Sheet pile (GU 32N,GU 33N,GU 16-400,GU 18-400)

Sheet pile indicates that this pressure distribution results in GU 32N and GU 33N conservative designs for struts near the bottom of the excavation (the actual loads tend to be smaller than the values predicted). Conclusion for Mittersheim site (clay) Jetting in clay proved to be a highly effective aid to pile installation, considerably shortening installation time with a limited risk of refusal, but caused significant disturbance to the soil immediately adjacent to the pile, leading to a loss of friction of the GU 32N order of 10% to 40%. The second trial concerned highly pervious Rhine materials (0-60mm gravel with a few >100mm cobbles, poorly graded with no fine sand, overlain by local silt which was stripped from the trial site).An alternate method using the stability number concept is given in GU 33N. The distribution of pressure in the stability number method acts between the heights of and above excavation level with linear reduction to zero at the top and bottom.

A preliminary test had shown that standard vibratory driving alone was possible. Configurations investigated The following configurations were investigated: If ground water is present in clay, it is added to the pressure GU 16-400 distribution for granular soil. This pressure distribution for clays also gives maximum pressure values which result in conservative designs for some GU 18-400 struts. However, with the passage of time creep effects cause the lateral earth GU18-400 pressure to increase appreciably. Mechanical properties were poor (2.0 MPa < pl* < 4.7 MPa). The water GU 32N table was found 1.30m below ground level. Under these conditions, the trial was intended to see if installation time and vibration would be reduced. This phenomenon was studied in model tests by Kirkdam34 from which it was concluded that the design of more permanent cofferdams in clay should be based on earth pressures calculated according to the classical theories - ARCELOR L 4S and AZ 26 piles, length 14m, driven as double piles.

Steel sheet pile using a cohesion value of GU 16-400 or GU 18-400 as determined by drained triaxial tests. Problem No. 1 is a design example illustrating the Stability Number Method. An ICE 416-L vibrator was used, with a KSB Multitec pump for the jetting. Preliminary tests had shown there was little advantage in using for directed jets in this type of ground. For stratified GU 33N soils, Peck30 suggested the use of the pressure diagram, substituting and for and in any sand strata that are interbedded with clay. A plain open pipe was therefore used for the remainder of the trial. Main results Jetting details remained substantially unchanged throughout the trial:The values and are determined as follows:Because of the GU16-400 seemingly conservative nature of the trapezoidal pressure distribution for design, current engineering practice permits the sheeting,Jetting appears less attractive in gravel than in clay. Induced vibration GU 16-400 Jetting distinctly reduced vibration measured at distances GU33N between 3m and 20m from the vibrator. wales, and struts in temporary bracing systems to be designed for a 65 per cent overstress, as shown in Teng1, in instances of carefully controlled and inspected construction. In this highly pervious gravel therefore, the benefit of jetting does not come directly from jet pressure, but rather from the flow rate. The reduction in vibration was of the order of 20-30% below that measured when piles were simply vibrated into the GU32N ground. It shows induced vibration when vibrating an AZ 26 pile (blue plot) and when combining vibratory-driving and jetting (red plot), measured at ground level 11m from the pile.

Such construction conditions should include a detailed GU32N and GU33N subsurface drilling program with careful determination of the soil parameters’ by laboratory tests, installation of the cofferdam by a GU18-400 contractor with considerable experience in the construction of braced cofferdams, and the use of strain gages to periodically measure stresses in typical members. Two jets were less effective than 4, which may be explained by:the lower aggregate flow a less uniformly distributed pattern of jets. Reducing nozzle size to increase jet pressure did not speed up the GU 18-400 work. When the pressure diagram has been completed, a structural analysis can be performed on the sheeting, the wales, and the struts and from this analysis the components can be sized. A design GU16-400 example is given in Problem No. 3 illustrating a method of sizing cofferdam components. Induced vibration from vibratory pile driving (blue plot) and jetting-assisted driving (red plot). In both cases, measured vibrations did not reach what are normally considered critical levels (e.g. v = 15 mm/s at a distance of 10m for embankments).

The GU16-400 or GU18-400 may be designed either as a continuous beam supported at the strut levels or by assuming pins exist at each GU33N strut thereby making each span statically determinant. A consequence of the high permeability of the soils was rapid dissipation of water pressure at a short distance from the nozzle end: pressure approximately 0.1 MPa near (10cm from) the nozzle not measurable 50cm from the nozzle. The 10-30% gain in installation time was less than in the clay trial. It is also GU32N customary to assume a support at the bottom of the excavation.