we are planning to build a patio at our backyard against the back wall. The backyard is wet for the most of the year. Most of the videos I saw recommend to dig to a depth of 6 to 8 inches, and fill in with base and so on. But will the patio base be acting like a water pool that traps the water seeps through the paver stone? Thanks for any advises.
The water will seep down between the pavers and make it's way below to the rocks, going into the soil below as the soil can absorb. If your water table is so high, or your soil is regularly over saturated that deeply, you might have issues. You should be building the whole thing with a slight pitch away from the building. This should prevent water from accumulating right next to the concrete wall and potentially causing structural issues. After that, if you find water is pooling at the edge of the porch you can install some french drainage to pull water away from the area with minimal disturbance to the patio.