CIGMAT Report 2013

By C. Vipulanadan, PhD, P.E., professor and director of Center for Innovative Grouting Materials and Technology (CIGMAT) and Texas Hurricane Center for Innovative Technology (THC-IT), Department of Civil and Environmental Engineering, University of Houston | October 2013, Vol. 68 No. 10
Figure 1. Piezo-resistive behavior of modified oil well cement

Several physical models have been designed and constructed at the CIGMAT laboratory to investigate the behavior of pipes on the seabed. In this preliminary study, a series of small model tests were performed using instrumented 1.625 in diameter (40 mm) pipes placed on the soft clay soil (undrained shear strength of 1.4 kPa or 29 psf) to better quantify the axial and lateral soil pipe interactions. The resistance to pipe sliding on the soft soil was monitored using a load cell (Fig. 3). The load cell was calibrated and was accurate to 0.01 pound. The pipe displacement was monitored using a linear variable differential transducer (LVDT). The strains in the pipe will be measured using strain gages. This instrumentation will help to better determine the distribution of the soil resistance along the pipe.

Effect of displacement rate and weight of the pipe (vertical load) were also investigated in this model study. Deepwater pipes are insulated with layers of polymers and the outside layer in contact with the soil is solid plastic. The interaction of loaded pipe with soil berms created as the pipe displaced laterally was also studied and quantified. The variation of the frictional parameter with the type (axial and lateral) and rate of loading and weight of the pipe have been quantified. The test results showed that when the axial rate of loading was increased, the frictional coefficient between the pipe and the soil reduced, and the weight of the pipe had no effect on the frictional coefficient within the range of variables studied. The lateral frictional coefficient was higher than the axial frictional coefficient.

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Figure 3. Schematic of the test setup for axial displacement study

Triple and double wall polypropylene water pipe-joint infiltration tests
While numbers of small to large older cities are undertaking repairs and maintenance, several other newer cities are planning on installing wastewater systems. Infiltration due to leaking pipes, manholes, laterals and other components of a wastewater system will add to the problem of overflow and substantially load the treatment facilities. Frequent overflows not only lead to regulatory problems but also increase treatment cost. Leaking systems will result in the erosion of soils through the leaking joints leading to the settlement of the ground surface, formation of sinkholes and damage to surrounding pavements and structures. Literature review indicated that Standard ASTM pipe-joint tests varied with the type and size of pipes.