Establishment of digital model for dynamic simulation analysis on hydraulic impact perforator

Hydraulic impact perforator is powerful tools for trenchless project. It has advantages in cabinet structure, low cost, long life and easy protected. Compared with pneumatic DTH, the hydraulic impact spear worked under high pressure and using uncompressible fluid thusgreater impact energy and higher efficiency can be supported. The authors founded the dynamic simulation model of HDI-146 hydraulic impact spear. The project for solving the differential equation was suggested also. By means of virtual machine technology, the dynamic mechanism of HDI-146 can be explored and tutoring us to optimize the structural parameters can be made.     

An analytical method of stage–fall–discharge rating

This paper presents an analytical method for establishing a stage–fall–discharge rating using hydraulic performance graphs (HPG). The rating curves derived from the HPG are used as the basis to establish the functional relation of stage, fall and discharge through regression analysis following the USGS procedure. In doing so, the conventional trial‐and‐error process can be avoided and the associated uncertainties involved may be reduced. For illustration, the proposed analytical method is applied to establish stage–fall–discharge relations for the Keelung River in northern Taiwan to examine its accuracy and applicability in an actual river. Based on the data extracted from the HPG for the Keelung River, one can establish a stage–fall–discharge relation that is more accurate than the one obtained by the conventionally used relation. Furthermore, the discharges obtained from the proposed rating method are verified through backwater analysis for measured high water level events. The results indicate that the analytical stage–fall–discharge rating method is capable of circumventing the shortcomings of those based on single‐station data and, consequently, enhancing the reliability of flood estimation and forecasting. Copyright © 2008 John Wiley & Sons, Ltd.     

Estimating finite difference block equivalent hydraulic conductivity for numerically solving the Richards' equation

A method is proposed for calculating the equivalent hydraulic conductivity (EHC) within a finite difference block (FDB). Application of the constant‐flux assumption of Darcy's Law, the EHC equals to the integration of effective hydraulic conductivity (K_w) as a function of pressure head (h_w) divided by the head difference at the ends of the FDB. Error analysis show that the constant‐flux (CF) EHC estimates are better than those computed by the commonly used arithmetic‐mean (AM), geometric‐mean (GM), and harmonic‐mean (HM) techniques. CF EHC results are even more superior at larger interblock head difference situations. Simulations of water infiltration experiments show that simulations using the CF EHC or AM or GM weighting technique have only slight difference while applying the Neumann type boundary condition at the ground surface. In case of the Dirichlet type boundary condition, however, the CF EHC is superior to the other two in correctly estimating the depth of infiltration while enlarging the grid size. Therefore, it is recommended to adopt the CF EHC with a larger grid size to the more stable and more efficient results. Copyright © 2007 John Wiley & Sons, Ltd.     

Gypsum treatment as a restoration method for sediments of eutrophied lakes – experiments from southern Finland

The internal load of phosphorus can be treated with chemicals improving a sediment's phosphorus binding capacity. Gypsum (CaSO₄?2H₂O) is a novel material to be applied for this purpose. In the hypereutrophic Lake Enäjärvi, southern Finland, sediments were treated with gypsum in test basins. The basins were isolated from open water to create artificial anoxia, which allowed the effects of the treatment on the internal load to be measured. The results indicate that gypsum treatment decreases the sediment's release of nutrients under anoxic conditions. This was demonstrated as less increased total-P and total-N concentrations and decreased chlorophyll-a concentrations in the water column of treated basins as compared with the control basins. Because the gypsum treatment prevents internal load, it has potential in lake restoration in cases where the internal load of phosphorus is accelerated by anoxic conditions at the sediment/water interface.     

Elastic settlements under linear surface pressures on rectangular areas

This paper presents the practical closed‐form solutions for elastic settlement under the linear full‐contact pressures on rectangular areas resting upon an elastic mass. The linear pressure distribution is mostly assumed in practice for the rectangular footing having biaxial bending. The equations presented here are determined by evaluating the integration of Steinbrenner's strain approximation based on the stress solutions from the Boussinesq equations. The presented formulae are validated to be used for the elastic settlement under any point of linear full‐contact loading, triangular and embankment types of pressure cases. In this respect, it represents a significant step forward in the understanding of elastic settlement and rotation under the practical loading cases. The presented solutions are concise and easy to use. The numerical examples are demonstrated and the resulting influence factors in graphical forms are presented for their practical use especially in the elastic settlement calculations of rectangular footing subjected to the biaxial bending. Copyright © 2008 John Wiley & Sons, Ltd.     

The timing and magnitude of changes to Hortonian overland flow at the watershed scale during the post-fire recovery process

Extreme hydrologic responses following wildfires can lead to floods and debris flows with costly economic and societal impacts. Process-based hydrologic and geomorphic models used to predict the downstream impacts of wildfire must account for temporal changes in hydrologic parameters related to the generation and subsequent routing of infiltration-excess overland flow across the landscape. However, we lack quantitative relationships showing how parameters change with time-since-burning, particularly at the watershed scale. To assess variations in best-fit hydrologic parameters with time, we used the KINEROS2 hydrological model to explore temporal changes in hillslope saturated hydraulic conductivity (K_sh) and channel hydraulic roughness (n_c) following a wildfire in the upper Arroyo Seco watershed (41.5 km²), which burned during the 2009 Station fire in the San Gabriel Mountains, California, USA. This study explored runoff-producing storms between 2008 and 2014 to infer watershed hydraulic properties by calibrating the model to observations at the watershed outlet. Modelling indicates K_sh is lowest in the first year following the fire and then increases at an average rate of approximately 4.2 mm/h/year during the first 5 years of recovery. The estimated values for K_sh in the first year following the fire are similar to those obtained in previous studies on smaller watersheds (<1.5 km²) following the Station fire, suggesting hydrologic changes detected here can be applied to lower-order watersheds. Hydraulic roughness, n_c, was lowest in the first year following the fire, but increased by a factor of 2 after 1 year of recovery. Post-fire observations suggest changes in n_c are due to changes in grain roughness and vegetation in channels. These results provide quantitative constraints on the magnitude of fire-induced hydrologic changes following severe wildfires in chaparral-dominated ecosystems as well as the timing of hydrologic recovery.     

An assessment of large-scale flood modelling based on LiDAR data

Large-scale flood modelling approaches designed for regional to continental scales usually rely on relatively simple assumptions to represent the potentially highly complex river bathymetry at the watershed scale based on digital elevation models (DEMs) with a resolution in the range of 25–30 m. Here, high-resolution (1 m) LiDAR DEMs are employed to present a novel large-scale methodology using a more realistic estimation of bathymetry based on hydrogeomorphological GIS tools to extract water surface slope. The large-scale 1D/2D flood model LISFLOOD-FP is applied to validate the simulated flood levels using detailed water level data in four different watersheds in Quebec (Canada), including continuous profiles over extensive distances measured with the HydroBall technology. A GIS-automated procedure allows to obtain the average width required to run LISFLOOD-FP. The GIS-automated procedure to estimate bathymetry from LiDAR water surface data uses a hydraulic inverse problem based on discharge at the time of acquisition of LiDAR data. A tiling approach, allowing several small independent hydraulic simulations to cover an entire watershed, greatly improves processing time to simulate large watersheds with a 10-m resampled LiDAR DEM. Results show significant improvements to large-scale flood modelling at the watershed scale with standard deviation in the range of 0.30 m and an average fit of around 90%. The main advantage of the proposed approach is to avoid the need to collect expensive bathymetry data to efficiently and accurately simulate flood levels over extensive areas.     

Finite element simulations of 3D planar hydraulic fracture propagation using a coupled hydro-mechanical interface element

Two-dimensional hydraulic fracturing simulations using the cohesive zone model (CZM) can be readily found in the literature; however, to our knowledge, verified 3D cohesive zone modeling is not available. We present the development of a 3D fully coupled hydro-mechanical finite element method (FEM) model (with parallel computation framework) and its application to hydraulic fracturing. A special zero-thickness interface element based on the CZM is developed for modeling fracture propagation and fluid flow. A local traction-separation law with strain softening is used to capture tensile cracking. The model is verified by considering penny-shaped hydraulic fracture and plain strain Kristianovich‑Geertsma‑de Klerk hydraulic fracture (in 3D) in the viscosity- and toughness-dominated regimes. Good agreement between numerical results and analytical solutions has been achieved. The model is used to investigate the influence of rock and fluid properties on hydraulic fracturing. Lower stiffness tip cohesive elements tend to yield a larger elastic deformation around the fracture tips before the tensile strength is reached, generating a larger fracture length and lower fracture pressure compared with higher stiffness elements. It is found that the energy release rate has almost no influence on hydraulic fracturing in the viscosity-dominated regime because the energy spent in creating new fractures is too small when compared with the total input energy. For the toughness-dominated regime, the released energy during fracturing should be accurately captured; relatively large tensile strength should be used in order to match numerical results to the asymptotic analytical solutions. It requires smaller elements when compared with those used in the viscosity-dominated regime.     

Numerical simulation of particle plugging in hydraulic fracture by element partition method

Hydraulic fracturing (HF) treatment often involves particle migration and is applied for propping or plugging fractures. Particle migration behaviors, e.g., bridging, packing, and plugging, significantly affect the HF process. Hence, it is crucial to effectively simulate particle migration. In this study, a new numerical approach is developed based on a coupled element partition method (EPM). The EPM is used to model natural and hydraulic fractures, in which a fracture is allowed to propagate across an element, thereby avoiding remeshing in fracture simulations. To characterize the water flow process in a fracture, a fully hydromechanical coupled equation is adopted in the EPM. To model particle transportation in fractures with water flow, each particle is treated as a discrete element. The particles move in the fracture as a result of being dragged by fluid. Their movement, contact, and packing behaviors are simulated using the discrete element method. To reflect the plugging effect, an equivalent aperture approach is proposed. Using this method, the particle migration and its effect on water flow are well simulated. The simulation results show that this method can effectively reproduce particle bridging, plugging, and unblocking in a hydraulic fracture. Furthermore, it is demonstrated that particle plugging significantly affects water flow in a fracture and hence the propagation of hydraulic fracture. This method provides a simple and feasible approach for the simulation of particle migration in a hydraulic fracture.     

Controls on evapotranspiration from jack pine forests in the Boreal Plains Ecozone

The exchanges of water, energy and carbon between the land surface and the atmosphere are tightly coupled, so that errors in simulating evapotranspiration lead to errors in simulating both the water and carbon balances. Areas with seasonally frozen soils present a particular challenge due to the snowmelt-dominated hydrology and the impact of soil freezing on the soil hydraulic properties and plant root water uptake. Land surface schemes that have been applied in high latitudes often have reported problems with simulating the snowpack and runoff. Models applied at the Boreal Ecosystem Research and Monitoring Sites in central Saskatchewan have consistently over-predicted evapotranspiration as compared with flux tower estimates. We assessed the performance of two Canadian land surface schemes (CLASS and CLASS-CTEM) for simulating point-scale evapotranspiration at an instrumented jack pine sandy upland site in the southern edge of the boreal forest in Saskatchewan, Canada. Consistent with past reported results, these models over-predicted evapotranspiration, as compared with flux tower observations, but only in the spring period. Looking systematically at soil properties and vegetation characteristics, we found that the dominant control on evapotranspiration within these models was the canopy conductance. However, the problem of excessive spring ET could not be solved satisfactorily by changing the soil or vegetation parameters. The model overestimation of spring ET coincided with the overestimation of spring soil liquid water content. Improved algorithms for the infiltration of snowmelt into frozen soils and plant-water uptake during the snowmelt and soil thaw periods may be key to addressing the biases in spring ET.