Long-term decay of the water pressure in the osmotic tensiometer

Matric suction is an important state variable required for the assessment of unsaturated soil properties.Tensiometers are commonly used for direct matric suction measurement but have a limited measuring range up to 90 kPa due to the cavitation problem.Osmotic tensiometer(OT)can improve the measuring range of tensiometers by increasing the osmotic pressure of water to avoid the cavitation.However,the long-term water pressure decay that appeared in OTs caused a gradual decrease in their measuring range.In this study,crosslinked poly(acrylamide-co-acrylic acid)potassium salt(PAM-co-PAAK)was used for the preparation of OTs(five in total)to explore the mechanism of water pressure decay of OTs.The maximum water pressure in the OT versus the volume fraction of polymer filled in the OT was described based on the Flory-Huggins polymer theories and validated using WP4C dewpoint hygrometer.The long-term pressure decay of OT-1,OT-2,and OT-3 was observed for 130 d and constant pressures were found for OT-1 and OT-2,indicating that the pressure decay of OT was mainly caused by the stress relaxation of the polymer hydrogels,and standard linear solid(SLS)rheological model was appropriate to fit the decay data.For OT-1,OT-2 and OT-3,the theoretical osmotic pressure that was calculated based on the mass of retrieved polymer from OTs after 130-d pressure observation was higher than the actual osmotic pressure as observed,indicating that polymer leakage cannot explain the pressure decay of the OT.The ultravioletevisible(UVevisible)spectrophotometry examined the change in polymer concentrations in the water containers of OT-4 and OT-5 and demonstrated that there was no increase in polymer leakage during the period of pressure decay of OT-4 and OT-5.As a result,the pressure decay of OT was not caused by polymer leakage.The results of this research suggested that the viscoelastic properties of polymers should be taken into consideration in further OT development.

Water Flow Path Characterization in Shallow Vadose Zone Using Tensiometers

In this project, we will present the findings of a study using Tensiometer systems designed to investigate the water flow path pattern in shallow vadose zone. The purpose of this paper is to evaluate water flow path in shallow vadose zone and to calculate the infiltration rate and hydraulic conductivity of a soil using Tensiometer. We have measured the subsurface water flow paths in sandy clay loam soil following infiltration experiment using Tensiometers. The matric potential and hydraulic conductivity measurements show that subsequent infiltration and water movement in unsaturated (vadose) zone are vertical, but it can have large lateral component under steady condition. This shows that water moves generally from high water content to lower water content region. Average pressure head for the percolation test conduction locations EB and HB was -30 and -80 cm respectively. Hysteresis produces another interesting situation when the soil is drained. We found that the wetter portion of the soil in vadose zone could be at a lower potential (head) than the dryer portions, resulting in lateral driving force for a preferential flow of water from the dryer to the wet soil. The infiltration rate for the 5 cm ponded water was calculated at 5.45 cm/hr. The infiltration rate curve shows that the rate of infiltration decreases with the time. When infiltration first starts, the wetting front is steep and very close to the surface. Similarly, due to the pressure head gradient, large value for infiltration is recorded. Under these conditions, we believe that the gradient in pressure head is responsible for the rapid movement of water into the dry soil. The effect of gravity is less on water during the initial stages of infiltration;however, it is more effective for preferential flow pattern. In the latter infiltration event, the wetting front has moved deeper into the soil. As a result, the pressure head gradient at the surface is much smaller and consequently has little effect. When the pressure head is equal zero, infiltration rate approaches almost to the lowest level. We also observed that even a minor change in soil-water pressure due to slope could change both direction and magnitude of water flux.

Studying the stress-suction coupling in soils using an oedometer equipped with a high capacity tensiometer

In the context of research into deep nuclear waste disposal,various works have concerned the hydromechanical behavior of Boom clay,a stiff plastic clay extracted in the SCK-CEN Underground Research Laboratory near the Mol City(Belgium),at a depth of 223 m.Due to some amount of smectite minerals in the clay fraction,Boom clay exhibits swelling properties when hydrated under low stresses.To investigate some aspects of the hydromechanical behavior of Boom clay,oedometer compression tests were carried out on samples of Boom clay close to saturation and submitted to an initial suction.During oedometer compression,the changes in suction with increased vertical stress are monitored by means of a high capacity tensiometer installed at the bottom of the sample.Some aspects related to hydromechanical couplings are examined through the investigation of the changes in suction during oedometer compression,a somewhat delicate and poorly documented experimental approach.A comparison is also made with a completely different soil sample under suction,i.e.a statically compacted unsaturated low plasticity silt.Some technical difficulties typical of this new experimental approach are first described in detail so as to optimize the interpretation of the data obtained.The experiment allows the determination of the point at which suction is changed to positive pressure during compression.Below this point,the ratio between the vertical stress and the change in suction are determined.Above this point,the data show that positive pore pressures are dissipated in a common way.The suction/stress behavior during unloading is also described and discussed.Finally,an interpretation in terms of microstructure effects is provided for both samples.The experimental approach initiated here seems to provide interesting further application to better understand hydromechanical couplings in natural soils in relation with suction increase during stress release.

An approach to measure infill matric suction of irregular infilled rock joints under constant normal stiffness shearing

Rock joints infilled with sediments can strongly influence the strength of rock mass. As infilled joints often exist under unsaturated condition, this study investigated the influence of matric suction of infill on the overall joint shear strength. A novel technique that allows direct measurement of matric suction of infill using high capacity tensiometers(HCTs) during direct shear of infilled joints under constant normal stiffness(CNS) is described. The CNS apparatus was modified to accommodate the HCT and the procedure is explained in detail. Joint specimens were simulated by gypsum plaster using threedimensional(3D) printed surface moulds, and filled with kaolin and sand mixture prepared at different water contents. Shear behaviours of both planar infilled joints and rough joints having joint roughness coefficients(JRCs) of 8-10 and 18-20 with the ratios of infill thickness to asperity height(t/a)equal to 0.5 were investigated. Matric suction shows predominantly unimodal behaviour during shearing of both planar and rough joints, which is closely associated with the variation of unloading rate and volumetric changes of the infill material. As expected, two-peak behaviour was observed for the rough joints and both peaks increased with the increase of infill matric suction. The results suggest that the contribution of matric suction of infill on the joint peak normalised shear stress is relatively independent of the joint roughness.

Future of Treatment of Temporomandibular Joint Dysfunctions in Parkinsonian Patients

The purpose of the study was designed to clarify the modern trends of physical therapy in treatment of temporomandibular joint dysfunctions in Parkinsonian patients, which in this respect included the degree of pain, the muscles power of both masseter and pterygoid, the range of TMJ motion, the angle of mouth opening and their effects on electromyography study in both sexes. Subjects: Thirty males and females were the same degree of disabilities according to modified Hoehn and Yahr scales (grade 3) of Parkinsonian patients, and their age ranged from 50 - 77 years old and their weight ranged from 60 - 88 kg. They were randomly divided into two equal groups (G1 and G2). G1 (control) consisted of 15 patients of both sexes and was treated by exercises therapy program and G2 (experimental) consisted of 15 Parkinsonian patients of both sexes and was treated by the same exercises therapy program and low level pulsed electromagnetic therapy. Vital signs such as blood pressure, body temperature, pulse rate and respiratory rate were measured before and after the treatment sessions. Assessments: Visual analogue scale was used to measure degree of pain. Tensiometer was used to measure the muscle power of masseter and pterygoid, the digital goniometer was used to investigate the range of TMJ movement. Moreover, standard electromyography test (EMG) was used to measure the compound muscle action potentials. Statistically the results for all groups were analyzed by t-test to compare the differences between the two groups. The statistical package of social sciences (SPSS, version 10) was used for data processing using the P-value 0.05 as a level of significance. Results showed that there were significant improvements in all variables in G2 only. However, there was a little improvement but not significant in both G1. Therefore, it could be concluded that the use of low level pulsed electro-magnetic therapy combined with exercises program was the good method to control pain of TMJ, increase of muscle power and the range of their movements together with determination of electro-myography. Our results opened a new link to manage the TMJ dysfunctions in Parkinsonian patients via the use of low level pulsed electromagnetic therapy combined with exercises program.

Experimental Set-up for Determining Soil Water Retention Curves for Granular Soils During Drying

Soil water retention curves（SWRCs） provide an important means of describing the response of unsaturated soils during drying / wetting processes in terms of variations of degree of saturation, water content or void ratio with suction. A key consideration in generating these curves is how to measure the suction. Frequently the filter paper technique is adopted, especially when high suctions are developed, e.g. with plastic clays. As each measurement takes at least a week with this technique, it can take months or years to generate a full SWRC in drying and wetting. Developments in laboratory tensiometers now allow matrix suctions up to about 1.5 MPa to be measured. With such a device it is possible to develop SWRCs for granular soils such as silts and clays in hours or days by continuous measurement. This paper describes an experimental set-up that was developed to measure changes in volume, water content and matrix suction during drying of three granular soils. Limitations of the apparatus and usefulness of the curves are discussed.

Field instrumentation for real-time measurement of soil-water characteristic curve

Suction measurement has a vital role in unsaturated soil analysis.However,measuring soil suction remains a challenging task due to a number of issues such as the limited range of suction measurement,cavitation,or long equilibrium time.It is even more challenging when the suction measurement is to be carried on the field.Hence,the development of a new suction measurement device which is able to measure high suction range for a long duration without tedious maintenance and yet portable enough for site measurement is required.In this study,a new sensor which is referred to as NTU Osmotic Tensiometer was developed along with the method to correct for decay and temperature.The NTU osmotic tensiometer is based on polymer swelling capacity in order to measure in-situ soil suction in real time for a very long duration.It requires minimum maintenance as the polymer-based sensor is not affected by the cavitation phenomenon.However,correction for decay and temperature is of paramount importance and therefore explained in this paper.Verification of the NTU osmotic tensiometer was carried out by comparing the field measurement results from the NTU osmotic tensiometer and the small tip tensiometer.The performance of the NTU osmotic tensiometer was found to be comparable with that of the small tip tensiometer,but the NTU osmotic tensiometer is able to measure more than 100 kPa soil suction.Therefore,it is possible to obtain the field soil-water characteristic curve by combining the measured in-situ soil suction from the NTU osmotic tensiometer with the measured in-situ water content from the moisture sensor as illustrated in the paper.