass and the pipe wall will resonate at a specific frequency,resulting in a significant increase in the radiation wave to the surrounding medium.The research contents have great guiding effect on the theory of acoustic wave propagation and the engineering application of leak detection technology in the buried pipe.

Comparison of Thermal Performance for Two Types of ETFP System under Various Operation Schemes

The earth to fluid pipe(ETFP)system has been widely applied to various energy engineering.The numerical model of the heat transfer process in the ETFP system with a shallow-buried horizontal or a deep-buried vertical U-shape pipe adopted in practical engineering was established and the model distinctions were pointed out.The comparison of the thermal performance between the two types of ETFP system under various schemes was conducted on the basis of numerical prediction.The results showed that the thermal parameters of the ETFP system with a shallow-buried horizontal pipe were influenced by the inlet velocity and ground temperature obviously.The variation of the fluid temperature was smooth and the thermal influence zone was limited under the fixed conditions.The proper intermittent operation scheme reduced 53.1%outlet fluid temperature rising.By contrast,the fluid temperature in the ETFP system with a deep-buried vertical U-shape pipe varied dramatically with the operation conditions.The intermittent operation scheme with a relatively short interval led to a less temperature fluctuation of soil around the pipe.The intermittent scheme is beneficial to the recovery of the thermal condition of soil around the U-shape pipe.These results indicated a stark difference in thermal performance between the two types of system.The study can provide guidance for the selection and operation of ETFP system in practical heat exchange engineering.

Application of a finite element method to stress distribution in buried patch repaired polyethylene gas pipes

Advantages of polyethylene pipes over traditional steel or metal pipes have increased industry interest in the use of polyethylene(PE)pipelines for underground applications and especially in gas distribution networks.In this study,finite element analysis is used to calculate the stress distribution in a patch repaired defective gas pipe under internal pressure.The pipe is assumed to be buried at a depth of 125 cm.The material is assumed to be medium density PE80B,where the patch material was selected from high density polyethylene(HDPE).During the loading process,the seasonal pipe temperature changes,surcharge loads,soil column weight,and soil-pipe interaction were included in the analysis.Four types of patch arrangements were selected to repair the damaged pipe.The shape of the defect hole was deemed as circular or elliptic.With respect to elliptic defects,various minor to major diameter ratios,a/b,were selected to simulate a circular to a crack shaped defect.Based on the results,the semi-circular and saddle fusion patches decrease the peak von Mises stress in the pipe by almost the same amount.However,the minimum peak von Mises stress in the patch corresponds to the saddle fusion repair arrangement.Based on the results,with respect to a saddle fusion repair,when the shape of the defect approaches a crack,the peak von Mises stress in the pipe almost doubles and exceeds the pipe allowable stress for a working life of 50 years.With respect to higher values of a/b,the stress level in the patch repaired pipe is significantly below its limiting value for the same life expectancy.

Application of the finite element method for evaluating the stress distribution in buried damaged polyethylene gas pipes

During the loading process,buried gas pipes can experience severe stresses due to soil-structure interaction,the presence of traffic load,the soil’s column weight,daily and/or seasonal temperature changes and uniform internal pressure.In this research,the finite element method is employed to evaluate the behavior of buried Medium Density Polyethylene(MDPE)pipes which have been subjected to damage at the pipe crown.The modeled pipe damage ranges from a very small circular hole to a large circular hole and elliptic holes with various minor to major diameter ratios,a/b,to simulate circular to crack-shaped defects.The computer simulation and stress analyses were performed using the ANSYS software finite element package.The stress distribution around the defect was determined under the aforementioned mechanical and thermal loading conditions.Then,the maximum values of Von Mises stresses in the damaged buried PE pipes,which were evaluated by finite element solution,were compared with their corresponding reduced strength for safe operation with a life expectancy of fifty years.Based on the results,the maximum Von Mises stress values in the defective buried polyethylene gas pipeline are significantly above the pipe strength limit at 35℃.The previously mentioned stress values increase with the following factors:temperature increase,increase in circular hole diameter and decrease in elliptic hole diameter ratio(a/b).The maximum stress in the damaged PE pipe is due to the simultaneous loading effects of soil column weight,internal pressure,vehicle wheel load and pipe temperature increase.Additionally,the novel finite element models and stress plots for the buried damaged pipe and the pipe material allowable strength will be used to investigate the correct repair method for the damaged gas pipeline and to choose the best patch arrangement which will assure a safe repair.

Analytical solution for upheaval buckling of shallow buried pipelines in inclined cohesionless soil

Upheaval buckling of pipelines can occur under thermal expansion and differential ground settlement.Research on this phenomenon has usually assumed the pipes are buried in horizontal ground.For long-distance transmission pipelines across mountainous areas,the ground surface is commonly inclined.Based on the Rankine earth pressure theory and Mohr-Coulomb failure criterion,analytical formulae for calculating the peak uplift resistance and the slip surface angles for a buried pipe in inclined ground are presented in this paper.Analyses indicate that the slip surfaces in inclined ground are asymmetric and rotate towards the downhill side.Under a shallow burial depth,the failure plane angle is highly impacted by the ground inclination.When the embedment ratio(H/D)is more than 4,the influence of the ground slope on the failure plane angle is negligible.The peak uplift resistance reduces in inclined ground,especially when H/D is less than 1.Finally,a simple equation considering the impact of ground inclination is proposed to predict the peak uplift resistance.

A DYNAMIC MIXED MODEL WITH NITROGEN LEACHING LOSSES FROM THE PONDED PADDY RICE FIELD UNDER SITUATION OF BURIED PIPE DRAINAGE

In order to study the law of nitrogen leaching losses from the paddy field under the condition of drainage, based on the theories of potential energy and solute transport, a water nitrogen dynamic mixed model by combining the flow net with dynamic method was established. In the computation of buried pipe drainage, the superposition principle was used to simplify the complex solving of the two dimensional problem about water nitrogen transportation in Soil Plant Air Continuous (SPAC) system into several one dimensional problems. The presented method is simple and practical. Some field experiments were carried out to demonstrate the validity of the model.