Excess Water Pressure Research Articles

側方流動地盤における群杭基礎の地盤反力発生メカニズム

Two series of shaking table tests, i.e., one had a quay wall and the other had not, are conducted to clarify a lateral ground force acting on piles in liquefied and laterally spreading soils. It is shown that (1) The lateral ground force acting on a pile in laterally spreading soil as well as that in liquefied soil has character of solid ground due to decrease of excess power water pressure and recovery of effective normal stress after liquefaction; (2) The lateral ground force acting on a pile near quay wall becomes nine times larger than the maximum inertial force at a pile head in laterally spreading soil.

Effects of Preloading and Prestressing on the Strength and Stiffness of Geosynthetic Reinforced Clay in Plane Strain Compression

A series of plane strain compression (PSC) tests was performed to evaluate effects of preloading and prestressing on the stress-strain properties of reinforced saturated relatively soft clay. Saturated specimens of compacted clay, either unreinforced or reinforced with two horizontal layers of a composite consisting of woven and nonwoven geotextiles, were consolidated anisotropically simulating typical field stress conditions. Without drained preloading, the undrained strength of reinforced clay specimens did not noticeably increase when compared to unreinforced specimens, because a high positive excess water pressure developed in the reinforced clay due to the original high contractibility of the clay, which was not eliminated by reinforcement alone. The drained compressive strength increased substantially with reinforcement, while the peak strength was attained only at a large strain and the initial stiffness did not increase. By drained preloading to a load level that was much higher than the drained strength of unreinforced clay, the overall pre-peak stiffness, yield strength, and peak strength of reinforced clay under undrained conditions became substantially larger than those of unreinforced clay that had not been preloaded. The initial stiffness of preloaded clay at small strains became larger with increases in the prestress level as long as the prestress level was not too close to the preload level.

Scour Countermeasures Using Geosynthetics and Partially Grouted Riprap

The main requirement of any scour countermeasure or scour protection measure is to prevent erosion, so a top layer has to be built that is sufficiently resistant against the hydrodynamic loads and that protects the subsoil. Single elements have to be large enough to withstand the scouring forces and require an appropriate layer thickness. Smaller, mutually connected elements allow for a moderate layer thickness but provide the same resistance. To avoid excess water pressures below the top layer, permeable systems are recommended. A very reliable system is partially grouted riprap, which meets all the requirements of strength, flexibility, and permeability. Permeable systems need a well-designed filter. Placement of a grain filter or a geotextile filter is complicated by the current, so special equipment is needed. In mild currents a “sandmat” (a sand-filled nonwoven geotextile) can be used. In stronger currents use of geosynthetic geocontainers is proposed to achieve both a high resistance against the current and a well-performing filter.

Installing Relief Valves the Right Way

This article discusses how to create a system whereby a water tank acts as a relief valve on the water system. This is usually a fail‐safe mechanism that stops excessive amounts of pressure from building up in the underground water lines. The article especially focuses on how to install relief valves, which are critical to the success of “replacing” the tank and relieving any excess water pressure.

Non-Rayleigh Convection Caused by Ground Surface Topography

Non-Rayleigh convection is studied in aquifers, where the lateral variations of the temperature field are caused by the ground surface. Analytical solutions for the stream function, the Darcy velocities and the excess water pressure are found for a confined, rectangular and homogeneous aquifer situated at a given depth. The Darcy velocity field and the excess pressure are also found for an unconfined aquifer with a prescribed fluid potential at the top surface of the aquifer. Approximate solutions for excess pressure and Darcy velocities are found for the unconfined aquifer with a free surface. General estimates for the convective Darcy velocities are derived from these solutions. It is also shown that non-Rayleigh flow is unlikely in an unconfined aquifer.

A finite element formulation in Lagrangian co‐ordinates for heat and fluid flow in compacting sedimentary basins

AbstractThis article presents a numerical model of heat and fluid flow in compacting sedimentary basins formulated in Lagrangian co‐ordinates. The Lagrangian co‐ordinates are the sediment particle positions of the completely compacted basin. A finite element formulation of excess water pressure and temperature in these Lagrangian co‐ordinates is presented, in addition to an equivalent formulation in the real co‐ordinates. The later formulation is also Lagrangian of nature, since the elements of the grid in the real co‐ordinates always frame the same sediment particles. In other words, it is the Lagrangian grid mapped to the real space. This is done in an iterative loop which solves for excess water pressure, and then updates the real co‐ordinates of the sediment particles. By comparing the two finite element formulations it is concluded that the one in real space is the simplest, most efficient and most precise.The model is validated by comparison with two dimensionless one‐dimensional solutions, one analytical for the linear case, and one numerical for the non‐linear case. Both these one‐dimensional solutions are obtained on the unit interval, where the moving top boundary caused by continuous sedimentation is incorporated.

Clearance of lung edema into the pleural space of volume-loaded anesthetized sheep

To determine whether lung edema leaks into the pleural space, we measured flow rates of visceral pleural liquid from exposed sheep lungs during volume loading and then compared the protein concentration of visceral pleural liquid and lung interstitial liquids (lymph and peribronchovascular cuff liquid). For 4 h, we volume loaded 24 anesthetized ventilated sheep with one side, both sides, or neither side of the chest open. During the experiment, we collected visceral pleural liquid from a bag surrounding the exposed lung and lung lymph; after the experiment, we collected peribronchovascular cuff liquid. We found that during volume loading visceral pleural liquid flow increased significantly by 2 h, and its protein concentration over the final hour was the same as that of lung interstitial liquids. The volume of visceral pleural liquid correlated with excess lung water and wedge pressure elevation. By our estimates, clearance of edema from the lung into the pleural space constituted 23-29% of all edema liquid collected, similar to measured lymph edema clearance. We conclude that edema liquid leaks directly from edematous sheep lungs into the pleural space and that this leakage provides an important additional route of edema clearance.

Law and Medicine

To the Editor.— The Journalin the Nov 8 issue ( 218 :934, 1971) in the LAW AND MEDICINE article on contributory negligence states in paragraph 1: Excessive water pressure ruptured his eardrums. This is not true. I demand a retraction.

Construction of hollow-pile walls for protecting dike and apron foundations of the takhiatashsk hydroelectric scheme

1. Hollow-pile guard walls can be recommended for the protection of the foundations of dikes and other hydraulic structures under similar hydrogeologic conditions, as a form of construction which allows labor-consuming work of critical importance to be carried out by industrial methods. 2. The sinking of hollow piles, employing augering in advance, according to the technology adopted in constructing the hydroelectric scheme, can be recommended for use when it is necessary to construct protective subsurface walls in foundation materials containing layers of rock. 3. The method of supporting well walls by applying excess water pressure can be recommended as the most efficient for carrying out augering work in dry valleys, particularly when drilling wells of large diameter. 4. The bucket auger used on the construction of the hydroelectric scheme can be recommended for augering wells in sandy, sandy-loam, and tight-clay soils. 5. The joining of hollow-pile units in the vertical position, currently practised on construction, cannot be considered justified, owing to the large expenditure of labor and time involved in the joining operations during the sinking process. It is essential to carry out the joining of hollow-pile units in the horizontal position, on a special bed which is also adapted for the application of the waterproofing coating, as this will increase the efficiency and improve the quality of the joining work and the standard of the waterproofing coatings. 6. The sealing of the hollow-pile protective walls by metallic sheet piling cannot be considered efficient, owing to its high cost and the large input of metal; in view of this, it is necessary to set up experimental-investigational works for developing methods of sealing the gaps between the hollow piles forming a subsurface wall.