Soap wsdl renvoi tableau multidimentionnel xml

<?php
require_once "lib/nusoap.php";
$client = new nusoap_client("http://localhost/sttpb/services/getprocessus.php");

$error = $client->getError();
if ($error)  echo "<h2>Constructor error</h2><pre>" . $error . "</pre>";

$result = $client->call("getprocessus", array("date"=>"jj/mm/yyyy"));

if ($client->fault) {
    echo "<h2>Fault</h2><pre>";
    print_r($result);
    echo "</pre>";
}
else {
    $error = $client->getError();
    if ($error)  echo "<h2>Error</h2><pre>" . $error . "</pre>";
    else {
         echo "<h2>Result:</h2>";
         echo $result;
    }
}

<?php
require_once "lib/nusoap.php";

function getprocessus($date){
$db=new PDO('mysql:host=localhost;dbname=logidb', 'root', '',array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES utf8"));
	$query="select id,reference,libelle from pr_processus";
	if(isset($date))
		if($date!=""){
$stm=$db->prepare($query." where date=?");
$stm->execute($date)
}
else{
$stm=$db->prepare($query);
$stm->execute()
}
	$result=$stm->fetchall(PDO::FETCH_ASSOC);
	
return join(",",$result);
}

$server = new soap_server();
$server->register("getprocessus");
$server->service($HTTP_RAW_POST_DATA);


?>

<?xml version="1.0" encoding="ISO-8859-1"?>
<SOAP-ENV:Envelope SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/">
	<SOAP-ENV:Body>
		<ns1:getProdResponse xmlns:ns1="http://tempuri.org">
			<return xsi:type="xsd:string">
				1,p1/2018,processus1,2,p2/2018,processus2,3,p3/2018,processus3
			</return>
		</ns1:getProdResponse>
	</SOAP-ENV:Body>
</SOAP-ENV:Envelope>