Data Analysis 



Sediment density data 



Sample raw data. The sample raw data for determination of in-place 

 density consist of data for the wet samples, dry samples, volume of the hole, 

 dry density, and water content. Sample data for 21 August 1991 are given in 

 Table 12-4. W VKt is the weight of the wet samples, W m is the weight of the 

 Ottawa sand and the container before it is poured into die hole, W m remaining 

 is the weight of the Ottawa sand remaining in the jug after pouring the sand, 

 W mi is the weight of the Ottawa sand filling the hole, and W^ is the weight 

 of the samples after oven-drying. To obtain the volume of the hole V hole , the 

 W^ filling the hole is divided by y , which is the unit weight of the Ottawa 

 sand. The unit weight dry is obtained by dividing W^ by V hole . The water 

 content w is obtained by 

 W - w 



-. - -_«* ^*y (12-3) 



W dry 



Sample interpreted data. The relative density D t was calculated using 

 Equation 12-1. Table 12-5 summarizes results for samples taken 21 August 

 1991. 



Identification of marginal data sets. The sand cone test used to 

 determine relative density requires the excavation of a small hole in the beach. 

 In the offshore region, the sand was still saturated on 8 August and the hole 

 was not stable. As a result, Samples 1A and 7A are considered marginal. 

 The sand cone test also requires a level working surface. As a result, samples 

 taken on or near the berm face may be subject to error. These samples 

 included 3B, 4B, 5B, 2C, 4C, ID, and 2D. 



Pore pressure data 



Analysis and interpretation methods. Pore pressure data were analyzed 

 for statistical and spectral properties. Statistical parameters include the mean 

 and standard deviation, computed in 256-sec blocks. Spectral properties were 

 computed from the sine and cosine transform of a 512-sec time series. The 

 longer time series is used to quantify a 25-sec seiche in the wave channel. 

 Spectral density is computed as the sum of the squares of the sine and cosine 

 amplitudes divided by twice the frequency interval. Total energy is summed 

 from the area under the spectral density curve. Zero-moment wave height is 

 computed as four times the square root of the total energy. 



Data fde format. The file header for each run is contained in the first 

 nine blocks of the file. Each block has the capacity to store up to 256 data 

 points. Block 10 begins with the first 256 data points for Channel 1 of the 

 64-channel data acquisition system. Channels 1 through 16 correspond to the 



Chapter 12 Pore Pressure and Sediment Density Measurements 



245 



