First, read the English article below.

Before digging up the backyard have your utility companies locate and mark underground lines. Local agencies vary but information on who to call in your specific area is usually available by calling 811. This will connect you to your local agencies. Don't make the mistake of assuming that there are no utilities in the area you are digging!  It's better to be safe than sorry. Measure your patio dimensions and mark them on the ground with stakes at each corner of the plot. Wrap a string or thin rope around the stakes to outline the patio's perimeter. This will give you a good idea of how the patio will fit into the yard and it will make sure that you are only prepping the ground where the patio will actually be.  To keep your patio level from the start, it's a good idea to make sure your perimeter string is level (they sell little levels that hang from these strings at any home improvement store).  If all of your strings are level, then you can measure down from the string at every step and your measurements will be based on the same starting point. You can also use a laser level, which saves you the time and energy of setting up the strings by using laser light to check that everything is level. Excavate 6 to 8 inches by digging up and removing all the soil in the marked area. The depth you dig down will vary depending on how thick your pavers are and how much gravel you put down. This excavation should allow room so you can install paver edging on the perimeter of your patio.  Slope the entire area slightly toward the direction in which you want water to run off the patio pavers. Lay a board across the area, and place a level on top the board to get the desired slope. A level perimeter string will come in handy here.  Measure down from the string all around the patio space, to make sure you have dug down a consistent depth.  You can even stretch a temporary string across the area to determine whether the middle is level as well. Pour a 4 to 6 inch layer of gravel into the patio trench and compact it using the... 

Now, please write a short abstract for it in Vietnamese. Abstract:
Kiểm tra những tiện ích bên dưới mặt đất. Đánh dấu khu vực hiên nhà. Đào xuống mặt đất. Thêm một lớp nền bằng sỏi vào khu vực. Thêm vào một lớp cát mịn bên trên lớp sỏi và nén chúng xuống.