DD285839A5 - DEVICE AND METHOD FOR PROPOSING BOEDEN'S CONDUCTIVITY COEFFICIENTS ACCORDING TO THE PIEZOMETER PRINCIPLE - Google Patents

Abstract

Apparatus and method for probing the conductivity coefficients of soils according to the piezometer principle for the saturated and adjacent unsaturated area with the aim of being able to choose the amount of water exchanged with the soil, independently of the difference between soil water pressure and internal pressure of the measuring system. For this purpose, a device is used, which consists of a completely filled with water probe tube, located between a conical tip and the lower end of the probe tube open-pore filter element made of a sintered metal, a pressure sensor, an additional water volume and a regulating element for the exchanged amount of water. The invention can be used, above all, in the field of agriculture and civil engineering for the exploration of site properties {conductivity coefficient; Piezometers; Ground; Soil water pressure; Pressure equalization; Sintered metal; Filterkoerper}

Description

For this 1 page drawing

Field of application of the invention

The invention can be used for the exploration of site characteristics in the field of agriculture and civil engineering, in particular the water permeability of soils.

Characteristic of the known state of the art

The water movement in soils takes place in their open pore system. The conductivity coefficient describes the ability of the soil to facilitate this water transport. The conductivity coefficient decreases with the water content, because in this case the transport is limited to the flow of finer pores.

To characterize the water movement in the soil, therefore, the conductivity coefficient must be determined as a function of the water content or the suction stress. Exact measurements of this kind can so far only be carried out on soil samples taken in undisturbed form from the ground. These procedures are very labor intensive and therefore not very suitable for a large-scale exploration.

For an estimate of the conductivity coefficients in the field, therefore, piezometers are preferably used. In these devices, the water level is observed in pipes, into the interior of the bottom open end of the bottom water penetrates and increases in equilibrium to the water level. For an estimation of the conductivity coefficients, this water level is changed and the subsequent compensation process is evaluated. Modern measuring systems of this type record the rise time of the soil water for several predetermined height levels. A shortcoming of this measuring principle is the coupling between the amount of water exchanged with the ground and the change in the static water pressure in the piezometer tube. For a given pressure change, the amount of water to be exchanged is always specified. Depending on the existing conductivity coefficients of the soils, the resulting measuring times can therefore assume extreme values. This measuring principle is limited to the saturated area for the soil water. For measurements in time periods with lower soil moisture or for soils in the unsaturated region, the inverse of the described principle by an infiltration method (permeamoter) is used, for which the findings on time and disadvantages apply mutatis mutandis.

Object of the invention

The aim of the invention is an apparatus and a method with which the conductivity coefficient of the soil in the unsaturated and saturated region can be probed with minimal effort at a low measuring time.

Explanation of the essence of the invention The object of the invention is an apparatus and a method for probing the conductivity coefficient of Soils according to the piezometric principle, in which the exchanged between the Roden and the measuring device amount of water

be selected independently of the applied pressure difference according to the expected conductivity coefficient

According to the invention, the object is achieved in that a probe tube completely filled with water between its

lower end and a screwed tip contains a nffenporigen filter body. Me the impressions of the Sondo in the

Bodon makes a water flow over the filler body until the pressure is equalized with dom Bodonwassor.

A pressure sensor in the water volume of the probe tube detects the applied static pressure, After the formation of the pressure equilibrium is via a regulating element at the head of the probe tube mi *. Air at atmospheric pressure filled additional volume V ₀ at time t _t . connected. At the same time, a pressure recording device is started which registers the pressure progression until the equilibrium between the sod water pressure and the static pressure in the probe tube is formed again.

The size of the additional voien determines the amount of water exchanged between the measuring system and the ground. From the pressure-time curve, the additional volume Vo and Je-n known conductivity coefficients for the filter body, the conductivity coefficient for the soil volume in the vicinity of the probe tip can be determined.

embodiment The invention will be explained in more detail with reference to an embodiment. 1 shows the device for probing

the conductivity coefficient.

A probe tube 1 completely filled with water contains between its lower end and a screwed-in tip 3

an open-pore filter body 2 through which, upon contact with the soil to be tested, a water flow up to

Pressure equalization takes place with the groundwater. A pressure sensor 4 in the water volume of the probe tube 1 detects the

applying static pressure. After the formation of the pressure equilibrium is via a tap 5 at the top of the

F nendenrohres 1 a filled with air at atmospheric pressure additional volume V ₀ at time t _o connected. simultaneously

a device is started to print recording which registers the pressure curve until the next training of the equilibrium ι vlechen ground water pressure and static pressure in the probe tube. 1 The size of the additional volume V ₉ determines the Wassermonge exchanged between the measuring system and the ground.

From the pressure-time curve, the additional volume Vo and the known conductivity coefficient for the filter body 2 can

the conductivity coefficient for the soil volume in the vicinity of the special tip 3 can be determined.

With the device described is always the conductivity coefficient of the combination of filter body 2 and the

measured adjacent soil volume. The amount of the filter body 2 can be separated with sufficient accuracy, as long as a conductivity coefficient is not significantly less than that of the soil volume to be examined. These

Demand is well met by thin-walled filter body with the widest possible pores in large numbers. The maximum suction to which this device can be applied is determined by the capillary closing pressure of the Limited filters in which uses a ventilation of the probe tube 1. Therefore, measurements at high suction voltages require Filter body 2 with narrow pores. These opposing demands for the unsaturated area of the soil water can be interchangeable with a set Filter body 2 are considered with graded pore size. These thin-walled filter body 2 with largely

homogeneous poron size are produced from nearly spherical metal particles of uniform grain size in the sintering process.

With a device according to FIG. 1, with a filter body 2 of grain size 40, the conductivity coefficient can be up to about 1 m / d

(Meters per day) and a soil suction of 16kPa. In the saturated region, an open-pore filter body 2 with a grain size of 100 μm is always used, with which the conductivity coefficient can be determined up to about 4 m / d.

In the exemplary embodiment, a piezoresistive pressure sensor is used as the pressure sensor 4, which has a negligible Change of Eigenvol'jmens at a pressure change shows. The between the measuring system and the floor volume

exchanged amount of water is therefore determined solely by the connected additional volume V ₀ .

The pressure-time curve at the pressure sensor 4 is registered in the exemplary embodiment of a microcomputer. After entering the Device parameter additional volume V ₀ and conductivity coefficient of the selected filter body 2 is with the same computer

the conductivity coefficient of the soil volume is determined as a function of the suction stress.

Claims (3)

1. A device for probing the conductivity coefficients of soils according to the piezometer principle, characterized in that a completely filled with water probe tube (1) between a conical tip (3) and one end of the probe tube (1) contains an open-pored filter body (2) establishes the contact between the volume of water in the probe tube (1) and the soil body to be examined. 2. Device according to item 1, characterized in that a sintered metal is used as an open-pored filter body (2), which is formed from almost spherical particles of uniform grain size and whose conductivity coefficient of the soil to be examined is at most by a factor of 5. 3. A method for probing the conductivity coefficients of soils according to the piezometer principle, characterized in that after formation of the equilibrium between soil water pressure and internal pressure of the probe tube (1) filled with air at atmospheric pressure additional volume V ₀ to the internal volume of the probe tube (1) is connected and the change in pressure taking place at the time of this connection is registered as a function of time.